Structure and Biological Roles of Sinorhizobium fredii HH103 Exopolysaccharide

Abstract

Here we report that the structure of the Sinorhizobium fredii HH103 exopolysaccharide (EPS) is composed of glucose, galactose, glucuronic acid, pyruvic acid, in the ratios 5∶2∶2∶1 and is partially acetylated. A S. fredii HH103 exoA mutant (SVQ530), unable to produce EPS, not only forms nitrogen fixing nodules with soybean but also shows increased competitive capacity for nodule occupancy. Mutant SVQ530 is, however, less competitive to nodulate Vigna unguiculata. Biofilm formation was reduced in mutant SVQ530 but increased in an EPS overproducing mutant. Mutant SVQ530 was impaired in surface motility and showed higher osmosensitivity compared to its wild type strain in media containing 50 mM NaCl or 5% (w/v) sucrose. Neither S. fredii HH103 nor 41 other S. fredii strains were recognized by soybean lectin (SBL). S. fredii HH103 mutants affected in exopolysaccharides (EPS), lipopolysaccharides (LPS), cyclic glucans (CG) or capsular polysaccharides (KPS) were not significantly impaired in their soybean-root attachment capacity, suggesting that these surface polysaccharides might not be relevant in early attachment to soybean roots. These results also indicate that the molecular mechanisms involved in S. fredii attachment to soybean roots might be different to those operating in Bradyrhizobium japonicum.

Improvement of rhizobium‐soybean symbiosis and nitrogen fixation under drought

“…All S. fredii strains, in particular strains SHM12 and HWG35, were more tolerant to these treatments in comparison to the B. diazoefficiens WB74‐1 reference strain. Sinorhizobium fredii strains HH103 and SHM12 are known to be fast‐growing rhizobial strains able to nodulate soybean and also form, depending on the plant species, determinate or indeterminate nodules (Margaret et al, ; Rodriguez‐Navarro et al, ). Our finding that SHM12 survives better salt treatment, with growth even under high salt conditions (500 mM in a medium), further confirms the previously reported high salt tolerance of S. fredii strains SMX11 and SMH12 (Rodriguez‐Navarro et al, ).…”

Sinorhizobium fredii HH103 bacteroids are not terminally differentiated and show altered O‐antigen in nodules of the Inverted Repeat‐Lacking Clade legume Glycyrrhiza uralensis

“…Very recently, it has been shown by in situ atomic force microscopy studies that NCR247 and NCR335 caused damage to the bacterial cell envelope when applied to E. coli or on natural purple membrane, most likely affecting the lipid matrix (Nagy et al, 2015). The fact that S. fredii HH103 and S. meliloti 1021 present remarkable differences in their cell envelopes, at least in their exopolysaccharide (EPS) and in their capsular polysaccharide (KPS) (Fraysse et al, 2003;2005;Margaret et al, 2011;Rodríguez-Navarro et al, 2014), might be one reason for their different sensitivities to the two NCR peptides tested.…”

Sinorhizobium fredii HH103 syrM inactivation affects the expression of a large number of genes, impairs nodulation with soybean and extends the host‐range to Lotus japonicus

“…Since EPS production is closely related to the biofilm formation in S. fredii HH103 (Rodríguez‐Navarro et al ., ), we decided to investigate whether this lack of EPS reduction could be turned into higher amount of biofilm formed by the syrM derivatives in the presence of genistein. As expected, none of the two syrM derivatives reduced the amount of biofilm formed in the presence of genistein compared to the dramatically reduction that take places in the wild‐type strain (Fig.…”