INORGANIC POLYPHOSPHATE AND THE INDUCTION OF RPOS EXPRESSION

Inorganic polyphosphate [poly(P)] levels in Escherichia coil were redu ced to barely detectable concentrations by expression of the plasmid-b orne gene for a potent yeast exopolyphosphatase [poly(P)ase]. As a con sequence, resistance to H2O2 was greatly diminished, particularly in k atG (catalase HPI) mutants, implying a major role for the other catala se, the stationary-phase KatE (HPII), which is rpoS dependent. Resista nce was restored to wild-type levels by complementation with plasmids expressing ppk, the gene for PPK [the polyphosphate kinase that genera tes poly(P)], Induction of expression of both katE and rpoS (the stati onary-phase sigma factor) was prevented in cells in which the poly(P)a se was overproduced, Inasmuch as this inhibition by poly(P)ase did not affect the levels of the stringent-response guanosine nucleotides (pp pGpp and ppGpp) and in view of the capacity of additional rpoS express ion to suppress the poly(P)ase inhibition of katE expression, a role i s proposed for poly(P) in inducing the expression of rpoS.