Lack ofO-polysaccharide enhances biofilm formation byBradyrhizobium japonicum

Abstract

To reveal the effects of the O-polysaccharide antigen of Bradyrhizobium japonicum LPS on biofilm formation and motility. Wild type and O-antigen-deficient mutant strains of B. japonicum were tested for biofilm formation on polyvinyl chloride (PVC) surfaces and motility on semi-solid (0.3%) agar media. After 7 days of incubation, the amount of biofilms formed by the mutant was c. 3.5-fold greater than that of the wild type. Unlike biofilm formation, the motility assay revealed that the mutant strain was less motile than the wild type. This study shows enhanced biofilm formation and decreased motility by the O-antigen-deficient mutant, suggesting that the lack of the O-polysaccharide of the rhizobial LPS is associated with biofilm-forming ability and movement. LPS plays an important role in both pathogenic and beneficial bacteria. It has also been reported that LPS deficiency negatively affects biofilm formation. However, our results demonstrate that the O-antigen-deficient mutant enhances biofilm formation, presumably through a significant increase in hydrophobicity. It is notable that the hydrophobicity of cell walls might be a key regulator in controlling biofilm development in B. japonicum.