RESPONSE OF THE CYANOBACTERIUM NOSTOC MUSCORUM TO CHROMIUM AND LEAD: THE EFFECT ON PHOSPHORUS METABOLISM

Significant amelioration of Cr and Pb toxicity was observed in Nostoc muscorum at high concentrations of phosphate. The effect of Cr and Pb on growth, photosynthetic oxygen evolution, carbon and nitrogen fixation of N. muscorum was less in cultures pre- and post-treated with high (80 μM) phosphate concentration than in those treated with a lower (20μM) orthophosphate concentration. The uptake of Cr and Pb in the cyanobacterial cells was not affected by phosphate concentration. Likewise phosphate uptake was not disturbed either by Cr or Pb. A rapid accumulation of polyphosphate bodies in the cells treated with Cr and Pb indicates that uptake and accumulation of phosphate was not inhibited. N. muscorum cells exposed to both the metals registered a notable decrease in the breakdown of polyphosphate bodies and acid and alkaline phosphatase activities. Cr and Pb competitively inhibited the activity of partially purified acid and alkaline phosphatases. It is concluded that Cr and Pb affect intracellular phosphate metabolism rather than the uptake and incorporation of phosphate in N. muscorum.