We have previously shown that species of Bradyrhizobium synthesize a novel class of cyclic beta glucans which contains both beta-1,6 and beta-1,3 glycosidic linkages [Miller KJ, Gore RS, Johnson R, Benesi AJ, Reinhold VN (1990) J Bacteriol 172:136-142]. In the present study we show that these cell-associated glucans are localized within the periplasmic compartment and that the biosynthesis of these glucans is osmotically regulated.