Analysis of cell death in Bacillus subtilis caused by sesquiterpenes from Chrysopogon zizanioides (L.) Roberty

[摘要] Recently, the antibacterial effects of essential oilshave been investigated in addition to their therapeutic purposes. Owing to their hydrophobic nature,they are thought to perturb the integrity of the bacterial cell membrane, leading to cell death. Againstsuch antibiotic challenges, bacteria develop mechanisms for cell envelope stress responses (CESR).In Bacillus subtilis, a gram-positive sporulating soilbacterium, the extracytoplasmic function (ECF)sigma factor-mediated response system plays a pivotal role in CESR. Among them, σM is stronglyinvolved in response to cell envelope stress, including a shortage of available bactoprenol. Vetiveressential oil, a product of Chrysopogon zizanioides (L.)Roberty root, is also known to possess bactericidalactivity. σM was exclusively and strongly inducedwhen the cells were exposed to Vetiver extract, anddepletion of multi-ECF sigma factors (ΔsigM, ΔsigW,ΔsigX, and ΔsigV) enhanced sensitivity to it. Fromthis quadruple mutant strain, the suppressor strains,which restored resistance to the bactericidal activity of Vetiver extract, emerged, although attemptsto obtain resistant strains from the wild type didnot succeed. Whole-genome resequencing of thesuppressor strains and genetic analysis revealedinactivation of xseB or pnpA, which code for exodeoxyribonuclease or polynucleotide phosphorylase,respectively. This allowed the quadruple mutantstrain to escape from cell death caused by Vetiverextract. Composition analysis suggested that thesesquiterpene, khusimol, might contribute to thebactericidal activity of the Vetiver extract.

[学科分类] 微生物学和免疫学

[关键词] Bacillus subtilis;cell death;essentialoils;sesquiterpenes;undecaprenol