Microbial interactions, whether symbiotic, beneficial, antagonistic, or pathogenic, are crucial in the marine environment, as they can shape community composition and influence nutrient cycles, energy flow, and overall ecosystem function. Despite their significance, the complex web of interactions among planktonic microbes remains enigmatic, mainly due to marine environments' dynamic nature and our limited ways of sampling the interactions that occur at the scale of the single cells. This session aims to bring together experts in aquatic microbial ecology to discuss the implications of recent advancements in technologies and methodologies that are revolutionizing our ability to decipher and characterize marine microbial interactions.
Lead Organizer: Uri Sheyn, Virginia Tech (urisheyn@gmail.com)
Co-organizers:
Shiri Graff van Creveld, University of Washington Center for Environmental Genomics (shirig@uw.edu)
Sheri Floge, Wake Forest University (floges@wfu.edu)
Presentations
04:30 PM
INTACT PHAGE-INFECTED MARINE CYANOBACTERIA ATTRACT CHEMOTACTIC HETEROTROPHIC BACTERIA (9380)
Tutorial/Invited: Invited
Primary Presenter: Sheri Floge, Wake Forest University (floges@wfu.edu)
Dissolved chemical compounds facilitate interactions among marine microbes and ultimately drive ecosystem-scale processes such as carbon and nutrient cycling. During infection, phage manipulate host metabolism, stimulating the release of varied metabolites, including signaling molecules from intact cells. However, the impact of such compounds on microbial ecology and nutrient and energy flow is poorly understood. We determined the influence of phage infection on exometabolite release from Synechococcus strain WH8102 and the chemotactic response of heterotrophic bacteria (Vibrio alginolyticus and Psuedoalteromonas haloplanktis) using time-resolved metabolomics and microfluidics-based chemotaxis assays over the course of an infection cycle. Heterotrophic bacteria exhibited strong chemoattraction to metabolites released during early stages of infection. In addition, V. alginolyticus demonstrated sustained chemotaxis toward whole, live phage-infected Synechococcus at environmentally relevant densities and no chemotaxis toward uninfected cyanobacterial cells. Using high-throughput microfluidics we identified several compounds that act as key attractants including 5’-deoxyadenosine, 5’-methylthioadenosine, leucine and cytosine. Our findings demonstrate that prior to cell lysis phage-infected picocyanobacteria release compounds that attract motile heterotrophic bacteria and highlight a novel mechanism by which marine phage may alter resource exchange, nutrient and energy flow and microbial community composition.
04:45 PM
Culture-independent characterization marine protists suggests complex, potentially antagonistic interactions with diverse bacteria (8901)
Primary Presenter: Fabian Wittmers, Oregon State University (wittmerf@oregonstate.edu)
Marine protists are diverse and play a significant role in global carbon fixation and cycling. However, their interactions with other microbes, particularly in the microenvironment surrounding the protist remain poorly characterized primarily due to disruptions that occur during cultivation. We utilized size-fractioned in-situ pump data from the Bermuda Atlantic Timeseries Study site (BATS), fluorescence-activated cell sorting and whole genome sequencing to identify and functionally characterize microbes associated with diverse marine protists. Their microbiome was dominated by members of the Planctomycetota, Verrucomicrobiota, and Bacteroidota. These taxa encoded a diverse repertoire of non-essential metabolic functions, centred around carbohydrate-active enzymes (CAZymes) and complementary modules. Most of the bacterial lineages encoded secretion systems, pili or flagella, enabling varying degrees of motility and attachment to surfaces. This suggests extracellular lifestyles and periods of attachment to the eukaryote. Notably, all bacteria encoded families of CAZymes that were specific to the breakdown of modified glycoproteins on the protists cell surface. This indicates that these lineages might not only utilize bioavailable carbohydrates secreted by phytoplankton during photosynthesis but could also break down live protist cell wall components. The diversity and evolutionary position of the novel symbiont-host relationships of marine protists revealed in this study enable us to better understand of the diverse interactions and flow of resources through marine protists.
05:00 PM
Grazing and behavioral response of Gyrodinium spirale to diatom-associated oxylipins (9594)
Primary Presenter: Matthew Johnson, Woods Hole Oceanographic Institution (mattjohnson@whoi.edu)
Heterotrophic dinoflagellates are major grazers of marine diatoms, and as part of the microzooplankton contribute to the removal of >50% of their daily production. Among naked heterotrophic dinoflagellates, Gyrodinium spirale is known to be key diatom predator and is globally distributed in productive neritic ecosystems. Here we analyzed the grazing and growth response of G. spirale to diatom cultures under nutrient replete and silicon limitation, which is known to induce dramatic changes in diatom oxylipin chemistry. In addition, we also tested the response of this heterotrophic dinoflagellate on different species of diatoms that are known to have major differences in their oxylipin profiles. Increases in the production of certain oxylipin compounds decreased grazing rates of G. spirale and had subtle, but significant effects on its motility and behavior. We propose that as aging diatom blooms become nutrient limited, they alter their interactions with their major grazers through changes in oxylipin chemistry, resulting in increased survival and greater potential for diatom biomass sedimentation.
