Department of Biological Sciences, University at Buffalo, Buffalo, NY, USA.
Microbiologyopen. 2019 Feb;8(2):e00636. doi: 10.1002/mbo3.636. Epub 2018 Apr 19.
Temperate phage encoded Shiga toxin (Stx) kills the bacterivorous predator, Tetrahymena thermophila, providing Stx Escherichia coli with a survival advantage over Stx cells. Although bacterial death accompanies Stx release, since bacteria grow clonally the fitness benefits of predator killing accrue to the kin of the sacrificed organism, meaning Stx-mediated protist killing is a form of self-destructive cooperation. We show here that the fitness benefits of Stx production are not restricted to the kin of the phage-encoding bacteria. Instead, nearby "free loading" bacteria, irrespective of their genotype, also reap the benefit of Stx-mediated predator killing. This finding indicates that the phage-borne Stx exotoxin behaves as a public good. Stx is encoded by a mobile phage. We find that Stx-encoding phage can use susceptible bacteria in the population as surrogates to enhance toxin and phage production. Moreover, our findings also demonstrate that engulfment and concentration of Stx-encoding and susceptible Stx bacteria in the Tetrahymena phagosome enhances the transfer of Stx-encoding temperate phage from the host to the susceptible bacteria. This transfer increases the population of cooperating bacteria within the community. Since these bacteria now encode Stx, the predation-stimulated increase in phage transfer increases the population of toxin encoding bacteria in the environment.
温和噬菌体编码的志贺毒素（Stx）杀死了噬菌的捕食者，嗜热四膜虫，为产志贺毒素的大肠杆菌提供了比产 Stx 细胞更具生存优势。尽管细菌死亡伴随着 Stx 的释放，但由于细菌以克隆方式生长，捕食者杀死的适应性益处会归属于牺牲生物体的亲缘，这意味着 Stx 介导的原生动物杀伤是一种自我毁灭的合作形式。我们在这里表明，Stx 产生的适应性益处不仅限于噬菌体编码细菌的亲缘。相反，附近的“免费搭车”细菌，无论其基因型如何，也能从 Stx 介导的捕食者杀伤中受益。这一发现表明，噬菌体携带的 Stx 外毒素表现为一种公共产品。Stx 由移动噬菌体编码。我们发现，编码 Stx 的噬菌体可以利用种群中的易感细菌作为替代物来增强毒素和噬菌体的产生。此外，我们的研究结果还表明，噬菌体内吞和浓缩编码 Stx 的和易感的 Stx 细菌会增强 Stx 编码的温和噬菌体从宿主转移到易感细菌的过程。这种转移增加了群落内合作细菌的数量。由于这些细菌现在编码 Stx，受捕食刺激的噬菌体转移增加了环境中编码毒素的细菌的数量。
