In Pseudomonas aeruginosa PAO1, we have found massive polyphosphate:AMP phosphotransferase activity and polyphosphate:ADP phosphotransferase activity known as the reverse catalytic activity of polyphosphate kinase which participates in polyphosphate synthesis in the bacterium. Biochemical analysis using the partially purified polyphosphate:ADP phosphotransferase has revealed that it is independent of polyphosphate kinase and can function as polyphosphate-dependent nucleoside diphosphate kinase which most prefers GDP to the other three nucleoside diphosphates as a phospho-acceptor. It has been also demonstrated that polyphosphate:AMP phosphotransferase activity marked in the bacterium mainly originates from the combined action of the polyphosphate:ADP phosphotransferase described above and adenylate kinase. Both of the polyphosphate-utilizing activities require short polyP as a phospho-donor whose chain length is <75.