Uses
Because of its high nutritional value, spirulina has been used both to promote weight gain in malnourished clients, to promote weight loss, and for oral leukoplakia.
Agricultural Uses
Cyanobacteria, earlier called blue-green algae (BGA), are unicellular, filamentous bacteria whose nitrogen fixing ability - both independently as well as in association with plants - makes them a valuable biofertilizer
Anabaena azolhe form large colonies in the leaf cavities of the free floating fern Azolla pinnata. Rice cultivation in South-East Asia uses enormous amounts of this fern as a source of biofertilizer. The water fern and tropical herb Gunnera macrophylla have a symbioticr elationship with blue-green bacteria.
Cyanobacteria can also fix nitrogen without associating with the plant. They are the main micro- organisms in desert soils, and are known to increase the nitrogen content of that soil. It should be noted, however, that only some species of blue-green algae of the genera Nostoc, Scytonema and Anabaena can fix atmospheric nitrogen in a solution culture. These bacteria derive food from sunlight and nitrogen from the atmosphere. Their respiration is either aerobic or anaerobic. The aerobic filamentous bacteria form heterocysts, the site of nitrogen fixation. Heterocysts are large, thick-walled cells that grow between pigmented cells on the algal filament. Vegetative cells and heterocyst cells are interdependent for nitrogen fixation. Heterocysts derive the enzyme reductase in the form of D-glucose-6 phosphate, pyruvate or isocitrate from photosynthesising vegetative cells. Vegetative cells depend on heterocysts for nitrogen nutrition in the form of glutamine, glutamate and other amino acids.
Mass production of cyanobacteria used in the production of biofertilizers utilizes soil-based algae inoculants. BGA production involves four methods which are (a) pit method, (b) trough method, (c) field method, and (d) nursery-cum-algae production method.
Anaerobic bacteria are facultative, meaning, they can live in different environments. They fix nitrogen without forming heterocysts. Cyanobacteria take 20hours to double. This biofertilizer is recommended for submerged rice crops as it enhances the yield by about 15 to 20%. Besides their ability to fix nitrogen, the cyanobacteria also produce some useful substances like auxins, vitamins of Blz group, indolacetic acid and gibberellic acid.
Blue-green algae are a source of biofertilizers and are available in the form of dried algal flakes They may contribute 25 to 30kg of nitrogen per hectare per cropping season, depending on the ecological conditions.
