Mechanism of the Combined Effects of Bacillus subtilis FHC 402-Derived Antibacterial Factor and Hexametaphosphate on Escherichia coli

The combined use of Bacillus subtilis FHC 402-derived antibacterial factor (BAF) and hexametaphosphate (HP) inhibited the growth of E. coli. To elucidate the mechanism of the inhibition, the effects of BAF and/or HP on respiration, liberation of cellular components, and macromolecular synthesis were studied. HP liberated protein, LPS, and Mg²⁺ from the cells, suggesting damage to the membrane. Further, HP decreased oxygen uptake and the incorporation of [¹⁴C]leucine, [³H]uridine, and [³H]thymidine into the cells. In contrast, BAF did not damage the outer membrane nor enhance the effects of HP on the membrane. HP or BAF had little or no effect on the incorporation of labeled compounds into the TCA-insoluble fraction. The combined use of BAF and HP decreased the incorporation of [¹⁴C]leucine into the fraction much more than that of [³H]uridine and [³H]thymidine, suggesting that the combined use essentially inhibits protein synthesis but not RNA and DNA synthesis. BAF also inhibited protein synthesis in the cell-free system. The antibacterial action of the combined use of BAF and HP in E. coli seems likely to be that the damage to the outer membrane caused by HP enables BAF to penetrate the membrane and inhibit protein synthesis.