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All Tn5 insertion mutants of Xanthomonas albilineans, the cause of leaf scald disease of sugar cane, which failed to produce albicidin antibiotics failed to cause chlorosis in inoculated sugar cane but remained resistant to albicidin. Southern analysis revealed that mutants deficient in albicidin production carried the transposon on different chromosomal restriction fragments spanning at least 50 kb in the X. albilineans genome, which is larger than any reported cluster of genes involved in the production of a bacterial phytotoxin. Albicidin-resistant cosmid clones from a Tox Tn5 insertion mutant did not carry the transposon, and the subcloned albicidin resistance gene did not hybridize to any of the restriction fragments carrying Tn5 in the Tox mutants, indicating that the albicidin biosynthesis and resistance genes are not closely linked in X. albilineans.