Tolerance of nitrogen-fixing cyanobacteria to NaCl

Abstract

Eleven species of nitrogen-fixing cyanobacteria belonging to six genera (Cylindrospermum, Anabaena, Nostoc, Calothrix, Scytonema, and Westiellopsis) tolerate different concentrations of NaCl (from 0.05 to 0.35 M). Wide variation in the chlorophyll (Chl) a content of the species of 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 fixing capacity of both the We 1 and We 6 was greatly impaired in comparison to the decrease in their Chl a content in the NaCl containing media. Cellular and extracellular saccharide and extracellular amino acid contents of the cyanobacteria species in the NaCl supplemented cultures were increased suggesting that presence of saccharides and amino acids enabled the cyanobacterial species to thrive under salt stress. Further, the We 1 did not adapt to the salt whereas Cy 6 showed adaptation to low concentrations of NaCl suggesting that the species which tolerate high concentrations of the salt may not possess the ability to adapt to NaCl.