Virginia P. Edgcomb, Geology & Geophysics
Marine sediments cover more than two thirds of the Earth’s surface and have been estimated to
contain as much as one-third of Earth’s prokaryotic biomass, yet relatively little is known about this habitat, in particular of the microbial eukaryotes. In terrestrial environments fungi encompass a significant portion of total microbial diversity and biomass and include key biological components in ecologically important symbioses, chemical cycles and food webs, yet very little is known about fungi in marine sediments. Microbial eukaryotes, including fungi are presumed to be important in the cycling of organic matter in all phases (particulate and dissolved) but their specific roles in these processes are not well constrained, and more knowledge is required to inform accurate models of marine sedimentary carbon and nitrogen cycling. The biogeochemical activities, composition, and temporal and spatial dynamics of marine subsurface communities are an emerging central topic in marine sciences and biogeochemistry.
The few initial studies of marine fungi to date suggest that fungi dominate eukaryotic life in the buried marine subsurface. The recovery of ribosomal RNA (and not just DNA) of fungi at these depths suggests that these sequences come from living cells, however many of the sequences detected to date from surface sediments and deeper samples are close relatives of terrestrial fungi. While fungi are increasingly found in deep-sea environments, a clear differentiation between marine and terrestrial fungi has been lost. For example, fungi thought to cause coral diseases are sometimes labeled as terrestrial invaders, however a few have been shown to be marine species of a typically terrestrial group. There is some evidence that terrestrial/surface-dwelling fungi may be capable of colonizing deep-sea habitats due to their ability to alter their membrane composition to accommodate high hydrostatic pressure. First, it is important to be able to interpret accurately the potential significance of finding particular fungal groups in diverse marine subsurface samples. Additionally, the potential adaptation to and survival of terrestrial fungi in the marine subsurface needs to be explored if we are to understand their ecological role and accurately model their activities. Preliminary data on the source and active state of fungal groups detected in marine sediments would enhance the possibility of obtaining NSF funding for a large-scale interdisciplinary investigation into the ecology and impact of fungi in marine sediments.
The aim of this study is to use the Delaware Bay system to track and enumerate fungi from a terrestrial environment out to a more pure marine system using molecular methods to confirm whether previously recovered fungal sequences come from living cells and to determine whether the marine sedimentary fungal biosphere is seeded by adaptable, opportunistic, terrestrial organisms or fungi that are truly marine in origin. This study fits within the Biodiversity in the Ocean theme of OLI. If these sequences are coming from intact fungal cells that are abundant in marine sediments then this has global implications for ocean carbon and nitrogen cycling, given the extent of the marine sedimentary biosphere. The data from this study will provide the foundation for a larger multidisciplinary proposal to NSF to conduct a detailed investigation into marine fungal biodiversity to determine using molecular, microscopic and cultivation means, what constitutes a marine fungus, which members of the fungi are more active in the subsurface vs. organisms that are merely preserved (either dead or inactive), and their ecological role/impact on nutrient cycling in mar
ine sediments. The first hypothesis is that: In an estuarine system a transition away from terrestrial fungal types in sampled pelagic and benthic fungi will be seen in a transect from a terrestrial, low salinity area to one that is typical of marine salinity and is further away from direct terrestrial influence. This distinction will be clear based on phylogenetic and morphological differences. The second hypothesis is that: the molecular method fluorescent in situ hybridization (FISH), which targets intact ribosomes, will show that fungi remain active in buried marine sediments. Sequencing of ITS region (from cDNA) will show a transition in active types of fungi as samples become more truly marine.