@phdthesis{8727459,
  abstract     = {{There is a blanket condemnation of dietary sugars following their association with metabolic disorders including type 2 diabetes, dental caries, irritable bowel syndrome, obesity, among others. It is worth noting, that simple sugars are the primary source of energy for human cells and should not be avoided but controlled for excess intake. Evidence suggests that glycosidic linkage and monomeric constituent of sugar (disaccharides) determine their digestibility by the host cells and microbiota. Substituting easily fermentable sugars with poorly digestible sugars presents a useful strategy in slowing the rapid acidification and hence caries formation in the oral cavity. Poor digestibility can also slow the absorption of glucose which is important for diabetes management. Moreover, some rare sugars in nature have shown prebiotic properties, therefore, are potential functional food ingredients. This Ph.D. provides an elaborate scientific insight into the cariogenicity of a rare disaccharide; kojibiose (Glc-α1,2-Glc) whose production has recently been made possible. In this study, we have demonstrated the inability of monocultures of selected oral bacteria to ferment kojibiose in comparison to sucrose (Glc-α1,β-2-Fru) and trehalose (Glc-α1,1α-Glc). A delayed fermentation was observed when medium supplemented with kojibiose was incubated with synthetic mixtures containing lactobacilli, Actinomyces viscosus, or with complex communities from human saliva. While sucrose (92%) and trehalose (56%) shifted the microbial community of saliva to the streptococcal community, kojibiose (5%) closely maintained the saliva inoculum community suggesting it is a low cariogenic sugar. In silico genomic screening, indicated that most oral strains in this study did not possess kojibiose hydrolyzing enzymes except for A. viscous and lactobacilli. Since sugar type can modulate biofilm-induced dental caries, this work further sought to characterize the biofilm-forming properties of phylogenetically diverse oral bacteria with novel and rare disaccharides; trehalose (Glc-α1,1α-Glc), kojibiose (Glc-α1,2-Glc), nigerose (Glc-α1,3-Glc), and L-arabinose glucoside (Glc-α1,3-L-Ara) and were benchmarked with sucrose and xylitol as biofilm-promoting and inhibiting sugars respectively. The study uncovered that the biofilm-forming capacity of individual streptococcal strains and their community was limited to sucrose and trehalose. In contrast, lactobacilli and A. viscosus and communities comprising them showed preference to develop biofilm with kojibiose, nigerose, and L-arabinose glucoside. Moreover, biofilm formation for up to 72 h on hydroxyapatite disc which was a more representative of the dental surface showed that kojibiose significantly formed low biofilm as compared to sucrose. Kojibiose, nigerose, and L-arabinose glucoside stimulated lactobacilli and suppressed Streptococcus mediated biofilm and are hence promising substitutes against pathogenic biofilms of streptococcal type. While dietary sugars are mostly absorbed and metabolized in the small intestine, 5-30% of these sugars can reach the large intestine. In this work, the interindividual differences in disaccharide fermentation were assessed with in vivo derived gut microbiota from four individuals for 24 h. Additional disaccharides 4’-epitrehalose (Glc-α1,1α-Gal), epikojibiose (Glc-α1,2α-Gal), and ribose glucoside (Glc-α1,2α-Rib) were included in the assessment. Fibrulose was also incorporated as a benchmark for bifidogenic properties. Fibrulose and L-arabinose glucoside significantly stimulated bifidobacteria. Relative to fibrulose, L-arabinose glucoside was established to be 18%, 4’-epikojibiose 11%, nigerose 9% while kojibiose 3% bifidogenic. On the contrary, trehalose, ribose glucoside, and epitrehalose suppressed bifidobacteria indicating their non-bifidogenic properties. Generally, α1,2- and α1,3-linked disaccharides tended to be bifidogenic. This study further demonstrated increased bifidogenic activities with kojibiose when the inoculum was first conditioned in a medium containing kojibiose (44%) or fibrulose (55%). Overall, this assessment demonstrated the importance of the structure-function relationship of disaccharides in driving the gut community and provides a predictive feature for the rational design of easy-to-digest yet selective prebiotics. Since over 70% of sugars are absorbed and fermented in the small intestine, their availability in the small intestine can selectively promote pathogens or commensals. To demonstrate this, we incubated enterotoxigenic E. coli (ETEC) in media supplemented with disaccharides and established that ETEC robustly fermented trehalose. Finally, in a gut model (SHIME), long-term exposure to trehalose and kojibiose supplemented medium established a clear community structure that was clustered by the disaccharide and the gut compartment. Differential abundance analysis identified the topmost genera Escherichia-Shigella, Akkermansia, and Bacteroides to be more abundant in trehalose treated medium while Enterococcus, Bifidobacterium, Klebsiella were abundant in kojibiose supplemented feed. With qPCR, we determined that the ETEC copy numbers under trehalose and kojibiose treatment were similar, although trehalose slightly stimulated ETEC more than kojibiose particularly in the lumen of the ileum compartment. Functionally, the total SCFA was similar but kojibiose supplemented feed was significantly high in butyrate and propionate while branched CFA was produced with trehalose treatment. This study has demonstrated the profound influence of the glycosidic linkage and monomeric composition on microbial response pointing at the potential dual application of kojibiose and related disaccharides as low cariogenic and prebiotic disaccharides.}},
  author       = {{Onyango, Stanley Omondi}},
  isbn         = {{9789463574556}},
  keywords     = {{Kojibiose,Oral microbiota,SHIME,Gut microbiota,CAZymes,Disaccharides,Biofilm}},
  language     = {{eng}},
  pages        = {{VI, 234}},
  publisher    = {{Ghent University. Faculty of Bioscience Engineering}},
  school       = {{Ghent University}},
  title        = {{Modulatory effects of kojibiose and related disaccharides upon oral and gut microbial digestion}},
  year         = {{2021}},
}