Blue-green algae (PROSEA)

Plant Resources of South-East Asia
Introduction

Aphanizomenon gracile - 1, bundle of planctonic trichomes; 2, trichome with long akinete and short heterocyst. Aphanothece caldariorum - 3, stages in the formation of endospores. Microcoleus vaginatus - 4, trichomes aggregated in a common sheath. Microcystis aeruginosa - 5, habit of a colony. Oscillatoria - 6, longitudinal section of a trichome; 7, tridimensional representation of cells. Scytonema hofmannii - 8, trichome with false branching and heterocyst.

Family: Cyanobacteria, Cyanophyceae, Cyanoprokaryota or Myxophyceae

Chromosome number: Prokaryotic, thus no chromosomes

Major species and synonyms

Anabaena (Bory) ex Bornet & Flahault - see separate article.

Aphanizomenon flos-aquae (Ralfs) ex Bornet & Flahault, Révis. Nostoc. hét.: 214 (1886) [1888], synonym (Drouetian): Microcoleus vaginatus Vaucher ex Gomont (1892).

Aphanothece stagnina (Spreng.) A. Braun, in Rabenh., Alg. Europas exsic. 1572 (1863), synonyms: Phylloderma sacrum Suringar (1872), (Drouetian) Coccochloris stagnina Spreng. (1807).

Arthrospira Stizenb. ex Gomont - see separate article.

Aulosira fertilissima S.L. Ghose, J. Linn. Soc., Bot. 46: 342, pl. 31, fig. 9 (1924), synonyms: Ghosea fertilissima (S.L. Ghose) Cholnoky (1952), (Drouetian) Calothrix parietina (Nägeli) Thur. ex Bornet & Flahault (1886).

Brachytrichia quoyi C. Agardh ex Bornet & Flahault - see separate article.

Calothrix scytonemicola Tilden, Minn. alg. Mycophyc.: 265 (1910), synonym (Drouetian): C. parietina (Nägeli) Thur. ex Bornet et Flahault (1886).

Cylindrospermum indicum C.B. Rao, Proc. Ind. Acad. Sci.: 169 (1936), synonym (Drouetian): Anabaena licheniformis Bory ex Bornet & Flahault (1886) [1888].

Hapalosiphon intricatus West & G.S. West, J. Linn. Soc., Bot. 30: 271 (1894), synonym (Drouetian): Stigonema muscicola (Thur.) Borzí ex Bornet & Flahault (1886) [1887].

Lyngbya majuscula (Dillwyn) Harv. ex Gomont, Monogr. Oscill.: 131 (1892) [1893], synonym (Drouetian): Microcoleus lyngbyaceus (Kütz.) P. Crouan & H. Crouan ex Gomont (1892).

Mastigocladus laminosus (C. Agardh) Cohn ex Bornet & Flahault, Révis. Nostoc. hét.: 56 (1886) [1887], synonym (Drouetian): Stigonema muscicola (Thur.) Borzí ex Bornet & Flahault (1886) [1887].

Microcoleus chthonoplastes (Mert.) Zanardini ex Gomont, Monogr. Oscill.: 353 (1892), synonym (Drouetian): Schizothrix arenaria (Berk.) Gomont (1892).

Microcystis aeruginosa (Kütz.) Kütz., Tab. phycol. 1: 6 (1846), synonyms: M. ichthyoblabe Kütz. (1833), M. flosaquae (Wittr.) Kirchn. ex Forti (1907), (Drouetian) Anacystis cyanea (Kütz.) F.E. Drouet & W.A. Daily (1952).

Nostoc Vaucher ex Bornet & Flahault - see separate article.

Oscillatoria agardhii Gomont, Monogr. Oscill.: 205 (1892) [1893], synonym (Drouetian): Microcoleus vaginatus Vaucher ex Gomont (1892).

Oscillatoria amphibia C. Agardh ex Gomont, Monogr. Oscill.: 221 (1892) [1893], synonym (Drouetian): Schizothrix calcicola C. Agardh ex Gomont (1892).

Scytonema bohneri Schmidle, Bot. Jahrb. 30: 60 (1901), synonym (Drouetian): Stigonema muscicola (Thur.) Borzí ex Bornet & Flahault (1886) [1887].

Spirulina Turpin ex Gomont - see separate article. on Arthrospira Stizenb. ex Gomont.

