Gene disruption in Lactobacillus plantarum strain 80 by site-specific recombination: isolation of a mutant strain deficient in conjugated bile salt hydrolase activity.

A chloramphenicol-resistance gene (cml) was introduced into the Lactobacillus plantarum gene encoding conjugated bile acid hydrolase (cbh) on a ColE1 replicon. This plasmid which is nonreplicative in Lactobacillus was used to transform L. plantarum strain 80. A homologous double cross-over recombination event resulted in replacement of the chromosomal cbh gene by the cml-containing cbh gene. The transformants obtained were unable to synthesize active conjugated bile acid hydrolase (Cbh). The Cbh- CmlR phenotype was stably maintained for more than 100 generations under nonselective conditions.