Next generation sequencing based transcriptomic analysis of bile stress response in Bifidobacterium longum BBMN68

Bifidobacterium longum is one of the natural inhabitants in human gastrointestinal tract. In order to colonize and exert particular functions in the gut, it has to be tolerant to the physiological concentrations of bile salts. In this work, we used RNA-Seq transcriptomics based on the Next-Generation Sequencing to investigate the global response to bile in B. longum BBMN68, a potential probiotic strain isolated from a healthy centenarian. In the presence of 0.75 g liter-1 ox-bile, the transcription of 236 genes were regulated (≥ 3-fold, p < 0.001). Function analysis and Gene Ontology suggested that the bile stress response of B. longum BBMN68 covers almost all biological processes, including bile stress resistance, general stress response, central metabolic process, transmembrane transport, gene expression, cell proliferation and interaction with the host. Remarkably, 3 two-component systems and 11 transcription factors were up- or down-regulated by bile, and target genes of the regulators were identified by bacterial one-hybrid system and bioinformatics methods, resulting in a putative regulatory network that controls bile stress response in B. longum for the first time. This study significantly develops our understanding on bile stress response and brings new insight to the regulatory mechanism in bifidobateria.