Modulation of Gut Microbiota In Vitro in Stools from Healthy and Diseased Individuals Using Soluble Plant Cell Wall-Based Dietary Fibers

Tingting Chen, Purdue University

Abstract

Related to the development of the food industry in the past century, dietary habits have been altered due to increased availability of animal-source foods, refined grain products, and in general low fiber processed food. Modern Western diets are associated with many chronic non-communicable diseases and conditions, including obesity, type 2 diabetes, inflammatory bowel disease, autoimmune diseases, and many more. Dysbiosis of the gut microbiota has been found to play an important role in their pathogenesis, and is related to increased intestinal permeability, abnormal immune response, and inflammation. In obese individuals and test animals, dietary fiber supplementation has been shown to attenuate body weight gain, insulin resistance and endotoxemia. Short chain fatty acids (SCFAs), produced by fermentation of dietary fiber, is proposed to be the major contributor of those benefits. Previous studies in our laboratory have shown that arabinoxylan extracted from corn has a more complex structure than sorghum arabinoxylan, and has a slower gas production rate during in vitro fermentation. In this thesis work, the first study was aimed to explore these two fibers in individuals with divergent microbiota community structures. In vitro fermentation was conducted on fecal samples from 6 individuals. Among those, previously shown different fermentation profiles from the two structurally different arabinoxylan were not observed in two subjects. 16S rRNA sequencing showed that one of these had a Prevotella dominant enterotype, which is associated with plant-based diets, and another individual with slower fermentation response to corn arabinoxylan had a Bacteroides enterotype. In the microbiota of the Prevotella enterotype, corn and sorghum arabinoxylans significantly promoted one single Prevotella OTU with equally high production of total SCFAs with propionate as the major product. On the other hand, in the Bacteroides enterotype, the two fibers enriched different OTUs leading to different levels and ratios of SCFAs. Enterotypes dominated by different fiber-utilizing bacteria may impact host health by way of producing different amounts and profiles of SCFAs from the same carbohydrate substrates. Both Prevotella and Bacteroides belong to Bacteroidetes phylum, which has been observed more in lean people and in rural area African children. A high proportion of the Firmicutes phylum has been observed in Western urban centers, and particularly in obese people. Firmicutes was also found dramatically increased in high fat diet-induced obese mice. The second study investigated the effects of soluble dietary fibers [fructooligosaccharides (FOS), beta glucan, pectin, arabinoxylan (SAX)], which were from plant cell wall structures, on mainly Firmicutes microbiota from individuals representing a healthy control (HC) group, Parkinson’s disease patients (PD), and inflammatory bowel disease patients [ulcerative colitis (UC) and Crohn’s disease (CD)]. PD had notably higher microbiota diversity than HC, and UC and CD had lower diversity than HC. SCFA production of CD microbiota was compromised, which was associated with an overall loss of members of the Bacteroidetes phylum. Of the fibers tested, pectin produced the highest acetate and total SCFAs. The mixture of different fibers did not improve alpha diversity. SCFA production was compared for the diseased and healthy microbiota under the different fiber treatments. FOS, beta glucan, and pectin increased propionate levels in PD to the level of the HC, and the four fiber mixture increased propionate higher than the HC. FOS, pectin, and the fiber mixture increased total SCFAs to the level of the HC. Lastly, the fermentation products were tested in the Caco-2 cell monolayer to study their effect on intestinal barrier function. At a moderate total SCFA concentration level, higher proportion of butyrate showed better effect on protecting and repairing the barrier function of the Caco-2 cell monolayer.

Degree

Ph.D.

Advisors

Hamaker, Purdue University.

Subject Area

Food Science|Microbiology

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