Nitrogen-fixation by non-heterocystous cyanobacteria in an antarctic ecosystem

Unicellular, non-heterocystous, diazotrophic cyanobacteria Gloeocapsa sp. i solated from Schirmacher Oasis, Antarctica. showed N-2-fixation (C2H2-reduc tion) which was comparable to that of Gloeocapsa sp. isolated from a tropic al rice field. The optimum temperature of the Antarctic isolate for nitroge nase activity was 20 degreesC, whereas the tropical isolate expressed its m aximum activity at 30 degreesC. Sucrose supported the nitrogenase activity of both the isolates in darkness. The results indicated that the Antarctic isolate behaved differently with respect to temperature compared to the tro pical isolate.