Cyanobacteria: Pioneers of Planet Earth
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Ceylon Journal of Science (Bio. Sci.) 40 (2): 71-88, 2011
Cyanobacteria: Pioneers of Planet Earth
S. A. Kulasooriya
Emeritus Professor of Botany, University of Peradeniya, Peradeniya, Sri Lanka and Visiting Professor
Institute of Fundamental Studies, Kandy, Sri Lanka.
ABSTRACT
Cyanobacteria are among the earliest of inhabitants of Planet Earth and their existence can be traced back
to 3.8 billion years. Their oxygenic photosynthesis led to the gradual conversion of the Earth‟s atmosphere
from an anaerobic to an aerobic one. This change enabled the advent of aerobic organisms that eventually
underwent rapid evolution and became the dominant, highly diverse members of the current global
biodiversity. Cyanobacteria are ubiquitous in their distribution and are found in all the latitudes from
Arctic and Anatarctic regions to the Tropical deserts perhaps reflecting their pioneering habitation of the
primitive earth. They are also unique in their ability to simultaneously perform oxygenic photosynthesis
and oxygen labile nitrogen fixation. Through these processes they make significant contributions to the
Carbon and Nitrogen bio-geochemical cycles, particularly in the deep oceans. The ability of these
organisms to fix N2 either independently or in symbiosis with other organisms not only contributes to
natural ecosystems but is applied in certain countries particularly for rice cultivation. Their ability to grow
in highly polluted environments is also used in the treatment of sewage and industrial effluents.
Cyanobacteria are the most efficient among all living organisms in the harvesting of solar energy and are
currently looked at as highly attractive candidates for biofuel production. A few species are being used for
the production of highly nutritive food supplements. On the negative side, some cyanobacteria form
massive growths called „blooms‟ in water bodies and many of them produce toxins harmful to fish,
digastric animals and are suspected to be responsible for certain human ailments. Having reviewed most of
these aspects of cyanobacteria, it is concluded that knowledge on these little known organisms would be
invaluable not only for students, scientists and environmentalists but also for industrialists and policy
makers.
Key words: cyanobacteria, blue-green algae, algal toxins, biofertilizers, biofuels
INTRODUCTION latitudes perhaps demonstrating the abilities of
their pioneering ancestors as the earliest
Cyanobacteria, also known as blue-green algae inhabitants of Earth. They are not only
include a highly diverse group of prokaryotic widespread in freshwater, marine and terrestrial
microorganisms exhibiting oxygenic ecosystems but also found in extreme habitats
photosynthesis. Oxygen released by this process such as hot springs, hypersaline localities,
gradually changed the original reducing freezing environments and arid deserts (Fogg et
atmosphere of the primitive earth to an oxidizing al., 1973). They often live in association with
one (Olsen, 2006) triggering off a dramatic other organisms forming microbial mats,
evolution of global biodiversity. The biofilms and benthic communities and such
chloroplasts of eukaryotic algae and higher associations are the predominant and sometimes
plants have originated from endosymbiotic the only life forms found in certain extreme
relationships with cyanobacteria (Martin and habitats. The fossilized stromatolites believed to
Kowallik, 1999 and Raven and Allen, 2003) and have been formed some 3.4 billion years ago
this event in the early evolution of life has (bya) are also microbial communities with
stimulated the advent of oxygen tolerant flora cyanobacteria as their autotrophic partners.
and fauna capable of aerobic respiration, a Diverse species having different ecological
highly efficient mechanism of energy utilization. demands exhibit differential adaptations to the
The rapid development of such organisms conditions at their source locality. The massive
resulted in the predominance of oxygenic and communities of Prochlorococcus in the
aerobic species diversity on earth. oligotrophic deep oceans that live in close
Cyanobacteria are genetically highly diverse; association with cyanophages enabling rapid
they occupy a broad range of habitats across all lateral transfer of genomic material opens up
__________________________________________
Author‟s email: ananda@kulasooriya.com
S. A. Kulasooriya 72
new vistas on biological adaptation and Various scientists have reported on these
evolution (Johnson et al., 2006). The endolithic processes which have resulted in the formation
Chroococcidiopsis living as the only inhabitant of amino acids (monomers and proteinoid
in the extremely inhospitable habitat of the arid polymers) that integrated to form aggregates
Atacama Desert provides a new tool for such as protobionts and microspheres with semi-
Astrobiology (Friedmann, 1982 and Wierzchos permeable membranes. Ribose-nucleic acid
et al., 2006). (RNA) is believed to have been the original
Sequencing of 16S rRNA while confirming hereditary molecule that grew, split and was
the existence of several morphologically uniform passed onto the progeny. These have given rise
and well-defined traditional genera, has also to the earliest life forms on earth which are
placed similar morphotypes in distant positions believed to be prokaryotic organisms, today
in phylogenetic trees. Molecular data therefore represented by the Archea, Eubacteria and the
provide basic criteria for cyanobacterial Cyanobacteria. Citing evidence from the Isua
taxonomy, but to construct a comprehensive super-crustal belt in Western Greenland and
phylogenetic system of cyanobacteria a similar formations in Akilia Island, Mojzsis et
combination with knowledge on their al. (1996) proposed life to have existed 3.8 bya.
morphology, physiology and biochemistry is They have also estimated the time that would be
essential (Komarek, 2006). taken for a 100 Kbp genome of a primitive
The ability of certain cyanobacteria to fix heterotroph to develop onto a 7500 Kbp gene of
atmospheric nitrogen make them unique in their a filamentous cyanobacterium to be 7 million
ability to independently secure their carbon and years.
nitrogen requirements (Kulasooriya, 2008). It is most likely that the original cells were
Some of these organisms and symbiotic systems heterotrophic utilizing plenty of organic
like Azolla are used as biofertilizers, particularly molecules available in the primordial soup
in rice production (Venkataraman, 1972 and together with those produced by other cells. As
Azolla Utilization, 1987). They are also applied these food supplies gradually became limiting
in oxidation ponds and sewage and sludge some of the cells would have developed
treatment plants (Lincoln et al., 1996). Recently strategies to use the readily available solar
a few species have been investigated for biofuel energy by anaerobic photosynthesis. These
production because their ability to convert solar archaic processes are still retained by a few
energy has been found to be the most efficient pigmented bacterial species like Chlorobium and
among all living organisms. Furthermore, their Rhodospirillum which utilizes energy from the
simple genomic structure has enabled the sun to reduce CO2 and form organic compounds
production of biofuel secreting strains through deriving electrons from substrates such as H2S
genetic engineering (Lane, 2010). Certain and FeS exhibiting non-oxygenic
cyanobacteria form blooms in eutrophied water photosynthesis.
