Impact of Rap-Phr system abundance on adaptation of Bacillus subtilis

Microbes commonly display great genetic plasticity, which has allowed them to colonize all ecological niches on Earth. Bacillus subtilis is a soil-dwelling organism that can be isolated from a wide variety of environments. An interesting characteristic of this bacterium is its ability to form biofilms that display complex heterogeneity: individual, clonal cells develop diverse phenotypes in response to different environmental conditions within the biofilm. Here, we scrutinized the impact that the number and variety of the Rap-Phr family of regulators and cell-cell communication modules of B. subtilis has on genetic adaptation and evolution. We examine how the Rap family of phosphatase regulators impacts sporulation in diverse niches using a library of single and double rap-phr mutants in competition under 4 distinct growth conditions. Using specific DNA barcodes and whole-genome sequencing, population dynamics were followed, revealing the impact of individual Rap phosphatases and arising mutations on the adaptability of B. subtilis. Ramses Gallegos-Monterrosa, Mathilde Nordgaard Christensen, and colleagues investigate how a single or double deletion of the rap-phr genes, parts of peptide-based quorum sensing systems, impacts the sporulation and biofilm formation of B. subtilis under four different conditions and a multitude of strains. Using strain-specific barcoding and complete genome sequencing, the authors show that competitive selection is driven by acquired mutations, and that selected strains demonstrate increased spore fitness relative to their ancestors and wild types.