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Lysis of a Lactococcus lactis Dipeptidase Mutant and Rescue by Mutation in the Pleiotropic Regulator CodY.

ABSTRACT: Lactococcus lactis subsp. cremoris MG1363 is a model for the lactic acid bacteria (LAB) used in the dairy industry. The proteolytic system, consisting of a proteinase, several peptide and amino acid uptake systems, and a host of intracellular peptidases, plays a vital role in nitrogen metabolism and is of eminent importance for flavor formation in dairy products. The dipeptidase PepV functions in the last stages of proteolysis. A link between nitrogen metabolism and peptidoglycan (PG) biosynthesis was underlined by the finding that deletion of the dipeptidase gene pepV (creating strain MGΔpepV) resulted in a prolonged lag phase when the mutant strain was grown with a high concentration of glycine. In addition, most MGΔpepV cells lyse and have serious defects in their shape. This phenotype is due to a shortage of alanine, since adding alanine can rescue the growth and shape defects. Strain MGΔpepV is more resistant to vancomycin, an antibiotic targeting peptidoglycan d-Ala-d-Ala ends, which confirmed that MGΔpepV has an abnormal PG composition. A mutant of MGΔpepV was obtained in which growth inhibition and cell shape defects were alleviated. Genome sequencing showed that this mutant has a single point mutation in the codY gene, resulting in an arginine residue at position 218 in the DNA-binding motif of CodY being replaced by a cysteine residue. Thus, this strain was named MGΔpepVcodY R218C Transcriptome sequencing (RNA-seq) data revealed a dramatic derepression in peptide uptake and amino acid utilization in MGΔpepVcodY R218C A model of the connections among PepV activity, CodY regulation, and PG synthesis of L. lactis is proposed.IMPORTANCE Precise control of peptidoglycan synthesis is essential in Gram-positive bacteria for maintaining cell shape and integrity as well as resisting stresses. Although neither the dipeptidase PepV nor alanine is essential for L. lactis MG1363, adequate availability of either ensures proper cell wall synthesis. We broaden the knowledge about the dipeptidase PepV, which acts as a linker between nitrogen metabolism and cell wall synthesis in L. lactis.

SUBMITTER: Huang C

PROVIDER: S-EPMC7117943 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Bacteria adapt to the constantly changing environment by regulating their metabolism. The global transcriptional regulator CodY is known to regulate metabolism in low-G+C Gram-positive bacteria. Systems-level identification of its direct targets by proteome and chromatin immunoprecipitation followed by sequencing (ChIP-seq) assays have rarely been reported. Here, we identified that CodY serves as an activator or a repressor of hundreds of genes involved in nitrogen metabolism, carbohydrate metabolism, and transcription through iTRAQ proteome and ChIP-seq. Combined with the electrophoretic mobility shift assay (EMSA), apart from the genes associated with amino acid biosynthesis (ilvD, leuA, optS, ybbD, dtpT, and pepN), genes involved in cell wall synthesis (murD and ftsW) and nisin immunity (nisI) were identified as being regulated by CodY. Moreover, it was demonstrated by nisin resistance assay that CodY activated the transcription of nisI and contributed to nisin immunity. Intriguingly, CodY showed a self-regulation through binding to the motif AAAGGTGTGACAACT in the coding sequence (CDS) region of codY, as verified by DNase I footprinting assay and MEME analysis. In addition, a novel conserved AT-rich motif, AATWTTCTGACAATT, was obtained in L. lactis F44. This study provides new insights into the comprehensive CodY regulation in L. lactis by controlling metabolism, nisin immunity, and self-expression. IMPORTANCE Lactococcus lactis, a species of lactic acid bacteria (LAB) widely used in food fermentation, has been the model strain in genetic engineering, and its application has extended from food to microbial cell factories. CodY is a global regulator in low-G+C Gram-positive bacteria. Its function and direct target genes at the genome-level are little known in L. lactis. In this study, we describe the comprehensive regulation mechanism of CodY. It widely modulated the metabolism of nitrogen and carbohydrate, cell wall synthesis, and nisin immunity in L. lactis F44, and its expression level was regulated by feedback control.

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Lysis of a Lactococcus lactis Dipeptidase Mutant and Rescue by Mutation in the Pleiotropic Regulator CodY.

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