bodies and most of such bloom forming strains In a comprehensive mini review Olson
produce cyanotoxins that are harmful and (2006) has presented possible pathways on the
sometimes lethal to animals and humans early evolution of photosynthesis primarily
(Carmichael, 1994 and Carmichael et al., 2001). based upon fossil evidence during the Archeon
A few species are utilized for the production of Era. According to him the earliest reductant for
highly nutritious food supplements CO2 fixation (even by primitive cyanobacteria)
(Kulshreshtha et al., 2008) would have been H2 some 3.8 bya. Fossilized
This paper reviews the current information filamentous mats found in the Buck Reef Cherts
on these aspects of cyanobacteria, the roles they of South Africa and Evaporites, Stromatolites
may have played in the origin and early and micro-fossils observed in the Warrawoona
evolution of life on earth and their current Megasequence in Australia have been attributed
impacts on global biodiversity. to the H2S driven photosynthesis between 3.5 to
3.4 bya and subsequently Proteobacteria and
Role in the oxygenation of the primitive Protocyanobacteria have utilized Fe2+ ions as
earth’s atmosphere reductants around 3.0 bya. Evidence of retention
The Planet Earth is believed to have cooled of such archaic processes can be observed in
down, solidified and formed oceans and certain present day species of cyanobacteria
terrestrial habitats some 4.8 to 4.5 (bya). During which exhibit light driven CO2 fixation through
the next billion years chemical or abiotic cyclic photophosphorylation under anaerobic
evolutionary processes in the primordial soup of conditions using electron donors such as H2S,
the oceans are believed to have given rise to thiosulphate, or even molecular H2. Citing
primitive entities capable of self replication. evidence from microfossils, stromatolites and
Cyanobacteria 73
chemical biomarkers Olson (2006) suggested sequences of cyanobacteria and of the higher
that cyanobacteria containing chlorophyll-a plant Arabidopsis thaliana leave no doubt that
capable of O2 evolving photosynthesis appeared the green plant chloroplast originated through
around 2.8 bya, but this process did not have a endosymbiosis with a cyanobacterium.
significant impact on the composition of the The oxygenic photosynthesis of
atmospheric gases for another 5 million years. cyanobacteria and chloroplast containing
The O2 released to the atmosphere became eukaryotes would have accelerated the
bound to limestone, iron and other minerals as oxygenation of the atmosphere and this would
evidenced from the iron-oxide rich geologic have had significant impacts on the existing life
strata observed from those periods. It is also forms of that time. Oxygen would have been
believed that such oxidative reactions of toxic to most of the primitive organisms which
minerals contributed to the „greening of oceans‟. were predominantly anaerobic and a large
Once most of the minerals got oxidized free O 2 number of them would have died in what was
gradually began to accumulate in the called the „oxygen catastrophe‟. As this process
atmosphere. Intense solar rays bombarding the of oxygenation had been very slow and gradual
earth converted some of the O2 to O3 which through several millions of years, it enabled the
collected in the upper part of the atmosphere to evolution of resistant forms some of which even
build up the ozone layer that absorbs the developed mechanisms to utilize O2 to secure
mutagenic UV rays and protects all life forms energy from food through aerobic respiration.
from unsustainable levels of mutation. Such a This metabolic process was far more efficient
build up of a protective O3 layer would also have than the anaerobic processes of fermentation and
enabled the evolution and migration of life forms the aerobes on earth developed at a dramatic
from the oceans to land. pace driving the anaerobes to near extinction.
Towards the end of the Archaeozoic era and Today aerobes are the predominant living forms
beginning of the Proterozoic era the earth began among both flora and fauna thriving in an
to cool and this led to the reduction of the major atmosphere containing 21% of oxygen.
greenhouse gases of the atmosphere e.g. water
vapour, CO2 and methane. This cooling also Distribution and associations with other
reduced the hygrometric capacity of air and organisms
water vapour condensed resulting in continuous Cyanobacteria are ubiquitous in their global
torrential rain. These changes of the physical distribution. They occupy a broad range of
environment led to the proliferation of habitats across all latitudes, widespread in
cyanobacteria in the marine phytoplankton freshwater, marine and terrestrial ecosystems,
which fixed and stored part of the carbon in the also found in extreme habitats such as hot
sea and contributed to the reduction of CO2 in springs, hypersaline localities, freezing
the atmosphere. Release of O2 to the atmosphere environments and arid deserts. Frequently they
due to oxygenic photosynthesis by cyanobacteria are the pioneer invaders (often as lichens), of
would also have contributed to the reduction of exposed habitats such as bare rocks, recently
atmospheric methane through oxidation. piled up soil or bare land after natural disasters,
Meanwhile the chloroplasts that are today so exposed walls and partly constructed buildings
common in eukaryotic algae and green plants and similar substrates which offer little or no
evolved through processes of endosymbioses nutrients. They are also common inhabitants of
between cyanobacterial and heterotrophic polluted water bodies, drains and garbage dumps
eukaryotic ancestors. This endosymbiotic which are generally inhospitable to most other
hypothesis was originally put forward by organisms. The versatile abilities of these
Mereschkowsky (1905). Though originally taken autotrophic prokaryotes are perhaps a reflection
with skepticism subsequent electron of their pioneering ancestry which at that time
microscopic, biochemical and molecular dominated the inhospitable primitive earth.
biological studies gave credence to this Initial colonization of habitats by cyanobacteria
hypothesis and later Martin & Kowallik (1999) if left undisturbed has the potential to develop
translated this paper into English and provided through progressive autotrophic successions to
evidence in support of it by molecular analysis reach even the final stage of a climax forest
of the chloroplast genome of Arabidopsis under favorable environmental conditions. Such
thaliana and comparing it with those of Nostoc important roles played by these simple
punctiforme, Prochlorococcus marinus and prokaryotes justify referring to them as Pioneers
Synechocystis sp. PCC 6803 (Martin et al., of Planet Earth.
