Microbial metabolisms drive many important biogeochemical processes in all aquatic ecosystems. In turn, microbial activity depends on the availability of nutrients like carbon, nitrogen, or phosphorus, which can also profoundly affect microbial community assembly. Recent technological advances in microbial and biogeochemical techniques have provided novel insights into the coupling between microbial activity and geochemistry, but it remains challenging to predict the effects of present and future environmental changes. Sequencing approaches such as metagenomics have opened the “black box” of environmental microbiology, using the presence of key genes to predict the metabolism of novel microbes. However, a disconnect still exists between connecting in situ geochemical measurements, such as nutrient cycling rates and fluxes, with the genetic potential of resident microbial communities.
This session highlights advances in linking aquatic geochemistry and microbiology. Any work related to microbial processes and biogeochemistry is welcome; methods from both fields need not be included in each presentation, as long as data has relevance to both microbes and biogeochemistry. For instance, studies of biogeochemical rate measurements or models are welcome, provided they are focused on microbially-driven processes, and as are studies solely on microbial ecology but focused on microbes with biogeochemical relevance. Studies may include field sampling, method development, computational analysis, and/or modeling. Biogeochemical focus may include any cycles and processes, including “traditional” cycles as well as other aquatic contaminants such as antimicrobial resistance genes, pharmaceuticals, PFAS, and others. We welcome submissions studying any aquatic ecosystem, whether freshwater, brackish, or marine, and including benthic and/or water column data. Studies including microbial data may use broad community-level data or targeted experiments with specific populations or species. We take a broad definition of “microbe” and welcome studies of archaea, bacteria, eukaryotic microbes, and viruses. In individual presentations or in the session as a whole, we strive to bring together interdisciplinary work using a variety of approaches to explore the intersection of aquatic microbial ecology and biogeochemistry and integrate knowledge from disparate fields and a wide range of ecosystems.
Lead Organizer: Julian Damashek, Hamilton College (jdamashe@hamilton.edu)
Co-organizers:
Benjamin Kramer, University of Minnesota Duluth (bjkramer@umn.edu)
Cody Sheik, University of Minnesota Duluth (cssheik@d.umn.edu)
Annika Mosier, University of Colorado Denver (annika.mosier@ucdenver.edu)
Presentations
09:00 AM
LAKEWIDE SAMPLING REVEALS HOW CIRCULATION PATTERNS STRUCTURE MICROBIAL COMMUNITIES IN LAKE ONTARIO (7955)
Primary Presenter: Augustus Pendleton, Cornell University (arp277@cornell.edu)
Microbial communities perform essential biogeochemical processes within the Great Lakes, but previous microbial studies have lacked the spatial resolution to make lake-wide inferences. This gap prevents estimation of the spatial and environmental drivers of microbial community structure. Here, we collected >140 microbial DNA samples across Lake Ontario from 16 sites, at three depths, and between two seasonal collection times. Using a combination of 16S rDNA gene sequencing, flow cytometry, and water quality data, we analyzed the environmental determinants of microbial abundance and composition in Lake Ontario. Taxonomic richness was highest in shallow samples in September, but communities were dominated by a few, highly abundant species. While all samples featured Alphaproteobacteriota LD12, Actinobacteriota acI, and Verrucomicrobiota, shallow May samples were defined by a dominance in Bacteroidota, shallow September samples by Cyanobacteria like Synechococcus, and deep (> 30 m) samples by Chloroflexi and Planctomycetota. Coabundance analysis revealed that potential upwelling zones along the southern shore in September produce highly diverse microbial communities. Further, functional analysis revealed these areas are hot-spots for nitrogen cycling which coincide with a decrease in cyanobacterial abundance coupled with a relative increase in Microcystis and Pseudanabaena. These data enhance our ability to predict the spatial and seasonal distribution of biogeochemical processes and the underlying microbial interactions which determine such processes.
09:15 AM
USING OMICS APPROACHES TO DECIPHER BACTERIAL AND VIRAL DYNAMICS IN LAKE CHAMPLAIN BEFORE, DURING, AND AFTER A CYANOBACTERIAL HARMFUL ALGAL BLOOM (8316)
Primary Presenter: Erin Eggleston, Middlebury College (eeggleston@middlebury.edu)
Lake Champlain is a freshwater lake known for its recreational activities and as a source of drinking water for local communities. However, despite nutrient loading mitigation efforts, cyanobacterial harmful algal blooms (CHABs) in Lake Champlain persist and negatively impact water quality in this aquatic ecosystem. We employed "omics" approaches to better understand the microbial ecology of CHABs. We hypothesized that prokaryotic and viral diversity would vary before, during, and after a bloom event, with decreased overall diversity during the bloom leading to dominant cyanobacteria and cyanophage during the bloom peak; and that toxin-production in key bloom-forming cyanobacteria will be influenced by both physicochemical factors and viral pressures. Viruses, particularly bacteriophage, play important roles in ecosystem nutrient cycling. Our metagenomes and viromes reveal shifts in total community diversity throughout the season, with notable shifts in taxa before, during, and after bloom events. However, the metagenomes suggest that there is a largely stable functional diversity in the metagenomes throughout time. This indicates that although the microbial communities change there is functional redundancy within the ecosystem to allow for continued metabolic processes. Intriguingly, our viromes reveal several genes related to carbon metabolism.
