Host nutrients drive paired-substrate growth and distinct biofilm lifestyles in Finegoldia magna

Host-associated bacteria navigate complex nutrient landscapes where metabolites act as both growth substrates and cues that shape behavior. Yet, for most commensal and pathogenic bacteria, the nutrients and metabolisms that support persistence in the host remain unknown. Finegoldia magna is an obligate anaerobe that normally colonizes human skin and mucosal surfaces but also causes persistent biofilm-associated infections on implanted medical devices and in chronic wounds. Here, we developed a defined medium to investigate how nutrients influence F. magna physiology. We found that F. magna has a remarkably restricted metabolism that is specialized to use a limited set of host-relevant nutrients, including glycine, fructose, nucleosides, and betaine. Carbon-source screens showed glycine was the only substrate that supported growth as a sole carbon source. Instead, growth typically required two carbon substrates: a compatible electron donor-acceptor pair, suggesting redox balance imposes major constraints on its metabolism. To determine whether these constraints extend to host environments, we cultured F. magna in media derived from human chronic wound tissue. Despite its chemical complexity, F. magna displayed a similarly restricted metabolic profile, primarily consuming peptides, nucleosides, and betaine. These nutrients also directed biofilm behavior, with different metabolites promoting surface attachment or aggregation. Our findings show that although F. magna lacks metabolic flexibility, this opportunistic pathogen appears specialized to exploit host-derived products of skin physiology, tissue damage, and inflammation. This work suggests that host-associated bacteria with highly specialized metabolisms may be especially responsive to nutrient availability, linking local metabolite composition to key persistence behaviors like biofilm formation.