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theses

Apigenin is a monomeric flavonoid widely distributed in plants and is found in human diet. It has low toxicity and multiple reported beneficial bioactivities. Apigenin reaches the colon region intact and interacts with the human gut microbiota. Published reviews on apigenin focused its pharmacokinetics, cancer chemoprevention potentials or interactions with drugs, but no review is available on the antimicrobial effects. There is little research on the mutual effects between apigenin and gut bacteria. Therefore, there exists a knowledge gap. The objective of the dissertation is to study the interactions between dietary flavonoids and human gut microbiota in vitro, at both single strain and community levels. To achieve this objective, three sub-objectives were established: to gain an overall understanding of the effects of apigenin on microbes on both a single species and a gut microbiota community; to study the effects of apigenin on the growth of Enterococcus caccae SS-1777 as a single strain and on a gut bacteria community in vitro, respectively; to study the degradation of apigenin by Enterococcus caccae SS-1777 and a human gut microbiota in vitro, respectively.
The effect of apigenin on the single gut bacteria strains, Bacteroides galacturonicus, Bifidobacterium catenulatum, Lactobacillus rhamnosus GG, and Enterococcus caccae, was examined by measuring their anaerobic growth profiles. The effect of apigenin on a gut microbiota community was studied by culturing fecal inoculum under in vitro conditions simulating the human ascending colon. 16S rRNA gene sequencing and GC-MS analysis quantified changes in the community structure. Single molecule RNA sequencing was used to reveal the response of Enterococcus caccae to apigenin. The degradation of apigenin in E. caccae culture and in human gut microbiota culture in vitro was measured by treating the cultures and quantifying the concentration of apigenin and its potential degradation products with UPLC-ESI-MS/MS.
Results show that there were two-way interactions between apigenin and human gut bacteria on both single strain and community levels. Enterococcus caccae was effectively inhibited by apigenin when cultured alone; however, genus Enterococcus was enhanced when tested in a community setting. Single molecule RNA sequencing found that Enterococcus caccae responded to apigenin by up-regulating genes involved in DNA repair, stress response, cell wall/membrane synthesis, and protein folding. Apigenin did not have a major effect on the structure and SCFAs production of the human gut microbiota in vitro. In Enterococcus caccae culture, apigenin concentration decreased with time, but not to zero and no targeted degradation product was detected. In the community, apigenin was fully degraded and 3-(4-hydroxyphenyl)propionic acid was the main end product. Apigenin was stable in sterile media. Such interactions provide more information on how the human gut microbiota would respond to dietary apigenin, the fate of apigenin in bacterial culture, and the potential mechanisms of the health benefits of apigenin.

ETD_9236

Ph.D.

Includes bibliographical references

by Minqian Wang

doi:10.7282/t3-2m7v-9f83

ETD doctoral

The author owns the copyright to this work.