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Cyanobacteria and green algae are phototrophic microorganisms showing high diversity in their cellular structure in response to the environmental conditions of the niche where they occur. Production of exopolysaccharides (EPS) in response to adverse conditions is one of the important features of these organisms. EPS are present mainly around their cells/ filaments as an enveloped layer and released outside. EPS play protective functions and are important for their survival in stressed habitats exposed to radiation, desiccation and elevated temperatures. This review discusses the production, extraction and possible commercial applications of EPS produced by cyanobacteria and green algae.

Cyanobacterial biofilms occurring on the exterior of three stone monuments at Santiniketan, India were analyzed. Species of Scytonema and Tolypothrix were the major components of these biofilms. Identification was obtained by morphometric procedures and 16S rRNA gene sequencing. Biofilms cultured for prolonged periods revealed the presence of several other cyanobacteria belonging to 14 different genera. Cyanobacteria on stone in the tropical environment of India formed a distinct cluster that was quite different from that of cyanobacteria reported for a similar substratum in temperate regions. Absorption spectra of the organisms from Santiniketan showed a high quantity of scytonemin, mycosporine-like amino acids, and carotenoids. All of the organisms survived in a desiccated state and rapidly revived after wetting. The organisms were heterocystous and nitrogenase activity was reactivated within 24 h of wetting by which time heterocysts in their filaments had also appeared.

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