Tolypothrix tenuis Kütz. ex Bornet & Flahault, Révis. Nostoc. hét.: 122 (1886) [1887], synonym (Drouetian): Scytonema hofmannii C. Agardh ex Bornet & Flahault (1886) [1887].

Trichodesmium erythraeum Ehrenberg ex Gomont, Monogr. Oscill.: 196 (1892) [1893], synonym (Drouetian): Oscillatoria erythraea (Ehrenb.) Kütz. ex Gomont (1892) [1893].

Vernacular names

Thailand: sarai sinum ghuan ganchiew.

Origin and geographic distribution

Blue-green algae are ubiquitous, abundant in fresh and marine waters, in soil and in extreme habitats such as hot springs and land covered by ice. Some occur in symbiosis with other organisms, including fungi (lichens), ferns (Azolla Lamk), sponges (Dysidea herbacea), gymnosperms (Cycas L.) and angiosperms (Gunnera L.). They are widely distributed in the whole of South-East Asia.

Uses

Several bluegreen algae (especially Nostoc spp.) are consumed as food in China, Japan, Thailand, Malaysia, Indonesia and the Philippines. Nostoc spp., as well as the marine Brachytrichia quoyi have been used as side dishes in Japan since ancient times.

Many free-living nitrogen-fixing blue-green algae are used as algal biofertilizers for paddy fields in India, Thailand, Vietnam, the Philippines and China. "Algalization" is a term currently used for the adjustment of introduced blue-green algae to the soil, including subsequent proliferation. A wide range of nitrogen-fixation rates has been recorded for cyanobacterial populations (diazotrophic algae) in soils and flooded fields.

The water fern Azolla and its algal symbiont Anabaena azollae Strasb. ex Wittr., Nordst. & Lagerh. are used as a green manure in wet-rice cultivation, as a feed for pigs and ducks, and in aquaculture.

Arthrospira platensis Gomont is commercially produced in many tropical countries. This alga is consumed as health food and is also used for animal feed.

Some cyanophycean microalgae have properties that make them good soil conditioners, especially in tropical and alkaline soils as well as in some deserts. They can help to improve soil structure and alter the surface tension of water. The aggregative effect of mucilaginous sheaths and the filamentous nature of many cyanobacteria help improve infiltration. They also retain water, buffer against rapid desiccation and slow down erosion.

Cyanobacteria can produce biohydrogen, which is a renewable energy production system. Generally, nitrogen-fixing blue-green algae are more efficient at producing hydrogen than other forms. To produce biohydrogen, cells of blue-green algae are immobilized on inert supporting materials such as agar, agarose, carrageenan or alginate. It is possible to produce hydrogen for about 60 days using this method. Levels of hydrogenase, nitrogenase or other oxygen sensitive enzymes will affect the efficiency of hydrogen production.

Some blue-green algae have antibiotic properties, while others can act as positive plant-growth regulators.

Production and international trade

Several Asian countries such as China, India, Burma (Myanmar), Vietnam, Thailand and the Phillipines have started to popularize the practice of using algal biofertilizer. Largescale production of algal biofertilizer for wet-rice farming is being carried out. In Thailand, the inoculum consists of Anabaena siamensis Antarik., Calothrix scytonemicola, Cylindrospermum indicum, Hapalosiphon intricatus, Nostoc commune Vaucher ex Bornet & Flahault, N. muscorum C. Agardh ex Bornet & Flahault, Scytonema bohneri, and Tolypothrix tenuis. The private sector produces between 30 000 and 60 000 t of biofertilizer annually.

Apart from cultivation of Arthrospira ("Spirulina") there is no commercial monospecific production of other blue-green algae, although farmers and governmental organizations are trying to promote the production of the water fern Azolla with its symbiont Anabaena azollae and mixed soil blue-green algae as nitrogen fixers in rice fields.

Properties

Per 100 g dry weight, bluegreen algal mixtures contain: protein 36-65 g, lipids 2-13 g, carbohydrates 8-20 g and nucleic acids 3-8 g. The average content of the predominant pigment phycobiliproteins is 20 g/100 g dry weight or 60 g/100 g total soluble proteins. There are three major types of phycobiliproteins: phycocyanin, allophycocyanin and phycoerythrin. The composition of phycobiliproteins in some bluegreen algae varies when grown under different light qualities; this phenomenon is known as chromatic adaptation. Illumination with red light enhances the production of phycocyanin but suppresses the synthesis of phycoerythrin. The content of phycoerythrin increases when cultures are grown under green light. Other pigments in bluegreen algae are chlorophyll a and carotenoids which include βcarotene (predominant), echinenone, zeaxanthin and myxoxanthophyll.

