TOLERANCE OF NITROGEN-FIXING CYANOBACTERIA TO NACL

Eleven species of nitrogen-fixing cyanobacteria belonging to six gener a (Cylindrospermum, Anabaena, Nostoc, Calothrix, Scytonema, and Westie llopsis) tolerate different concentrations of NaCl (from 0.05 to 0.35 M). Wide variation in the chlorophyll (Chi) a content of the species o f the same genus and between genera in presence of NaCl was observed. The least tolerant (Cylindrospermum sp., Cy 6), the maximum tolerant ( Westiellopsis sp., We 1), and the intermediate tolerant (Westiellopsis sp., We 6) species of cyanobacteria were selected, and their response to various concentrations of NaCl (growth, nitrogen-fixing capacity, and production of extracellular substances) was studied. Nitrogen fixi ng capacity of both the We 1 and We 6 was greatly impaired in comparis on to the decrease in their Chi a content in the NaCl containing media . Cellular and extracellular saccharide and extracellular amino acid c ontents of the cyanobacteria species in the NaCl supplemented cultures were increased suggesting that presence of saccharides and amino acid s enabled the cyanobacterial species to thrive under salt stress. Furt her, the We 1 did not adapt to the salt whereas Cy 6 showed adaptation to low concentrations of NaCl suggesting that the species which toler ate high concentrations of the salt may not possess the ability to ada pt to NaCl.