Fungi thrive in aquatic habitats and have important roles in ecosystem functioning and health. Aquatic fungi participate in nutrient cycles, symbiosis, process organic matter and impact food webs by parasitising other aquatic organisms. Recent technological advances, including the application of stable isotope and omics-based approaches, have revealed a widespread functional and taxonomic diversity of aquatic fungi and fungal-like organisms (e.g. Oomycetes). A better understanding of aquatic fungi supports a more comprehensive view of aquatic ecosystems, including food web dynamics. This session covers all aquatic ecosystems, from freshwater ponds, lakes and rivers to estuaries, coastal marine waters, and the open deep ocean, ranging from tropical to temperate and polar regions including sea ice. The session is open to the full taxonomic diversity of aquatic fungi, including hyphal and yeast forms, aquatic lichens and zoosporic groups, such as chytrids, as well as fungal-like organisms (e.g. Oomycetes). We welcome those working both in the field and with model laboratory systems, across the range of aquatic functional roles (e.g. phytoplankton parasites, saprotrophs, symbionts) and diversity-focused studies (e.g. eDNA-based). Our aim is to stimulate a cross-ecosystem and cross-taxa synthesis of aquatic fungi in all their forms and functions, including showcasing recent technological advances to promote wider update across the aquatic mycology field, aquatic sciences in general, and across fundamental and applied interests.
Lead Organizer: Michael Cunliffe, Marine Biological Association (micnli@mba.ac.uk)
Co-organizers:
Serena Rasconi, Université Savoie Mont Blanc, INRAE, CARRTEL (Serena.Rasconi@inrae.fr)
Federico Baltar, University of Vienna (federico.baltar@univie.ac.at)
Eva Breyer, University of Vienna (eva.breyer@univie.ac.at)
Hans-Peter Grossart, IGB-Berlin (hanspeter.grossart@igb-berlin.de)
Presentations
06:30 PM
FUNGAL CANNONS IN AQUATIC PARASITES (6761)
Primary Presenter: Patrick Wilson, University of Illinois Urbana-Champaign (pwilson5@illinois.edu)
Metschnikowia bicuspidata was first described infecting Daphnia magna by Metscnikoff in 1884. Since then, similar parasites have been described infecting a number of different ecologically and economically important species in both freshwater and marine environments. Previous work has found that these parasites use a fungal cannon mechanism that is common in Ascomycetes to penetrate host epithelial tissue. However, little work has been done to examine the triggers and acceleration of ascospore release in aquatic environments. We examine the morphology of the ascospores, where they are penetrating in Daphnia gut epithelium, and potential cannon trigger mechanisms. To do this, we utilize SEM and TEM imaging of the spores penetrating the single cell thick gut epithelium of the host and test a range of different trigger mechanisms on Metschnikowia bicuspidata asci.
06:30 PM
Environmental control of chytrids infecting bloom forming cyanobacteria (5970)
Primary Presenter: Bastiaan Ibelings, University of Geneva (bastiaan.ibelings@unige.ch)
In this presentation we present results from several chytrid infection experiments using bloom forming cyanobacteria as hosts. Two potentially toxic cyanobacteria were used, isolated together with their chytrid parasites, Planktothrix rubescens and Dolichospermum spec. For P.rubescens we performed a full-factorial experiment to study how temperature and light interact to affect the dynamics of host and chytrid parasite. We used a dynamic host-parasite model to explore how temperature and light affect long term dynamics. Model exploration indicates that increasing temperature and light shifts equilibrium outcomes from P. rubescens persisting alone to stable coexistence and then to limit cycles. The results shed new light on the specific habitat of P. rubescens in the metalimnion of deep lakes. For Dolichospermum we used a newly isolated and described chytrid, which specializes on infecting heterocysts of the cyanobacterial host only. Chytrid infection resulted in a nearly 70-fold decrease in the heterocysts ability to fix nitrogen. Our results indicate that chytrid infection strongly decreased host growth, but only when nitrogen in the medium was absent, forcing the cyanobacterium to rely on nitrogen fixation from its - infected - heterocysts. The results will be discussed in light of their interest for two different fields in lake ecology, host x parasite interactions and harmful cyanobacterial blooms.
