Biochemical fingerprints of marine fungi: implications for trophic and biogeochemical studies

Fungi are ubiquitous in the marine environment, but their role in carbon and nitrogen cycling in the ocean, and in particular the quantitative significance of fungal biomass to ocean biogeo-chemistry, has not yet been assessed. Determination of the biochemical and stable isotope composition of marine fungi can provide a basis for identifying fungal patterns in relation to other microbes and detritus, and thus allow evaluation of their contribution to the transformation of marine organic matter. We characterized the biochemical composition of 13 fungal strains isolated from distinct marine environments in the eastern South Pacific Ocean off Chile. Proteins accounted for 3 to 21% of mycelial dry weight, with notably high levels of the essential amino acids histidine, threonine, valine, lysine and leucine, as well as polyunsaturated fatty acids, ergosterol, and phosphatidylcholine. Elemental composition and energetic content of these marine-derived fungi were within the range reported for bacteria, phytoplankton, zooplankton and other metazoans from aquatic environments, but a distinct pattern of lipids and proteins was identified in marine plank-tonic fungi. These biochemical signatures, and an elemental composition indicative of a marine plank-tonic source, have potential applications for the assessment of fungal contribution to marine microbial biomass and organic matter reservoirs, and the cycling of carbon and nutrients.