Identification of MupP as a New Peptidoglycan Recycling Factor and Antibiotic Resistance Determinant in .

Peptidoglycan (PG) is an essential cross-linked polymer that surrounds most bacterial cells to prevent osmotic rupture of the cytoplasmic membrane. Its synthesis relies on penicillin-binding proteins, the targets of beta-lactam antibiotics. Many Gram-negative bacteria, including the opportunistic pathogen , are resistant to beta-lactams because of a chromosomally encoded beta-lactamase called AmpC. In , expression of the gene is tightly regulated and its induction is linked to cell wall stress. We reasoned that a reporter gene fusion to the promoter would allow us to identify mutants defective in maintaining cell wall homeostasis and thereby uncover new factors involved in the process. A library of transposon-mutagenized was therefore screened for mutants with elevated promoter activity. As an indication that the screen was working as expected, mutants with transposons disrupting the gene were isolated. Defects in DacB have previously been implicated in induction and clinical resistance to beta-lactam antibiotics. The screen also uncovered and mutants that, upon further characterization, displayed nearly identical drug resistance and sensitivity profiles. We present genetic evidence that , renamed , encodes the missing phosphatase predicted to function in the MurU PG recycling pathway that is widely distributed among Gram-negative bacteria. The cell wall biogenesis pathway is the target of many of our best antibiotics, including penicillin and related beta-lactam drugs. Resistance to these therapies is on the rise, particularly among Gram-negative species like , a problematic opportunistic pathogen. To better understand how these organisms resist cell wall-targeting antibiotics, we screened for mutants defective in maintaining cell wall homeostasis. The screen identified a new factor, called MupP, involved in the recycling of cell wall turnover products. Characterization of MupP and other components of the pathway revealed that cell wall recycling plays important roles in both the resistance and the sensitivity of to cell wall-targeting antibiotics.