SULFATE-LIMITED GROWTH IN THE N-2-FIXING UNICELLULAR CYANOBACTERIUM GLOEOTHECE (NAGELI) SP PCC-6909

The unicellular diazotrophic cyanobacterium Gloeothece PCC 6909 was gr own in batch and continuous culture. It was found that the organism sc avenged sulphate from the medium and incorporated it in the polysaccha ride sheath. As a result batch cultures became sulphur-depleted whilst continuous cultures were sulphur-limited. This was observed regardles s of the nitrogen source of the culture. Sulphur-depletion was the rea son for the low nitrogenase activities usually observed in batch cultu res of Gloeothece. Sulphate-amended cultures showed sustained high nit rogenase activity in the light. Sulphate uptake from the medium was li ght-dependent. Earlier work on N-2 fixation in Gloeothece is discussed in the light of possible sulphur limitation.