The DigH glycosyl hydrolase is conditionally required for daughter cell separation in Escherichia coli

The peptidoglycan (PG) cell wall is a mesh-like layer that shapes bacteria and protects against osmotically induced lysis. PG is composed of glycan strands and peptide chains that link together to form a continuous layer that surrounds the cell. PG hydrolases are required for cell wall maturation, and many are employed during cell separation. During cell division, amidases remove peptides from the glycan backbone, and the resulting denuded glycans (dnGs) are degraded by lytic transglycosylases (LTs). The gram-negative bacterium Escherichia coli encodes eight functional LTs ( mltA-G and slt ) and one putative LT ( rlpA ), and a mutant strain lacking six (Δ mltACDE Δ slt Δ rlpA ), which we refer to as ΔLT cells, accumulates dnGs and produces short chains of cells. A morphological suppressor of the ΔLT chaining defect was isolated, and deletion analysis indicated that suppression relied primarily on increased activity of DigH, a denuded-specific hydrolase that accumulates at the midcell during cell division. Further analyses revealed that DigH is critical for cell separation in ΔLT but not wild-type cells and that dnGs accumulate even more in ΔLT cells when DigH is absent. Thus, DigH is a denuded-specific hydrolase that is conditionally required for cell separation in E. coli . Altogether, our findings deepen our understanding of the specific cellular function of DigH and of PG maturation in E. coli . IMPORTANCE Most bacteria are surrounded by an essential polymer known as the peptidoglycan cell wall. During cell division, a transient form of peptidoglycan is generated between the developing daughter cells that must be cleaved so that cells can separate. Here, we show that the DigH hydrolase is conditionally required for cell separation when this transient cell wall structure accumulates in the gram-negative bacterium Escherichia coli . These findings deepen our understanding of how the peptidoglycan layer is remodeled during cell division.