Abstract
Rhodobacter sphaeroides NR3 produced significant amounts of inorganic polyphosphates (polyPs) with visible volutin granules when grown phototrophically at external orthophosphate (Pi) concentrations of 10 mM and above with 20 mM malate as the sole carbon source. The maximum level of the accumulated polyPs, amounting to 6.2% of the cell dry weight, was found with 300 mM Pi. On the other hand, the stimulatory effect of excess Pi on polyP accumulation was not so pronounced in the cells grown under aerobic-dark conditions. The fractionation of the cellular phosphorous compounds revealed that the alkali-soluble and cold acid-soluble polyPs were the major polyPs in the high Pi-loaded phototrophic cultures. The phosphorus/carbon ratio in cell growth media was also found as an important factor affecting polyP accumulation in the bacterium. There was an antagonistic relationship between the polyP content and the RNA/DNA ratio during batch phototrophic growth. Ecophysiological implications of polyP accumulation in the phototrophic bacterium were also discussed.
