A transposon insertion in the gumG homologue of Xanthomonas oryzae pv. oryzae causes loss of extracellular polysaccharide production and virulence

Xanthomonas oryzae pv, oryzae causes a serious disease of rice called bacte rial leaf blight. It produces copious amounts of extracellular polysacchari de (EPS). An EPS- and virulence-deficient mutant of X. oryzae pv. oryzae wa s isolated by Tn5 mutagenesis. The mutant allele in this strain was cloned by transposon tagging in the Escherichia coli vector pBluescript and the DN A sequences flanking the transposon insertion site were determined. Compute r-based similarity searches in the DNA database using the BLAST algorithm s howed these sequences to be 78% identical at the nucleotide level to a gene , gumG, in the gum cluster, which is required for EPS biosynthesis in Xanth omonas campestris pv. campestris. A 36-kb X. oryzae pv. oryzae genomic clon e containing the putative EPS biosynthetic gene cluster of X. oryzae pv. or yzae restored both EPS production and virulence proficiency to the gumGXo:: Tn5 mutant. The results suggest that EPS is an important virulence factor o f X. oryzae pv. oryzae. (C) 1999 Federation of European Biochemical Societi es. Published by Elsevier Science B.V. All rights reserved.