2002). Raven and Allen (2003) confirmed these Among the planktonic cyanobacteria, the
evidences and stated that the complete genome ocean dwelling Prochlorococcus marinus
S. A. Kulasooriya 74 occupies a unique position. Reported as the Mediterranean Sea, 50 m in the Arabian Sea, 35 tiniest photosynthetic organisms and the most m in the Gulf Stream and 90 m in the Sargasso populous autotrophic prokaryotes in the oceans, Sea. The Low light tolerant group was observed they are found among the phytoplankton of the down to 10 m in the North Atlantic, 83 m in the oligotrophic deep ocean habitats in dense Equatorial Pacific, 120 m in the Sargasso sea populations sometimes around 105 cells per ml and 135 m in the Gulf Stream. Quoting the of water. The vast extents of these populations in works of Sally W. Chisholm of the MIT and the oligotrophic deep oceans make a significant Robert J. Olsen of the Woods Hole contribution to primary production and C- Oceanographic Institute, Nadis (2003) compares sequestration that ameliorates global warming. this tiny cyanobacterium to the archaic ancestors Research studies led by Professor Sally W. that originally developed oxygenic Chisholm of the Massachusetts Institute of photosynthesis on Planet Earth and claims that Technology, Boston, USA, have shown the they account for 50% of the total oceanic important role played by the massive photosynthesis. Prochlorococcus is also unique populations of these minute organisms in carbon among all cyanobacteria as the only genus to sequestration in the vast expanses of the deep possess chlorophyll-b in addition to chlorophyll- open ocean ecosystems. When we realize that a, resembling green algae. In fact this feature led over 70% of the earth‟s surface is covered by to some debate over its taxonomic position, but oceans it is easy to comprehend the significance all the prokaryotic features that it shares with of the contribution made by them to global C- other cyanobacteria have eventually kept it sequestration. Another astounding finding of the within this taxonomic group. Massachusetts research team is the close Another deep ocean dwelling association Prochlorococcus cells are having cyanobacterium of ecological importance is with numerous viruses that facilitate rapid lateral Trichosdesmium, a filamentous non- gene transfers among them. With these new heterocystous cyanobacterium which fixes findings they were able to get a clear picture of atmospheric N2. How this organism has gene diversity and gene flow among these reconciled the O2 sensitive N2-fixation while organisms and postulate that such lateral gene carrying out oxygenic photosynthesis is still an transfers endow upon them an intrinsic ability to enigma and this will be discussed later under the rapidly adapt to environmental variables such as section on N2-fixation in cyanobacteria. Marine temperature, predators, light and nutrient plankton species of cyanobacteria are not as changes which these organisms constantly common as freshwater species but encounter in the deep ocean ecosystems. The Trichodesmium is arguably one of the team‟s studies have shown that closely related commonest among them. T.erythraenum is more Prochlorococcus strains display an array of frequently encountered than other species like physiological differences regulated by the T.theibautii, T.hilderbrandi and T.rubescens. genetic diversity of the constituent cells that Drouet (1968) in his revision of the Family provide an extraordinary stability to the overall Oscillatoriaceae has grouped all these species as community which internally adjusts itself to ever Oscillatoria erythraea but this did not receive changing environmental conditions. These novel universal acceptance. Trichodesmium exists in observations perhaps warrant the introduction of nature as bundles of filaments visible to the new terminology to such ecosystems. What is naked eye (Fig. 1). Usually this cynaobacterium seen here are homogenous populations of is red in colour due to the high content of the Prochlorococcus marinus that are accessory red pigment phyco-erythrin but they “heterogenomic”. This dynamic hetero- have been reported to have a range of colours genomicity due to the continuous lateral gene from grey through yellow, green, and purple transfer through closely associated viral vectors (Fogg et al., 1973). enable the homogenous cyanobacterial It is believed by some that the “Red Sea” got community to sustain itself in the ever changing its name due to thick blooms of T.erythraenum environment of the deep ocean. Johnson et al. that frequently formed in it. Trichodesmium (2006) have categorized these heterogenomic occurs in tropical oceans where the surface groups as ecotypes and presented a temperature is above 25oC and salinity near comprehensive report on their niche distribution 3.5%. It normally occurs as long windrows from in ocean scale environmental gradients. a few feet to several miles in length. Wood Populations of Procholorococcus have been (1965) has reported a massive bloom of nearly categorized into two broad groups. The High 52,000 km2 (almost 80% of the area of Sri light tolerant group found on the surface of the Lanka). Carpenter and Romans (1991) present Equatorial Pacific, down to 5 m in the Trichodesmium as the most important primary
Cyanobacteria 75
producer in the North Atlantic Ocean (ca 165 than their marine counterparts. Several
mgC/m2/day) which also introduces the largest unicellular, colonial and filamentous species
fraction of new nitrogen to the euphotic zone have been recorded both as plankton, and
through fixation (ca 30 mgN/m2/day). Capone et benthic micro flora. They are invariably present
al. (1997) confirmed this report and illustrates in together with other photosynthetic organisms in
a map its global distribution in all the major mesotrophic waters, the common genera being
oceans along the tropical belt showing its Microcystis, Synechococcus, Anacystis,
extension to the sub-tropical waters just above Gloeocapsa, Agmenellum (syn. Merismopedia)
and just below the latitudes of 26.5oN and 26.5oS as unicellular and colonial types and
respectively. It is however claimed that its Oscillatoria, Lyngbya, Spirulina, Ananbaena,
activities are confined to water temperatures Aphanizomenon, Nostoc, Cylindrospermopsis,
above 20oC. Karl et al. (1997) presenting results Planktothrix, Calothrix, Rivularia and
of seven years of time series observations in the Gleoetrichia as filamentous types. With
North Pacific Ocean Gyre, claimed that N2 pollution and nutrient loading such water bodies
fixation by cyanobacteria accounted for half of become eutrophic and very often certain
the new production and demanded a cyanobacteria that prefer such environments
reassessment of previous bio-geochemical outgrow their counterparts producing explosive
nutrient cycling budgets of one of the world‟s growths to form „algal blooms‟. The common
largest biomes. bloom forming genera are Microcystis,
Another marine planktic cyanobacterium is Cylindrospermopsis, Anabaena and
Richelia intracellularis which lives as an Aphanizomenon. Some times these blooms could
endosymbiont within some large diatoms that be massive. The author once had the experience
are frequently encountered among the of measuring such a bloom in 1991 that formed
phytoplankton of the oligotrophic oceans adjacent to the Kotmale Hydro-Power Reservoir
(Carpenter and Romans, 1991). Although not as Dam which was 1.5 m deep and extended to
common as eukaryotic algae, cyanobacteria are more than 2000 m2 (unpublished personal
found in the marine intertidal and littoral observation). They foul the water and most of
ecosystems, the common species being Lyngbya them produce „algal toxins‟ that are often lethal
majuscula, Microcoleus ethnoplasts, (a common to fish and digastric mammals, cause diseases,
mat former), Spirulina sp. (a highly nutritious irritations, allergies and also contribute to liver
cyanobacterium) and several species of and kidney ailments among humans. (A more
Oscillatoria. They are also found in association detailed analysis is included in the section on
with marine coralline algae and marine lime „toxigenic cyanobacteria‟). In the aquatic
stones e.g. Hyella stella and Scytonema ecosystems cyanobacteria play a crucial role as
endolithicum. oxygenic primary producers as well as nitrogen
Nevertheless, the greatest abundance and fixers.
