SEVERAL PHENOTYPIC CHANGES IN THE CELL-ENVELOPE OF AGROBACTERIUM-TUMEFACIENS CHVB MUTANTS ARE PREVENTED BY CALCIUM LIMITATION

The chvB gene of Agrobacterium tumefaciens encodes a 235 kDa proteinac eous intermediate involved in the synthesis of beta-1,2-glucan. chvB m utants show a pleiotropic phenotype. Besides not to produce cyclic bet a-1,2-glucan, chvB mutants have been reported to be avirulent, attachm ent-deficient, and nonmotile. In this study we report additional diffe rences from the parent strain, probably all linked to changes in the c ell envelope. This pleiotropic phenotype - except for attachment and v irulence - could largely be prevented by growing chvB cells with low l evels of calcium. Although a role for beta-1,2-glucan in osmoadaptatio n has been proposed, the mode of action of beta-1,2-glucan is not know n. We speculate that in A. tumefaciens beta-1,2-glucan stabilizes memb ranes, which would be important especially in hypotonic media containi ng calcium.