Functional genome analysis of Bifidobacterium breve UCC2003 reveals type IVb tight adherence (Tad) pili as an essential and conserved host-colonization factor

Abstract

Development of the human gut microbiota commences at birth, with bifidobacteria being among the first colonizers of the sterile newborn gastrointestinal tract. To date, the genetic basis of Bifidobacterium colonization and persistence remains poorly understood. Transcriptome analysis of the Bifidobacterium breve UCC2003 2.42-Mb genome in a murine colonization model revealed differential expression of a type IVb tight adherence (Tad) pilus-encoding gene cluster designated "tad 2003." Mutational analysis demonstrated that the tad 2003 gene cluster is essential for efficient in vivo murine gut colonization, and immunogold transmission electron microscopy confirmed the presence of Tad pili at the poles of B. breve UCC2003 cells. Conservation of the Tad pilus-encoding locus among other B. breve strains and among sequenced Bifidobacterium genomes supports the notion of a ubiquitous pili-mediated host colonization and persistence mechanism for bifidobacteria.