diversity of cyanobacteria are encountered in
freshwaters where they are far more common
Figure 1. Colonies of Trichodesmium erythraenum. (Source: Reproduced from Fogg et al.,1973)S. A. Kulasooriya 76
Their environmental sensitivity and short life cryptoendolithic organisms in the frigid deserts
cycles resulting in rapid species turnover are of the Antarctic dry valleys where no other life
helpful to use them as biological indicators in forms are visible on the surface. They live in
environmental assessment studies. For example between crystals of porous rocks and their
N2 fixing cyanobacteria have been used to activities contribute to the weathering of these
understand the water quality especially high rocks. The common genus observed in these
turbidity, low N:P ratio, metal toxicity and freezing habitats is Chroococcidiopsis, a
nitrogen limitations in the environment. The unicellular cyanobacterium belonging to the
photosynthetic pigments and resting stages they Order Chroococcales. In these habitats
produce to survive harsh environmental temperatures are normally around -20o C and
conditions have sometimes remained even for even in the warmest periods do not go over 0o C.
thousands of years. Such remains provide On the other hand the extremophile
reliable historical information when monitoring Chroococcidiopsis has also been reported as the
data are not available. Recent developments in only life form found in the hyper arid core of the
environmental science and biostatistics help Atacama Desert in South America living as an
quantify ecological optima and tolerances of endolithic organism beneath halite rocks
such indicator organisms, enable the assessment (Weirzchos et al., 2006). Cyanobacteria are also
of past environmental conditions and predict found endolithically in large columnar calcified
future global scenarios such as climate change structures called stromatolites in the Australian
(Yatigammana, 2004). tidal flats. Stromatolites are extremely slow
Free living cyanobacteria are found in all growing structures and some of the fossilized
terrestrial habitats but are frequently observed in stromatolites of Australia believed to be 3.4
moist environments. They produce luxuriant billion years of age depict remains of endolithic
growth in wetlands, marshy lands and rice fields. fossil cyanobacteria. The ability of
Common terrestrial genera are Aphanocapsa, Chroococcidiopsis to grow in such extreme
Gloeocapsa, Merismopedia, Eucapsis as habitats has prompted the NASA scientist E.
unicellular and colonial types, Oscillatoria, Imre Friedmann to suggest it as a candidate of
Lyngbya, Microcoleus, Spirulina as choice to be used in its Astrobiology Programs
undifferentiated filamentous types, Nostoc, to introduce life to the Red Planet Mars.
Anabaena, Cylindrospermum, Calothrix, Cyanobacteria often live in association with
Scytonema, Tolypothrix as differentiated other organisms forming microbial mats,
filamentous forms and Mastigocladus, biofilms and benthic communities and such
Fischerella, Westiella, Westiellopsis and associations are the predominant and sometimes
Stigonema as true branched, differentiated the only life forms found in certain extreme
filaments This range of morphological diversity habitats like hot springs. Certain species like
extending from simple unicellular forms to Rickelia intracellularis lives as endosymbionts
multicellular, heterotrichous, true branched in large diatoms. Cyanobacteria are also
filamentous morphotypes bestow upon the endosymbiotic in fungi (lichens), bryophytes
cyanobacteria a unique position as the most (Anthoceros), pteridophytes (Azolla), cycads
complex organisms among all the Prokaryota. (coralloid roots), angiosperms (Gunnera) and
Cyanobacteria either by themselves or in certain marine sponges and corals.
symbiosis with fungi as lichens are often the
pioneering colonizers of bare soils, rocks and Morphology, taxonomy and molecular
other exposed surfaces with little or no nutrients biology
indicating their ability to adapt to inhospitable Cyanobacteria exhibit the most diverse and
environments. Such abilities have sometimes complex morphology among all prokaryotic
being utilized by soil microbiologists as in the groups, perhaps indicating that they would have
reclamation of alkaline „Usar Soils‟ of India by been the dominant life forms at some period of
bio-fertilization with Aulosira fertilissima the early earth. External gross appearance under
(Singh, 1961). aquatic and/or moist conditions is often
The adaptability of cyanobacteria to extreme gelatinous, slimy and occasionally filamentous
environments is exemplified by certain species clusters, with colours ranging from dark green,
being extremophiles i.e. inhabitants of extreme blue-green, yellow, brown to black, and rarely
habitats. They are found in freezing habitats as red (Fig. 2).
“green snow”, in glaciers and as endolithic This variable colour range is primarily due to
members in the sub surface of Arctic and their photosynthetic pigments consisting of
Antartic rocks Friedmann (1982). Friedmann et chlorophyll-a (which all of them possess)
al. (1988) reported cyanobacteria and lichens as together with different concentrations of theCyanobacteria 77
accessory phyco-biliprotein pigments, with false and true branching. As these
phycocyanin (blue) and phycoerythrin (red). The organisms do not show sexual reproduction their
final external colour of a specimen is largely taxonomy has been entirely based upon
dependent upon the concentrations of these morphology until the mid 20th century (Geitler,
pigments. Characteristically all cyanobacteria 1932, Fritsch, 1942 and Desikachary, 1959). A
have thin or thick gelatinous sheaths outside sample of a brief classification based on
their cell walls, their thickness and sometimes morphological diversity is given below:
their colour contribute to the final appearance of
the organism. Group: Algae (Eukaryotic)
Although cyanobacteria perform oxygenic Division: Chlorophyta (Green algae)
photosynthesis just like eukaryotic green algae Class Cyanophyceae or Myxophyceae (Blue-
and higher plants, they do not store food in the Green algae)
form of starch. Their principal storage product is
cyanophycean starch and glycogen together with Order Chroococcales – unicellular and colonial
specialized intracellular storage compounds like members.
lipids, protein containing cyanophycean granules Unicells e.g. Anacystis, Synechococcus and
and polyphosphate bodies. Some cyanobacteria Chroococcus,
particularly the plankton species produce Loose colonies e.g. Microcystis,
intracellular „gas vacoules‟. These are quite Compact colonies e.g. Gloeocapsa,
different from typical membrane bound vacoules Colonies of definite shape e.g. flat plates
of eukaryotic cells and are actually groups of gas Merismopedia (syn. Agmenellum) and cuboidal
filled vesicles that collapse under sudden shock colonies e.g. Eucapsis.
and pressure. These vesicles enhance buoyancy
and this helps such species to move up and down Order Chaemosiphonales - A small group that
a water column and occupy a depth that provides grows attached and produces a type of asexual
the best micro-niche in an aquatic environment. exospores e.g. Chaemosiphon and Dermocarpa.
