Polyphosphate Formation from Pyrophosphate in Intact Cells of a Photosynthetic Bacterium, Rhodospirillum rubrum

The hypothesis that the photosynthetic bacterium, Rhodospirillum rubrum, may synthesize polyphosphate using pyrophosphate as a precursor has been tested. The cells were cultured in the pyrophosphate media, and the cell yield, cell shape, and the polyphosphate content were determined and compared with that grown in the orthophosphate media. In the control experiment, the total amount of polyphosphate formed by the cultures grown in the pyrophosphate media was found to be up to 70% less than that grown in orthophosphate media. When the ATP formation was blocked by using the phosphorylation inhibitor, antimycin A, however, the cells grown in the pyrophosphate media formed up to 50% more polyphosphate than that grown in the orthophosphate media. The results seem to support the hypothesis that Rhodospirillum rubrum may use pyrophosphate as the precursor of polyphosphate.