In this thesis, we explore the overall diversity, distribution, and functional roles of fungi in the global ocean with the TARA ocean & Haima Cold Seep as case study datasets.

Chapter two highlights the substantial fungal diversity in the sunlit marine environment and its contribution to carbohydrate metabolism and protein degradation. Despite their low relative abundances (<1%), fungi play vital roles in organic matter and dissolved organic carbon degradation. Ascomycota and Basidiomycota dominate the fungal groups, with a sporadic distribution of Chytridiomycota in mostly coastal samples. We find that fungal community structure is influenced by multiple factors rather than specific environmental conditions, and explore fungal carbohydrate-active enzymes (CAZymes), including the AA3 protein family involved in lignin degradation, and the GH family (GH16, GH17, GH5, GH72 subfamilies) responsible for hydrolyzing glycosidic bonds in complex carbohydrates and Peptidases involved in protein degradation. We conclude that fungal CAZymes & peptidases are abundant and their roles are vital to ecosystem functioning.

In Chapter Three, we investigate the functional role of fungi in cold seep environments sustained by methane and inorganic energy sources. Network analysis reveals fungi as central species in prokaryotic networks, enhancing resilience and information transfer efficiency. We report the active transcription of over 2500 fungal genes in cold seep sediments, with genera Fusarium and Moniliella correlating with high meth...[ Read more ]

In this thesis, we explore the overall diversity, distribution, and functional roles of fungi in the global ocean with the TARA ocean & Haima Cold Seep as case study datasets.

Chapter two highlights the substantial fungal diversity in the sunlit marine environment and its contribution to carbohydrate metabolism and protein degradation. Despite their low relative abundances (<1%), fungi play vital roles in organic matter and dissolved organic carbon degradation. Ascomycota and Basidiomycota dominate the fungal groups, with a sporadic distribution of Chytridiomycota in mostly coastal samples. We find that fungal community structure is influenced by multiple factors rather than specific environmental conditions, and explore fungal carbohydrate-active enzymes (CAZymes), including the AA3 protein family involved in lignin degradation, and the GH family (GH16, GH17, GH5, GH72 subfamilies) responsible for hydrolyzing glycosidic bonds in complex carbohydrates and Peptidases involved in protein degradation. We conclude that fungal CAZymes & peptidases are abundant and their roles are vital to ecosystem functioning.

In Chapter Three, we investigate the functional role of fungi in cold seep environments sustained by methane and inorganic energy sources. Network analysis reveals fungi as central species in prokaryotic networks, enhancing resilience and information transfer efficiency. We report the active transcription of over 2500 fungal genes in cold seep sediments, with genera Fusarium and Moniliella correlating with high methane abundance in the Sulfate Methane Transition Zone (SMTZ). Fungi in cold seeps regulate biological networks and biogeochemistry.

This thesis ultimately underscores the importance of quantitative investigations using advanced multi-omics techniques, including metatranscriptomics, to understand fungal ecology in marine environments. The limited knowledge of marine fungi emphasizes the significant potential for future research to uncover their contributions, interactions, and impacts on marine ecosystems.