Sodium transport in filamentous nitrogen fixing cyanobacteria.

ABSTRACT

Two filamentous, nitrogen fixing cyanobacteria were examined for their salt tolerance and sodium (Na+) transport. Anabaena torulosa, a saline form, grew effi ciently and fixed nitrogen even at 150 mM salt (NaCl) concentration while, Anabaena L 31, a fresh water cyanobacterium, failed to grow beyond 35 mM NaCl. Anabaena torulosa showed a rapidly saturating kinetics of Na+ transport with a high affinity for Na+ (Km , 0.3 mM). Anabaena L 31 had a much lower affinity for Na+ (Km , 2.8 mM) than Anabaena torulosa and the pattern of uptake was somewhat different. Both Ana baena spp. exhibited an active Na+ extrusion which seems to be mediated by a Na+ K+ ATPase and aided by oxidative phosphorylation. Anabaena L 31 was found to retain much more intracellular Na+ than Anabaena torulosa. The results suggest that the saline form tolerates high Na+ concentrations by curtailing its influx and also by an efficient Na+ extrusion, although these alone may not entirely account for its success in saline environment.