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Author ORCID Identifier

https://orcid.org/0000-0001-5365-1550

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Food Science

Year Degree Awarded

2019

Month Degree Awarded

September

First Advisor

David A. Sela

Second Advisor

Matthew D. Moore

Third Advisor

Carrie-Ellen Briere

Subject Categories

Food Microbiology | Food Science

Abstract

Our diet contains indigestible carbohydrates that are available for microbial metabolism within the gastrointestinal tract. These carbohydrate sources are oligosaccharides found in plants and human milk. Oligosaccharide utilization phenotypes are often consistent with the ecological niche that microbes occupy (e.g. adult gut, infant gut, plants). This study represents an in-depth metabolic analysis for utilization of human milk oligosaccharides (HMOs) including lacto-N-tetraose (LNT) and lacto-N-neotetraose (LNnT), and cranberry oligosaccharides (i.e. xyloglucans) within in vitro modeled systems. These model systems include microplate systems for pure cultures as well as an adapted bioreactor system to mimic microbial interactions within the gut.

Infant-colonizing Bifidobacterium longum subsp. infantis (B. infantis) metabolized both LNT and LNnT that vary by a single glycosidic linkage with inefficient metabolism resulting in increased formate production. The utilization of LNT and LNnT varied by strain. The strain-variant metabolism was also observed during pooled HMO utilization.

The differential HMO metabolism of B. infantis is of interest in terms of microbe-microbe interactions within in the infant gut. A modeled microbe-microbe interaction was conducted by supplementing B. infantis to the infant fecal derived modeled microbiomes. Depending on the microbial composition to be used for modeled microbiomes, LNT and LNnT metabolism differed. Moreover, B. infantis addition to the modeled microbiomes shifted complex microbial metabolism during LNnT towards formate production and transformed microbial structure towards Clostridium spp. as well as butyrate producers.

Plant-based foods also contain bioactive compounds that are impervious to host digestion but modulate the gut microbiome. Xyloglucans are oligosaccharides found in plant cell walls in cranberries. The phylogenetic near-neighbor B. longum subsp. longum (B. longum), isolated from the infant gut, was capable of utilizing xyloglucans, resulting in formate production. Probiotic Lactobacillus plantarum also utilized cranberry xyloglucans to a greater extent than bifidobacterial strains. Interestingly, crude cranberry extracts that contain additional molecules stimulated bacterial growth. Thus, we hypothesized that secondary products, e.g. polyphenols from cranberries, with oligosaccharides might synergistically impact on L. plantarum physiology. This strain deployed differential metabolic response to proanthocyanidins (PACs) from cranberries depending on the carbohydrate source. In summary, this study characterizes the structure-function relationships between dietary oligosaccharides and bifidobacteria, lactobacilli, and within the microbiome.

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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