Genetic Manipulation and Gene Modification Technologies in Bifidobacteria

Bifidobacteria comprise one of the representative members of commensal bacteria in human and animal gastrointestinal tracts. Although established transformation systems using Escherichia coli–Bifidobacterium shuttle vectors are available, bifidobacteria have been known to be recalcitrant to gene modifications. In conjunction with the accumulation of bifidobacteria genomic information, the need for gene modification systems, such as a targeted gene mutagenesis and transposon mutagenesis to allow functional genomic studies to be conducted in this genus has also increased. Accordingly, several gene modification systems have been successfully developed over the past decade. In this chapter, transformation and heterologous gene expression will be introduced as fundamental genetic manipulation technologies in bifidobacteria. Subsequently, the progression of bifidobacterial gene modification system development will be reviewed from the early works to the currently available systems. Future applications of these modification systems will be also discussed.