Fatty acids of bluegreen algae are usually shorter than 18 carbon length, with 16:0, 16:1, 18:1, 18:2 and 18:3(π3) being the major constituents. Fifty percent of the total fatty acids are made up of 16:0 and 16:1.

Some genera of blue-green algae may form toxic blooms that cause the death of pets, livestock, and wild animals after ingestion of algal scum. Usually, no antidotes or treatments are available. Luckily, acute poisoning of humans has almost never been reported, because most people are repelled by the idea of eating or drinking an algal bloom. Toxic algal blooms have been recorded in freshwater areas of several Asiatic countries, but not yet in South-East Asia. The effects of ingesting toxic algal blooms vary. Transmission of neural signals may be blocked by aphanotoxins released by some strains of Aphanizomenon flos-aquae, while anatoxins released by some strains of Anabaena flos-aquae (L.) Bory ex Bornet & Flahault can paralyze skeletal and respiratory muscles or can act as an cholinesterase inhibitor. Strains of species including Anabaena flos-aquae, Aphanizomenon flos-aquae, Microcystis aeruginosa, Oscillatoria agardhii and several others are known or suspected to produce hepatotoxins, which cause death because of liver failure. Because of the toxicity of some blue-green algal strains, commercial harvest, drying, and sale of natural blooms for use as animal feed is not recommended.

In marine environments eukaryotic microalgae are usually involved in toxic blooms, but the marine filamentous cyanophyte Lyngbya majuscula causes rashes (dermatitis) on the skin of susceptible swimmers.

Description

Bluegreen algae are prokaryotic micro-organisms characterized by a low state of cell organization. Cells lack a well-defined nucleus and cell division is by division of the protoplast. These prokaryotic algae are characterized by the absence of flagellated reproductive bodies and sexual reproduction has not yet been recorded. They are unicellular, colonial or filamentous.

The unicellular blue-green algae have cells which are usually spherical, cylindrical or elliptical, with or without a well-defined sheath. Examples include the genera Aphanothece Nägeli, Chroococcus Nägeli, Gloeocapsa Kütz. and Microcystis Kütz. ex Lemmerm.

The simple filamentous types without heterocysts have untapered, unbranched filaments with cells arranged in a linear series (trichomes) like in the genera Lyngbya C. Agardh ex Gomont, Microcoleus Desm. ex Gomont, Oscillatoria Vaucher ex Gomont, Phormidium Kürz. ex Gomont, Plectonema Thuret ex Gomont and Trichodesmium Ehrenb. ex Gomont. In Arthrospira and the genuine Spirulina, the trichomes are helical. The term "filament" is applied here to denote the trichome and the sheath together, although sheaths are lacking in several genera.

The second group of filamentous bluegreen algae has similar untapered and unbranched filaments, but produces specialized cells in the trichomes, such as heterocysts and spores. The heterocysts are the sites of nitrogen fixation. Examples of this type are Anabaena, Aphanizomenon Morren ex Bornet & Flahault, Aulosira Kirchn. ex Bornet & Flahault, Cylindrospermum Kütz. ex Bornet & Flahault, Nodularia Mert. ex Bornet & Flahault. and Nostoc. In Anabaena, some Cylindrospermum and all Nostoc spp. the trichomes have a beaded appearance. The heterocysts are either intercalary or terminal, adjacent to or far away from the spores.

The third group of filamentous bluegreen algae has false branches and untapered heterocystous filaments; typical examples include Scytonema C. Agardh ex Bornet & Flahault and Tolypothrix (Kütz.) ex Bornet & Flahault. These false branches may either be single or paired.

The fourth group of filamentous blue-green algae includes forms in which filaments may or may not show false branching but are distinctly tapered, often ending in a hair. The filaments have basal and sometimes intercalary heterocysts. Examples are Brachytrichia Zanardini ex Bornet & Flahault, Calothrix C. Agardh ex Bornet & Flahault, Gloeotrichia J. Agardh ex Bornet & Flahault and Rivularia C. Agardh ex Bornet & Flahault.

