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

Abstract

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 biogeochemistry, 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 planktonic fungi. These biochemical signatures, and an elemental composition indicative of a marine planktonic 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.

Adapting an Ergosterol Extraction Method with Marine Yeasts for the Quantification of Oceanic Fungal Biomass

“…Ergosterol is the most abundant fungal sterol [ 30 ] and it is almost exclusively produced by fungi [ 13 ]. Hence, it has been used to determine fungal biomass in terrestrial and aquatic environments [ 19 ]. However, quantifying ergosterol in open ocean waters and the deep sea requires highly sensitive methods due to the expected low fungal abundance in these environments.…”

“…A property that makes ergosterol especially well-suited as a proxy for fungal biomass is that it contains a 5,7-double bond, which is rare among other sterols [ 9 ]. Additionally, it represents more than 80% of sterols in fungal strains [ 19 ]. Not all fungi are capable to synthesize ergosterol such as many fungi belonging to the division Chytridiomycota [ 20 ].…”

Planktonic Marine Fungi: A Review

“…The ergosterol extraction method was recently adapted to marine fungi to allow for the quantification of fungal biomass in the oligotrophic (low productive) regions (Salazar Alekseyeva et al., 2022). However, the ergosterol‐based method falls short when dealing with Chytridiomycota taxa (Gutiérrez et al., 2020), which is important to consider during phytoplankton blooms.…”

“…There are currently 1,898 described species of marine fungi (https://www.marinefungi.org/, 12 September 2023; Calabon et al., 2023), but their actual diversity is estimated to be much higher, with some studies stating that only around 1% of marine fungi have been identified (Gladfelter et al., 2019; Jones, 2011). In coastal waters, planktonic fungi are commonly found on aggregates or detritus associated (Gutiérrez et al., 2010, 2020). Moreover, they can be associated with other eukaryotes or phytoplankton as pathogens or symbionts (Grossart et al., 2016; Gutiérrez et al., 2010; Raghukumar, 2017a; Richards et al., 2015; Sen et al., 2022).…”

Lipidomics of Environmental Microbial Communities. I: Visualization of Component Distributions Using Untargeted Analysis of High-Resolution Mass Spectrometry Data

“…Lipids are the main building blocks of microorganisms and occur ubiquitously in the environment. A large number of lipids are synthesized by many different genera and orders of microbes but some lipids are unique to specific organisms or groups of organisms or to specific biogeochemical processes (e.g., Koga et al, 1998;Cvejic et al, 2000;Sinninghe Damsté et al, 2002b;Belt et al, 2007;Rossel et al, 2008;Bauersachs et al, 2009;Elling et al, 2017;Rush and Sinninghe Damsté, 2017;Longo et al, 2018;Gutiérrez et al, 2020), and hence serve as biomarker lipids. Furthermore, intact polar lipids (IPLs) are thought to degrade rapidly upon cell death indicating recent activity of microbial cells (White et al, 1979;Harvey et al, 1986).…”