Chemostat Predation by Bdellovibrio Induces Stable Rcs Phosphorelay-Based Mucoidy in E. coli
A key aspect of bacterial survival in nature is their ability to respond to adverse conditions, a concept related with critical fields, particularly the development and spread of antibiotic resistance. One condition that has not been explored extensively, however, is how bacterial prey respond to and, possibly, evolve when predated on by Bdellovibrio-and-like organisms (BALOs). This is particularly important as these predatory microbes have been heralded as possible alternatives to conventional antibiotics. Here, we describe the development of a stable phenotypic response in E. coli MG1655 during continuous, long-term predation in a chemostat, and that this phenotype persisted long after (>7 days) they were grown in the absence of the predator. While these prey not only formed smaller colonies, entered the stationary phase sooner and were mucoid, their genome sequences were identical to that of our wild-type E. coli MG1655. Predatory activities against these small colony variants (SCVs) were slightly slower, providing a selective growth fitness over wild-type E. coli in the presence of the predator. Multi-omic analyses found this altered phenotype stemmed from a perpetual activation of the Rcs phosphorelay, a non-canonical two component regulatory system that detects and responds to outer membrane stress. Taken together, the results imply our SCV E. coli experience self-induced outer membrane stress, even after prolonged growth independent of the predator.