Involvement of Lipopolysaccharide in Metal Binding of Bradyrhizobium japonicum

초록

Bacterial cell surface components are major factors responsible for the pathogenesis and bioremediation. Especially, gram-negative bacterium cell surface has a variety of components compared to the gram-positive bacterium. Lipopolysaccharide (LPS) is one major component in gram-negative cell surface domain that has several anion groups, which interact with various cation groups and ions such as metals (Cd2+, Cu2+, Pb2+, and Zn2+), in the environment. Bradyrhizobium japonicum is a soil bacterium that can infect soybean and fix nitrogen in the atmosphere. We have previously isolated an isogenic mutant, which lacks anionic group of LPS. This LPS mutant is extremely hydrophobic compared to the wild type strain. In this study, atomic absorption spectrophotometry was used to examine the involvement of LPS in metal binding of B. japonicum. By using three strains (B. japonicum 61A101c, the wild type; JS314, the LPS deficient Tn5-mutant; JS314, complemented strain) we have shown that the LPS is indeed involved in metal binding. Binding capacity of the LPS mutant to various metals (Cd2+, Cu2+, Pb2+, and Zn2+) was 50∼70 % lower than that of the wild type. We propose that the LPS molecules as a whole may contribute to the overall cell surface properties, which favor the precipitation of distinct metal-rich mineral phase.