Involvement of a 120-MDa plasmid of Azospirillum brasilense Sp245 in the production of lipopolysaccharides.

Using Omegon-Km mutagenesis, six Azospirillum brasilense Sp245 mutant derivatives lacking the capability to synthesize either one of the two major O-specific polysaccharides (O-PSs) were constructed in vivo. In all of the Lps mutants obtained, single Omegon-Km insertions were shown to be located on an indigenous plasmid DNA with molecular weight 120 MDa (p120). Physical and immunochemical analyses revealed two p120 loci coding for O-PSI and two p120 loci involved in the production of O-PSII. One of the lps loci from both groups was also shown to act in the production of Calcofluor-binding polysaccharides. It was demonstrated that two Sp245 plasmid bands with apparent molecular weights of 120 and 130 MDa (as visualized by analytical gel electrophoreses) seem to be the two topological forms of the same plasmid species (p120). Transfer properties of p120 were also examined.