Active transport and accumulation of bicarbonate by a unicellular cyanobacterium

Abstract

The rates of inorganic C accumulation and C fixation in light by the unicellular cyanobacterium Coccochloris peniocystis were determined. Cells incubated in the light in medium containing H14CO3- were rapidly separated from the medium by centrifugation through silicone oil into a strongly basic terminating solution. Samples of these inactivated cells were assayed to determine total 14C accumulation, and acid-treated samples were assayed to determine 14C fixation. The rate of transport of inorganic C into illuminated cells was faster than the rate of CO2 production in the medium from HCO3- dehydration. This evidence for HCO3- transport in these cells is in agreement with previous results based upon measurements of photosynthetic O2 evolution. A substantial pool of inorganic C was built up within the cells presumably as HCO3- before the onset of the maximum rate of photosynthesis. Large accumulation ratios were observed, greater than 1000 times the external HCO3- concentration. Accumulation did not occur in the dark and was greatly suppressed by the photosynthesis inhibitors 3-(3,4-dichlorophenyl)-1,1-dimethyl urea and 3-chloro-carbonylcyanide phenylhydrazone. The accumulation of inorganic C in these cells probably involves a light-dependent active transport process.