Identification and cloning of a cyclic β-(1 → 3) β-(1 → 6)-d-glucan synthesis locus from Bradyrhizobium japonicum

A cosmid clone complementing a cyclic β-(1 → 2)-glucan biosynthesis (ndvB) mutant of Rhizobium meliloti was isolated from a Bradyrhizobium japonicum gene library. This clone specified synthesis of β-(1 → 3),β-(1 → 6)-linked glucans in R. meliloti. The complemented strain was osmotically tolerant and symbiotically competent on alfalfa. Thus, β-(1 → 3),β-(1 → 6)-glucans can substitute functionally for β-(1 → 2)-glucans in R. meliloti.