The somatic diversity of cyanobacteria
extends from unicellular forms, colonial
assemblages, unbranched filaments to filaments
Figure 2. External appearance of some cyanobacteria collected from paddy fields in Sri Lanka.S. A. Kulasooriya 78
Order: Oscillatoriales - Unbranched, phylogenetic trees. Molecular data therefore,
undifferentiated filaments e.g. Oscillatoria and provide basic criteria for cyanobacterial
Spirulina (thin sheaths), Lyngbya (thick sheath), taxonomy, but to construct a comprehensive
Microcoleus (several trichomes within a phylogenetic system of cyanobacteria a
common sheath). combination with knowledge on their
morphology, physiology, biochemistry and
Order Nostocales - Unbranched filaments ecology is essential. For a comprehensive review
exhibiting cell differentiation into vegetative of combined molecular and phenotype
cells, heterocysts and akinetes (spores). taxonomic evaluations of cyanobacteria readers
Family Nostocaceae: Simple filaments e.g. are referred to Komarek (2006). In this review
Nostoc, Anabaena, Cylindrospermum (terminal he has emphasized the necessity to adopt a
heterocysts with large basal akinete). „polyphasic‟ approach combining the knowledge
Family Rivulariaceae: Whip-like tapering gained through modern ecological, ultra
filaments e.g Calothrix (non-colonial with or structural and molecular methods supported by
without spores), and colonial Rivularia (non the cultivation of numerous cyanobacterial
sporing) and Gloeotrichia (sporing). morphotypes. It is stated that while molecular
Family Scytonemataceae: Filaments with false data provide basic criteria for cyanobacterial
branching e.g. Tolypothrix (more single taxonomy, a correct phylogenetic system cannot
branches) and Scytonema (more double be constructed without combining the data from
branches). previous 150 years of studies on cyanobacterial
diversity. The limitations of using „type strains‟
Order Stigonematales - Members having true from standard culture collections for systematic
branches. and nomenclatural purposes, are also highlighted
Family Nostochopsidaceae: Members do not in this review.
exhibit heterotrichous habit e.g. Nostochopsis.
Family Stigonemataceae: Those showing Nitrogen fixation and its applications
heterotrichous thalli with prostrate and erect The ability of certain cyanobacteria to fix
systems e.g.: atmospheric nitrogen make them unique in their
Mastigocladus both prostrate and erect systems being autotrophic in both carbon and nitrogen
uniseriate. nutrition. It is also intriguing to find how these
Frischerella prostrate system multiseriate and prokaryotic organisms (without intracellular
erect system uniseriate. organelles) simultaneously perform two
Stigonema climax thallus development with both incompatible processes of oxygen evolving
systems multiseriate. photosynthesis and oxygen sensitive nitrogen
fixation.
With the advent of electron microscopy and Phylogenetic studies have indicated that all
molecular biology these simple classification nitrogenases have been derived from a common
systems had to be reviewed and revised. prokaryotic ancestral group that existed prior to
Revisions of different groups have been reported the oxygenation of the Earth‟s atmosphere
by Drouet & Daily (1956) and Drouet (1968, (Berman-Frank et al., 2003). In this anoxic
1973, 1977). The realization of the prokaryotic atmosphere having a predominance of CH4,
cell structure of the „blue-green algae‟ warranted CO2, N2, and NH3, ultra-violet radiation would
a radical change in their taxonomy and it was have dissociated NH3 releasing N2. Primitive
proposed by a leading team of blue-green nitrogenases could have initially arisen as
algologists (at that time) to place the respiratory enzymes where N2 acted as a sink for
nomenclature of these organisms under the anaerobic respiration of certain heterotrophs.
International Code of Nomenclature of Bacteria The slow process of oxygenation over several
(Stanier et al., 1978), but this proposal has been millions of years primarily due to the oxygenic
questioned (Komarek, 2006). Rippka et al. photosynthesis of cyanobacteria, resulted in the
(1979) revised the generic assignments of a partial pressure of atmospheric oxygen to
number of pure cultures of cyanobacteria. increase from 4 x 10-6 to >0.03%. This
Application of modern molecular biological oxygenation was inimical to N2 fixation and all
techniques has brought about radical changes in organisms had to adopt various methods to
the taxonomy of cyanobacteria. Sequencing of protect their nitrogenase enzyme from damage
16S rRNA while confirming the existence of by O2. Gallon et al. (1991) has extensively
several morphologically uniform and well- discussed these mechanisms as behavioural
defined traditional genera, has also placed adaptations, physical barriers, physiological and
similar morphotypes in distant positions in biochemical strategies and treated theCyanobacteria 79
cyanobacteria as a special group and these have Meanwhile reports came in on the detection
been discussed by Kulasooriya (2008). of nitrogenase activity in certain unicellular as
Major adaptations among cyanobacteria are well as non-heterocystous, filamentous species
structural changes among their cells. The vast of cyanobacteria. The first report of a unicellular
majority of cyanobacteria that exhibit aerobic species was that of Wyatt and Silvey (1969) who
nitrogen fixation possess a type of specialized demonstrated nitrogenase activity in Gloeocapsa
cell called heterocyst. Compared to vegetative (syn.Gloeothece and Cyanothece). These were
cells heterocysts are generally larger in size, followed by reports on other unicellular species
lighter in colour, have thicker cell walls and such as Synechococcus and Aphanothece (Mitsui
have thickenings called polar nodules at the et al., 1986), and filamentous non-heterocystous
points of attachment to adjacent cells. forms like Microcoleus chnoplastes (Pearson et
Kulasooriya et al. (1972) reported on the al., 1981) and Oscillatoria sp. (Gallon et al.,
differentiation of heterocysts in Anabaena 1991). In all these cases it has been found that
cylindrica and its coincidence with the there was a temporal separation of the two
restoration of nitrogenase activity. When incompatible processes of oxygenic
cultured in the laboratory in media with photosynthesis and oxygen sensitive nitrogen
combined nitrogen (particularly NH4 ions), the fixation along the growth cycle of these
filaments did not produce heterocysts and they organisms. The other reported physiological and
lost their nitrogenase activity. When such biochemical strategies adopted by these
induced „non-heterocystous‟ filaments were organisms have been reviewed in Kulasooriya
transferred to N-free media, pro-heterocysts (2008).