06:30 PM
The last of BATS: fungal plankton distribution in the epi- and mesopelagic ocean (5967)
Primary Presenter: Leocadio Blanco Bercial, Bermuda Institute of Ocean Sciences - Arizona State University (leocadio_blanco@hotmail.com)
Planktonic fungi are, arguably, the last major taxonomic group that has been neglected from biological oceanography studies. We are barely beginning to understand their abundance, distribution and role in ecological and biogeochemical cycles in the open ocean. An initial study, based on metabarcoding at the Bermuda Atlantic Time-series Study site, provided many interesting insights regarding taxonomy and potential functionality, but at the same time raised even more questions owing to the lack of abundance and biomass data. Here we build on that prior work, presenting microscopy data of multicellular fungal plankton from the surface, deep chlorophyll maximum, 200 m and 300 m. Our results demonstrate a maximum of multicellular fungal plankton at upper epipelagic, ranging in morphology from long, isolated hyphae to large, complex colonies, close to a millimeter in size. These large colonies were often associated with dead, visible, organic particles or natural semitransparent aggregates, but sometimes they were observed without a foreign base for development. Abundance and carbon biomass profiles of the fungal plankton were found to be similar in range to those of the heterotrophic eukaryotes. Biomass and nature (developed hyphae vs yeast/pseudohyphae) of the fungal plankton changed with the months and hydrography, which would indicate a seasonal response of the fungal community. These results are compared to those from previous metabarcoding data, for a better understanding of the potential ecological profiles and roles of the fungal plankton in the oligotrophic oceans.
06:30 PM
GIANT dsDNA FUNGAL VIRUSES DISCOVERED IN THE MARINE DEEP BIOSPHERE: IMPLICATIONS ON FUNGI ECOLOGY (5960)
Primary Presenter: Joaquin Martinez Martinez, Bigelow Laboratory for Ocean Sciences (jmartinez@bigelow.org)
The oceanic igneous crust is a vast reservoir of microbial life that remains largely unexplored. Fungi are the only eukaryotes that have been found in this ecosystem, and there is increasing evidence that they are viable and transcriptionally active. Additionally, archaeal and bacterial viruses were previously detected by metagenomics in oceanic crustal fluids. Viruses play crucial roles in ecology, evolution, and biogeochemical cycling through host infection. However, until now, the diversity and impacts of fungal viruses in this environment had not been investigated. Here we report the discovery of two eukaryotic Nucleocytoviricota genomes in crustal fluids from the Juan de Fuca Ridge by sorting and sequencing single virions. The dominance of Ascomycota fungi as the main eukaryotes in the crustal fluids, the presence of eukaryotic tRNA genes in the two viral genomes, and the evidence of fungal genes acquired through horizontal gene transfer events point to these fungi as the putative hosts, making these the first putative fungi-Nucleocytoviricota specific association. Our study suggests active fungal-viral dynamics in the subsurface oceanic crust and raises important questions about the impact of viral infection on productivity and biogeochemical cycling in this ecosystem.
