Iron limitation promotes metabolic cross-feeding between cheese ripening bacteria.

Iron is a limiting micronutrient in various environments, and its scarcity orchestrates microbial interactions across diverse ecosystems. The cheese surface, which is oxic, iron-limited, and a host of moderately complex ecosystems, can serve as a model system to study iron-mediated microbial interactions. In this work, we focused on two ripening bacteria isolated from cheese, Hafnia alvei and Brevibacterium aurantiacum. We combine growth measurements, transcriptomics, proteomics, and metabolomics to examine the role of iron in their interactions within a synthetic medium designed to mimic late cheese ripening conditions, using mono and coculture systems under iron limitation. Coculturing resulted in significant differences in the physiology of both strains, with a more notable effect on H. alvei. H. alvei, the only siderophore producer of the two, appeared to experience iron limitation in the coculture. This is partially attributed to sharing siderophores, and thus, iron, with B. aurantiacum. Multi-omics analysis points to several key exchanges. First, putrescine acts as a cross-fed metabolite, where B. aurantiacum synthesizes it and H. alvei uses it as an energy source. Next, we found evidence for the activity of quorum sensing and potential quorum quenching mechanisms, previously implicated in siderophore biosynthesis. Additionally, coculturing led to increased production of volatile sulfur compounds, contributing to positive organoleptic characteristics of cheese. Our model system reveals the modifications of C, N, S metabolisms in response to an abiotic stress and provides a framework to study such responses in numerous iron-limited ecosystems.