Respiration and Substrate Utilization by Marine Fungi: Their Ecological Role in an Upwelling Ecosystem

Marine fungi are relevant ecological components of microbial communities and play crucial roles in the degradation of organic matter and the cycling of nutrients in oceanic ecosystems. However, their metabolic adaptations to dynamic, nutrient-rich coastal upwelling environments remain scarcely known. The aim of our research is to contribute to the understanding of the ecological and biogeochemical roles of marine fungi in upwelling systems. To this end, we investigated the metabolic responses of three fungal strains (Sarocladium sp., Penicillium sp., and Fusarium sp.) isolated from the coastal upwelling off central-south Chile. The growth and respiration rates of these marine fungi were comprehensively evaluated using a diverse array of substrates, including glucose, cellobiose, sucrose, glycogen, asparagine, alanine, and glycine. The highest respiration rates were consistently recorded with glycogen, with no significant differences observed among species. Glucose yielded higher respiration rates in Sarocladium sp., and sucrose stimulated greater respiration in Penicillium sp. Phenotype microarrays were used to evaluate mycelium growth on various organic and inorganic nitrogen, phosphorus, and sulfur substrates. All three species exhibited high utilization indices for all substrate types, with organic components promoting the greatest growth. l-Amino acids were the preferred nitrogen sources. Adenosine and guanosine were the primary sources of phosphorus, while cysteine and methionine were the main sources of sulfur necessary for growth. Based on these species' preferred substrates for growth and respiration, we offer new insights into the previously underexplored ecological roles of these fungi in the degradation of marine organic matter and biogeochemical cycling in upwelling ecosystems.