Bottlenecked reproduction enables cooperating bacteria to purge cheaters.

Bacteria engage in social cooperations to ensure survival and reproduction in adverse environments. Numerous bacterial sociality genes (SGs) are dedicated to such cooperations. Mutant bacteria carrying loss-of-function mutations (LOFMs) in SGs are frequently shielded from purifying selection by cooperative wild-type peers. Yet, in absence of active purging, such mutants would persist and proliferate in bacterial populations, ultimately crippling cooperation. We propose the hypothesis of bottlenecked reproduction at foci of cooperation (BRFC) to address this problem. This hypothesis stipulates that bacterial reproduction at foci of cooperative colonization is bottlenecked, allowing extremely few individuals to initiate proliferation and dispersal. Note that mutant individuals carrying SG LOFMs are just as likely to escape as their wild-type peers. However, if this is to occur, the resulting mutant lineage, upon dispersing to a new site, would fail at renewed reproduction. Interrogation of this hypothesis should unveil bacterial vulnerabilities that can be exploited to combat bacterial diseases.