GENETIC-ANALYSIS OF A DNA REGION INVOLVED IN EXPRESSION OF 2 EPITOPESASSOCIATED WITH LIPOPOLYSACCHARIDE IN XANTHOMONAS-CAMPESTRIS PV VESICATORIA

We report on the cloning of DNA involved in expression of two epitopes associated with lipopolysaccharide (LPS) in Xanthomonas campestris pv . vesicatoria and on the use of part of this region for differentiatin g A (nonpectolytic/amylolytic) and B strains (pectolytic/amylolytic) o f this pathogen. From a genomic library of A-strain 75-3 that expresse s two epitopes, two recombinant cosmids conferred expression of two ep itopes in 87-13, an A strain that does not express the two epitopes. O ne of the two overlapping clones, pEC795, contained a 27-kb insert and was used for further analysis. Immunoblots revealed that the epitopes are components of LPS in 75-3. Transposon mutagenesis of the insert i dentified a 4.5- to 5.5-kb region necessary for expression of the two epitopes in 87-13. A 0.65-kb internal fragment from this region reacte d strongly in hybridization tests with A strains, weakly with B strain s, and with only two of eight pathovars of X. campestris. PCR (polymer ase chain reaction) amplification using primers from the 0.65-kb fragm ent resulted in the predicted DNA product in all A strains (12), in on e of 12 B strains, and in one of 10 other pathovars (i.e., X. c. pv. a lfalfae). Digestion of the PCR products by two enzymes resulted in ide ntical restriction patterns for A strains and X. c. pv. alfalfae but r esulted in a different pattern for the B strain.