Genetic screen identifies cell wall enzyme is key for freshwater survival of .

Human infection with , a potentially lethal bacterial pathogen, typically occurs after exposure to contaminated water, soil, food, or an infected animal. While can persist in environmental sources over long periods of time, the genetic requirements that permit its long-term viability are not understood. To address this question, we developed a laboratory model for persistence of in fresh water, finding that viable cells could be recovered for 3 - 8 weeks after incubation at 4°C. Using this model, we took an unbiased, transposon insertion sequencing approach to identify genes critical for this persistence of cells. We found that mutants in , a gene encoding murein peptide ligase, are defective for persistence in fresh water. Previous studies had identified as critical for intramacrophage survival. Murein peptide ligase plays a role in peptidoglycan recycling, suggesting that uses this enzyme to maintain cell wall integrity during hypoosmotic and intramacrophage stress conditions. Our results highlight the importance of understanding how bacterial cell envelopes have evolved and adapted to maintain their integrity in a variety of stress conditions.