The fifth group of filamentous bluegreen algae exhibits a complex organization. They are often differentiated into a prostrate and erect system with true branching. The cells divide predominantly in two, and sometimes, in three directions. Forms belonging to this group are Hapalosiphon Nägeli ex Bornet & Flahault, Mastigocladus Cohn ex Bornet & Flahault, Stigonema C. Agardh ex Bornet & Flahault and Westiellopsis M. Janet.

Aphanizomenon flos-aquae. Trichomes planktonic, in a bundle, seldom single, straight or bent, without sheath; cells 5-6 μm × 5-15(-60) μm, up to 10 times as long as broad in terminal portions, with gas-vacuoles; heterocysts almost cylindrical, 5-7 μm × 7-20 μm; spores cylindrical, with rounded ends, 6-8 μm × 60-80 μm, epispore smooth and hyaline.

Aphanothece stagnina. Thalli free-floating, gelatinous, spherical or ellipsoidal, up to many cm in diameter, pale blue-green, dull brown or brownish; cells arranged in colonies by homogeneous mucilage, oblong, ovoid or cylindrical, 3-6.5 μm × 4.5-11 μm.

Aulosira fertilissima. Thalli expanded, dark blue-green, membranous; trichomes straight or a little flexuous, parallel or densely intricate; cells (4-)6-11 μm × (5-)7-–10 μm, cylindrical when young, later barrel-shaped, contents granular; sheath thick, at first gelatinous and hyaline, later firm and brown; heterocysts intercalary, oblong or elliptical, 8-9 μm × 10-14 μm; spores in series usually alternating with dead cells, generally -oblongelliptical, sometimes angular due to compression, 10-13 μm × 18-24 μm.

Calothrix scytonemicola. Filaments erect, single or in small groups, lower portion attached to host, 7-8 μm broad in broadest lower portion, tapering into a narrow pointed hair, sheath not distinct; heterocysts basal, 6-8 μm in diameter, usually two in number, somewhat globose.

Cylindrospermum indicum. Trichomes single, motile, with deep constrictions at the joints, 3.7 μm broad, dark blue-green; cells almost quadrate or more or less barrel-shaped, 3-4.5 μm long; heterocysts (sub)spherical, subconical, or ellipsoidal, one at each end of the trichome, 2.8-5.8 μm × 3-7.6 μm; spores ellipsoidal or cylindrical, subterminal at either end of trichome, with thick yellowish-brown outer membrane possessing a smooth outer margin, 8.8-9 μm × 15-18.5 μm without membrane, 10-12 μm × 18-22 μm with membrane.

Hapalosiphon intricatus. Thalli caespitose, blue-green, floccose, thin; filaments densely interwoven, free, not coalescing laterally, 4-7 μm broad, sparsely branched; true branches irregularly lateral, often arising only on one side of filaments, false branches erect from primary prostrate filaments, most branches as broad as and similar to main filaments; sheath close to trichome, colourless, often indistinct; cells in one row, spherical to cylindrical, 1.5-3 times as long as broad; heterocysts intercalary, subquadrate to cylindrical, 3.8-5.5 μm broad; hormogonia formed from side branches; spores spherical to ellipsoidal, rarely nearly cylindrical.

Lyngbya majuscula. Thalli expanded, up to 3 cm long, dull blue-green to brown or yellowish-brown; filaments very long, curved or only slightly coiled, with colourless lamellated sheath up to 11 μm thick, often with rough exterior; trichome blue-green, brownish-green or grey-violet, single in a sheath, not constricted at cross-walls, not attenuated at the ends, 16-60(-80) μm broad; cells very sort, 2-4 μm, 5-6 times broader than long, cross-walls not granulated; end cells rotund, without calyptra.

Mastigocladus laminosus. Thalli membranous to spongy, often firm, hard layered, with calcium carbonate, blackish, blue or olive-green; filaments densely entangled, 4-6(-8) μm broad, curved, when older torulose, with reverse V-shaped short branches (about 3 μm broad) arising on one side; true lateral branching as well as false branches often present; sheath distinct; cells in single series, in main filaments barrel-shaped to short cylindrical, those of side branches cylindrical; heterocysts intercalary, spherical or ellipsoidal, single or two together, up to 6.5 μm broad, thus often broader than vegetative cells.

