PERIPLASMIC CYCLIC 1,2-BETA-GLUCAN IN BRUCELLA SPP IS NOT OSMOREGULATED

Biosynthesis of periplasmic cyclic 1,2-beta-glucans in Brucella ovis s train REO198 and B. abortus strain S19 was found to be carried out by membrane-bound enzymes that use UDP-glucose (UDP-Glc) as donor substra te. Contrary to what happens in species of the genera Agrobacterium an d Rhizobium, the accumulation of the reaction products in Brucella app eared not to be osmotically regulated. Incubation of permeabilized cel ls with UDP-[C-14]Glc led to the formation of soluble neutral cyclic 1 ,2-beta-glucans and [C-14]glucose-labelled glucoproteins. PACE of puls e-chase experiments carried out with permeabilized cells showed that t he molecular mass of the labelled protein was indistinguishable from A grobacterium tumefaciens A348 and Rhizobium fredii USDA191 glucoprotei ns known to be intermediates in the synthesis of cyclic glucans. Bruce lla total membrane preparations were less efficient than permeabilized cells in the formation of cyclic glucan; this was attributed to defec tive cyclization. Accumulation of protein intermediates having oligosa ccharides of high molecular mass that were not released from the prote in was observed after chase with 2 mM UDP-Glc. This defect was not obs erved when permeabilized cells were used as enzyme preparation, thus s uggesting that in Brucella a factor(s) that was lost or inactivated up on the preparation of membranes was required for the effective regulat ion between elongation and cyclization reactions.