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.

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过程中发挥核心作用。然而，目前学界对这类真菌如何适应动态且富营养的海岸上升流环境的代谢机制仍知之甚少。本研究旨在加深人们对海洋真菌在上升流生态系统中所扮演的生态与生物地球化学角色的认知。为此，我们针对从智利中南部海岸上升流区域分离得到的3株真菌菌株（柱顶孢属（Sarocladium sp.）、青霉属（Penicillium sp.）及镰孢属（Fusarium sp.））的代谢响应展开了研究。我们采用涵盖葡萄糖、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，对这些海洋真菌的生长速率与呼吸速率进行了全面评估。实验结果显示，糖原诱导的呼吸速率始终最高，且不同菌株间无显著差异。柱顶孢属菌株在以葡萄糖为底物时呼吸速率更高，而青霉属菌株则在蔗糖底物下表现出更强的呼吸活性。我们采用表型微阵列（Phenotype microarrays）技术，评估了3株真菌在多种有机、无机氮、磷及硫底物上的菌丝生长情况。3株真菌对所有底物类型均表现出较高的利用指数，其中有机底物对其生长的促进效果最为显著。左旋氨基酸为这类真菌的首选氮源。腺苷与鸟苷为主要磷源，而半胱氨酸与蛋氨酸则是其生长所需的主要硫源。基于上述菌株偏好的生长与呼吸底物，本研究为阐明这类真菌在上升流生态系统中尚未被充分探索的海洋有机质降解与生物地球化学循环生态角色提供了全新视角。