Mobile genetic elements, cloning vectors and genetic manipulation of bifidobacteria

Growth difficulties, because of their fastidious nutritive nature and oxygen sensitivity, and a lack of efficient genetic tools have impeded until recently proper development of molecular studies in Bifidobacterium. These studies, however, are critical to uncover the cross-talk between bifidobacteria and their hosts' cells, and also to prove unequivocally the supposed beneficial activities supplied through the gastrointestinal tract of mammals either endogenously or after ingestion as probiotics. Analysis of gene sequences provided by whole genome sequencing projects has opened new avenues to decipher the genetic basis of bacteria-cell interactions and probiotic effects. However, the purposeful development of stable cloning and expression vectors based on robust replicons -either from temperate phages or resident plasmids- is additionally needed. This chapter addresses the current knowledge on the mobile genetic elements of bifidobacteria (phages, plasmids, and transposons) and reviews the different types of vectors already available for the Bifidobacterium species, together with the transformation procedures for introducing DNA into bifidobacterial cells. It also covers recent molecular studies performed with such vectors and incipient results on the genetic modification of these organisms, establishing the basis that would allow the use of bifidobacteria for many biotechnological applications. Pitfalls, drawbacks, and future needs in the field are also discussed.