Synthesis of glycerophosphorylated cyclic β-(1,2)-glucans by Rhizobium meliloti ndv mutants

Abstract

The periplasmic cyclic β-(1,2)-glucans of Rhizobium spp. are believed to provide functions during hypoosmotic adaptation and legume nodulation. In Rhizobium meliloti, cyclic β-(1,2)-glucans are synthesized at highest levels when cells are grown at low osmolarity, and a considerable fraction (≥35%) of these glucans may become substituted with phosphoglycerol moieties. Thus far, two chromosomally encoded proteins, NdvA and NdvB, have been shown to function during cyclic β-(1,2)-glucan biosynthesis; however, the precise roles for these proteins remain unclear. In the present study, we show that R. meliloti mutants lacking up to one-third of the downstream region of ndvB synthesize cyclic β-(1,2)-glucans similar to those produced by wild-type cells with respect to size and phosphoglycerol substituent profile. In contrast, no phosphoglycerol substituents were detected on the cyclic β- (1,2)-glucans synthesized by an R. meliloti ndvA mutant.