Lack of O-polysaccharide enhances biofilm formation by Bradyrhizobium japonicum

Aims: To reveal the effects of the O-polysaccharide antigen of Bradyrhizobium japonicum LPS on biofilm formation and motility. Methods and Results: 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 center dot 3%) agar media. After 7 days of incubation, the amount of biofilms formed by the mutant was c. 3 center dot 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. Conclusions: 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. Significance and Impact of the Study: 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.