https://orcid.org/0000-0001-8199-5502
Figures & data
Figure 1. Colonization Factors in gut commensal bacteria.
Schematic representation of some of the molecular and cellular mechanisms that commensal bacteria evolved to survive in the gastrointestinal tract. (Top left panel) To tolerate the wide range of pH during the transit through different gut locations, bacteria use an ATP-driven proton pump to keep an optimum cytoplasmic pH. (Bottom left panel) Surface exopolysaccharide (EPS), and pili produced by several commensal bacteria have been shown to be essential for their adherence and colonization in the GIT. (Right panel) Bile is synthesized in the liver and then secreted into the duodenum. Bile is made of primary bile acids (BAs) and is toxic to bacteria. To protect themselves from BA-mediated toxicity several commensal bacteria use hydrolytic enzymes to deconjugate BAs.
Table 1. Intracellular accumulation of glycogen reported in gut-related bacteria.
Figure 2. Glycogen metabolism pathways in gut commensal bacteria.
Phosphoglucomutase (Pgm) converts glucose-6-phosphate into glucose-1-phosphate, which serves as a substrate for ADP-glucose synthesis catalyzed by GlgC in the presence of ATP and Mg2+. GlgA catalyzes the transfer of glucosyl units from ADP-glucose to the elongating chain of linear α-1,4-glucan with the concomitant release of ADP. Then, GlgB cleaves off portions of this α-1,4-glucan and links it to internal glucose molecules in existing chains via α-1,6 glycosidic bonds to form the glycogen structure. Glycogen catabolism is mediated by glycogen phosphorylase (GlgP) which removes glucose units from the non-reducing ends of the glycogen/maltodextrin molecules with concomitant phosphorylation, thereby liberating glucose 1-phosphate. At the same time, a debranching enzyme (GlgX) cleaves the α-1,6-bonds of the limit dextrins generated by GlgP releasing maltodextrins that can be further metabolized by GlgP. An alternative pathway employs trehalose or maltose to produce maltose 1-phosphate that is used by GlgE to elongate the glucan chain. Furthermore, enzymes involved in maltose/maltodextrin metabolism may play a role in glycogen synthesis and degradation. MalQ produces maltodextrins, using maltose or malto-oligosaccharides as substrates, and then GlgB can form glycogen from these linear maltodextrins. These maltodextrins can be cleaved by MalP liberating glucose-1-phosphate.
Table 2. Biosynthetic and degradative enzymes in the metabolism of glycogen.
Figure 3. Presence/Absence of predicted glycogen biosynthetic and degradative enzymes in gut bacteria.
Heatmap representing the distribution across gut-related strains of proteins homologous to the enzymes involved in glycogen metabolism, using the protein sequences of GlgC, GlgA, GlgB, GlgP, GlgX and MalQ) from E. coli SE11, GlgD from Lactobacillus acidophilus ATCC 4796 and GlgE from Corynebacterium glutamicum DSM 20300 as query. Gene products from 70 representative strain genomes available on line from the Human (gut) Microbiome.Citation136 The significant homology of 20% identity over 50% of protein length are represented in the matrix, employing a color code that represents the degree of identity. Members of the same phylum are indicated by the same color. The numbers indicate copies of a given protein. MalP and GlgP present a high identity of protein sequence and the BlastP analysis retrieved the same results using both sequences as query.
Figure 4. Genetic organization of glycogen genes in gut commensal bacteria.
Schematic representation of the gene arrangements of some bacteria, as indicated, containing glycogen genes identified in this review. The genes with identical function are represented by the same color.
Figure 5. Role of glycogen metabolism in gut commensal bacteria.
Glycogen accumulation confers several potential advantages to bacteria enabling them to persist and survive into the gut environment. Among others, this metabolic process can: i) mediate sporulation, a strategy used by gut bacteria to survive under life-threatening conditions; ii) ensure long-term survival in periods of famine; iii) facilitate gut colonization; iv) efficiently response to stress conditions such as nutrient starvation, biofilm formation and promote acid tolerance and bile resistance.
