Lipid Biomarkers for Marine Fungi
Abstract
Marine fungi play key roles as parasites and saprotrophs in marine ecosystems and are important degraders of organic matter. They likely facilitate the remineralisation of marine carbon, thus have a profound impact on marine biogeochemical cycles. However, as little is known about their global abundance and biomass, fungi are yet to be included in biogeochemical models. Lipid biomarkers can be used to assess microbial abundance and biomass due to their specificity and may be utilised to explore the viability and trophic dynamics of marine microbial communities. Although lipid biomarkers for fungi have been used in terrestrial environments, such as soils, for many years, seldom few have investigated whether these are applicable for fungi in marine environments. This thesis set out to explore the composition of lipids across a range of marinederived fungi and assess how environmental fluctuations might induce lipid remodelling in fungal cells. Although intact polar membrane lipids have been widely used as biomarkers of marine bacteria and archaea, Chapter 3 of this thesis includes only the second survey of intact polar lipids in cultures of marine fungi. The results of this chapter indicate that fungal lipids can be used to generate a ‘fingerprint’ using multivariate statistical approaches, which can distinguish marine isolates from fungi obtained from soils. Due to the dynamic nature of marine environments, microbes can be subjected to nutrient and oxygen deprivation over short timescales. In Chapter 4, we explored the impact of starvation on intact polar lipids and fatty acids in the marine yeast Aureobasidium pullulans, a saprotroph found throughout the global oceans. The results indicated that starvation induced rapid phospholipid degradation and increased the production of exophilins. In addition, fatty acids were remodelled and Aureobasidium pullulans accumulated the signature fungal biomarkers, the 18:2ω6 fatty acid and membrane sterol, ergosterol, during starvation. Although cell growth was arrested during starvation, cultures of A. pullulans could be rejuvenated by nutrient resupply. In Chapter 5 the effect of anoxic growth was assessed on the fatty acid and sterol constitution of Mucor circinelloides, a facultative anaerobe isolated from intertidal sediments. Although sterols are often analysed in low-oxygen environments, such as sediments, to study microbial communities, this work demonstrated that anoxic growth diminished the synthesis of ergosterol in Mucor circinelloides. This indicates that sterols do not afford a quantitative estimate of fungal biomass in low-oxygen environments. Nucleic acid-based research, which has extraordinary taxonomic specificity, has enabled the characterisation of fungi from a range of marine environments. However, environmental DNA (eDNA) does not necessarily afford a quantitative estimate of fungal biomass. In Chapter 6, a dual approach combining lipid biomarkers and eDNA was utilised to explore how different methods of environmental analysis may result in divergent accounts of fungal abundance in coastal sediment. Results indicated that fatty acids could distinguish unique microbial assemblages over a short vertical depth gradient, but that signature biomarkers for fungi (i.e., ergosterol) did not corroborate with abundance profiles obtained from eDNA. Collectively, the chapters of this thesis provide a study of the intact polar lipids, fatty acids, and sterols produced by marine-derived fungi. In addition, some insight is obtained about how extreme environmental conditions may impact the physiology of fungi in marine environments.
Document Type
Thesis
Publication Date
2025
Embargo Period
2025-09-20
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License
Recommended Citation
Cooper, E. (2025) Lipid Biomarkers for Marine Fungi. Thesis. University of Plymouth. Retrieved from https://pearl.plymouth.ac.uk/gees-theses/463