Microcoleus chthonoplastes. Filaments single or forming expanded dirty to dark green lamellated thalli, unbranched or rarely branched, coiled; sheath colourless, uneven, thick, not lamellated, gelatinizing when old; many densely aggregated trichomes together in one sheath, coiled and contorted like a rope, constricted at cross-walls, 2.5-6 μm broad, not granulated at cross-walls; cells 1-2 times as long as broad, blue-green, 3.6-10 μm long, ends of trichomes straight, mostly attenuated; end cell conical, not capitate.

Microcystis aeruginosa. Colonies planktonic, when young solid, globose or slightly longer than broad, when old becoming net-like, often with attached daughter colonies; cells spherical, 3-7 μm in diameter, without individual envelope, very densely arranged in homogeneous, hyaline mucilage; cell-division in all directions; gas-vacuoles present.

Oscillatoria agardhii. Thalli leathery or in the form of small bundles, free-swimming, trichomes without sheath, straight or curved, not constricted at cross-walls and at ends gradually tapering; cells mostly shorter than long, quadrate, 2.5-4 μm long, granulated at septa, with gas-vacuoles; end cells convex, bluntly conical or more or less pointed, with calyptra, seldom capitate.

Oscillatoria amphibia. Trichomes single, free-swimming, without sheath, straight or coiled, not constricted at cross-walls and not tapering at ends; cells 2-3 times longer than broad, 2-3(-3.5) μm × 4-8.5 μm, with two granules at septa, pale blue-green; end cells not capitate, rounded, calyptra absent.

Scytonema bohneri. Thalli filamentous, blackish-green; filaments partly creeping, partly ascending, 10-12 μm broad, false-branched; branches mostly single, generally narrow, 8-11(-19) μm in diameter, 200-300 μm long, narrower at apex, 6-7 μm in diameter; sheath colourless, 1-1.8 μm thick, homogeneous; trichomes bluish-green, single in each sheath, straight, 5-8 μm broad, not constricted and indistinctly granulated at cross-walls; hormogones terminal; cells rectangular, short at apices, in other parts 0.5-1.5 times as long as broad; heterocysts compressed, ellipsoid to rectangular, 6-8 μm × 5-16 μm, with hyaline wall.

Tolypothrix tenuis. Thalli caespitose or cushion-like, blue-green or brown; repeatedly false-branched, mostly free, erect; false branches single, mostly subtending heterocysts; filaments (4-)6-17(-18) μm broad, up to 2 cm long; sheath thin, close to single trichome, at first colourless, later yellowish-brown, often lamellated; cells (4-)5-13 μm broad, quadrate or longer than broad, blue-green, slightly or not constricted at cross-walls; trichomes with apical growth; heterocysts cylindrical, rounded or discoid, 6-14 μm × 2.3-6 μm, colourless or yellowish, solitary or 2-5 in a row; hormogonia formed from tips.

Trichodesmium erythraeum. Trichomes cylindrical without sheath, in free-swimming purple-red bundles, straight, parallel, constricted at cross-walls, ends gradually attenuated, 7-11(-21) μm broad; cells 0.3-1 times as long as broad, 5.4-11 μm long; apex slightly capitate, with depressed conical or convex calyptra.

Growth and development

Bluegreen algae reproduce vegetatively either by hormogonia, hormocysts, endospores, exospores or akinetes. Hormogonia are small pieces of trichomes with one or many uniform cells. Hormogonium formation is one of the common modes of vegetative reproduction and in some cases (e.g. Nostocales and Stigonematales) the only known mode of propagation. Endospores are small spores formed endogenously within a cell, common in certain unicellular members. Exospores are serially abstracted from the open ends of sporangia by transverse division. In some forms like Microcystis, the cells undergo repeated divisions so that groups of very small cells are formed in each parent cell. These are generally naked protoplasts called nanocytes. Resting spores or akinetes are very large cells with thick walls. They are formed in specific positions in relation to heterocysts and may germinate immediately, giving rise to new trichomes, while others require a resting period. They remain viable for a long time and can often withstand high temperatures and desiccation. An extensive study on blue-green algae of wet-rice fields in Orissa (India) concluded that, in starter cultures for field inoculation of nitrogen-fixing blue-green algae, the emphasis must be both on fast growth and a high nitrogen fixation potential. For that reason members of the genera Aulosira, Calothrix, Tolypothrix and Westiellopsis were preferred over the members of the genera Anabaena, Cylindrospermum, Hapalosiphon and Nostoc which occur naturally in Orissa (India). There is no reason, however, to expect that research in other areas will result in a list of similar genera of blue-green algae.

