Growth of Corynebacterium glutamicum on 5-oxo-L-proline (pyroglutamate) as carbon and nitrogen source requires the PxpR-controlled pxpTABC genes

ABSTRACT 5-Oxo-L-proline (5-OP) is inevitably formed in all cells by spontaneous cyclization of L-glutamate, L-glutamine, or γ-glutamyl phosphate. Its use as a substrate by bacteria has rarely been described. Here, we show that the actinobacterial species Corynebacterium glutamicum can grow well in minimal medium with 5-OP as sole carbon and nitrogen source. We identified the pxpTABC gene cluster as being essential for growth on 5-OP. The pxpT gene encodes a secondary transporter of the APC superfamily which most likely catalyzes 5-OP uptake into the cell. The pxpABC genes encode a recently identified ATP-dependent 5-oxoprolinase that converts 5-OP into L-glutamate for further metabolism. Both PxpT and PxpABC were required for growth with 5-OP. Upstream and divergent to pxpT, the gene pxpR is located, encoding a GntR-type transcriptional regulator. Deletion of pxpR improved growth on 5-OP suggesting that PxpR acts as repressor of the pxpTABC operon. This function was further supported by reporter gene studies. Purified PxpR was shown by isothermal titration calorimetry (ITC) to bind 5-OP with a KD of 726 ± 23 nM. L-proline, L-glutamate, L-glutamine, and L-aspartate were not bound under the conditions tested, suggesting that PxpR is a specific 5-OP biosensor. IMPORTANCE The utilization of 5-OP as a carbon and nitrogen source for bacteria has rarely been investigated in the past, although this metabolite is ubiquitous in cells due to its non-enzymatic formation from the amino acids L-glutamate and L-glutamine. In Corynebacterium glutamicum cells, but also in other bacteria such as Escherichia coli, L-glutamate is present at concentrations in the range of 100 mM, suggesting a substantial and continuous 5-OP formation. Our results demonstrate that 5-OP can serve both as carbon and nitrogen source for C. glutamicum and presumably also for other bacteria. Competing Interest Statement The authors have declared no competing interest. Footnotes This version of the manuscript includes the supplementary information.