Long-chain polyphosphate causes cell lysis and inhibits Bacillus cereus septum formation, which is dependent on divalent cations

We investigated the cellular mechanisms that led to growth inhibition, morp hological changes, and lysis of Bacillus cereus WSBC 10030 when it was chal lenged with a long-chain polyphosphate(polyP). At a concentration of 0.1% o r higher, polyp had a bacteriocidal effect on log-phase cells, in which it induced rapid lysis and reductions in viable cell counts of up to 3 log uni ts. The cellular debris consisted of empty cell wall cylinders and polar ca ps, suggesting that polyp-induced lysis was spatially specific, This activi ty was: Strictly dependent on active growth and cell division, since polyp failed to induce lysis in cells treated with chloramphenicol and in station ary-phase cells, which were, however, bacteriostatically inhibited by polyp , Similar observations were made with B. cereus spores; 0.1% polyp inhibite d spore germination and outgrowth, and a higher concentration (1.0%) was ev en sporocidal, Supplemental divalent metal ions (Mg2+ and Ca2+) could almos t completely block and reverse the antimicrobial activity of polyp; i.e., t hey could immediately stop lysis and reinitiate rapid cell division and mul tiplication. Interestingly, a sublethal polyP concentration (0.05%) led to the formation of elongated cells (average length, 70 mu m) after 4 h of inc ubation, While DNA replication and chromosome segregation were undisturbed, electron microscopy revealed a complete lack of septum formation within th e filaments. Exposure to divalent cations resulted in instantaneous formati on and growth of ring-shaped edges of invaginating septal walls. After appr oximately 30 min, septation was complete, and cell division resumed. We fre quently observed a minicell-like phenotype and other septation defects, whi ch were probably due to hyper-division activity after cation supplementatio n. We propose that polyP may have an effect on the ubiquitous bacterial cel l division protein FtsZ, whose GTPase activity is known to be strictly depe ndent on divalent metal ions. It is tempting to speculate that polyp, becau se of its metal ion-chelating nature, indirectly blocks the dynamic formati on (polymerization) of the Z ring, which would explain the aseptate phenoty pe.