In vitro and in vivo infection models reveal connection between periplasmic protease Prc and alternative peptidoglycan synthase PBP3SAL in Salmonella enterica serovar Typhimurium

A hallmark in salmonellosis is the ability of the bacteria to proliferate within host cells. Most notably, Salmonella proliferates within professional phagocytes in a vacuolar compartment. During proliferation Salmonella has to build new cell wall, but how this is regulated within the intraphagosomal niche is not known. Here we show that genetically inactivating the periplasmic protease Prc, involved in cleaving peptidoglycan-processing enzymes, results in decreased fitness in macrophage-like RAW264.7 cells and in BALB/c mice, and in a decreased tolerance to redox stress. All these prc mutant phenotypes were conditional depending on pbp3sal, a recently defined paralogue for ftsl coding for the essential penicillin binding protein 3. These phenotypic connections between Prc and PBP3SAL adds to the phenotypes governed by Prc, and possibly adds PBP3SAL to the pool of target proteins involved in cell wall homeostasis that are regulated by Prc.