Deletion of the genes encoding the MtrA–MtrB two‐component system of Corynebacterium glutamicum has a strong influence on cell morphology, antibiotics susceptibility and expression of genes involved in osmoprotection

Abstract

SummaryThe MtrAB two-component signal transduction system is highly conserved in sequence and genomic organization in Mycobacterium and Corynebacterium species, but its function is completely unknown. Here, the role of MtrAB was studied with C. glutamicum as model organism. In contrast to M. tuberculosis , it was possible to delete the mtrAB genes in C. glutamicum . The mutant cells showed a radically different cell morphology and were more sensitive to penicillin, vancomycin and lysozyme but more resistant to ethambutol. In order to identify the molecular basis for this pleiotropic phenotype, the mRNA profiles of mutant and wild type were compared with DNA microarrays. Three genes showed a more than threefold increased RNA level in the mutant, i.e. mepA ( NCgl2411 ) encoding a putative secreted metalloprotease, ppmA ( NCgl2737 ) encoding a putative membrane-bound protease modulator, and lpqB encoding a putative lipoprotein of unknown function. Expression of plasmid-encoded mepA in Escherichia coli led to elongated cells that were hypersensitive to an osmotic downshift, supporting the idea that peptidoglycan is the target of MepA. The mRNA level of two genes was more than fivefold decreased in the mutant, i.e. betP and proP which encode transporters for the uptake of betaine and proline respectively. The microarray results were confirmed by primer extension and RNA dot blot experiments. In the latter, the transcript level of genes involved in osmoprotection was tested before and after an osmotic upshift. The mRNA level of betP , proP and lcoP was strongly reduced or undetectable in the mutant, whereas that of mscL (mechanosensitive channel) was increased. The changes in cell morphology, antibiotics susceptibility and the mRNA levels of betP , proP , lcoP , mscL and mepA could be reversed by expression of plasmid-encoded copies of mtrAB in the D D D D mtrAB mutant, confirming that these changes occurred as a consequence of the mtrAB deletion.

Modulation of Mycobacterium tuberculosis proliferation by MtrA, an essential two‐component response regulator

“…Presumably, MtrA recruits DnaA to control the expression of cell cycle genes during intramacrophage growth, while independently regulating phago-lysosomal trafficking along with other unidentified processes necessary for establishing infection. It is interesting to note that the nonessential MtrAB system in C. glutamicum is implicated in the expression of genes involved in cell wall metabolism and osmoprotection (Moker et al, 2004). The sequence and the genome organization of the mtrAB region of M. tuberculosis and C. glutamicum are very similar.…”

“…These earlier studies clearly indicate that MtrA plays an important role in M. tuberculosis life cycle. A recent study showed that the MtrAB 2CR system in Corynebacterium glutamicum , a non-pathogenic Gram-positive soil bacterium, closely related to pathogenic M. tuberculosis , can be dispensable for survival in defined media (Moker et al ., 2004). The MtrAB 2CR system in this organism is implicated in the regulation of cell wall metabolism and osmoprotection (Moker et al ., 2004).…”

The AraC-type Regulator RipA Represses Aconitase and Other Iron Proteins from Corynebacterium under Iron Limitation and Is Itself Repressed by DtxR

“…In the exponential growth phase at an A 600 of 4-6, 25 ml of the cultures were used for the preparation of total RNA as described previously (15). Isolated RNA samples were analyzed for quantity and quality by UV spectrophotometry and denaturing formaldehyde-agarose gel electrophoresis (4), respectively, and stored at Ϫ70°C until use.…”

Septal Localization of the Mycobacterium tuberculosis MtrB Sensor Kinase Promotes MtrA Regulon Expression

“…Other recent findings implicate MtrB in cell wall homeostasis in part through its association with the lipoprotein LpqB (10). Although the characterization of an Mycobacterium avium mtrB transposon mutant and a Corynebacterium glutamicum mtrB deletion mutant implicated MtrB in cell wall metabolism (11,12), the role, if any, of MtrB in M. tuberculosis cell division and cell wall synthesis remains elusive.…”