Abstract
In prokaryotic species equipped with glycogen metabolism machinery, the co-regulation of glycogen biosynthesis and degradation has been associated with the synthesis of energy storage compounds and various crucial physiological functions, including global cellular processes such as carbon and nitrogen metabolism, energy sensing and production, stress response and cell-cell communication. In addition, the glycogen metabolic pathway was proposed to serve as a carbon capacitor that regulates downstream carbon fluxes, and in some microorganisms the ability to synthesize intracellular glycogen has been implicated in host persistence. Among lactobacilli, complete glycogen metabolic pathway genes are present only in select species predominantly associated with mammalian hosts or natural environments. This observation highlights the potential involvement of glycogen biosynthesis in probiotic activities and persistence of intestinal lactobacilli in the human gastrointestinal tract. In this review, we summarize recent findings on (i) the presence and potential ecological distribution of glycogen metabolic pathways among lactobacilli, (ii) influence of carbon substrates and growth phases on glycogen metabolic gene expression and glycogen accumulation in L. acidophilus, and (iii) the involvement of glycogen metabolism on growth, sugar utilization and bile tolerance. Our present in vivo studies established the significance of glycogen biosynthesis on the competitive retention of L. acidophilus in the mouse intestinal tract, demonstrating for the first time that the ability to synthesize intracellular glycogen contributes to gut fitness and retention among probiotic microorganisms.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-014-0094-3) contains supplementary material, which is available to authorized users.
Highlights
Glycogen, a soluble multi-branched glucose homopolysaccharide, is a common form of energy storage synthesized by animals and eukaryotic microorganisms
We present our most current in vivo studies demonstrating that the capability of synthesizing intracellular glycogen contributes to the competitive retention of L. acidophilus in the mouse GI tract
The inactivation of glgA or glgB alone abolished the ability of the mutants to synthesize glycogen, confirming that (a) the glg operon is functional in L. acidophilus; (b) glgA and glgB encodes for a glycogen synthase and a glycogen-branching enzyme, respectively, and (c) both functional glgA and glgB are required for the formation of intracellular glycogen
Summary
A soluble multi-branched glucose homopolysaccharide, is a common form of energy storage synthesized by animals and eukaryotic microorganisms. The presence of intact glycogen metabolism gene sets in L. acidophilus and other glg-encoding Lactobacillus species, in specific host-associated strains of L. helveticus and L. delbrueckii subsp. The inactivation of glgA or glgB alone abolished the ability of the mutants to synthesize glycogen, confirming that (a) the glg operon is functional in L. acidophilus; (b) glgA and glgB encodes for a glycogen synthase and a glycogen-branching enzyme, respectively, and (c) both functional glgA and glgB are required for the formation of intracellular glycogen Both ΔglgA and ΔglgB mutants, but not the ΔglgP or Δamy mutant, exhibited less robust growth on raffinose compared to the parent strain [23]. Competitive co-colonization of glycogen-deficient ΔglgA mutant and parent strains On the initial day (Day 0) of the mouse experiment, both parent (NCK2300) and ΔglgA mutant (NCK2301) derivatives
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