Other botanical information

The taxonomy of blue-green algae is very complicated. The usage of species and genus limits varies greatly among cyanobacterial taxonomists. The earliest and most practical method used is to compare a species at hand to the morphological description that most closely fits and then designate the use of the taxon name according to the publication that has been used. The morphological phenotype of the originally described species and the species at hand may, however, be totally unrelated because of the scanty and partly unreliable morphological characters. Moreover, a large number of recently described new species have not yet been incorporated into a comprehensive identification handbook. A regrouping of cyanobacteria, almost entirely based on strains in culture, and mainly attempting to redefine or emend the generic limits within these organisms, is known as the "Stanier" system and is based on bacteriological criteria. Species epithets were seldom employed and perhaps never will be; strain numbers replace these. However, it is likely that less than 10% of what will eventually be recognized as genera are now represented as clonal isolates in culture, and an even smaller percentage of the species. Representatives of some genera are difficult or impossible to culture. Another general regrouping and simplification of the blue-green algae taxonomy has been executed mainly by F.E. Drouet and uses the assumption that many of the described taxa represent merely phenotypic variations of the same genotype. These ecophenes are thought to represent pleomorphic responses to environmental diversity. The assumptions used in this regrouping have been made on the basis of vague and non-tested criteria, however, and thus the system is not generally accepted.

The apparent simplification represented by the "Stanier" system is just the beginning of a complex system based on ultrastructure, physiology, biochemistry and genetics, always together with morphology. It also uses molecular data, but is not a phylogenetic classification based on nucleotide sequence data. Some rRNA nucleotide sequence comparisons have already shown that several of the genera in the "Stanier" system are unnatural and should be re-evaluated. A natural, evolutionary classification of cyanobacteria remains far off. The present volume uses cyanobacteria (blue-green algae) names that have been characterized using morphological data. The alternative names according to the "Drouetian" system are included for comparison. Species and genus names of blue-green algae are subject to complicated additional rules in the International Code of Botanical Nomenclature, hence the complicated authors' citations.

Ecology

Bluegreen algae occur in the littoral zone of marine habitats as a black encrusting film on rocks at the upper limit of the hightide mark. The blackish algal zone consists of genera such as Calothrix, Gloeocapsa, Nodularia, Phormidium and Rivularia. Many species are found as epiphytes on larger algae. In salt marshes and mud flats, bluegreen algae (e.g. Microcoleus chthonoplastes) are abundant under microaerophilic conditions; such algal flora are important in stabilizing the mud surfaces. The macroalga Lyngbya majuscula often blooms in coastal areas. Freshwater blooms of bluegreen algae such as Anabaena, Aphanizomenon, Gloeotrichia, Lyngbya, Microcystis and Oscillatoria occur in lakes over the whole year. Some bluegreen algae can grow in hot springs up to temperatures of 70-73°C. A common thermophilic bluegreen alga is Mastigocladus laminosus. In soil habitats, bluegreen algae are restricted to the upper 50 cm of the profile, although some have been found as deep as 20 m below the surface. Bluegreen algae prevent erosion by binding sand and soil particles with their gelatinous sheaths. In paddy soils, up to 70% of the algal flora may consist of blue-green algae. In general, bluegreen algae are only found in waters or soils with a pH > 5. Aphanothece stagnina forms free-floating colonies in lakes, streams and paddy fields. Aulosira fertilissima, Calothrix scytonemicola, Hapalosiphon intricatus, Lyngbya majuscula, Oscillatoria amphibia and Tolypothrix tenuis grow on submerged parts of plants and on soil in pools, ponds and paddy fields, while Cylindrospermum indicum moves slowly (gliding movement) over substrates in these environments. Both Oscillatoria agardhii and O. amphibia as well as Scytonema bohneri occur on moist soils, while Mastigocladus laminosus thrives in muddy locations. When these wet locations dry out, Microcoleus chthonoplastes takes over. Aphanizomenon flos-aquae, Microcystis aeruginosa , Oscillatoria agardhii and O. amphibia are planktonic freshwater algae, of which especially Microcystis aeruginosa often forms water-blooms. Lyngbya majuscula and Microcoleus chthonoplastes occur also in brackish and marine habitats. Brachytrichia quoyi and the nitrogen-fixing Trichodesmium erythraeum are strictly marine; the former is benthic, the latter typically pelagic, forming water-blooms in high seas.

