The effect of light and phosphate concentrations on phosphatase activities of the photosynthetic bacteriumChlorobiumspp.

Abstract

Two species of photosynthetic sulphur bacteria, Chlorobium phaeobacteroides and Chlorobium limicola, found growing under different environmental conditions in the Kinneret, were cultured in the laboratory under various orthophosphate (Pi) concentrations and light intensities. Growth was followed using direct ceil counts, protein content, and pigment content. In general, the same growth pattern was shown by all three parameters and the final cell yields of both species were dependent on ambient Pi concentrations. Chlorobium limicola compensated for low light intensities by increasing pigment production. In addition, light (but not apparently the Pi concentration) influenced the lag period of these cells, with a longer lag observed at lower light intensities. Intra- and extra-cellular activities of both acid and alkaline phosphatases were generally detected in both bacterial species. As Pi levels dropped, both the intra- and extra-cellular activities of acid and alkaline phosphatases increased, suggesting that both enzymes were inducible, although the interaction of P and light limitations was often complex. At high Pi concentrations, residual activities of both acid and alkaline phophatases were detected, probably reflecting the activity of constitutive enzymes not involved in P nutrition of the cells. Extracellular acid and alkaline phophatase activities were low and approximately constant at all light levels. Intracellular activities were relatively high and influenced by light, exhibiting saturation kinetics, and suggest that alkaline phosphatase is more sensitive to light than acid phosphatase. At low Pi concentrations, intracellular phosphatase activities were high and approximately constant over the range of light intensities examined, whereas activities of the extracellular enzymes were low but increased at lower light levels.Key words: photosynthetic bacteria, Chlorobium phaeobacteroides, Chlorobium limicola, growth, phosphate concentration, phosphatases.