Deciphering the presence and activity of fungal communities in marine sediments using a model estuarine system
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Fungi are known to play key roles in ecologically important biogeochemical cycles and food webs. Most knowledge of environmental groups of fungi comes from terrestrial environments, and little is known about the potential for terrestrial fungi to colonize marine environments. We investigated the Delaware River estuary and bay as a model estuarine system to study the fungal community changes occurring along a transect from terrestrially influenced waters and sediments to a higher salinity, truly marine system. DNA-based clone libraries and a culture collection built using subseafloor sediment samples revealed that Ascomycota dominated the detected diversity ahead of Basidiomycota and Chytridiomycota. A clear transition in fungal communities from terrestrially influenced and low salinity environments to marine environments was visualized. A complementary RNA-based analysis coupled with fluorescence in situ hybridization of sediments indicated that only few fungi were metabolically active in marine sediments. Cultivation of pelagic and sedimentary fungi allowed clear identification and physiology testing of fungal communities of the Delaware Bay. Most isolates were affiliated to Ascomycota and Basidiomycota, and their growth was analyzed under different concentrations of salinity to test for habitat preference and degree of adaptability. Interestingly, most of the fungi isolated were halotolerant. The present study informs us on the source and fate of fungi that may be buried in the deep marine subsurface and is informative for future investigations of this environment.