A protocol was developed for the introduction of foreign plasmid DNA into various Bifidobacterium strains. The method, which is applicable to all Bifidobacterium species tested so far, is based on electroporation of bacteria made competent by preincubation in electroporation buffer for several hours at 4 "C. Transformation of Bifidobacterium could be achieved with a plasmid vector originating from Bifidobacterium and with plasmid vectors from Corynebacterium, but not with vectors carrying replicons from Lactococcus or Lactobacillus.

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