B vitamin-mediated interactions in synthetic microbial communities.

Microbial communities drive fundamental processes across the globe, from biogeochemical cycling to human health. Yet, their complexity often obscures mechanistic understanding. Synthetic communities (SynComs) have emerged as powerful tools to distill this complexity into tractable, rationally designed systems to study community function. Metabolic interactions - competition and sharing of resources between organisms - are a frequent focus of these controlled studies. The role of B vitamin cross-feeding remains a critical frontier because B vitamins are required in trace quantities for metabolism, but not all organisms can make their own, necessitating cross-feeding interactions. Here, we review recent advances in microbial ecology that use SynComs to investigate B vitamin-mediated interactions through mechanistic approaches across scales, domains of life, environments, and disciplines. We highlight key findings that demonstrate how auxotrophy, obligate cross-feeding networks, precursor sharing, exploitation and interference competition, and cell lysis together encompass B vitamin interactions. Collectively, these processes demonstrate how microbial B vitamin exchanges drive macroscale community functions like host-microbiome interdependencies. The mechanistic insights into microbial community interactions synthesized from these integrative approaches provide foundational insight into the structure and function of natural microbial communities, advancing the potential to engineer microbiomes for therapeutic and environmental applications.