reformed within 24 hours. Once these pro- The most enigmatic situation was
heterocysts matured into heterocysts within the encountered with the large marine blooms of the
next 24 hours (which could be detected by the non-heterocystous, filamentous cyanobacterium
formation of polar nodules), nitrogenase activity Trichodesmium erythraenum which showed very
was restored. It was also found that the cellular high nitrogenase activity and it was the main
C:N ratio was critical for heterocyst formation as contributor to the nitrogen budget of the deep
well as expression of nitrogenase activity. A oceans (Karl et al., 1997). Two other species T.
mature heterocyst has a thick envelope that theibautii and T. aureum have also being
consists of an outer polysaccharide fibrous layer, identified as nitrogen fixing, non-heterocystous,
a middle homogenous layer and an inner marine cyanobacteria. Certain studies have
glycolipid laminated layer (Lang and Fay, 1971). demonstrated the presence of some specialized
This cell envelope has been shown to be cells called diazocytes in these organisms and it
critically important for nitrogen fixation and has been suggested that the nitrogenase enzyme
limit the ingress of O2 into the heterocysts is confined to these cells (Jansen et al., 1994,
(Murry et al., 1984 and Murry and Wolk, 1989). Fredrickson and Bergman, 1995 & 1997, Lin et
Isolated heterocysts showed higher levels of al., 1998 and Mulholland and Capone, 2000).
respiration and their absorption spectrum Nitrogen fixation in Trichodesmium peaked
coincided more closely than that of the around midday and varied inversely with
vegetative cells, with the action spectrum of photosynthetic O2 evolution. It has also been
nitrogenase activity of whole filaments (Fay and suggested that N2 fixation and photosynthesis in
Walsby, 1966). Isolated heterocysts contained Trichodesmium is regulated by circadian
very little chlorophyll-a and were devoid of rhythms (Chen et al., 1998). Molecular studies
phycocyanin and phycoerythrin pigments which on natural populations of T. theibautii have
are associated with the O2 evolving shown that nitrogenase is synthesized early
photosystem-II of photosynthesis (Thomas, morning and nifH mRNA is highest before dawn
1970). Using 14C labeled CO2 Wolk (1970) (Wyman et al., 1996). This enzyme remained
showed that heterocysts do not fix carbon and active until noon when it reached a peak, then
Fay and Kulasooriya (1972) demonstrated the declined in the afternoon and got degraded
prevalence of reducing conditions in heterocysts during the night (Capone et al., 1990 and Zer et
by the reduction of Triphenyl Tetrazolium al., 1993). Twelve nif genes cloned and
Chloride. Eventually Wolk and Wojciuch (1971) sequenced from Trichodesmium are basically
demonstrated photo-reduction of acetylene and similar to those of other cyanobacteria, but show
(Janaki and Wolk, 1982) showed the presence of a closer resemblance to „vegetative cell
nitrogenase in isolated heterocysts. Wolk (1982) nitrogenase genes‟ induced in Anabaena
reviewed and summarized all the available variabilis under micro-aerobic conditions. Many
evidences and concluded that the main function other non-heterocystous cyanobacteria such as
of the heterocyst is nitrogen fixation. species of Oscillatoria, Lyngbya, MicrocoleusS. A. Kulasooriya 80
and Plectonema boryanum have been induced to endophytic in the leaf sheaths of deepwater rice
fix nitrogen under micro-aerobic conditions. (Kulasooriya et al., 1981b) and the nitrogen they
Among other strategies, aggregation of fix has been shown to be available to the
unicellular and non-heterocystous cyanobacteria associated host plants (Watanabe et al.1982).
to form algal mats, colonies, biofilms among Free living nitrogen fixing cyanobacteria and
themselves and with other microorganisms have the aquatic fern Azolla (which has nitrogen
been reported to exhibit low levels of fixing Anabaena azollae as an endosymbiont),
nitrogenase activity in marine Synechococcus have been used as biofertilizers in rice
and Trichodesmium and terrestrial and cultivation. Venkataraman (1972) provides a
freshwater Oscillatoria, Lyngbya, Microcoleus comprehensive account of the large scale
and Plectonema. Physical barriers such as thick production of cyanobacterial bio-fertilizers in
mucilaginous sheaths and capsules have enabled India. Cyanobacteia are initially isolated from
expression of nitrogenase activity in Gleoetheca rice fields, purified and screened for rapid
(syn. Gloeocapsa and Cyanothece). As a growth and high N2-fixation. Selected isolates
biochemical protective mechanism nitrogenase are then semi-mass cultured in laboratory media
activity has been shown to be regulated by ADP- and these are used as inoculants for soil based
ribosylation of the Fe-protein (the more O2 outdoor mass cultures in open ponds or large
sensitive component of the nitrogenase enzyme trays under non-sterile conditions. A sprinkle of
complex). Such adaptations originally P fertilizer, lime and pesticides are usually added
demonstrated in photosynthetic bacteria have to ensure uninhibited rapid growth. After
been found to be widespread among sufficient growth is obtained the cultures are
cyanobacteria such as Anabaena CA, Anabaena allowed to sun dry and the soil based algal flakes
variabilis, Aphanizomenon flos-aqaue, are packed and distributed among farmers to be
Oscillatoria limosa, Trichodesmium, Gloeotheca used as bio-fertilizers. This low cost technology
and Microcoleus chthnoplasts as reviewed by quite suitable for resource poor rural farmers has
Kulasooriya (2008). Continuous synthesis of been successful only in a few areas in India
nitrogenase enzyme has also been demonstrated where edaphic conditions are favourable for the
in certain taxa like Anabaena CA, Anabaena growth of cyanobacteria. Reports from certain
variabilis, Anabaena flos-aquae and Gloeothece, areas of Myannmar, China and Egypt have also
but this strategy appears to be of limited recorded some successes. Roger and
distribution. Kulasooriya (1980) reviewed most of the
All these evidences support the idea that literature on the use of cyanobacterial
although heterocysts are specialized cells for N2 biofertilizers and concluded that their N-input
fixation in cyanobacteria the potential to fix N2 potential ranged from 0 to 80 Kg/ha/season with
is present even in the vegetative cells but this is an average of 25 Kg/ha. Attempts to adopt this
expressed only under reduced oxygen technology in Sri Lanka was successful only up
concentrations. These observations have to the stage of pot experiments and most of the
important ecological implications and it is quite cyanobacterial fertilizers added to the rice fields
likely that the subterranean layers of thick mats could not overcome consumption by the rice
of non-heterocystous cyanobacteria may be field micro-fauna and competition by indigenous
fixing nitrogen particularly under low light micro-flora and failed to colonize the fields
conditions or in the dark. This idea is also (Kulasooriya and Hirimburegama, 1989).
compatible with the evolution of the process of Compared to free living cyanobacteria, the
N2-fixation from an archaic reducing Earth‟s application of Azolla in rice cultivation has been
atmosphere through a micro-aerobic atmosphere more successful and widely used particularly in
to the oxygenated atmosphere of present times Vietnam, China and certain parts of Philippines.
