Biology subjects

Dyhrman, S. T.

Publications and source records attributed to Dyhrman, S. T..

6 recordsLinked to original sources

bioRxiv2025

Characterization of Phytoplankton-Excreted Metabolites Mediating Carbon Flux through the Surface Ocean

The marine labile dissolved organic carbon (DOC) pool is a dynamic reservoir of thousands of molecules that cycles approximately one-quarter of Earths primary production within days to weeks. After excretion by phytoplankton and other microbes, metabolites are rapidly consumed, resulting in low standing concentrations (picomolar to low nanomolar). Despite the decades-long search for labile DOC sources and molecular identities, marine phytoplankton exometabolomes are not well characterized, largely due to difficulties in measuring small polar molecules in saline water. Here, we profiled the exometabolomes of six axenic phytoplankton species representing key functional groups including a diatom (Thalassiosira pseudonana CCMP1335), a picoeukaryote (Micromonas commoda RCC299), a coccolithophore (Gephyrocapsa huxleyi CCMP371), a diazotrophic cyanobacterium (Crocosphaera watsonii WH8501), and two picocyanobacteria (Prochlorococcus marinus MIT 9301 and Synechococcus WH8102). From these cultures, we quantified 56 amine- and alcohol-containing exometabolites representing 11 compound classes which in sum comprised up to 23.4% of phytoplankton-excreted DOC. We estimated that these phytoplankton-derived exometabolites could supply up to 5% of the daily carbon quota of the dominant heterotrophic bacterium SAR11 in the surface ocean. Substantial variations in exometabolite identity and concentration across phytoplankton taxa underscore taxonomic diversity as a key driver in the supply and composition of labile DOC. This taxonomic variation predicts geographic and seasonal differences in the distribution of marine dissolved metabolites that underpin the cycling of labile DOC back to CO2. Overall, our work suggests that phytoplankton exometabolites are key chemical currencies that mediate significant carbon fluxes within the oceans carbon cycle. Significance StatementPhytoplankton exometabolites are key components of the marine labile dissolved organic carbon (DOC) pool, which drives major a fraction of the oceanic carbon flux. Yet, their composition and flux are poorly constrained. Leveraging new methods, we quantified amine- and alcohol-containing exometabolites in diverse phytoplankton and found they varied taxonomically. These exometabolites accounted for up to 23.4% of excreted DOC, potentially supporting a sizable fraction of the global heterotrophic growth. Integrating our results with ecological models suggest that exometabolite composition varies geographically and seasonally in response to changing phytoplankton community structures. Our findings illuminate the long-standing "black box" of labile DOC and link taxonomic diversity to the chemical currencies underpinning the microbe-metabolite networks at the heart of the marine carbon cycle.

ecology↗

bioRxiv2024

Intraspecific diversity in thermal performance determines phytoplankton ecological niche

Temperature has a primary influence on phytoplankton physiology and affects biodiversity and ecology. To examine how intraspecific diversity and temperature shape plankton populations, we grew 12 strains of the ecologically-important coccolithophore Gephyrocapsa huxleyi isolated from regions of different temperature for [~]45 generations (2 months), each at 6-8 temperatures, and characterized the acclimated thermal response curve of each strain. Even with virtually identical temperature optima and overlapping cell size, strain growth rates varied between 0.45 and 1 day-1. While some thermal curves were effectively symmetrical, others had more slowly declining growth rates above the "thermal optimum," and thermal niche widths varied between 16.7 and 24.8 {degrees}C. This suggests that different strains use distinct thermal response mechanisms. We investigated the ecological implications of such intraspecific diversity on thermal response using an ocean ecosystem simulation resolving distinct phytoplankton thermal phenotypes. Resolving model analogs of thermal "generalists" and "specialists" (similar to those observed in G. huxleyi) resulted in a distinctive global biogeography of preferred thermal niche widths with a nonlinear latitudinal pattern. We leveraged the model output to predict the ranges of the 12 strains we studied in the laboratory and demonstrated how this approach could refine predictions of phytoplankton thermal geographic range in situ. Our combination of observed thermal traits and modeled biogeography highlights the capacity of diverse groups to persist through temperature shifts. Significance StatementIntraspecific diversity in the phytoplankton may underpin their distribution. We show that within a single coccolithophore species, thermal response curves have diverse trait parameters. For example, many strains had a variable range of temperatures at which they could survive (thermal niche width). Adding this thermal niche width diversity to an ecosystem model simulation impacted phytoplankton coexistence and overall biomass. These observations show that thermal niche width is a gap in phytoplankton representation in ecosystem models that impacts modeled phytoplankton biogeography and concomitant carbon cycle dynamics. Including thermal tolerance is crucial to predictive modeling as ocean temperature dynamics change.

ecology↗

bioRxiv2021

Nitrogen fixation in mesoscale eddies of the North Pacific Subtropical Gyre: patterns and mechanisms

