GENE DISRUPTION IN LACTOBACILLUS-PLANTARUM STRAIN-80 BY SITE-SPECIFICRECOMBINATION - ISOLATION OF A MUTANT STRAIN DEFICIENT IN CONJUGATED BILE-SALT HYDROLASE ACTIVITY

A chloramphenicol-resistance gene (cml) was introduced into the Lactob acillus plantarum gene encoding conjugated bile acid hydrolase (cbh) o n a ColE1 replicon. This plasmid which is nonreplicative in Lactobacil lus was used to transform L. plantarum strain 80. A homologous double cross-over recombination event resulted in replacement of the chromoso mal cbh gene by the cml-containing cbh gene. The transformants obtaine d were unable to synthesize active conjugated bile acid hydrolase (Cbh ). The Cbh- Cml(R) phenotype was stably maintained for more than 100 g enerations under nonselective conditions.