Turning the tide on marine fungi: insights from the global biogeography of the seagrass mycobiome

Cassandra L. Ettinger, Microbiology and Plant Pathology, University of California, Riverside, Riverside, CA, Cassandra L. Ettinger, Laura E. Vann and Jonathan A. Eisen, Evolution and Ecology, University of California, Davis, Davis, CA, Cassandra L. Ettinger, Laura E. Vann and Jonathan A. Eisen, Genome Center, University of California, Davis, Davis, CA, Laura E. Vann, Genomics and Bioinformatics, Novozymes, Davis, CA, Jonathan A. Eisen, Medical Microbiology and Immunology, University of California, Davis, Davis, CA

Background/Question/Methods
Marine fungi are often overlooked in marine studies, despite fungi on land having critical roles as decomposers, pathogens or endophytes globally. Seagrasses are marine flowering plants with important ecosystem functions with a worldwide distribution, but understanding of fungal communities associated with these marine plants has been limited. Previously, we characterized the diversity of the fungal community associated with the seagrass, Zostera marina (ZM) from one location in Bodega Bay, CA through culture-independent sequencing. We found that there were many fungal taxa for which a taxonomic assignment could not be made associated with ZM. Here we expanded our investigative efforts to characterize the distribution of ZM-associated fungi across ZM's full biogeographic range (leaves, roots, and rhizosphere sediment from sixteen sites). Using culture-independent sequencing of the ribosomal internal transcribed spacer (ITS) region and 18S ribosomal RNA gene, we first characterized global ZM-associated fungal community composition and diversity. We then tested hypotheses of neutral community assembly theory and then identified taxa of particular interest by interrogating the degree to which deviations suggested taxa were plant-selected or dispersal-limited. Finally, we defined a core mycobiome and investigated the global distribution of differentially abundant taxa.
Results/Conclusions
We found that the fungal community was significantly different between sites globally and that there is a weak, positive pattern of distance decay associated with the leaf mycobiome. The majority of taxa were found to assemble through stochastic processes, although we were able to identify taxa that were deterministically assembled which can serve as good targets for future work on ZM-fungal interactions. We found that the ZM core leaf and root mycobiomes were dominated by unclassified Sordariomycetes spp., unclassified Chytridiomycota lineages (including Lobulomycetaceae spp.), unclassified Capnodiales spp. and Saccharomyces sp. There were an abundance of unclassified fungal taxa and fungal functional guilds, further highlighting that knowledge of marine fungi is particularly underdeveloped. Future work characterizing marine fungi is needed to turn the tide on our understanding of the roles of these microorganisms generally and when associated with seagrasses.