biostudies-literatureKalamara MWellcome TrustBiotechnology and Biological Sciences Research Councile1012050https://www.ebi.ac.uk/biostudies/studies/S-EPMC12935306biostudies-literatureUnknown22(2)Intraspecies interactions shape microbial community structure and evolution, yet the mechanisms determining competitive outcomes among closely related strains remain unclear. The soil bacterium Bacillus subtilis is a model for microbial social interactions, where quorum-sensing systems regulate cooperation and antagonism. Here, we take a multifaceted approach to dissect the role of quorum-sensing regulation in competitive fitness. Isolate NCIB 3610 carries a signal unresponsive RapP-PhrP module that alters quorum-sensing control and promotes faster growth. Modelling and mutant analysis demonstrate that the small differences in growth rate conferred by RapP-PhrP3610 are sufficient to drive competitive exclusion. The importance of quorum sensing control is further exemplified by experimentalPLoS geneticsRegulatory rewiring drives intraspecies competition in Bacillus subtilis.PMC12935306BB/M010996/1BB/R012415/1225350/Z/22/ZBB/X002950/1BB/Z516600/1218520/Z/19/ZBB/P001335/1Griffin JKalamara MBonsall AWood AStevenson DGierlinski MCarneiro JDorfmueller HCPorter MStanley-Wall NREigentler LMacPhee CEAbbott JCfalseRegulatory rewiring drives intraspecies competition in Bacillus subtilis.Intraspecies interactions shape microbial community structure and evolution, yet the mechanisms determining competitive outcomes among closely related strains remain unclear. The soil bacterium Bacillus subtilis is a model for microbial social interactions, where quorum-sensing systems regulate cooperation and antagonism. Here, we take a multifaceted approach to dissect the role of quorum-sensing regulation in competitive fitness. Isolate NCIB 3610 carries a signal unresponsive RapP-PhrP module that alters quorum-sensing control and promotes faster growth. Modelling and mutant analysis demonstrate that the small differences in growth rate conferred by RapP-PhrP3610 are sufficient to drive competitive exclusion. The importance of quorum sensing control is further exemplified by experimental2026-01-01T00:00:00Z2026 Feb2026-07-16T21:34:03.769Z2026-07-12T03:08:28.888ZS-EPMC129353064170178210.1371/journal.pgen.1012050