Bacteria and other prokaryotes evolve primarily through rapid changes in their gene content by quickly losing and gaining genes whenever an ecological opportunity emerges. As gene loss and horizontal gene transfer (HGT) appear to be the most common events across the prokaryotic tree of life, we need to think beyond gradual sequence evolution if we wish to understand the microbial world. Especially genes that reside on mobile genetic elements (MGEs) may spread much more rapidly through a microbial population than genes that reside on the bacterial chromosome. This raises the question: why are some genes associated with MGEs, while others are not? Here, I briefly review a recently proposed class of genes for which we have coined the term “rescuable genes”. The fitness effect of carrying these genes is so small, either constantly or on average, that they are prone to be lost from a microbial population. I argue that HGT, even when costly to the individual cells, may play an important role in maintaining these rescuable genes in microbial communities.

细菌和其他原核生物的进化主要是通过其基因内容的快速变化，每当生态机会出现时，就会快速失去和获得基因。由于基因丢失和水平基因转移（HGT）似乎是原核生命树中最常见的事件，如果我们希望了解微生物世界，我们需要超越渐进序列进化的思维。尤其是位于移动遗传元件（MGE）上的基因在微生物群体中的传播速度可能比位于细菌染色体上的基因快得多。这就提出了一个问题：为什么有些基因与 MGE 相关，而另一些则不然？在这里，我简要回顾一下最近提出的一类基因，我们为它们创造了术语“可拯救基因”。携带这些基因的适应性效应无论是持续的还是平均的都很小，以至于它们很容易从微生物种群中消失。我认为，即使 HGT 对单个细胞来说代价高昂，它也可能在维持微生物群落中这些可挽救基因方面发挥重要作用。