Utilisation potential of human milk oligosaccharides and mucin by Ruminococcus gnavus in the human infant gut
Year: 2021
Type: dissertation
Abstract: The human gut microbiota plays an important role in the health and immune development of the body. Gut bacteria can utilise carbohydrates that are unavailable to human enzymes, like human milk oligosaccharides (HMOs) present in breast milk, and produce short chain fatty acids (SCFAs) as fermentation products. HMOs are thought to be a selective force for colonisation of the gut the first months of life. The gut microbe Ruminococcus gnavus is found present in both infants and adults, and has previously been associated with disorders like Crohn’s and eczema, and general dysbiosis. R. gnavus is a known utiliser of mucin glycans produced by the epithelium of the intestine, which resembles HMOs in structure. The idea that R. gnavus might utilise HMOs instead of or in addition to mucin stirs the thought that colonisation of R. gnavus might affect the colonisation of Bifidobacterium and other favourable bacteria. The aim of this thesis was to investigate the mucin and HMO degrading potential of R. gnavus and the potential for propionic acid production by R. gnavus in the infant gut.\n\nFaecal samples from 6-month-old infants, collected through the study Prevent Atopic Dermatitis and Allergies (PreventADALL), were analysed. Microbial composition was determined through 16S rRNA gene sequencing, short chain fatty acid composition was determined using gas chromatography, genes in the R. gnavus genome were identified through shotgun sequencing, proteins were identified using mass spectrometry, and expression of genes coding glycan degrading proteins was determined using quantitative PCR (qPCR).\n\nThe results showed a complete pathway for propionic acid production in the genome and proteome, indicating propionic acid production by R. gnavus in the infant gut, as previously shown in the adult gut. Fucosidases, β-galactosidases, sialidases and several mucin specific enzymes were identified in the proteome of all or some of the samples, while no HMO specific enzymes were found in any proteome. Complete pathways for degradation of glucose, galactose and N-acetylglucosamine (GlcNAc) were identified. The results indicate that mucin degradation is more important than HMO in R. gnavus, but that HMOs might be partially degraded. It is difficult to predict the preferred substrate, as many of the identified enzymes can be used on both mucin and HMOs. High abundance of R. gnavus is thought to be unfavourable, because of the properties of R. gnavus and the negative correlation with Bifidobacterium. Lack of Bifidobacterium is a sign of a more adult gut which is unwanted during infancy. The results from this thesis lay the foundation for further studies on glycan degradation by R. gnavus, like gene expression analysis and growth experiments on different mucins and HMOs.
Author: Bergene, Marte
Language: English
Topic: Infant Nutrition and Health
Subfield: Nutrition and Dietetics
Field: Nursing
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W7053321227