Inorganic polyphosphate in Bacillus cereus: Motility, biofilm formation, and sporulation

Chains of inorganic polyphosphate (poly-P) with hundreds of P_i residues linked by phosphoanhydride bonds, as in ATP, are found in every bacterial, fungal, plant, and animal cell, in which they perform various functions. In the spore-forming Bacillus cereus, we have identified three principal enzymes and genes involved in the metabolism of poly-P, namely, (i) poly-P kinase (PPK), which synthesizes poly-P reversibly from ATP, (ii) exopolyphosphatase (PPX), which hydrolyzes poly-P to P_i, and (iii) poly-P/AMP phosphotransferase (PAP), which uses poly-P as a donor to convert AMP to ADP, reversibly. In the null mutant of ppk, poly-P levels are reduced to <5% of the WT; in the ppx mutant, the PPK activity is elevated 10-fold, and the accumulation of poly-P is elevated ≈1,000-fold. All of the null mutants of ppk, ppx, and pap showed defects in motility and biofilm formation, but sporulation efficiency was impaired only in the ppx mutant. These enzymes and genes in B. cereus are nearly identical to those in the very closely related pathogen Bacillus anthracis, and, thus, they may provide attractive targets for the treatment of anthrax.