Ser/Thr kinase-dependent phosphorylation of the peptidoglycan hydrolase CwlA controls its export and modulates cell division inClostridioides difficile

Cell growth and division require a balance between synthesis and hydrolysis of the peptidoglycan (PG). Inhibition of PG synthesis or uncontrolled PG hydrolysis can be lethal for the cells, making it imperative to control peptidoglycan hydrolase (PGH) activity. The serine/threonine kinases (STKs) of the Hanks family control cell division and envelope homeostasis, but only a few kinase substrates and associated molecular mechanisms have been identified. In this work, we identified CwlA as the first STK-PrkC substrate in the human pathogen Clostridiodes difficile and showed that CwlA is an endopeptidase involved in daughter cell separation. We demonstrated that PrkC-dependent phosphorylation inhibits CwlA export, therefore controlling the hydrolytic activity in the cell wall. High level of CwlA at the cell surface led to cell elongation, whereas low level caused cell separation defects. We thus provided evidence that the STK signaling pathway regulates PGH homeostasis to precisely control PG hydrolysis during cell division.