05:15 PM
IDENTIFYING B-VITAMIN REQUIREMENTS AND PHYCOSPHERE INTERACTIONS FOR THE HAB FORMING DINOFLAGELLATE, PYRODINIUM BAHAMENSE VAR. BAHAMENSE (9256)
Primary Presenter: Lydia Ruggles, University of South Florida (lruggles@usf.edu)
Pyrodinium bahamense is a saxitoxin-producing dinoflagellate in tropical and subtropical estuarine waters. Pyrodinium is an emerging HAB species in Florida estuaries, with blooms yet to be reliably forecast. Thus, factors not currently included in prediction models, such as micronutrient (i.e., vitamin) availability and biological interactions, may influence Pyrodinium bloom occurrence and intensity. As many HAB-forming dinoflagellates are auxotrophic for at least one B vitamin, we first evaluated which B vitamins Pyrodinium requires for growth and determined that Pyrodinium is a vitamin-B12 auxotroph. Next, since bacteria in the phycosphere are often able to fulfill algal B12 requirements, we co-cultured Pyrodinium with bacterial communities isolated from estuaries where Pyrodinium often blooms (Old Tampa Bay and Indian River Lagoon). Nanopore full-length 16S rRNA metabarcode sequencing confirmed that inoculated Pyrodinium cultures contained diverse and distinct bacterial communities representative of each estuary. The bacterial community from Indian River Lagoon restored some growth when B12 limitation was induced in Pyrodinium but neither inoculum restored growth to the same levels as media including B12, despite both inoculum bacterial communities containing putative B12-producing bacteria. Our results demonstrate that Pyrodinium bahamense must attain vitamin B12 from the environment to reach bloom levels but bacteria in the surrounding seawater may not provide this critical resource, hence implicating other B12 sources in estuaries where Pyrodinium blooms.
05:30 PM
STRAIN-SPECIFIC EFFECTS ON GEPHYROCAPSA HUXLEYI BACTERIAL COMMUNITIES UNDER TEMPERATURE AND NITROGEN CO-STRESS (8919)
Primary Presenter: Miah Manning, MIT-WHOI Joint Program in Oceanography/Applied Ocean Science and Engineering (miahm@mit.edu)
Environmental factors of climate change alter the interactions between bacteria and their algal hosts, known as the phycosphere, with broader implications for marine microbial community ecology. We examined the interactive effects of warming and nitrogen limitation on Gephyrocapsa huxleyi, a widely abundant and physiologically flexible coccolithophore, and its phycosphere. We subjected xenic cultures of G. huxleyi (strains RCC874 and RCC914) to N-replete and N-limited conditions at 3 temperature regimes: thermal optimum, moderate heat stress, and high heat stress. N limitation primarily drove cellular C:N:P ratios, while inter-strain differences in C:P ratio emerged with warming conditions. The main determinant of bacterial community composition was algal strain; temperature was also significant, but N had minimal impact. We identified strain-specific bacterial taxa in RCC914 (n=187) and RCC874 (n=303), indicating that unique physiological traits (e.g. variations in organic molecule production) support different bacterial communities. We measured osmolyte concentrations, which regulate osmotic pressure and cellular homeostasis. Notably, ectoine, an osmolyte not known to be synthesized by G. huxleyi, varied significantly between strains and N concentrations, suggesting bacterial modulation. Overall, our findings highlight how N limitation and warming interact to impact G. huxleyi physiology and phycosphere interactions at the strain level, emphasizing the importance of inter-strain differences in understanding marine ecosystems under changing climate conditions.
05:45 PM
Latency and Activity of a Giant Endogenous Viral Element in Chlamydomonas reinhardtii Explored at the Single-Cell Level (9135)
Primary Presenter: Uri Sheyn, Virginia Tech (urisheyn@gmail.com)
Viruses in the phylum Nucleocytoviricota, termed "giant viruses," are known for their remarkable size, reaching diameters of up to 1.5 µm, and genomes that can achieve lengths of up to 2.7 Mb. Endogenous viral elements derived from nucleocytoviruses are commonly found in eukaryotic genomes, yet the implications of this integration remain elusive. Our investigation centered on Giant Endogenous Viral Elements (GEVEs) within genomes of the model green alga Chlamydomonas reinhardtii, for which we describe the activity and viral production from a 617 kbp integrated GEVE. Using long-read sequencing, we identified the GEVE insertion site in strain CC2937 on C. reinhardtii chromosome 15. We showed that viral particles are produced and released during stationary growth, with increased GEVE gene transcription correlating with this growth phase. Flow cytometry indicated low-level viral production and single-cell transcriptional analysis revealed significant GEVE gene transcription in about 15% of the host population, with high transcription in less than 0.2%. Notably, this small subset of cells with elevated GEVE expression could represent the primary contributors to viral particle production, suggesting a possible mechanism for the controlled release of viral particles from latent GEVE reservoirs. Additionally, by comparing prokaryotic transcripts captured alongside single algae cells, we aim to explore how viral infection might alter the composition and activity of the phycosphere microbiome, shedding light on the broader ecological impacts of viral infections. Our work reports the largest temperate virus documented to date and the first active GEVE identified in a unicellular eukaryote, establishing C. reinhardtii as a model system for studying giant virus latency, host-virus dynamics, and interactions with the surrounding microbial community.
SS25 - Marine microbial interactions at the molecular and cellular scale
Description
Time: 4:30 PM
Date: 28/3/2025
Room: W201CD