Insights into the Functional Role of Fungi in Deep-Sea Hydrothermal Vents Through the Analysis of Stable Isotopes of Carbon, Nitrogen, and Sulfur

The functional diversity of fungi remains poorly explored in the deep-sea, particularly in hydrothermal vents. Here, we approached this gap through the analysis of stable isotopes of carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) of fourteen isolates obtained from three deep-sea vent systems of the southern Gulf of California. The δ13C results indicated that 60% of the isolates relied on mixed carbon sources fixed by the Calvin-Benson-Bassham and the reductive Tricarboxylic Acid (rTCA) cycles, whereas 40% relied exclusively on rTCA carbon. The δ15N and δ34S values suggested a dependence on local and external nitrogen sources and the assimilation of chemosynthetic and photosynthetic inputs. Fungal δ13C and δ15N overlapped with those of primary and secondary vent macroconsumers, implying the assimilation of bacterial and invertebrate necromass and their ecological role as parasites. These findings provide insights into the unexplored trophic versatility of fungi in chemosynthetic ecosystems, highlighting their importance in deep-sea trophic dynamics.