Abstract Description

Bifidobacteria are recognized as keystone beneficial microbes in the gastrointestinal tract (GIT), contributing to host health through mechanisms such as metabolic cross-feeding with Bacteroides and other GIT microbes (resulting in production of microbial metabolites with positive impact on GIT mucosa and host health) and colonisation resistance against GIT pathogens. To advance the development of rationally designed multi-species synthetic GIT communities, we are exploring the growth dynamics of GIT bifidobacterial species (Bifidobacterium bifidum and Bifidobacterium pseudocatenulatum) as anchor strains in co-culture with GIT commensals. Using the Cerillo Duet system, we systematically are analysing mono- and anaerobic co-culture growth profiles in nutritionally rich media (Brain Heart Infusion, BHI) and defined media (with selected carbon sources and prebiotics). The first set of data generated showed that both bifidobacterial species and Bacteroides spp. (B. fragilis, B. thetaiotaomicron, B. koreensis) reached optical densities (OD) ≥1 within 8 hours when grown as monocultures in rich media. However, when bifidobacteria were co-cultured with the Bacteroides species, growth plateaued at OD ~0.9 by 8 hours and subsequently declined, whereas the Bacteroides species continued to grow for an additional 2 – 3 hours before entering stationary phase. This suggests potential competitive or inhibitory interactions that may limit bifidobacterial persistence in rich media. In contrast to bifidobacteria and Bacteroides, Veillonella spp. exhibited poor growth in BHI, reaching OD ~0.5 in monoculture. Co-culture with bifidobacteria led to a modest increase in Veillonella OD, but did not alter bifidobacterial growth trajectories, indicating limited or no negative metabolic interplay under these conditions. These preliminary findings highlight the complexity of microbial interactions even amongst previously described cross-feeders and underscore the limitations of rich media in resolving functional relationships. Our next phase involves transitioning to minimal media with defined carbon sources to improve understanding of metabolic dependencies and cooperative dynamics. This work lays the foundation for the systematic construction of stable, multi-species GIT consortia anchored by bifidobacteria, with potential applications in microbiota-based therapeutics and fermented product development.