Abstract
Cyanobacteria (also known as blue-green algae) are a group of extraordinarily diverse Gram-negative prokaryotes that originated 3.5 billion years ago. Their diversity ranges from unicellular to multicellular, coccoid to branched filaments, nearly colourless to intensely pigmented, autotrophic to heterotrophic, psychrophilic to thermophilic, acidophilic to alkylophilic, planktonic to barophilic, freshwater to marine including hypersaline (salt pans). They are found both free living and as endosymbionts. They are considered to be one of the potential organisms which can be useful to mankind in various ways. A number of important advances have occurred in cyanobacterial biotechnology in the recent years. World wide attention is drawn towards cyanobacteria for their possible use in mariculture, food, feed, fuel, fertilizer, colourant, production of various secondary metabolites including vitamins, toxins, enzymes, pharmaceuticals, pharmacological probes and pollution abatement. Only a few cyanobacterial strains (including Spirulina) have been well-characterized or exploited commercially. Basic research is needed to identify new cyanobacterial strains of high value products, strain improvement using molecular tools for rapid growth rate, ability to withstand varied environmental conditions and enhancement of synthesis of high value products. This review is intended to focus on the biodiversity of cyanobacteria in various environments, recent application and new developments that are diversifying the directions for commercial exploitation.