[Photosynthetic oxygen evolution and CO2 photoassimilation by cyanobacteria that form water-bloom spots in a sulfur spring with a high sulfide content]

Cyanobacteria belonging mainly to the genera Anabaena and Oscillatoria were isolated from water-bloom spots of a sulfur spring in Staraya Matsesta. Their suspensions evolved O2 at a rate of 6--8 nM/min per 1 mg of dry cell weight at an intensity of solar radiation being 60--75 mV/cm2 per 1 sec. The cells were also capable of CO2 photoassimilation in the presence of solfide at a rate of 10(-4) mg C per mg per hour. DCMU at a concentration of 10(-5) M completely inhibited O2 evolution and inhibited CO2 fixation by 80%. Oxygen assimilation in dark by the suspensions did not depend on the addition of cyanide and was caused apparently by nonenzymatic reduction of O2 with sulfide dissolved in the spring water. Oxygen assimilation by the suspensions in light in the presence of DCMU was by 20--30% greater than in dark. Therefore, the cells of cyanobacteria are characterized by photorespiration at the level of photosystem I. Presumably, sulfide at a concentration of 9 mM cannot significantly inhibit the photosynthetic processes in cyanobacteria producing water-bloom spots in the sulfur spring.