Propagation and planting

In India, dry flakes of a soilbased mixture containing Aulosira, Anabaena, Nostoc, Plectonema, Scytonema and Tolypothrix spp. are distributed to farmers. Farmers then culture the "starter" in 40 m² ponds, producing their own inoculum for their rice fields. Superphosphate fertilizer and insecticide are added to the nonagitated ponds. Recently, there has been a shift towards using pure liquid cultures as inoculum rather than soil-based ones. In this new approach, polythene bags are used as containers, which result in more successful algalization and atmospheric nitrogen productivity in fields.

Bluegreen algae can be cultured using inorganic media such as BG11 and Bold's Basal Medium which contain NO₃ as N-source, and HPO₄² and H₂PO₄ as P-source and as buffering agents. Basal media without combined nitrogen (e.g. Antarikanonda-medium) can be used for culturing species which fix atmospheric nitrogen. In the laboratory, the cultures are aerated with CO₂ enriched air (usually 5% v/v) or agitated by orbital shaking. Stock cultures can be maintained on agar slants (2% w/v) and placed on illuminated shelves. Illumination can be provided by fluorescent lamps (Grolux or Truelite) at an intensity of 42 μmol photon/m² per second in a 12:12 hours lightdark cycle or continuously.

Phycoculture

Blue-green algae, when introduced into the field, are exposed to soil conditions, including chemical constituents.

Algalization is influenced by pH, temperature, light, desiccation and moisture, the presence of indigenous strains of cyanobacteria in the soil, the availability of phosphorus and the methods of N-fertilizer application. Addition of lime can be beneficial to shift the pH of acidic soils to near neutral levels. Phosphorus is often a limiting factor. Molybdenum, being a constituent of the enzymes nitrogenase and nitrate reductase, is important as well. Algalization experiments with high doses of N-fertilizer showed reduced supplementation effects of the blue-green algae. Studies on the physiology and biochemistry of N₂-fixing blue-green algae under metal stress showed that many metals (Cu, Cr, Cd, Fe, Hg, Ni, Pb, Zn) have an inhibitory effect on growth, pigment macromolecules and nitrate uptake. However, agrochemicals such as herbicides, fungicides and insecticides often stimulate cyano-bacterial growth.

It has been shown that nitrogen from cyanobacteria is directly transferred to rice plants, using up to 40% of the cyanobacterial nitrogen within 60 days.

Algalization with blue-green algae has, in general, a positive effect on grain yield. In India, field experiments showed an average yield increase of about 15%. In Thailand yields of wet rice under algalization were 10-20% higher than those without algalization. The beneficial effects of algalization are attributed to growth-promoting substances produced by the blue-green algae and/or to temporary immobilization of the nitrogen fixed by the algae, followed by a slow release after algal decomposition, permitting efficient crop nitrogen utilization. Algalization also has a positive effect on saline and sodic soils, resulting, in laboratory experiments and extrapolations, in reduction of electrical conductivity, soil pH and exchangable sodium.

Diseases and pests

Grazing by ostracods, protozoa, cladocerans, copepods, mosquito larvae and molluscs can have a selective effect on the composition and mixed growth of blue-green algae, as can the action of selected cyanophages, bacteria and fungi.

Harvesting

Blue-green algae are generally not harvested, except when collected as food or grown as inoculum for algalization.

Yield

In Thailand, the yield of bluegreen algae cultivated in culture tanks may reach 200 g dry weight/m² per day. In closed circulation cultures under outdoor conditions, the maximum yield obtained was 7.9 g dry weight/m² per day. The maximum yield obtained from cement algal ponds in Bangkok was 10-15 g dry weight/m² per day.

Genetic resources

Although studies on genetic improvement of blue-green algae for atmospheric nitrogen fixation are frequently undertaken, the results are not yet very promising. The same holds for experiments to genetically improve hydrogen photoproduction.

