Stationary-phase variation due to transposition of novel insertion elements in Xanthomonas oryzae pv. oryzae

Xanthomonas oryzae pv. oryzae causes bacterial leaf blight, a serious disea se of rice. Spontaneous mutants which are deficient for virulence and extra cellular polysaccharide (Eps) production accumulate in large numbers in sta tionary-phase cultures of this bacterium, a phenomenon which we have called stationary-phase variation. A clone (pSD1) carrying the Eps biosynthetic g ene (gum) cluster of X. oryzae pv. oryzae restored Eps production and virul ence to several spy (for stationary-phase variation) mutants, Data from loc alized recombination analysis, Southern hybridization, PCR amplification, a nd sequence analysis showed that the mutations are due to insertion of eith er one of two novel endogenous insertion sequence (IS) elements, namely, IS Xo1 and ISXo2, into gumM, the last gene of the gum gene cluster. The result s of Southern analysis indicate the presence of multiple copies of both IS elements in the genome of X. oryzae pv, oryzae. These results demonstrate t he role of IS elements in stationary-phase variation in X. oryzae pv, oryza e.