Reducing the Level of Undecaprenyl Pyrophosphate Synthase Has Complex Effects on Susceptibility to Cell Wall...

Undecaprenyl pyrophosphate synthase (UppS) catalyzes the formation of the C₅₅ lipid carrier (UPP) that is essential for bacterial peptidoglycan biosynthesis. We selected here a vancomycin (VAN)-resistant derivative of Bacillus subtilis W168 that contains a single-point mutation in the ribosome-binding site of the uppS gene designated uppS1 Genetic reconstruction experiments demonstrate that the uppS1 allele is sufficient to confer low-level VAN resistance and causes reduced UppS translation. The decreased level of UppS renders B. subtilis slightly more susceptible to many late-acting cell wall antibiotics, including β-lactams, but significantly more resistant to fosfomycin and d-cycloserine, antibiotics that interfere with the very early steps of cell wall synthesis. We further show that the uppS1 allele leads to slightly elevated expression of the σ^M regulon, possibly helping to compensate for the stress caused by a decrease in UPP levels. Notably, the uppS1 mutation increases resistance to VAN, fosfomycin, and d-cycloserine in wild-type cells, but this effect is greatly reduced or eliminated in a sigM mutant background. Our findings suggest that, although UppS is an attractive antibacterial target, incomplete inhibition of UppS function may lead to increased resistance to some cell wall-active antibiotics.