Seven-transmembrane receptor protein RgsP and cell wall-binding protein RgsM promote unipolar growth in Rhizobiales

Abstract

Members of the Rhizobiales (class of α-proteobacteria) display zonal peptidoglycan cell wall growth at one cell pole, contrasting with the dispersed mode of cell wall growth along the sidewalls of many other rod-shaped bacteria. Here we show that the seven-transmembrane receptor (7TMR) protein RgsP (SMc00074), together with the putative membrane-anchored peptidoglycan metallopeptidase RgsM (SMc02432), have key roles in unipolar peptidoglycan formation during growth and at mid-cell during cell division in Sinorhizobium meliloti. RgsP is composed of a periplasmic globular 7TMR-DISMED2 domain, a membrane-spanning region, and cytoplasmic PAS, GGDEF and EAL domains. The EAL domain confers phosphodiesterase activity towards the second messenger cyclic di-GMP, a key regulatory player in the transition between bacterial lifestyles. RgsP and RgsM localize to sites of zonal cell wall synthesis at the new cell pole and cell divison site, suggesting a role in cell wall biogenesis. The two proteins are essential for cell wall biogenesis and cell growth. Cells depleted of RgsP or RgsM had an altered muropeptide composition and RgsM binds to peptidoglycan. RgsP and RgsM orthologs are functional when interchanged between α-rhizobial species pointing to a conserved mechanism for cell wall biogenesis/remodeling within the Rhizobiales. Overall, our findings suggest that RgsP and RgsM contribute to the regulation of unipolar cell wall biogenesis in α-rhizobia.

Tol-Pal system and Rgs proteins interact to promote unipolar growth and cell division inSinorhizobium meliloti

“…1C, Table 2). These changes in muropeptide composition are similar to those in RgsP- or RgsM-depleted cells reported previously (12). To monitor cellular localization of RgsA by fluorescence microscopy, we replaced rgsA with rgsA-mCherry at the native genomic location in the rgsP-egfp strain.…”

“…1A, Table 1). This cell morphology was different from the shorter, rounded rods, observed upon RgsP or RgsM depletion (12). Muropeptide analysis of PG isolated from RgsA-depleted cells revealed the following changes in the PG composition: an increase in monomeric tetra- and pentapeptides, and the glycine-containing dimer (TetraTetra(Gly4)), and a decrease in the dimeric (TetraTetra) and trimeric (TetraTetraTetra) cross-linked muropeptides (Fig.…”

“…We previously identified RgsA (SMc00644) as a potential interaction partner of RgsP and RgsM (12) and recently, a massively parallel transposon insertion sequencing (Tn-seq) study suggested large growth impairment caused by transposon insertions in rgsA (17). To test for a functional relation between RgsA, RgsP and RgsM, we attempted to knock out rgsA in strain Rm2011 rgsP-egfp , carrying replacement of rgsP by the gene fusion at the native genomic locus.…”

“…In S. meliloti , 7TMR-DISM-cdGMP phosphodiesterase RgsP (Rgs for rhizobial growth and septation) and putative membrane-anchored periplasmic PG metallopeptidase RgsM were identified as important factors for unipolar cell growth (12). Both are essential proteins and conserved in Rhizobiales (12). These proteins localize to sites of zonal PG synthesis at the growing cell pole and septum.…”

“…These proteins localize to sites of zonal PG synthesis at the growing cell pole and septum. Depletion of RgsP or RgsM results in cell growth inhibition and altered muropeptide composition (12).…”