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Effect of transposon Tn5 on exopolysaccharide production by Xanthomonas campestris

Suzete A.L. Destefano; Yoko B. Rosato

Departamento de Genética e Evolução, Instituto de Biologia, Cidade Universitária, UNICAMP, 13081 Campinas, São Paulo, Brasil. Send correspondence to Y.B.R.

ABSTRACT

Tn5-induced mutants were produced in Xanthomonas campestris pv. campestris by mating a streptomycin resistant mutant with an E. colt WR 6016 strain containing the lac Ts ::Tn5 plasmid. This plasmid showed suicidal behaviour and it was transfered at a frequency of approximately 3 x 10^-5 per recipient cell. 90 mutants were selected according to mucoid morphology and the viscosity of the culture broth was measured. These selected mutants showed high values of viscosity, when compared to the original Sm^r strain. Crude gum was extracted from five mutants and the gum solution (1%) was analysed in comparison with commercial xanthan gum. The viscosity values measured at different rotations showed similarities except for the original Sm^r strain which showed the lowest values. High temperatures decreased viscosity in all samples. The 228 and Sm^r strains gave the greatest reduction. Viscosity was also reduced under acidic conditions, whereas at an alkaline pH it was generally higher.

Keywords: Transposon Tn5; N exopolysaccharide; Xanthomonas campestris.

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