Project: The Role of Fungi in Biogeochemical Transformations of Mn and Other Micro- and Macro-nutrients Along Chemoclines of the Baltic Sea

NSF Award Abstract:

Mounting evidence suggests that fungi constitute an active and diverse fraction of the microbial community inhabiting marine environments. Among these, globally-distributed low-oxygen, and low salinity open-ocean and coastal waters are expected to expand and intensify with climate change. Manganese (Mn) is a nutrient that is distributed throughout low-oxygen marine systems that plays an essential role in major elemental cycles, including those performed by microorganisms. Manganese is thus intricately linked to the health, metabolism, and function of the ocean microbiome. Despite the potential for active fungi in low-oxygen and brackish ecosystems to make significant contributions to Mn and other nutrient cycling, little is known about the roles and impacts of fungi on those processes. Ascomycota and Basidiomycota fungal species are identified as important nutrient and carbon recyclers in various marine settings, however there are few studies of fungi in chemocline settings (water columns with transitions in oxygen concentration). Fungal isolates are known that link chemical transformation of Mn (Mn(II) oxidation) to organic carbon degradation and production of reactive oxygen species (ROS), and fungal production of ROS may play a central role in the cycling and bioavailability of metals like Mn, as well as carbon and nitrogen in low-oxygen/anoxic (zero oxygen) marine environments. The Mn-rich Baltic Sea is an ideal model ecosystem for studying the future coastal ocean due to anthropogenic impacts experiences, and its salinity gradients. This project aims to contribute to understanding of fungal diversity and roles in manganese, nitrogen and sulfur cycling, as well as production of reactive oxygen species in low oxygen and brackish marine ecosystems. Fungal activities in these habitats may influence important global marine biogeochemical cycles, and knowledge of their role(s) and impacts allows more accurate predictions of the biogeochemistry of a future ocean and climate. The culture collection generated by this study is anticipated to recover many new fungal strains, whose ecology, novel properties, and potential medically-relevant bioactive compounds can be explored by interested researchers. Six undergraduate students, one graduate student, and 2 high school students per year are included in this research, and a collaboration is established with a local high school art teacher to teach an art-in-science unit, and to displayed its product at the community library, along with education materials on marine fungi and their ecological roles. The project involves international collaboration, as well as training of early career and under-represented minority scientists.

This proposal leverages a sampling opportunity during a scheduled cruise in early 2024 to collect water samples from 3 depths along the chemocline at two stations in the Baltic Sea with distinct profiles of O2 concentration, and N and Mn species. The overall goal of this project is to characterize the diversity of prokaryotic (bacteria and archaea) and fungal taxa present in these samples, and those expressing genes involved in biogeochemical cycles related to transformations of manganese, iodine, oxygen, and nitrogen, with a specific emphasis on the role of fungi. The workplan incorporates analysis of taxonomic marker genes for fungi and micro-eukaryotes, and prokaryotes, as well as catalyzed-reporter deposition fluorescence in situ hybridization (CARD-FISH) to estimate the in situ abundance of major fungal groups. Poly-A and non polyA transcriptomics of water samples provide a general overview of expressed metabolic genes, and specifically identify genes involved in Mn oxidation. High-throughput culturing efforts incorporating laser nephelometry are used to gather the broadest possible representation of culturable marine fungi in these chemocline habitats, and to identify those that carry genes of interest involved in coupling Mn(II) oxidation to organic carbon degradation. Shipboard incubation studies incorporating fungal and prokaryotic inhibitors are used to determine the extent to which fungi contribute to Mn transformation processes. Coupled RT-qPCR and metatranscriptome analyses of incubation studies are used to elucidate expression of fungal genes related to Mn transformations (e.g., Mn peroxidases), nitrogen cycling (e.g., key fungal denitrification genes p450nor, nirK), and ROS production/decay (SOD1, NOXA).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.