Polyphosphate accumulation by Rhodobacter sphaeroides grown under different environmental conditions with special emphasis on the effect of external phosphate concentrations.

Abstract

hedobacter sphaeroides NR3 produced significant amounts of inorganic polyphosphates (polyPs) with visible velutin granules when grown phototrophically at external orthophesphate (Pi) conoentratiens of 10 mM and above with 20 mM malatc as the sole carbon source. The maximum level of the accumulated pelyPs, amounting to 6,2% of thc cell dry weight, was ibund with 3oo mM Pd. On the other hand, the stimulatory effect of excess P, on polyP accumulation was not so prenounced in the cells grown under aerobic-daTk conditions. The fractionation of the cel]ular pbosphorous eom- pounds reycaled that the alkali-soluble and cold acid-soluble polyPs were the major polyPs in the high Pd-loaded phototrephic cultures. The phosphorus/carbon raLio in eell growth media was also found as an important factor atrecting pulyP accpmulation in the bacterium. There was an antagonistic relationship between the polyP centent and lhe RNAIDNA ratio during batch phototrophic growth. Ecophysiological implications of pelyP accumuLation in the phototrophic bacterium were also discus- sed,