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1. Genomic signatures of Lake Erie bacteria suggest interaction in the Microcystis phycosphere

   https://doi.org/10.1371/journal.pone.0257017  

   Hoke, Alexa K.; Reynoso, Guadalupe; Smith, Morgan R.; Gardner, Malia I.; Lockwood, Dominique J.; Gilbert, Naomi E.; Wilhelm, Steven W.; Becker, Isabella R.; Brennan, Grant J.; Crider, Katherine E.; et al (September 2021, PLOS ONE)

   Humbert, Jean-François (Ed.)

   Microbial interactions in harmful algal bloom (HAB) communities have been examined in marine systems, but are poorly studied in fresh waters. To investigate HAB-microbe interactions, we isolated bacteria with close associations to bloom-forming cyanobacteria, Microcystis spp., during a 2017 bloom in the western basin of Lake Erie. The genomes of five isolates ( Exiguobacterium sp. JMULE1, Enterobacter sp. JMULE2, Deinococcus sp. JMULE3, Paenibacillus sp. JMULE4, and Acidovorax sp. JMULE5.) were sequenced on a PacBio Sequel system. These genomes ranged in size from 3.1 Mbp ( Exiguobacterium sp. JMULE1) to 5.7 Mbp ( Enterobacter sp. JMULE2). The genomes were analyzed for genes relating to critical metabolic functions, including nitrogen reduction and carbon utilization. All five of the sequenced genomes contained genes that could be used in potential signaling and nutrient exchange between the bacteria and cyanobacteria such as Microcystis . Gene expression signatures of algal-derived carbon utilization for two isolates were identified in Microcystis blooms in Lake Erie and Lake Tai ( Taihu ) at low levels, suggesting these organisms are active and may have a functional role during Microcystis blooms in aggregates, but were largely missing from whole water samples. These findings build on the growing evidence that the bacterial microbiome associated with bloom-forming algae have the functional potential to contribute to nutrient exchange within bloom communities and interact with important bloom formers like Microcystis . 

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2. Laboratory Experiments Suggest a Limited Impact of Increased Nitrogen Deposition on Snow Algae Blooms

   https://doi.org/10.1111/1758-2229.70052  

   Almela, Pablo; Elser, James_J; Giersch, J_Joseph; Hotaling, Scott; Rebbeck, Victoria; Hamilton, Trinity_L (November 2024, Environmental Microbiology Reports)

   ABSTRACT Snow algal blooms decrease snow albedo and increase local melt rates. However, the causes behind the size and frequency of these blooms are still not well understood. One factor likely contributing is nutrient availability, specifically nitrogen and phosphorus. The nutrient requirements of the taxa responsible for these blooms are not known. Here, we assessed the growth of three commercial strains of snow algae under 24 different nutrient treatments that varied in both absolute and relative concentrations of nitrogen and phosphorus. After 38 days of incubation, we measured total biomass and cell size and estimated their effective albedo reduction surface. Snow algal strains tended to respond similarly and achieved bloom‐like cell densities over a wide range of nutrient conditions. However, the molar ratio of nitrogen to phosphorus at which maximum biomass was achieved was between 4 and 7. Our data indicate a high requirement for phosphorus for snow algae and highlights phosphorus availability as a critical factor influencing the frequency and extent of snow algae blooms and their potential contribution to snow melt through altered albedo. Snow algae can thrive across a range of nitrogen (N) and phosphorus (P) conditions, with a higher P requirement for optimal growth. Our study suggests that increased N deposition may have a limited impact on snow algae bloom occurrence and size, emphasising P as a key factor influencing these blooms and their potential to accelerate snow melt by lowering albedo. 

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3. Albedo change from snow algae blooms can contribute substantially to snow melt in the North Cascades, USA

   https://doi.org/10.1038/s43247-023-00768-8  

   Healy, Shannon M.; Khan, Alia L. (May 2023, Communications Earth & Environment)

   Abstract Snow algae are ubiquitous in the Pacific Northwest cryosphere in the summer where snowmelt is an important contribution to regional watersheds. However, less attention has been given to biological impurities as drivers of snowmelt compared to inorganic light-absorbing particles. Here we map snow algae near Mt. Baker with a multispectral camera on an uncrewed aerial vehicle using (1) principal components and (2) spectral indexing. The two approaches are tested under differing bloom states and verified with coincident algal pigment and cell count data. During high bloom intensity we found an average instantaneous radiative forcing of 237 W m⁻²with a maximum of 360 W m⁻². This translated to 1,508 ± 536 m³of melted snow water equivalent in the 0.1 km²basin. These results demonstrate snow algae contribute to snowmelt at mid-latitudes and the potential for uncrewed autonomous vehicles to map snow algae over expansive areas of the cryosphere. 