(Gallon et al., 1991 and Berman-Frank et al., The status of this technology has been well
2003). In symbiotic associations it is always the reviewed at a workshop held in Fuzhou in Fujian
cyanobacterial partners that fix nitrogen. They Province, China and published by the
provide nitrogen to the ecosystem in which they International Rice Research Institute, Philippines
live and often the rates of fixation by these in 1987 as „Azolla Utilization‟. Even in Sri
systems are higher than those of free-living Lanka this technology appeared to be more
cyanobacteria, perhaps due to the additional feasible than free living cyanobacterial
nutrition and micro-aerobic conditions provided biofertlizers. Azolla grew well in rice fields at
by the host. Occasionally cyanobacteria have Ambalantota (Fig. 3), Bombuwela, and
been reported to be epiphytic on rice plants Peradeniya and showed a potential to replace an
(Roger et al., 1981) and weeds in wetland rice equivalence of 55 to 85 KgN/ha of chemical N-
fields (Kulasooriya et al.,1981a) and even fertilizer (Kulasooriya et al., 1987). The majorCyanobacteria 81
Figure 3. Growth of Azolla in a rice field at Ambalantota, Sri Lanka.
constraints for the adoption of this technology What factors trigger toxin production is not
by the rice farmers are, handling of fresh bulky definitely known although it has been suggested
material, maintaining fresh cultures during the to be a defense mechanism.
dry (fallow) periods, the need for frequent P- In mesotrophic, unpolluted waters the total
fertilizer applications and the susceptibility of algal populations are small but their diversity is
Azolla to pests and pathogens particularly under high with almost equal representations from
warm weather. It is therefore evident that the use green algae, cyanobacteria (blue-green algae)
of N2-fixing cyanobacteria and their symbiotic and diatoms. When such a water body gets
systems as biofertilizers for rice have only polluted and is subjected to high light and
limited potential for widespread application. temperature, most of the eukaryotic algae tend to
decline and a few blue-green algae
Toxigenic cyanobacteria (cyanobacteria) particularly those that produce
Though cyanobacteria make positive toxins become dominant and sometimes form
contributions to global biodiversity and the blooms. This has happened with the ancient
environment particularly through carbon and irrigation reservoirs of Sri Lanka (Kulasooriya,
nitrogen fixation they also cause severe 2004 and 2005a and b). Surveys conducted by
problems in fresh water ecosystems and sewage Kulasooriya and others in collaboration with the
treatment facilities by the production of toxins National Water Supply and Drainage Board
(Carmichael, 1994). It has already been from late 1980s to early 1990s were
mentioned that certain species form „algal communicated in several seminars and symposia
blooms‟ in polluted eutrophic waters (see section (Kulasooriya, 1997 and 1998, Jayawardana et
on Ecology and Distribution). Bloom forming al., 1998 and Weerakoon et al., 1998) and the
species notably Microcystis, Anabaena, general public were made aware by newspaper
Aphanizomenon, Cylindrospermopsis and articles (Kulasooriya, 2005b). Reports from
Nodularia frequently produce cyanobacterial Silva and Samarawickrama (2005) showed the
toxins. Many such toxins have been initially presence of toxigenic cyanobacteria in the
named after some of these genera e.g. Kandy Lake and their dominance in most of the
Microcystins from Microcystis, Anatoxins from reservoirs of the Mahaweli river basin (Silva and
Anabaena, Cylindrospermopsin from Wijeyaratne, 1999). Jayatissa et al. (2006) in a
Cylindrospermopsis and Nodularin from comprehensive study covering 43 freshwater
Nodularia, although the production of such water bodies have shown that most of the
toxins is not confined to these genera but also irrigation tanks and reservoirs in Sri Lanka
produced by others. Toxins are not always including the recent ones constructed under the
produced and the mere presence of these genera Mahaweli project, have a predominance of toxin
should be considered only as a potential danger. producing cyanobacteria except the reservoirs atS. A. Kulasooriya 82
Kalatuwawa and Labugama in which the On the other hand, cyanobacteria have been
catchment areas are under strict nature reserves. found to be useful in the bioremediation of
This is an indication that if pollution is industrial effluents and extraction of heavy
minimized the occurrence of toxin producing metals. A number of species belonging to the
cyanobacteria can be reduced. How such genera of Synechococcus, Cyanothece,
conditions can be established and sustained in Oscillatoria, Nostoc and Nodularia isolated
irrigation tanks (reservoirs) would always from pharmaceutical and textile industry
remain a dilemma. Jayatissa et al. (2006) also effluents were demonstrated to be capable of
reported for the first time the presence of biodegradation and biosorption of several heavy
microcystin LR toxin in some of the metals (Dubey et al., 2011). Using lyophilized
cyanobacterial samples collected in Sri Lanka. Synechococcus sp. PCC 7942 immobilized in a
More recent studies have confirmed these results silica polymer, Gardia-Torresday et al. (2011)
and it is now quite evident that a large number of demonstrated that this cyanobacterium could
inland freshwater bodies of Sri Lanka carry effectively bind Cu2+, Pb2+, Ni2+, Cd2+, Cr3+ &
heavy populations of toxigenic cyanobacteria Cr4+ and these metals could be recovered by
with Cylindrospermopsis being the dominant elution with 0.1M HCl. It has even being
genus in a majority of them (Perera et al., 2011a, reported that certain cyanobacteria can be useful
Perera et al., 2011b, Kulasooriya and Padmasiri, in the cleaning of oil spills (Cohen, 2002). He
unpublished). The Institute of Fundamental tested species isolated from cyanobacterial mats
Studies, Sri Lanka, now possesses facilities to developing in oil-contaminated sabkhas along
detect and quantify cyanobacterial toxins in the African coasts of the Gulf of Suez and in the
water samples. A number of samples collected pristine Solar Lake, Sinai. He found that axenic
from reservoirs and irrigation tanks from the dry cultures of the isolated cyanobacteria by
zones of North Central and Wayamba Provinces themselves are unable to degrade oil. In
have shown the presence of such toxins association with sulphate reducing and other
sometimes well over the levels permitted by heterotrophic bacteria from the mats, when
WHO standards (Dr. D. N. Magana-Arachchi, exposed to light rapid degradation of oil was
IFS, personal communication). It is evident from observed. The oxygenic photosynthesis of the
these results that immediate steps should be cyanobacteria stimulated the aerobic
taken to ameliorate the predominance of decomposition by the associated bacteria. This
toxigenic cyanobacteria in water bodies of Sri shows the potential of producing cyanobacterial
Lanka, commencing from those used as sources - eubacterial biofilms as efficient microbial
for water supply schemes. It is also imperative to consortia for cleaning of oil spills. Abed (2010)
conduct well formulated scientific studies to has reported the commencement of such a
verify the claims that toxigenic cyanobacteria project in Oman.
