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Author ORCID Identifier

https://orcid.org/0000-0002-4877-9450

AccessType

Open Access Dissertation

Document Type

dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Food Science

Year Degree Awarded

2023

Month Degree Awarded

February

First Advisor

David A Sela

Second Advisor

Matthew Moore

Third Advisor

Zhenhua Liu

Subject Categories

Food Microbiology | Laboratory and Basic Science Research | Maternal and Child Health | Microbiology | Molecular, Genetic, and Biochemical Nutrition

Abstract

Human milk contains human milk oligosaccharides (HMOs) that are indigestible and pass intact through the infant gastrointestinal tract where they are available for microbial metabolism. HMOs incorporate the same monosaccharide building blocks but vary structurally in primary sequence of monomeric components. Primary sequences are further diversified by degree of polymerization, branching, and secondary modifications such as fucosylation. Fucosylated HMOs (fHMOs) are highly abundant and can account for over 30% of total HMOs. Infant-colonizing Bifidobacterium longum subsp. infantis (B. infantis) possesses a specialized gene cluster conveying the ability to metabolize fHMOs. This study presents an in-depth analysis of B. infantis 2ʹfucosyllactose (2ʹFL), difucosyllactose (DFL), and constituent component metabolism in pure culture as well as in a modeled infant gut microbial community. B. infantis metabolized both free and 2ʹFL-derived fucose through a common metabolic pathway to produce 1,2-propanediol (1,2-PD). While free fucose was inefficiently metabolized, co-fermentation with trace constituents significantly increased fucose metabolism. 2ʹFL metabolism is also concentration-dependent, though only biomass showed clear dependence. Regardless of concentration, 2ʹFL metabolism upregulated fucose-associated genes as well as genes in the central metabolic pathway. B. infantis secretes bioactive short chain fatty acids (SCFAs) that can be absorbed by the infant host or be further metabolized by other microbes to additional bioactive compounds. B. infantis and Eubacterium hallii cross-feeding was characterized in pure culture during 2ʹFL and DFL fermentation. Bifidobacterial fHMO metabolism is strain-dependent, giving rise to strain-dependent syntrophy between two studied B. infantis strains and E. hallii. The addition of a modeled fecal community background shifts E. hallii and B. infantis syntrophy through competitive interactions. In the modeled community, DFL is cleaved to free fucose and 3ʹFL, reducing propionate production. Supplementation of B. infantis and/or E. hallii into the modeled community altered butyrate production, but propionate production was unchanged. In the absence of E. hallii supplementation other butyrate- and propionate-producing genera increased in relative abundance depending on fHMO structure, demonstrating functional redundancy within the infant gut microbiome. In summary, this work characterized B. infantis fHMO metabolism as well as structure-function relationships between fHMOs and the infant gut microbiome.

DOI

https://doi.org/10.7275/32298269

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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