Inactivation of the lpcC gene alters surface-related properties and symbiotic capability of Bradyrhizobium japonicum

Abstract

Significance and Impact of the Study: This study demonstrates the role of the B. japonicum lpcC in nodulation with soybean and importance of cell surface hydrophobicity. The results also highlight that intact LPS is required for successful symbiosis between B. japonicum and soybeans. Our findings not only support previous studies emphasizing the necessity of LPS on the interaction between the two symbiotic partners, but also contribute to a better understanding of the symbiotic mechanisms. AbstractWe investigated the role of the Bradyrhizobium japonicum lpcC gene, encoding a mannosyl transferase, involved in the lipopolysaccharide (LPS) biosynthesis. The inactivation of the lpcC gene considerably altered the LPS structure and the cell surface properties. LPS analysis showed that the lpcC mutant JS715 had an abnormal LPS structure deficient in O-antigen. The cell surface hydrophobicity increased approximately threefold in JS715 compared to the wild type. The increased cell surface hydrophobicity is likely to be related with cell aggregation in the mutant culture. For the growth comparison, JS715 showed slower growth rate than the wild type. The motility of JS715 decreased in soft agar plates, but it showed enhanced biofilm-forming ability. Interestingly, JS715 was not able to nodulate the host legume soybean (Glycine max). This study shows not only that lpcC is involved in the biosynthesis of O-antigen in the B. japonicum LPS, but also that inactivation of the lpcC gene affects symbiotic capability of B. japonicum and surface-related properties such as cell hydrophobicity, biofilm formation and motility.

Effects of the Bradyrhizobium japonicum waaL (rfaL) Gene on Hydrophobicity, Motility, Stress Tolerance, and Symbiotic Relationship with Soybeans

“…JS015 had a relatively long cell pellet pattern compared to the wild type and CS015 ( Figure 3 B). This result is consistent with cell pellet patterns of the previous LPS-deficient mutants [ 2 , 18 ].…”

“…In a previous study, we identified a 5.5-kb gene region involved in LPS synthesis of B. japonicum 61A101C and characterized rfaD , rfaF , lpcC , and galE encoding heptose epimerase, heptosyl transferase, mannosyl transferase, and glucose epimerase, respectively, [ 14 , 15 , 16 , 17 , 18 ]. Further sequence analysis of the downstream region of rfaD revealed an additional ORF whose deduced amino acid sequences (426 amino acids in length) exhibited 100% identity with an rfaL gene, encoding an O -antigen ligase, from Bradyrhizobium elkanii .…”

“…Our previous studies on the LPS-deficient mutants revealed that their cell surface was more hydrophobic than that of the wild type [ 2 , 18 ]. As expected, JS015 also had increased hydrophobicity of its cell surface compared to the wild type and its complemented strain CS015 ( Figure 3 A).…”

“…Several mutation studies on LPS biosynthesis pathways revealed that LPS mutants either failed to form normal nitrogen-fixing nodules or formed non-nitrogen-fixing pseudonodules [ 10 , 11 , 12 , 13 ]. In addition, our mutant studies on the 5.5 kb LPS-gene region previously identified in B. japonicum 61A101C showed that mutation of either rfaD , rfaF , lpcC , or galE encoding heptose epimerase, heptosyl transferase, mannosyl transferase, or glucose epimerase, respectively, affects initiation and maintenance of the nodulation process [ 14 , 15 , 16 , 17 , 18 ]. Here, we further analyze the downstream region of rfaD and identify another open reading frame (ORF), waaL (formerly rfaL ), presumably encoding O -antigen ligase in B. japonicum .…”

Characterization of MocR, a GntR-like transcriptional regulator, in Bradyrhizobium japonicum: its impact on motility, biofilm formation, and soybean nodulation

“…Like SadB and SadC, MocR may inversely regulate biofilm formation and motility via exopolysaccharide (EPS) production and control of flagellar machinery. In contrast, several lipopolysaccharide (LPS) mutants of B. japonicum showed the opposite phenotype such as reduced motility, but increased biofilm formation (Lee et al, 2010(Lee et al, , 2014.…”