Identification And Analysis Of A Gene Cluster Involved In EPS Production Of Xanthomonas Campestris Pv. Campestris

A 9.4kb HindIII-DNA fragment harbouring a gen (or gens) inolved in EPS production was cloned preiously from Xcc wild-type strain 8004 in our laboratory. In this study, a restriction nap with 6 enzymes of the fragment was constructed. By inserton mutagenesis with transposon Tn5 A5 of the fragment and construction of mutants by marker exchange it was revealed that there is a gene cluster involved in EPS production spanning 7 kb continuous region within the 9.4kb DNA fragment. It is not known if the rest 2 kb region is involved in EPS production, as no insertion or mutation was obtained within this region.Introduction of the recombinant plasmid harbouring the 9. 4kb Hind HI DNA fragment into the strain 8004 resulted in 2.8-fold increase of EPS production.A"1.9kb"EcoRl fragment within the above mentioned 9.4kb DMA was sequenced and analyzed in this study. The results revealed that the fragment contains 1880bp nucleiotide with a complete open reading frame (0RF2) and an incomplete ORF(ORFl). The deduced products encoded by 0RF1 and 0RF2 show 100X indentity with the reported GumA and GumB proteins of Xec at amino acid level, respectively. The GumA is a regulator with extensive regulations, often referred to integration host factor alpha (IHFa )encoded by the himA gene in Escherichia coli. The GumB probably play a role in the polymerization of sugar nucleiotides or exportation of EPS.This work studied also the effect of EPS in the pathogenicity of Xcc by inoculating the constructed EPS mutants(EPS-) on host plants.The results showed that EPS has an important role in the pathogenicity, the inoculation closes affect the symptom production. The results of scanning electron microscopy revealed that EPS might be important for infection of Xcc via stomata.