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 (<i>Sarocladium</i> sp., <i>Penicillium</i> sp., and <i>Fusarium</i> 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 <i>Sarocladium</i> sp., and sucrose stimulated greater respiration in <i>Penicillium</i> 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.

海洋真菌是微生物群落的关键生态组分，在海洋生态系统的有机质降解与养分循环中发挥核心作用。然而，目前学界对这类真菌如何适应动态且富营养的近岸上升流环境的代谢适应机制仍知之甚少。
本研究旨在加深对上升流系统中海洋真菌的生态及生物地球化学功能的认知。为此，我们对分离自智利中南部近岸上升流区域的3株真菌菌株——枝顶孢霉属（Sarocladium）未定种、青霉属（Penicillium）未定种以及镰刀菌属（Fusarium）未定种——的代谢响应开展了研究。
我们通过涵盖葡萄糖、纤维二糖、蔗糖、糖原、天冬酰胺、丙氨酸及甘氨酸在内的多种底物，全面评估了这些海洋真菌的生长速率与呼吸速率。所有菌株在糖原底物上的呼吸速率均为最高，且不同菌株间无显著差异。其中，枝顶孢霉属未定种在葡萄糖底物上的呼吸速率更高，青霉属未定种则在蔗糖底物下表现出更强的呼吸活性。
本研究利用表型微阵列技术，检测了菌株在各类有机、无机氮源、磷源及硫源底物上的菌丝生长情况。结果显示，3株真菌对所有底物类型均表现出较高的利用指数，有机底物对其生长的促进效果最为显著。
左旋氨基酸为菌株偏好的氮源，腺苷与鸟苷为主要磷源，而半胱氨酸与甲硫氨酸则为菌株生长所需的主要硫源。
基于上述菌株对生长与呼吸底物的偏好性，本研究为揭示上升流生态系统中海洋真菌在海洋有机质降解及生物地球化学循环中此前未被充分探索的生态功能提供了全新视角。