A Lipopolysaccharide-Deficient Mutant of Bradyrhizobium japonicum Is Altered In Its Cell Surface Hydrophobicity

초록

We have previously isolated a lipopolysaccharide (LPS) deficient Tn5-mutant of Bradyrhizobium japonicum, and subsequently isolated the LPS gene region. In this study the LPS deficiency of B. japonicum was studied in terms of cell surface characteristics. By monitoring the kinetics of partition to hexadecane the LPS mutant was found to be far more hydrophobic than the wild type strain; the partition coefficients were 3.01 min-1 for the mutant, as compared with only 1.54 min-1 for the wild type. When the mutant was transformed with the cloned LPS gene, the transformant regained the wild type phenotypes, including cell surface hydrophobicity (CSH) and LPS profile. Polyacrylamide gel electrophoresis of LPS demonstrated that the O-antigenic part of the LPS was completely absent in the mutant. The LPS mutant of B. japonicum was visually distinguished from the wild type by simple centrifugation of the cells. Although the sequence data is not complete, the cloned LPS gene region appears to have an open reading frame which has a significant amino acid sequence homology to rfaF protein of several gram-negative bacteria. The rfaF gene was inferred to determine heptosyltransferase II for transfer of second heptose to the inner core of LPS.