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
02:00 PM
Capture of light energy to support lake productivity: Beyond oxygenic photosynthesis (8122)
Primary Presenter: Matthew Church, Flathead Lake Biological Station, University of Montana (matt.church@flbs.umt.edu)
Oxygenic photosynthetic microorganisms are thought to dominate the capture of solar energy by lake food webs. However, microorganisms possessing largely overlooked modes of light harvesting have been shown to be ubiquitous and abundant across freshwater ecosystems. We used more than 2 years of near-monthly observations in oligotrophic Flathead Lake, Montana, to estimate light-driven oxygen production and carbon fixation by planktonic microorganisms. In addition, we used shotgun metagenomic sequencing to identify pathways of microbial light harvesting. Flathead Lake demonstrates highly seasonal changes in primary productivity, with rates of production varying strongly with changes in light. Seasonal increases in insolation coincide with elevated productivity through the spring and summer, driving seasonal depletion in nutrients. Metagenomic sequencing revealed that diverse and abundant microorganisms in the lake use pathways of light harvesting that are largely independent of oxygen production and carbon fixation. For example, rhodopsin genes are widely scattered across members of the Actinobacteria, Alphaproteobacteria, and Chloroflexi, and diverse members of the Gammaproteobacteria are capable of anoxygenic photosynthesis. Vertical distributions of these light-harvesting genes vary with seasonal changes in light and lake mixing. Taken together, these observations emphasis the need for quantifying how diverse modes of microbial light harvesting influence energy flow into lake food webs.
02:15 PM
Phytoplankton and Bacterial Assemblage Responses to Nitrogen Inputs in River- Dominated Estuaries Surrounding New York City (8445)
Primary Presenter: Dianne Greenfield, City University of New York (secretary@aslo.org)
New York City (NYC) is surrounded by ‘urban estuaries’ that receive excessive nitrogen (N) inputs from wastewater associated with combined sewer overflow (CSO) systems, non-point source runoff, atmospheric deposition, and other sources. This elevated N-load contributes to numerous water quality impairments, such as harmful algal blooms (HABs) and seasonal hypoxia from microbial respiration of dissolved organic carbon (DOC). In partnership with NY and CT state long-term water quality and hypoxia monitoring efforts and regional collaborators, we have been conducting multi-year surveys of Long Island Sound (LIS) physical water quality, ecological (bacteria, phytoplankton), and biogeochemical (nutrients, chlorophyll) features, emphasizing the Western LIS channel and shoreline. We have identified distinct spatial patterns of how variations in N-form (inorganic vs. organic) and source (particularly their proximity to CSOs) drive dominant phytoplankton taxa, including HAB- forming dinoflagellates, their linkages with bacterial population numbers, and transitions in N- form pre- during, and post-hypoxia. Recently, we have extended these observations to additional NYC rivers, including the Hudson River and adjacent watersheds. Here we compare and contrast how dissolved organic N vs. inorganic N (nitrate vs. ammonium) loadings combined with DOC availability governs the relative prevalence of dinoflagellates to diatoms in Western LIS and surrounding NYC waterways and their associations with bacterial assemblages. Results are broadly relevant to N-management across other temperature, urban estuaries.
02:30 PM
Metagenomic analysis of a meromictic humic lake revealed microbial community patterns structured by light, redox gradients and cryptic interactions (8192)
Primary Presenter: Shaomei He, University of Wisconsin-Madison (she@wisc.edu)
Humic lakes and ponds are net sources of greenhouse gases and hotspots in the global carbon cycle. Microbial communities in the darkly stained humic water, especially in the O2-depleted compartments are under-studied. Here, we performed metagenomic analyses on samples from a meromictic humic lake collected at 12 depths ranging 0 to 17 m and recovered 157 metagenome-assembled genomes (MAGs). MAG abundance profiles revealed that cyanobacteria peaked within the first meter, together with aerobic photoheterotrophs that rely on bacteriochlorophylls or rhodopsins. Anaerobic anoxygenic phototrophic Chlorobium with genes for sulfur (S) and Fe(II) oxidation peaked below the oxycline at the 4 m depth. Coincidently, MAGs for Fe(III) reducers (Geothrix and Rhodoferax) and sulfate reducers (Desulfatirhabdiaceae) also peaked at 4 m, suggesting cryptic Fe and S cycles facilitated by the Chlorobium-Fe(III) reducer and Chlorobium-sulfate reducer couples, respectively. Similarly, an Fe cycling couple peaked at 7.5 m, including a Geobacteraceae Fe(III) reducer and Gallionella which can use oxidized nitrogen compounds to oxidize Fe(II). The most abundant methanotroph (Methylomonadaceae) capable of denitrification peaked at 7.5 m and largely sustained its abundance below 10 m, where methanogens (Methanoregula) started to emerge, suggesting cryptic methane cycling. In addition, putative extracellular electron transfer (EET) genes were frequently detected in MAGs from anoxic samples, suggesting the importance of EET in humic-rich anoxic water. Overall, our analyses revealed that humic water microbial community is structured by light, redox gradients and inter-species syntrophic interactions. Such interactions facilitate cryptic redox cycling and impact the overall carbon metabolism by recharging the electron accepting capability of humic water.
02:45 PM
CONTRIBUTIONS TO MICROBIAL BIOGEOCHEMICAL CYCLING IN MEROMICTIC LAKES BY AUXILIARY METABOLIC GENES IN BACTERIOPHAGES OF PHOTOTROPHS (7926)
Primary Presenter: Cassandra Marnocha, Niagara University (cmarnocha@niagara.edu)
Bacteriophages can carry and integrate auxiliary metabolic genes (AMGs) into the genomes of their host, redirecting energy investment of the host to facilitate lytic or lysogenic lifestyles. Many of these AMGs produce critically important changes in energy metabolism in bacteria, including photosynthesis. These phage-induced changes to metabolism can alter microbial biogeochemical cycles in the environment, particularly carbon and sulfur. Meromictic lakes are useful models for studying these processes due to the stratification of both the water column and corresponding microbial community, though few have been studied in this capacity. Here, we present the results of a metagenomic study of bacteriophages and their AMGs in two meromictic lakes: ferruginous, eutrophic Devil’s Bathtub (DBT; Rochester, NY), and euxinic, oligotrophic Fayetteville Green Lake (FGL; Syracuse, NY). We found a greater diversity of cyanobacterial taxa in DBT compared to FGL; however, a significant proportion of bacteriophages in both lakes use Synechococcus as the host cell. While Synechococcus is the primary cyanobacterial taxon in FGL, it is notable that more abundant cyanobacterial taxa in DBT did not have many or any corresponding detectable bacteriophages. Despite the considerable geochemical differences between these lakes, the overall composition of phototrophic bacteriophages. This may suggest a similar biogeochemical impact of cyanophage AMGs across aquatic systems, independent of their nutrient status.
03:00 PM
SS03B - Uncovering Links Between Aquatic Geochemistry and Microbial Communities, from Genomes to Nutrient Cycles
Description
Time: 2:00 PM
Date: 6/6/2024
Room: Hall of Ideas F