Temperate phages are pervasive in bacterial genomes, existing as vertically inherited islands termed prophages. Prophages are vulnerable to predation of their host bacterium by exogenous phages. Here, we identify BstA, a family of prophage-encoded phage-defense proteins in diverse Gram-negative bacteria. BstA localizes to sites of exogenous phage DNA replication and mediates abortive infection, suppressing the competing phage epidemic. During lytic replication, the BstA-encoding prophage is not itself inhibited by BstA due to self-immunity conferred by the anti-BstA (aba) element, a short stretch of DNA within the bstA locus. Inhibition of phage replication by distinct BstA proteins from Salmonella, Klebsiella, and Escherichia prophages is generally interchangeable, but each possesses a cognate aba element. The specificity of the aba element ensures that immunity is exclusive to the replicating prophage, preventing exploitation by variant BstA-encoding phages. The BstA protein allows prophages to defend host cells against exogenous phage attack without sacrificing the ability to replicate lytically.

温带噬菌体普遍存在于细菌基因组中，作为称为原噬菌体的垂直遗传岛存在。噬菌体很容易被外源噬菌体捕食宿主细菌。在这里，我们确定了 BstA，这是一个在不同革兰氏阴性细菌中的原噬菌体编码的噬菌体防御蛋白家族。BstA 定位于外源噬菌体 DNA 复制的位点并介导流产感染，抑制竞争性噬菌体流行。在裂解复制过程中，由于抗 BstA ( aba ) 元件（bstA基因座内的一小段DNA）赋予的自身免疫，BstA 编码原噬菌体本身不会被 BstA 抑制。来自沙门氏菌、克雷伯氏菌和大肠杆菌原噬菌体通常可以互换，但每个都具有同源的aba元素。aba元件的特异性确保免疫是复制原噬菌体所独有的，防止被变异的 BstA 编码噬菌体利用。BstA 蛋白允许原噬菌体保护宿主细胞免受外源噬菌体攻击，而不会牺牲裂解复制的能力。