Relationships between dietary fiber structural features and growth and utilization patterns of human gut bacteria
Intake of dietary fiber is considered an essential strategy to influence gut microbiota, which is associated with many diet-related chronic diseases such as obesity, diabetes, and inflammatory bowel diseases. In order to make a better choice of dietary fiber for a desired microbiota shift related to a health outcome, knowledge of fiber degradation and utilization by gut bacteria is critical. However, it is still unclear how specific dietary fiber structures may influence the growth of target bacteria. In this thesis, arabinoxylan (CAX) from corn bran was applied as a model fiber and a range of hydrolyzate structures were made differing in structural complexity to use as tools to investigate gut bacteria utilization and competition. The first study investigated the structural parameters in fiber molecules, which may be related to bacterial utilization, such as different molecular size, and branch features including type (i.e. mono- and disaccharide branches), density of substitution, and linkage patterns. In the second study, modified discrete hydrolyzate structures with subtly changed arabinosyl branches markedly delayed the lag phase of Bacteroides xylanisolvens XB1A ( B. xylanisolvens) (up to 6 h), a key member of the gut microbiota, though not of two other xylan degraders, Bacteroides ovatus 3-1-23 (B. ovatus) and Bacteroides cellulosyliticus. DSM 14838 (B. cell). This, in turn, decreased the competitiveness of B. xylanisolvens in an artificial community additionally containing the other bacteria resulting in notable alterations of the community composition. Small changes in arabinoxylan branched structure, as well as increase in degree of branching and linkage combinations, suppressed the growth of B. xylanisolvens in the competitive community environment. Thus, changes in structural complexity of the fiber either conceivably could be used to promote or suppress target bacteria. Further work showed that transcription of arabinoxylan utilization genes in B. xylanisolvens was similarly delayed for the CAX hydrolysates. Subsequently, the influence of fiber structures on interactions of the same gut bacteria was studied in the artificial microbial community. B. ovatus survived on complex fiber structures that itself could not utilize when in the presence of B. xylanisolvens. Though such cross-feeding has been demonstrated before, this work showed further that bacteria cross-feed when they are required to do so, and when another utilizable substrate is there they do so to a much lesser extent. Accordingly, while on relatively simple substrates that B. ovatus can utilize, the cooperation between two bacteria was markedly reduced, suggesting a fiber structure-dependent survival strategy. The results suggest that it may be possible to achieve rationale interventions in microbiota species composition by identifying discrete fiber structures that are only used by particular bacterial species.
Hamaker, Purdue University.
Off-Campus Purdue Users:
To access this dissertation, please log in to our