06:30 PM
AQUATIC FUNGAL DIVERSITY ACROSS CONTRASTING ARCTIC FRESHWATER AND MARINE ECOSYSTEMS (5758)
Primary Presenter: Michael Cunliffe, Marine Biological Association (micnli@mba.ac.uk)
Arctic aquatic ecosystems are important at both regional and global scales, however at present we have a limited understanding of the fungi that thrive in these habitats. Sea ice ecosystems were sampled along a transect from second year ice (SYI) on Greenland’s shelf to first year ice (FYI) at the North Pole and off Svalbard. Two major Arctic River systems, the Lena and Kolyma, were also sampled in a separate campaign. Environmental DNA and RNA were used to assess fungal abundance and diversity. Greenland shelf SYI contains distinct fungal communities compared to younger FYI in other regions. Surface SYI was dominated by yeasts. Chytrids dominated the fungal communities in the bottom ice and showed potential diatom host specificity. Chytrids also dominated the Kolyma fungal communities. In the Lena, fungi were more diverse, with chytrids, as well as Ascomycota and unidentified fungi showing similar abundances. Chytrid in both river systems were dominated by the algal parasite Zygophlyctis. The dominating Zygophlyctis were compared with diatom and cyanobacterial hosts to determine possible parasite-host relationships. Zygophlyctis correlated significantly with the diatoms Aulacoseira and Synedra, both genera have been shown to be hosts for Zygophlyctis in temperate aquatic ecosystems. Potential Zygophlyctis dynamics showed seasonal-scale shifts in the Kolyma River. This work is set in the context of the rapidly changing Arctic and developing a better understanding of the Arctic ecosystems that are being lost or drastically modified because of global climate change.
06:30 PM
POLYETHYLENE DEGRADATION AND ASSIMILATION BY THE MARINE FUNGUS RHODOTORULA MUCILAGINOSA (5620)
Primary Presenter: Annika Vaksmaa, NIOZ (annika.vaksmaa@gmail.com)
Ocean plastic pollution is a severe environmental problem, but most of the plastic that has been released to the ocean since the 1950s is unaccounted for. Although fungal degradation of marine plastics has been suggested as a potential sink mechanism, the unambiguous proof is scarce. We isolated a marine fungus, the yeast Rhodotorula mucilaginosa from the marine environment and tested the capability of R. mucilaginosa to degrade plastic by applying stable isotope tracing assays with UV-irradiated 13C-labelled polyethylene (PE) as a sole energy and carbon source. Accumulation of excess 13C in the CO2 pool during the 5-day incubation experiments with R. mucilaginosa and the 13C labelled PE translates to degradation rates of 3% yr-1 of the added substrate. Further nanoSIMS measurements allowing to measure the isotopic composition of individual cells revealed substantial incorporation of PE-derived carbon into fungal biomass. Our results demonstrate the potential of R. mucilaginosa to mineralize and assimilate carbon from plastics and suggest that fungal plastic degradation may be an important sink for polyethylene litter in the marine environment.
06:30 PM
Diversity and ecology of fungi and prokaryotes in the sediments and water column of brackish and salt marshes (5485)
Primary Presenter: Madeleine Thompson, School of the Earth, Ocean, and Environment (mthompson@seoe.sc.edu)
Both fungi and prokaryotes are key drivers of biogeochemical processes in brackish and salt marshes. However, only a few studies have examined fungi and prokaryotes together and their potential interactions in marsh ecosystems. We performed a metabarcoding survey of prokaryotes and microbial eukaryotes in the sediment and overlying water column of the North Inlet salt marsh and the Winyah Bay brackish marsh in South Carolina, USA. We targeted the small and large rRNA genes (16S, 18S, 28S) and the internal transcribed spacer region (ITS2) during four seasons from 2020 to 2021. Early diverging fungi, primarily Zygomycota and Chytridiomycota, dominated brackish marsh communities. In contrast, salt marsh communities were dominated by Dikarya fungi, primarily Dothideomycetes in the water column and Sordariomycetes in sediments in the summer. In the autumn and winter, the dominant taxa in sediments shifted to Dothideomycetes. Network analyses revealed nearly exclusively negative interactions between fungi and prokaryotes in the sediment, suggesting competition. Zygomycota, Sordariomycetes, and Dothideomycetes were identified as potential keystone species in sediments. Interactions among early diverging fungi were primarily positive, suggesting a shared niche. Our work reveals novel fungal diversity in estuarine sediments and water column. The identification of potential keystone species and their interactions with other microbial community members enables the design of targeted experiments to elucidate the mechanism of such interactions and their impact on biogeochemical cycles.
