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.
Highlights
Rod-shaped bacteria have evolved diverse modes of cell growth
Bacteria face the challenge of maintaining their peptidoglycan cell wall integrity during growth and division
In the α-proteobacterium C. crescentus, the spatial organization of proteins involved in c-di-GMP metabolism contributes to cell polarity and cell cycle progression [14], and we showed previously that strong overproduction of this second messenger inhibited growth and resulted in cell filamentation in S. meliloti [17]
Summary
Rod-shaped bacteria have evolved diverse modes of cell growth. In Bacillus subtilis, Escherichia coli and Caulobacter crescentus, cells grow by elongating along the lateral sidewall, incorporating peptidoglycan (PG) cell wall material in a dispersed pattern along the sidewall [1]. Because the integrity of the PG sacculus is essential for maintaining cell shape and resisting turgor [6], cell growth and PG synthesis require precise spatial and temporal regulation of the incorporation of new material into the PG sacculus [7]. Rod-shaped bacteria with a dispersed mode of PG incorporation along the lateral cell wall utilize the cytoplasmic actin-like MreB protein to direct PG synthesis. Most rod-shaped bacteria with polar growth do not contain MreB homologs [10] and it is currently unknown how polar cell wall elongation is regulated in these bacteria
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