are responsible for the prevalence and rapid Recently a few species of cyanobacteria have
increase of chronic kidney diseases of unknown been investigated for biofuel production because
etiology in certain areas of Sri Lanka. their ability to convert solar energy to chemical
energy has been found to be the most efficient
Some industrial applications among all living organisms. The efficiency of
Cyanobacteria are of common occurrence in solar energy conversion in corn and sugarcane is
waste water treatment plants. In some instances 1–2%, for eukaryotic algae it is around 5% while
they have been found to be useful as low cost for cyanobacteria it is 10%. This can be
converters of odour causing and pollution understood if one looks at the photosynthetic
creating dairy effluents into micro-algal biomass pigments of cyanobacteria. In addition to
using sunlight (Lincoln et al., 1996). They were chlorophyll-a these organisms contain
found to be very effective in removing NH4 ions phycobilisomes attached to the thylakoid
and other nitrogen rich compounds from such membranes and these act as antennae in
effluents. In other cases toxigenic species have harvesting light for photosystem II. Among the
reduced the efficiency of waste water treatment pigments contained in the phycobilisomes,
plants (Martins et al., 2011). Toxins produced, Phycoerythrin absorbs energy between the wave
particularly microcystins have not been lengths of 500 – 600 nm, Phycocyanin absorbs
antibacterial but they have adversely affected the between 550 – 650 nm and Allophycocyanin
protozoan populations. Nonetheless, other absorbs between 600 – 675 nm. Together with
secondary metabolites of cyanobacteria have chlorophyll-a, their light absorption capacity will
been found to be anti-bacterial and affected the therefore extend right across the entire spectrum
decomposition rates of both aerobic and of visible light (Dr. Celia Smith, Department of
anaerobic bacteria. Botany, University of Hawaii at Manoa,Cyanobacteria 83
http://www. biologie.uni-hamburg.de/ b-online/ studies in Sri Lanka that could lead us to a
librarywebb/ BOT311/ Cyanobacteria). commercially viable break through in biofuel
Furthermore, the simple genomic structure of production. Most of the other industrial
these organisms has enabled gene sequencing platforms for biofuel production based upon feed
and genetic engineering relatively easier. stocks derived from higher plants require vast
Professor James C. Liao of the University of areas of cultivable land. For a small country like
California, Los Angeles, has inserted and spliced Sri Lanka it is a formidable task to allocate such
genes from other organisms to increase the CO2 extents of land without compromising on other
fixing ability of Rubisco enzyme of more important economic uses. Algae based
Synechococcus elongatus. This transgenic strain biofuels therefore appear to be an attractive
produced isobutyraldehyde gas which could be option. Already unicellular cyanobacteria
recovered and converted to butanol. Prof. belonging to Synechococcus, Synechocystis,
Malcolm R. Brown and Dr. David Nobles of the Chroococcidiopsis and Cyanothece have been
University of Texas, Austin have inserted a gene isolated from different localities in Sri Lanka
from Acetobacter xylinum to a cyanobacterium including brackish water and hot springs and
which could secrete alcohol and sugars. Prof. P. partially sequenced (Wanigatunga et al., in
Fu and Dr. J. Dexter of the University of Hawaii preparation). With the commissioning of coal
have transformed Synechocystis strain PC 6803 powered electricity generation systems
by inserting pyruvate dehydrogenase and alcohol sequestering CO2 emissions would be a major
dehydrogenase II genes from Zymomonas problem and such waste gases could be
mobilis to produce ethanol. The biggest break harnessed to grow biofuel cyanobacteria. Even
through has been reported by a private company the CO2 emitted by other industries like
Joule Technologies of Boston, Massachusetts, breweries and cement production factories can
which has developed Bioreactors containing be used for algal cultivation.
genetically modified cyanobacteria that could
continuously secrete biofuel and ethanol (Lane, Cyanobacteria as a food supplement
2010). Reports on biofuel production capacities Among the vast array of cyanobacteria, two
from different sources are given in Table 1. species have been used as food supplements of
high nutritive value. They are Spirulina
Table 1. Production capacities of biofuel from plantensis (syn. Arthrospira plantensis) and
different sources. Aphanizomenon flos-aquae. These species have
come from the traditional food habits of ancient
civilizations of Aztecs, Mayans and Chinese and
Source Gals/ac* L/ha+
have been harvested from natural freshwater
Soybean 50 92 lakes such as Lake Chad in Africa, Upper
Corn 250 458 Klamath in North America, Lake Texcoco in
Sugarcane 450 825 Mexico, and Lake Titicaca in Peru, South
America. Currently they are also cultivated in
Oil palm 650 1192 large open raceway ponds with paddle wheel
Algae 2000 3668 stirring under high pH and high temperature to
Joule technologies 15,000 27,512 minimize contamination by human pathogenic
Source: *Original report, + Converted microorganisms. Such commercial production
facilities are today found in the United States,
The 15,000 gals/ac given by Dr. Dan Thailand, India, Taiwan, China, Pakistan,
Roberts, the principal scientist at Joule Myanmar and Chile. Spriulina is marketed as a
Technologies, eclipses all other claims. (Mail source of complete nutrition which no other
Online, Science & Technology March 2, 2011). single organism can offer. Besides having a very
It is interesting to note that in all these cases high protein content (65 – 71% of dry weight)
the most productive cyanobacteria have been with all the essential amino acids, it is claimed to
unicellular species. This is perhaps due to their contain a wide spectrum of prophylactic and
ability to harvest maximum solar energy per cell therapeutic nutrients including B-complex
because the single cells turn and rotate with vitamins, minerals, proteins gamma linolenic
minimum self shading as they move up and acid and super antioxidants such as beta
down a bioreactor. Also their simple genomes carotene, Vitamin E, trace elements and a
permit easy genetic engineering compared to number of unexplored bioactive compounds
more complex counterpart resources. This opens (Kulshreshtha et al., 2008).
a window of opportunity to conduct fundamentalYou can also read
