Intracellular polysaccharide synthesis in the gut commensal Bifidobacterium breve UCC2003: role in survival and host colonization

Abstract

Bifidobacteria are predominant commensal bacteria of the human gastrointestinal tract (GIT) and widely used as probiotics. Although gut colonization and persistence are critical to elicit a probiotic effect, the genetic basis for these processes in Bifidobacterium remains poorly understood. Many (gut commensal) bacterial species synthesize and store intracellular polysaccharides (IPS), and has been implicated in host persistence. In silico genome analysis of Bifidobacterium breve UCC2003 (and other bifidobacteria) has revealed the presence of genes predicted to be involved in the metabolism of intracellular storage carbohydrates. In this regards, the aim of this study was to investigate the role of polysaccharide production in the adaptation of bifidobacteria to the human GIT. To achieve this objective, the genes codifying a glycogen phosphorylase (glgP, Bbr_0060) and a phosphoglucomutase (pgm, Bbr_1595) involved in glycogen breakdown, were inactivated in B. breve UCC2003. Phenotypic analysis of the mutants revealed that both genes are essential to grow on sugars composed of glucose units with alpha bonds (i.e. maltose, maltodextrin, and starch), probably due to the accumulation of IPS which cannot be metabolized. Furthermore, the mutants stored more IPS compared to the wild type strain. Additional analysis of the IPS isolated suggested that B. breve UCC2003 indeed produces a polysaccharide composed by glucan with ¿-1,4 and ¿-1,6-linked bonds. To investigate the role of intracellular energy storage in host colonization, survival experiments were performed under GIT stress factors in B. breve UCC2003. The results showed a lower resistance of the mutants to survive to different concentrations of bile (ox-gall) compare to the control. Here we described the polysaccharide stored in B. breve UCC2003 and its role in the survival under certain GIT stress conditions.