A Bifunctional UDP-Sugar 4-Epimerase Supports Biosynthesis of Multiple Cell Surface Polysaccharides in Sinorhizobium meliloti

Abstract

Sinorhizobium meliloti produces multiple extracellular glycans, including among others, lipopolysaccharides (LPS), and the exopolysaccharides (EPS) succinoglycan (SG) and galactoglucan (GG). These polysaccharides serve cell protective roles. Furthermore, SG and GG promote the interaction of S. meliloti with its host

Cyclic di-GMP signaling controlling the free-living lifestyle of alpha-proteobacterial rhizobia

“…Moreover, c-di-GMP stimulates production of arabinose-containing polysaccharide (APS) and an adhesion polysaccharide of unknown composition, likely similar to A. tumefaciens unipolar adhesion polysaccharide UPP. These polysaccharides facilitate cell aggregation, surface attachment and biofilm formation, however they are not required for effective symbiotic interaction (Pérez-Mendoza et al 2015;Schäper et al 2016;Schäper et al 2019;Xu et al 2012).…”

“…Furthermore, at high c-di-GMP levels, S. meliloti produced arabinose-containing polysaccharide (APS) (Figure 3). Its biosynthesis is controlled by the uxs1-uxe-apsS-apsH1-apsE-apsH2 operon (Schäper et al 2019). Expression of the uxs1-aspH2 operon is repressed by MucR and is activated by the cognate transcription regulator CuxR, encoded upstream of the uxs1-apsH2 operon (Schäper et al 2019).…”

“…Its biosynthesis is controlled by the uxs1-uxe-apsS-apsH1-apsE-apsH2 operon (Schäper et al 2019). Expression of the uxs1-aspH2 operon is repressed by MucR and is activated by the cognate transcription regulator CuxR, encoded upstream of the uxs1-apsH2 operon (Schäper et al 2019). CuxR requires c-di-GMP for DNA binding and therefore transcription of the operon is activated at high c-di-GMP levels (Schäper et al 2017).…”

“…ApsS is a putative glycosyl transferase, ApsE is a putative endoglycanase and the two remaining proteins are of unknown function. APS production significantly increased biofilm formation in strains that lacked the ability to produce the putative polar adhesion polysaccharide, whose biosynthesis is controlled by the SMc01796-SMc01790 gene cluster (Schäper et al 2019).…”

Generating asymmetry in a changing environment: cell cycle regulation in dimorphic alphaproteobacteria

“…However, also in this case, it is unclear whether the UPP is limited to one of the cell poles and whether it is specially associated with the mother cell. Furthermore, it appears that other polysaccharides might be more important for S. meliloti biofilm formation (Schäper et al 2019). B. abortus cells were shown to produce unipolar adhesins, and strikingly these adhesins were consistently detected at the new pole (Ruiz-Ranwez et al 2013) rather than the old pole, as observed for C. crescentus and H. neptunium.…”