VARIATIONS IN XANTHAN PRODUCTION BY ANTIBIOTIC-RESISTANT MUTANTS OF XANTHOMONAS-CAMPESTRIS

Mutants resistant to different antibiotics (streptomycin, tetracycline , ampicillin and penicillin) were obtained from several strains of Xan thomonas campestris and evaluated for xanthan production. Most of the mutants showed alterations in their polysaccharide production, either increasing, decreasing or totally losing their polymer-production capa city. The existence of two types of antibiotic-resistance mechanisms f or the assayed drugs is suggested: one that affects xanthan production and another that does not. Differences in outer-membrane protein patt erns of mutants that were simultaneously altered in antibiotic resista nce and xanthan production were found, in comparison with their parent al strains. These findings suggest the existence of a genetic relation ship between antibiotic-resistance mechanisms and xanthan production. Some of the mutants obtained showed significant increases in broth vis cosity and xanthan concentration. These results suggest that resistanc e to streptomycin and ampicillin can be used to obtain improved strain s in plate screening assays.