Synthesis of beta(1-2)glucan in Rhizobium loti. Expression of Agrobacterium tumefaciens chvB virulence region

Fast growing strains of Rhizobium loti isolated from nodules of Lotus tenuis of the flooding Pampas of Argentina produced cellular beta(1-2)glucans having a higher degree of polymerization and more anionic substituents than beta(1-2)glucans accumulated by Agrobacterium tumefaciens cells. Inner membranes of R. loti contained a 235 kDa beta(1-2)glucan intermediate protein indistinguishable by polyacrylamide gel electrophoresis from the intermediate protein present in A. tumefaciens inner membranes. Incubation of inner membranes of R. loti with UDP-Glc led to the formation of neutral beta(1-2)glucans with a higher degree of polymerization than glucans formed by A. tumefaciens inner membranes. Introduction in R. loti strains of plasmid pCD523 containing A. tumefaciens chvA and chvB virulence regions yielded strains that accumulated 4 times more cellular beta(1-2)glucans than wild type cells. This glucan was, regarding anionic substitution and degree of polymerization, indistinguishable from A. tumefaciens beta(1-2)glucans. Furthermore inner membranes of these R. loti exoconjugant cells contained higher levels of the 235 kDa beta(1-2)glucan intermediate protein and formed in vitro 8 times more neutral beta(1-2)glucan with a degree of polymerization corresponding to A. tumefaciens beta(1-2)glucan than inner membranes isolated from wild type cells. It was concluded that A. tumefaciens chvB gene is expressed in R. loti and determined the degree of polymerization of beta(1-2)glucan.