Distinct Amino Acid Availability-Dependent Regulatory Mechanisms of MepS and MepM Levels in Escherichia coli.

Han Byeol Lee,Chang-Ro Lee,Yung Jae Kim,Umji Choi,Won-Jae Chi,Ji Eun Son,Byoung Jun Choi,Si Hyoung Park

doi:10.3389/fmicb.2021.677739

Han Byeol Lee, Chang-Ro Lee + Show 6 more

Open Access

https://doi.org/10.3389/fmicb.2021.677739

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Abstract

Peptidoglycan (PG) hydrolases play important roles in various aspects of bacterial physiology, including cytokinesis, PG synthesis, quality control of PG, PG recycling, and antibiotic resistance. However, the regulatory mechanisms of their expression are poorly understood. In this study, we have uncovered novel regulatory mechanisms of the protein levels of the synthetically lethal PG endopeptidases MepS and MepM, which are involved in PG synthesis. A mutant defective for both MepS and MepM was lethal in an amino acid-rich medium, whereas it exhibited almost normal growth in a minimal medium, suggesting the expendability of MepS and MepM in a minimal medium. Protein levels of MepS and MepM dramatically decreased in the minimal medium. Although MepM was revealed as a substrate of Prc, a periplasmic protease involved in the proteolysis of MepS, only the decrease in the MepS level in the minimal medium was affected by the prc depletion. Phenotypic and biochemical analyses showed that the presence of aromatic amino acids in the medium induced the accumulation of MepS, but not MepM, while the presence of glutamate increased the level of MepM, but not MepS. Together, these results demonstrate that the protein levels of the two major PG endopeptidases are regulated in an amino acid availability-dependent manner, but their molecular mechanisms and signaling are significantly distinct.

Highlights

Bacteria adapt to various environmental stresses through changes in gene expression, which induces optimal growth of bacteria and increases the survival rate
These results support that MepS and MepM are two major PG endopeptidases that are required for E. coli growth in the LB medium
The requirement of MepS and MepM was almost abolished in the M9 minimal medium containing glucose; the growth of the mepS mepM double mutant and wildtype strains was almost similar in the M9 minimal medium (Figure 1B; Supplementary Figure 2)

Summary

INTRODUCTION

Bacteria adapt to various environmental stresses through changes in gene expression, which induces optimal growth of bacteria and increases the survival rate. Our recent report based on phenotypic analysis showed that PG endopeptidases have distinct roles in penicillin-binding protein 1a (PBP1a)- and PBP1b-related functions, which are involved in PG synthesis (Park et al, 2020). We investigated the regulatory mechanisms of the expression of two major PG endopeptidases, MepS and MepM, in E. coli. We showed that the presence of aromatic amino acids in the medium induced the accumulation of MepS, but not MepM, and the presence of glutamate increased the MepM level, but not MepS. We demonstrated that MepS and MepM are required for normal growth under the amino acid-rich conditions, and their protein levels are enhanced under these conditions through distinct signaling and mechanisms

MATERIALS AND METHODS

RESULTS

DISCUSSION