06:30 PM
ITS VERSUS 18S SEQUENCING OF MARINE FUNGAL COMMUNITIES (5387)
Primary Presenter: Judith van Bleijswijk, Netherlands Institute for Sea Research (judith.van.bleijswijk@nioz.nl)
Slowly we start to discover the role of fungi in aquatic ecology. In freshwater habitats with abundant plant detritus, biomass of higher fungi generally exceeds bacterial biomass. In marine systems still much less is known. To identify potential key players in conversion of (algal) detritus in the bathypelagic Atlantic Ocean (during a Sahara dust event), Whittard Canyon and in the North Sea we took water samples for sequence analyses and cultivation of novel marine fungal strains. We will show community compositions of fungi and fungi-like organisms resulting from short read (600bp) SSU Illumina sequencing. For a selection of samples, we will also show results from long read (2500bp) ONT sequencing and compare taxonomy assignments based on SSU, ITS and LSU DNA fragments that were extracted from the long reads in silico using the tool ITSx.
06:30 PM
LOSING AMPHIBIANS: TRACKING A GLOBAL PANDEMIC IN FRESHWATER ECOSYSTEMS (5217)
Primary Presenter: Federico Castro Monzón, Universidad Nacional Autónoma de México (fcastro.biol@gmail.com)
Amphibians are known to play an important role in freshwater ecosystems. These organisms function as both predators and prey for other organisms and play a role in the transport of nutrients between terrestrial and aquatic ecosystems due to their unique biphasic life cycles. However, these important roles have been threatened by a pandemic of amphibian chytrid pathogens that are affecting amphibian populations worldwide. In some cases, infection has lead to local disappearance of species and even their extinction. In this presentation, I will share the findings of my research, in which I compiled a vast database of infection records. I tracked records of infection by the chytrid pathogens <em>Batrachochytrium dendrobatidis</em> and <em>Batrachochytrium salamandrivorans</em> to understand which species have been affected and where. This allows for a comprehensive overview of the global situation of amphibians and helps identify spatial and temporal patterns. I will discuss cases where infection has affected freshwater ecosystems and present preliminary results on an ongoing effort to compile data about the different explanations given regarding the susceptibility or resilience of different amphibian communities.
06:30 PM
Temporal dynamics of marine fungi on epiphytic protist assemblage on macroalgae: Demonstration of a parasitoid chytrid-dinoflagellate association (4789)
Primary Presenter: Alan D Fernández, Institute of Marine Science (ICM-CSIC) (alan@icm.csic.es)
The field of marine fungal diversity and ecology remains largely unexplored. This study provides new and valuable insights into the diversity, ecology, and temporal dynamics of epiphyte protist and fungal assemblages on coastal Mediterranean macroalgae during the summer season. The temporal sampling results showed that dinoflagellates become the most abundant taxonomic group, and its structure and relation with fungi, especially on Chytridiomycota, were evaluated in detail. The study revealed that temporal dynamics of the chytrid community are significantly impacted by the assemblage of epiphytic dinoflagellate species. The Chytridiomycota group was found to be primarily represented by Dinomyces arenysensis and a Lobulomycota representative yet to be described. The relative abundance of chytrids was at its highest following the peak of the dinoflagellate Ostreopsis sp. proliferation with D. arenysensis being the dominating chytrid, having a maximum infection prevalence of 2%. The results of laboratory experiments showed a low prevalence of D. arenysensis over its host Ostreopsis and a stable coexistence. Moreover, although the chytrid demonstrates a preference for parasitizing dinoflagellate cells, it has been shown to utilize pollen as a resource to sustain viable infections demonstrating a facultative and generalist parasite. The study underscores the diversity and potential impact of marine chytrids on epiphyte protist communities, bringing attention to the presence of zoosporic parasites in this understudied benthic habitat.
SS010P Fungi in Aquatic Ecosystems: Structure, Function and Health
Description
Time: 6:30 PM
Date: 7/6/2023
Room: Mezzanine