ISOLATION AND CHARACTERIZATION OF THE UDP-GLUCOSE 4'-EPIMERASE-ENCODING GENE, GALE, FROM BRUCELLA-ABORTUS-2308

The UDP-glucose 4'-epimerase-encoding gene, galE or exoB, was isolated from Brucella abortus 2308 by complementation of an exoB mutant of Si norhizobium meliloti. Confirmation of the identity was done by constru cting an in-frame deletion of 660 bp with galE of the B. abortus genom e by marker exchange. The resulting galE mutant lacked UDP-glucose 4'- epimerase activity. This activity was restored by in tr ans complement ation with the intact gene. The B. abortus gal E mutant is not altered in colony morphology compared to wt 2308. The lack of UDP-glucose 4'- epimerase activity in the mutant and PCR analysis strongly suggest tha t only one copy of galE exists in B. abortus 2308. The galE sequence o f B. abortus 2308 is more similar to galE from other animal-inhabiting bacteria than it is to exoB from the Sinorhizobium legume symbionts. We propose that galE in B. abortus evolved by lateral transfer from ot her animal-inhabiting bacteria rather than from a common ancestor of B rucella and Sinorhizobium. (C) 1997 Elsevier Science B.V.