Deciphering the metabolic interactions between mucus associated Ruminococcus gnavus and Limosilactobacillus reuteri strains

Reynolds, Raven Sinèad (2024) Deciphering the metabolic interactions between mucus associated Ruminococcus gnavus and Limosilactobacillus reuteri strains. Doctoral thesis, University of East Anglia.

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Abstract

Cross-feeding between gut microbiota members is crucial for maintaining gut homeostasis. Cobamides, the vitamin B12 family of enzyme cofactors, are synthesised by approximately 25% of gut microbes while 80% rely on cobamides to conduct enzymatic reactions such as methionine (Met) synthesis through cobamide-dependent enzymes. To gain insights into the mechanisms underpinning cobamide cross-feeding in the gut, we focused on two human gut symbionts, Ruminococcus gnavus and Limosilactobacillus reuteri.

R. gnavus is a prevalent member of the healthy gut microbiota and its disproportionate abundance has been associated with a growing number of diseases. There is therefore great interest in understanding R. gnavus adaptation to the gut. L. reuteri is a known cobamide producer, with our bioinformatics analyses revealing that 50% of genome-sequenced strains contained a pseudocobalamin (PsCbl) biosynthetic pathway. We demonstrated that L. reuteri MM4-1A produces PsCbl extracellularly. In contrast, we showed that R. gnavus is auxotrophic for cobamides with 98% of genome-sequenced R. gnavus strains encoding cobamidedependent proteins.

In anaerobic growth assays, R. gnavus utilised exogenous cobamides and PsCbl produced by L. reuteri MM4-1A. Transcriptomics of R. gnavus revealed upregulation of a putative cobamide transporter and cobamide-dependent protein genes in response to cyanopseudocobalamin (CNPsCbl) and PsCbl-producing L. reuteri, suggesting cobamide cross-feeding to support cobamide-dependent reactions. This effect was reduced with Met supplementation. Additionally, R. gnavus cobamide biosynthetic genes were upregulated upon porphobilinogen (PBG) supplementation in Met-supplemented conditions, suggesting potential PBG salvaging for cobamide production, consistent with the partial cobamide biosynthetic pathway found in 94% of R. gnavus strains. In the human gut microbiota, R. gnavus exhibited improved fitness with high doses of CNPsCbl and PBG while supplementation had no major impact on the whole microbial community.

This study provides insights into cobamide metabolic interactions occurring between human gut symbionts opening the door for novel strategies to modulate human gut bacteria.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Chris White
Date Deposited:	14 Jan 2025 11:24
Last Modified:	14 Jan 2025 11:24
URI:	https://ueaeprints.uea.ac.uk/id/eprint/98201
DOI:

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