1.Mesoscale eddies have been shown to support elevated dinitrogen (N2) fixation rates (NFRs) and abundances of N2-fixing microorganisms (diazotrophs), but the mechanisms underlying these observations are not well understood. We explored relationships among NFRs and cyanobacterial diazotroph abundances in eddy pairs of opposite polarity sampled in the North Pacific Subtropical Gyre and compared our observations to seasonal trends from the Hawaii Ocean Time-series (HOT) program. Consistent with previous reports, we found that NFRs were anomalously high for this region (up to 3.7-fold above previous monthly HOT observations) in the centers of the sampled anticyclones, coinciding with elevated abundances of Crocosphaera in the summertime. We then coupled our field-based observations, together with transcriptomic analyses of nutrient stress marker genes and ecological models, to evaluate potential mechanisms controlling diazotroph abundance and activity at the mesoscale. Specifically, we evaluated the role of biological (via estimates of growth and grazing rates) and physical controls on populations of Crocosphaera, Trichodesmium, and diatom symbionts. Our results suggest that increased Crocosphaera abundances associated with summertime anticyclones resulted from the alleviation of phosphate limitation, allowing cells to grow at rates exceeding grazing losses. In contrast, distributions of larger, buoyant taxa (Trichodesmium and diatom symbionts) appeared less affected by eddy-driven biological controls. Instead, they appeared driven by physical dynamics along frontal boundaries that separate cyclonic and anticyclonic eddies. Together, the interplay of eddy-specific changes in bottom-up control, top-down control, and the physical accumulation of cells likely explains the elevated diazotroph abundances and NFRs associated with anticyclones and eddy fronts.

ecology↗

bioRxiv2020

Community-scale Synchronization and Temporal Partitioning of Gene Expression, Metabolism, and Lipid Biosynthesis in Oligotrophic Ocean Surface Waters

Sunlight drives daily rhythms of photosynthesis, growth, and division of photoautotrophs throughout the surface oceans. However, the cascading impacts of oscillatory light input on diverse microbial communities and community-scale metabolism remains unclear. Here we use an unsupervised machine learning approach to show that a small number of diel archetypes can explain pervasive periodic dynamics amongst more than 65,000 distinct time series, including transcriptional activity, macromolecules, lipids, and metabolites from the North Pacific Subtropical Gyre. Overall, we find evidence for synchronous timing of carbon-cycle gene expression that underlie daily oscillations in the concentrations of particulate organic carbon. In contrast, we find evidence of asynchronous timing in gene transcription related to nitrogen metabolism and related metabolic processes consistent with temporal niche partitioning amongst microorganisms in the bacterial and eukaryotic domains.

ecology↗

bioRxiv2020

Combined pigment and metatranscriptomic analysis reveals synchronized diel patterns of phenotypic light response across domains in the open ocean

Sunlight is the most important environmental control on diel fluctuations in phytoplankton activity, and understanding diel microbial processes is essential to the study of oceanic biogeochemical cycles. Yet, little is known about the in situ frequency of phytoplankton metabolic activities and their coordination across different populations. We investigated the diel orchestration of phytoplankton activity involved in photosynthesis, photoacclimation, and photoprotection by analyzing the pigment and quinone distribution in combination with metatranscriptomes in the surface waters of the North Pacific Subtropical Gyre (NPSG). We found diel cycles in pigment abundances resulting from the balance of their synthesis and consumption. The night represents a metabolic recovery phase to refill cellular pigment stores, while the photosystems are remodeled towards photoprotection during the day. Transcript levels of genes involved in photosynthesis and pigment metabolism had highly synchronized diel expression patterns among all taxa, suggesting that there are similar regulatory mechanisms for light and energy metabolism across domains, and that other environmental factors drive niche differentiation. Observed decoupling of diel oscillations in transcripts and related pigments in the NPSG indicates that pigment abundance is modulated by environmental factors extending beyond gene expression/regulation, showing that metatranscriptomes may provide only limited insights on real-time photophysiological metabolism.

molecular biology↗

bioRxiv2016

VIRUS-HOST INFECTION DYNAMICS OF MARINE SINGLE-CELLED EUKARYOTES RESOLVED FROM METATRANSCRIPTOMICS

Metatranscriptomics has emerged as a tool in microbial ecology that can resolve the functional landscape of both prokaryotes and eukaryotes within a community. In this study, we extend the potential of metatranscriptomics to probe active virus infections and virus-host relationships in marine systems. Polyadenylation-selected RNA-seq data were examined from microbial communities in two productive marine environments: a brown tide bloom event dominated by Aureococcus anophagefferens in Quantuck Bay, NY, and a diatom-dominated plankton community in Narragansett Bay, RI. Active infections by diverse giant viruses (NCLDVs) of algal and non-algal hosts were found at both sites. Ongoing infections of A. anophagefferens by a known Mimiviridae (AaV) were observed during both the peak and decline of the bloom. Bloom decline was also accompanied by increased activity for viruses other than AaV, including (+) ssRNA viruses. In Narragansett Bay, increased temporal resolution revealed active NCLDVs with both boom-and-bust as well as steady-state infection-like ecologies. Statistical co-occurrence examinations of the dsDNA, ssRNA and dsRNA markers within the data revealed a broad spectrum of statistically strong and significant virus-host relationships that included both known as well as novel interactions. Our approach offers a method for screening the diversity and dynamics of active viral infections in natural systems and develops links between viruses and their potential hosts in situ.\n\nSignificanceViruses are important partners in ecosystem scale ecology, yet their study to date is primarily limited to single virus-host infection models in the laboratory or limited to \"potential-actions\" derived from metagenomics analyses. Using metatranscriptomic sequences from polyadenylated-RNA selected samples, we have simultaneously captured information regarding eukaryotic diversity and active infection by viruses with dsDNA genomes, resulting in a statistical opportunity to predict \"who is infecting whom\". This approach further provides concurrent insight regarding viruses with ssRNA and dsRNA genomes, capturing dynamics for the communities of viruses infecting single-celled eukaryotes. Given the central role of these plankton in global scale processes, our efforts result in a transformational step-forward regarding the study of in situ virus-host interactions.

microbiology↗