Prospects

As long as chemical N-fertilizers remain less expensive than the cost of producing, distributing and applying cyanobacteria inocula that do not perform consistently, the incentive for product development by the private sector will not be strong. Nevertheless, freel-iving species of nitrogen-fixing blue-green algae form the only option for possible use of organic N₂-fixation on non-flooded soils.

Research must focus on microbial ecology of bluegreen algae in paddy soils, and screening for fastgrowing species that fix nitrogen. Molecular genetics of nitrogenfixation in bluegreen algae is another area of research that needs to be intensified. Simple quantitative and qualitative methodologies to study blue-green algae in nature should be further developed to prove that algalization is an effective technology.

Phycobiliproteins from blue-green algae can be used as natural pigments in the food, drug and cosmetic industries, and as fluorescent tags in biomedical research. More bluegreen algae should be screened for these pigments, and studies to optimize production of potential species should be carried out. Another promising area is the screening of bluegreen algae for bioactive compounds. Neurotoxins may serve as a tool in the study of neural transmission. Moreover, research on antimicrobial compounds of bluegreen algae should be intensified so that potential new drugs may be developed. In that respect research on inhibiting compounds of different strains of Microcystis aeruginosa, Oscillatoria agardhii and some other blue-green microalgae is promising. These compounds may have medical and laboratory uses. Anti-tumour activities imputable to compounds of cyanobacteria are also currently under study.

Literature

Antarikanonda, P. & Amarit, P., 1992. Research and development of algal biofertilizer in Thailand. Microbial Utilization of Renewable Resources 8: 434-440.
Antarikanonda, P. & Lorenzen, G.H., 1982. N₂-fixing bluegreen algae (Cyanobacteria) of high efficiency from paddy soils of Bangkok, Thailand: characterization of species and N₂fixing capacity in the laboratory. Archives of Hydrobiology (Supplement) 63, Algological Studies 30: 53-70.
Codd, G.A., Edwards, C., Beattie, K.A., Lawton, L.A., Campbell, D.L. & Bell, S.G., 1995. Toxins from cyanobacteria (blue-green algae). In: Wiessner, W., Schnepf, E. & Starr, R.C. (Editors): Algae, environment and human affairs. Biopress Limited, Bristol, United Kingdom. pp. 1-17.
Jha, M.N., Sharma, S.G. & Jha, V.K., 1995. Agroecology of diazotrophic cyanobacteria. In: Kargupta, A.N. & Siddiqui, E.N. (Editors): Algal ecology: an overview. International Book Distributor, Dehradun, India. pp. 195-238.
Metting, B., Zimmermann, W., Crouch, I. & Van Staden, J., 1990. Agronomic uses of seaweed and microalgae. In: Akatsuka, I. (Editor): Introduction to applied phycology. SPB Academic Publishing BV, The Hague, The Netherlands. pp. 589-627.
Nayak, H., Sahu, J.K. & Adhikary, S.P., 1996. Blue-green algae of rice-fields of Orissa State II. Growth and nitrogen fixing potential. Phykos 35: 111-118.
Roger, P.A. & Watanabe, I., 1986. Technologies for utilizing biological nitrogen fixation in wetland rice: potentialities, current usage, and limiting factors. Fertilizer Research 9: 39-77.
Sinha, R.P. & Häder, D.P., 1996. Photobiology and ecophysiology of rice field cyanobacteria. Photochemistry and Photobiology 64: 887-896.
Venkataraman, L.V., 1994. Status of microalgal research and application in India. In: Phang, S.M., Lee, Y.K., Borowitzka, M.A. & Whitton, B.A. (Editors): Algal biotechnology in the Asia-Pacific region. Proceedings of the First Asia-Pacific Conference on Algal Biotechnology. Institute of Advanced Studies, University of Malaya, Kuala Lumpur. pp. 103-112.
Yamaguchi, K., 1997. Recent advances in microalgal bioscience in Japan, with special reference to utilization of biomass and metabolites; a review. Journal of Applied Phycology 8: 487-502.

Sources of illustration

Blue-green algae: van den Hoek, C., Mann, D.G. & Jahns, H.M., 1995. An introduction to phycology. Cambridge University Press, Cambridge, United Kingdom. Figs. 2.4 and 2.5, pp. 21 and 23. Redrawn and adapted by P. Verheij-Hayes.

Authors

S.-M. Phang & P. Antarikanonda