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Enterococcal plasmid-encoded bacteriolysin Bac41 is a selective antimicrobial system that is considered to provide a competitive advantage toEnterococcus faecaliscells that carry the Bac41-coding plasmid. The Bac41 effector consists of the secreted proteins BacL1 and BacA, which attack the cell wall of the targetE. faecaliscell to induce bacteriolysis. Here, we demonstrated thatgalU, which encodes UTP-glucose-1-phosphate uridylyltransferase, is involved in susceptibility to the Bac41 system inE. faecalis. Spontaneous mutants that developed resistance to the antimicrobial effects of BacL1 and BacA were revealed to carry a truncation deletion of the C-terminal 288–298 a.a. region of the translated GalU protein. This truncation resulted in the depletion of UDP-glucose, leading to a failure to utilize galactose and produce the enterococcal polysaccharide antigen (EPA), which is expressed abundantly on the cell surface ofE. faecalis. This cell surface composition defect that resulted fromgalUor EPA-specific genes caused an abnormal cell morphology, with impaired polarity during cell division and alterations of the limited localization of BacL1. Interestingly, these mutants conferred reduced susceptibility to beta-lactams, despite their increased susceptibility to other bacteriostatic antimicrobial agents and chemical detergents. These data suggest that a complex mechanism of action underlies lytic killing, as exogenous bacteriolysis induced by lytic bacteriocins or beta-lactams requires an intact cell physiology inE. faecalis.ImportanceCell wall-associated polysaccharides of bacteria are involved in various physiological characteristics. Recent studies demonstrated that the cell wall-associated polysaccharide ofEnterococcus faecalisis required for susceptibility to bactericidal antibiotic agents. Here, we demonstrated that agalUmutation resulted in resistance to the enterococcal lytic bacteriocin Bac41. ThegalUhomologue is reported to be essential for biosynthesis of species-specific cell wall-associated polysaccharides in other Firmicutes. InE. faecalis, thegalUmutant lost theE. faecalis-specific cell wall-associated polysaccharide EPA (enterococcal polysaccharide antigen). The mutant also displayed reduced susceptibility to antibacterial agents and an abnormal cell morphology. We firstly demonstrated thatgalUwas essential for EPA biosynthesis inE. faecalis, and EPA production might underlie susceptibility to lytic bacteriocin and antibiotic agents by undefined mechanism. |
