RagB stimulates the activity of the peptidoglycan polymerase RodA in Bacillus subtilis

The bacterial cell wall is primarily composed of peptidoglycan (PG), a polymer essential for its protective envelope function, and any defect in its synthesis or repair can potentially result in bacterial lysis. Class A Penicillin-Binding Proteins (aPBPs) and Shape, Elongation, Division, and Sporulation (SEDS) proteins are PG polymerases acting in concert to ensure bacterial cell wall growth. Here, we identify the first regulator of the SEDS protein RodA in the Gram-positive model bacterium Bacillus subtilis. In the presence of the antibiotic moenomycin, which specifically inhibits glycosyltransferase activity of aPBPs, or in a strain deleted for all four aPBPs, bacterial survival depends on the presence of the YrrS protein (renamed RagB) and can be rescued by overexpression of RodA. No effect of RagB is observed on the rodA gene expression level or on the speed of circumferentially moving RodA associated with PG elongation by the Rod complex. However, we demonstrate that RagB interacts with RodA. We propose that RagB stimulates RodA activity and becomes essential in the absence of aPBPs and in particular of the major aPBP, PBP1.