The ytrGABCDEF operon controls cell size, growth arrest, and lysis of distinct Bacillus subtilis subpopulations

ABSTRACT The Bacillus subtilis ytrGABCDEF operon has been implicated in various cellular processes, including antibiotic and cold stress adaptation, cell wall synthesis, autolysis, sporulation, biofilm formation, motility, competence, and acetoin utilization. Yet, how these different observations fit together and the precise function of the operon remain enigmatic. In addition to its function, its topology is also uncertain. Early studies proposed a single YtrBCDEF ATP-binding cassette (ABC) transporter, while more recent studies showed evidence of two distinct ABC transporters, YtrB 2 CD and YtrE 2 F 2 . Here, we phenotypically characterized diverse ytr deletion mutants overexpressing or lacking the whole operon or parts thereof. Unexpectedly, we found a distinct population heterogeneity in ytr mutants that constitutively express either the whole operon or parts thereof. These strains displayed a substantial subpopulation of non-growing cells with measurably decreased cell length and width (“small cells”). This phenotype was most prevalent during adaptation from slow to fast growth and was exacerbated by cold. In mutants expressing an incomplete operon, small cells eventually underwent cell lysis. Taken together, our results suggest a role of the operon in controlling cell size, growth arrest, and autolysis of distinct subpopulations during growth phase transitions and temperature shifts. IMPORTANCE Bacillus subtilis is a crucial bacterial model organism with considerable importance to fundamental and applied microbiology, frequently used as a model in bacterial cell biology and physiology and as a production host for various industrial applications. Despite being one of the best-characterized microbes, the B. subtilis genome still contains many genes and operons of unknown or poorly characterized function. The ytrGABCDEF operon has been the subject of a number of studies, yet neither its function nor the structure of the encoded proteins has so far been conclusively elucidated. Here, we provide new insight into the function of this operon that reconciles previous observations and suggests new directions for the further characterization of the structure-function relationship of the Ytr protein complexes.