09:30 AM
Phytoplankton Iron Nutrient Limitation within Lake Superior's Watershed: Investigating Oligotrophic Algal Blooms from a Land to Lake Gradient (8005)
Primary Presenter: Robert McManus, University of Minnesota - Duluth (mcman247@d.umn.edu)
Recent impacts of the global climate crisis, coupled with anthropogenic eutrophication, have amplified the magnitude and frequency of Cyanobacterial Harmful Algal Blooms (cHABs) globally. The relatively pristine, cold, and oligotrophic Lake Superior, while typically considered an environment resistant to cHAB forming conditions, has begun to develop blooms along its southwest shore. While trace metal limitation has been broadly explored in marine settings, freshwater studies into micronutrient limitation are comparatively rare. This study investigates how iron limitation impacts algal communities in a land to lake transect on the south shore of Lake Superior. We performed five day, trace metal clean, nutrient addition bioassays with an iron chelator (EDTA), phosphorus, and iron treatments on whole water samples to measure growth differences among sites and treatments. We also extracted and sequenced RNA from a subset of bioassay bottles to identify community differential gene expression responses to the nutrient additions. This research reveals how trace iron concentrations affect primary producers along an inland lake to river to Lake Superior gradient in a location subject to cHABs.
09:45 AM
Cell-specific nitrogen uptake by natural cyanobacterial harmful algal bloom communities in Lake Erie (7936)
Primary Presenter: Jenan Kharbush, University of Michigan (jenanjk@umich.edu)
Each summer western Lake Erie experiences an annual cyanobacterial harmful algal bloom (cyanoHAB), often dominated by the non-diazotrophic and toxigenic cyanobacteria species, Microcystis. The annual phosphorus (P) load has a well-established role in determining the overall bloom size each year, but nitrogen (N) availability is also important as it likely influences the production of the N-rich toxin microcystin, as well as the population dynamics of toxic and non-toxic Microcystis strains. Both the dominant form of N (organic vs. inorganic) and the cyanobacterial strain composition shift as the bloom progresses, as does the composition of the heterotrophic bacterial communities associated with Microcystis colonies. Recent metagenomics and culture-based work suggests that some of these heterotrophs may be involved in N acquisition and cycling processes with Microcystis. In this study we examined the relative N uptake of both Microcystis and heterotrophic bacteria in natural bloom communities during the 2021 Lake Erie CyanoHAB. We used nano-secondary ion mass spectrometry (nano-SIMS) complemented with shotgun metagenomic community data, to measure N incorporation of three substrates (nitrate, ammonia, and urea) at single cell resolution during early, peak, and late bloom phases. Results show that the amount of N assimilated by Microcystis and heterotrophic bacteria varies between substrates and bloom stage, and provide insight into the role of heterotrophs in N assimilation by CyanoHAB bloom communities.
10:00 AM
BACTERIAL AND PHYTOPLANKTON PRODUCTIVITY IN THREE EUTROPHIC ENVIRONMENTS WITH CONTRASTING NUTRIENT REGIMES (8254)
Primary Presenter: Mark Fitzpatrick, Fisheries and Oceans Canada (mark.fitzpatrick@dfo-mpo.gc.ca)
Heterotrophic microbial activity in nutrient enriched environments is often masked by excess autotrophic activity. The present study will examine direct measurements of both bacterial and phytoplankton productivity using radioisotope tracers in three eutrophic habitats within the Lake Ontario basin. While the study sites, Hamilton Harbour, Toronto Harbour and the Bay of Quinte, all experience phosphorus enrichment to some degree, the underlying nutrient regimes are different in terms of P, N and Si resulting in fundamentally different food web processes. In the highly urbanized Toronto Harbour watershed for example, bacterial productivity averaged 2.0 mg C m-3 h-1 over the May – Oct (2019) period and was about double what observed in the more rural Bay of Quinte (May – Oct, 2018). By contrast, primary productivity in the Bay of Quinte averaged 44 mg C m-3 h-1 compared to about 17 mg C m-3 h-1 in Toronto Harbour over the same time frame. The goal of the current work is to explore how heterotrophic and autotrophic processes within the microbial and planktonic food web are affected by differing nutrient regimes.
10:15 AM
RESOURCE COMPETITION THEORY EXPLAINS TRADEOFF BETWEEN DISSIMILATORY NITRATE REDUCTION TO AMMONIUM AND DENITRIFICATION (7950)
Primary Presenter: Jemma Fadum, Carnegie Science, Stanford (jfadum@carnegiescience.edu)
Organic matter (OM) loading is a ubiquitous anthropogenic disturbance in aquatic ecosystems which alters nutrient cycling dynamics. Not only does OM loading introduce mineralizable nutrients, but it may also create anoxic microsites on sinking particulates which support anaerobic processes in otherwise oxic waters. Furthermore, OM loading may promote an electron donor rich environment, thus altering microbial metabolic competition dynamics. The combination of anoxia and electron donor availability alters the biogeochemical landscape and, as one example, dictates the degree to which bioavailable nitrogen (N) is retained in an ecosystem (via dissimilatory nitrate reduction to ammonium, DNRA), rather than converted to nitrous oxide or dinitrogen gas (via denitrification). To improve our predictive abilities of these critically important transformations, we developed a microbial population model that mechanistically resolves the competition of DNRA and denitrification for nitrate (or nitrite) under varying OM loading intensities. The redox chemistry underlying each metabolism informs the model parameters, providing a theoretically grounded quantitative framework. In the model, when the ratio of OM to nitrate supply is sufficiently high such that nitrate becomes limiting, DNRA can competitively exclude denitrification. As the redox-constrained parameters may be more broadly applicable than species or location-specific parameters, our framework can aid in improving our understanding of N cycling in environments where microbial community dynamics are largely unknown.
SS03A - Uncovering Links Between Aquatic Geochemistry and Microbial Communities, from Genomes to Nutrient Cycles
Description
Time: 9:00 AM
Date: 6/6/2024
Room: Hall of Ideas F