RHICADHESIN-MEDIATED ATTACHMENT AND VIRULENCE OF AN AGROBACTERIUM-TUMEFACIENS CHVB MUTANT CAN BE RESTORED BY GROWTH IN A HIGHLY OSMOTIC MEDIUM

Cyclic beta-1,2-glucan is considered to play a role in osmoadaptation of members of the family Rhizobiaceae in hypotonic media. Agrobacteriu m tumefaciens chvB mutants, lacking beta-1,2-glucan, exhibit a pleiotr opic phenotype, including nonmotility, attachment deficiency, and avir ulence. Here we report that by growth of chvB mutant cells in tryptone -yeast extract medium supplemented with 7 mM CaCl2 and 100 mM NaCl2 th e mutant cells become motile, attach to pea root hair tips, and are vi rulent on kalanchoe; leaves. Moreover, whereas chvB mutants grown in t ryptone-yeast extract medium containing 7 mM CaCl2 do not produce acti ve rhicadhesin, addition of 100 mM NaCl to this medium resulted in res toration of rhicadhesin activity. The presence of CaCl2 appeared to be required for attachment, virulence, and activity of rhicadhesin. The results support a role for cyclic beta-1,2-glucan in osmoadaptation an d strengthen the notion that rhicadhesin is required for attachment an d virulence of A. tumefaciens.