Peptidoglycan recycling is critical for cell division, cell wall integrity and β-lactam resistance in Caulobacter crescentus

Most bacteria possess a peptidoglycan sacculus, which is continuously remodeled during cell growth and division. The peptidoglycan (PG) fragments generated in this process are typically imported into the cell and recycled for entry into the PG biosynthesis pathway. While the underlying pathways have been studied intensively in gammaproteobacteria, knowledge of their presence and physiological roles in other bacterial lineages remains limited. Here, we comprehensively investigate PG recycling in the alphaproteobacterial model organism Caulobacter crescentus . We show that this species contains a functional PG recycling pathway by characterizing the activities of key enzymes in vitro and in vivo . Our results reveal that PG recycling is critical for C. crescentus cell morphology and division, and is dynamically regulated to balance the flux of metabolic intermediates toward PG biosynthesis and central carbon metabolism. Importantly, defects in PG recycling strongly impair the intrinsic ampicillin resistance of C. crescentus without changing the activity of its β-lactamase BlaA, likely by limiting PG precursor biosynthesis and thereby decreasing the activity of the cell wall biosynthetic machinery in the presence of residual antibiotic. These findings underscore the central role of PG recycling in bacterial fitness and suggest that inhibiting this process could provide a promising strategy to combat β-lactam-resistant pathogens.