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4. Physical drivers facilitating a toxigenic cyanobacterial bloom in a major Great Lakes tributary

   https://doi.org/10.1002/lno.11558  

   Matson, Paul G.; Boyer, Gregory L.; Bridgeman, Thomas B.; Bullerjahn, George S.; Kane, Douglas D.; McKay, Robert M.; McKindles, Katelyn M.; Raymond, Heather A.; Snyder, Brenda K.; Stumpf, Richard P.; et al (January 2020, Limnology and Oceanography)

   The Maumee River is the primary source for nutrients fueling seasonal Microcystis-dominated blooms in western Lake Erie’s open waters though such blooms in the river are infrequent. The river also serves as source water for multiple public water systems and a large food services facility in northwest Ohio. On 20 September 2017, an unprecedented bloom was reported in the Maumee River estuary within the Toledo metropolitan area, which triggered a recreational water advisory. Here we (1) explore physical drivers likely contributing to the bloom’s occurrence, and (2) describe the toxin concentration and bacterioplankton taxonomic composition. A historical analysis using 10-years of seasonal river discharge, water level, and local wind data identified two instances when high-retention conditions occurred over ≥ 10 d in the Maumee River estuary: in 2016 and during the 2017 bloom. Observation by remote sensing imagery supported the advection of cyanobacterial cells into the estuary from the lake during 2017 and the lack of an estuary bloom in 2016 due to a weak cyanobacterial bloom in the lake. A rapid-response survey during the 2017 bloom determined levels of the cyanotoxins, specifically microcystins, in excess of recreational contact limits at sites within the lower 20 km of the river while amplicon sequencing found these sites were dominated by Microcystis. These results highlight the need to broaden our understanding of physical drivers of cyanobacterial blooms within the interface between riverine and lacustrine systems, particularly as such blooms are expected to become more prominent in response to a changing climate. 

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5. Metagenomics reveals spatial variation in cyanobacterial composition, function, and biosynthetic potential in the Winam Gulf, Lake Victoria, Kenya

   https://doi.org/10.1128/aem.01507-24  

   Hart, Lauren N; Zepernick, Brittany N; Natwora, Kaela E; Brown, Katelyn M; Obuya, Julia Akinyi; Lomeo, Davide; Barnard, Malcolm A; Okech, Eric O; Kiledal, E Anders; Den_Uyl, Paul A; et al (January 2025, Applied and Environmental Microbiology)

   Biddle, Jennifer F (Ed.)

   ABSTRACT The Winam Gulf in the Kenyan region of Lake Victoria experiences prolific, year-round cyanobacterial harmful algal blooms (cyanoHABs) which pose threats to human, livestock, and ecosystem health. To our knowledge, there is limited molecular research on the gulf’s cyanoHABs, and thus, the strategies employed for survival and proliferation by toxigenic cyanobacteria in this region remain largely unexplored. Here, we used metagenomics to analyze the Winam Gulf’s cyanobacterial composition, function, and biosynthetic potential.Dolichospermumwas the dominant bloom-forming cyanobacterium, co-occurring withMicrocystisat most sites.MicrocystisandPlanktothrixwere more abundant in shallow and turbid sites. Metagenome-assembled genomes (MAGs) ofDolichospermumharbored nitrogen fixation genes, suggesting diazotrophy as a potential mechanism supporting the proliferation ofDolichospermumin the nitrogen-limited gulf. Over 300 biosynthetic gene clusters (BGCs) putatively encoding the synthesis of toxins and other secondary metabolites were identified across the gulf, even at sites where there were no visible cyanoHAB events. Almost all BGCs identified had no known synthesis product, indicating a diverse and novel biosynthetic repertoire capable of synthesizing harmful or potentially therapeutic metabolites.MicrocystisMAGs containedmcygenes encoding the synthesis of hepatotoxic microcystins which are a concern for drinking water safety. These findings illustrate the spatial variation of bloom-forming cyanobacteria in the Winam Gulf and their available strategies to dominate different ecological niches. This study underscores the need for further use of genomic techniques to elucidate the dynamics and mitigate the potentially harmful effects of cyanoHABs and their associated toxins on human, environmental, and economic health. 

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