細菌の細胞競合

Not so simple, not so subtle: the interspecies competition between Bacillus simplex and Bacillus subtilis and its impact on the evolution of biofilms.  NPJ Biofilms and Microbiomes 2: 15027.

Bacillus subtilis biofilms have a fundamental role in shaping the soil ecosystem. During this process, they unavoidably interact with neighbour bacterial species. We studied the interspecies interactions between biofilms of the soil-residing bacteria B. subtilis and related Bacillus species. We found that proximity between the biofilms triggered recruitment of motile B. subtilis cells, which engulfed the competing Bacillus simplex colony. Upon interaction, B. subtilis secreted surfactin and cannibalism toxins, at concentrations that were inert to B. subtilis itself, which eliminated the B. simplex colony, as well as colonies of Bacillus toyonensis. Surfactin toxicity was correlated with the presence of short carbon-tail length isomers, and synergistic with the cannibalism toxins. Importantly, during biofilm development and interspecies interactions a subpopulation in B. subtilis biofilm lost its native plasmid, leading to increased virulence against the competing Bacillus species. Overall, these findings indicate that genetic programs and traits that have little effect on biofilm development when each species is grown in isolation have a dramatic impact when different bacterial species interact.

バイオフィルムを形成中の細菌のコロニーが他種のコロニーに出会ったとき、競合が起こる。といってもこれはinterspecies competitionなので、うちらが見ている細胞競合とはちょっと違うけど、こういう異種細胞間での拮抗現象（antibiosis）というのは 昔々から微生物学で研究されてきたものであり、抗生物質なんかはまさにそのcompetitionにおいて他種の細胞機能を阻害するものなんやね。ここで出てくる枯草菌も、他種のコロニーに近づくとSurfactinやcannibalism toxinsといった毒素を放出して、相手にgrowth inhibitionやcell deformationを誘導する。そしてさらに、バイオフィルムの中から運動性のやつらが出てきて競合相手のコロニーを飲み込んでしまう。上皮組織でのcell competitionにおいても隣接細胞によるengulfmentは報告されているけど、微生物が使う抗生物質みたいなものは発見されていない。