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1. The global Microcystis interactome

   https://doi.org/10.1002/lno.11361  

   Cook, Katherine V.; Li, Chuang; Cai, Haiyuan; Krumholz, Lee R.; Hambright, K. David; Paerl, Hans W.; Steffen, Morgan M.; Wilson, Alan E.; Burford, Michele A.; Grossart, Hans‐Peter; et al (November 2019, Limnology and Oceanography)

   Abstract Bacteria play key roles in the function and diversity of aquatic systems, but aside from study of specific bloom systems, little is known about the diversity or biogeography of bacteria associated with harmful cyanobacterial blooms (cyanoHABs). CyanoHAB species are known to shape bacterial community composition and to rely on functions provided by the associated bacteria, leading to the hypothesized cyanoHAB interactome, a coevolved community of synergistic and interacting bacteria species, each necessary for the success of the others. Here, we surveyed the microbiome associated withMicrocystis aeruginosaduring blooms in 12 lakes spanning four continents as an initial test of the hypothesizedMicrocystisinteractome. We predicted that microbiome composition and functional potential would be similar across blooms globally. Our results, as revealed by 16S rRNA sequence similarity, indicate thatM. aeruginosais cosmopolitan in lakes across a 280° longitudinal and 90° latitudinal gradient. The microbiome communities were represented by a wide range of operational taxonomic units and relative abundances. Highly abundant taxa were more related and shared across most sites and did not vary with geographic distance, thus, likeMicrocystis, revealing no evidence for dispersal limitation. High phylogenetic relatedness, both within and across lakes, indicates that microbiome bacteria with similar functional potential were associated with all blooms. WhileMicrocystisand the microbiome bacteria shared many genes, whole‐community metagenomic analysis revealed a suite of biochemical pathways that could be considered complementary. Our results demonstrate a high degree of similarity across globalMicrocystisblooms, thereby providing initial support for the hypothesizedMicrocystisinteractome. 

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2. Genome evolution and host‐microbiome shifts correspond with intraspecific niche divergence within harmful algal bloom‐forming Microcystis aeruginosa

   https://doi.org/10.1111/mec.15198  

   Jackrel, Sara L.; White, Jeffrey D.; Evans, Jacob T.; Buffin, Kyle; Hayden, Kristen; Sarnelle, Orlando; Denef, Vincent J. (August 2019, Molecular Ecology)

   Abstract Intraspecific niche divergence is an important driver of species range, population abundance and impacts on ecosystem functions. Genetic changes are the primary focus when studying intraspecific divergence; however, the role of ecological interactions, particularly host‐microbiome symbioses, is receiving increased attention. The relative importance of these evolutionary and ecological mechanisms has seen only limited evaluation. To address this question, we usedMicrocystis aeruginosa, the globally distributed cyanobacterium that dominates freshwater harmful algal blooms. These blooms have been increasing in occurrence and intensity worldwide, causing major economic and ecological damages. We evaluated 46 isolates ofM. aeruginosaand their microbiomes,collected from 14 lakes in Michigan, USA, that vary over 20‐fold in phosphorus levels, the primary limiting nutrient in freshwater systems. Genomes ofM. aeruginosadiverged along this phosphorus gradient in genomic architecture and protein functions. Fitness in low‐phosphorus lakes corresponded with additional shifts withinM. aeruginosaincluding genome‐wide reductions in nitrogen use, an expansion of phosphorus assimilation genes and an alternative life history strategy of nonclonal colony formation. In addition to host shifts, despite culturing in common‐garden conditions, host‐microbiomes diverged along the gradient in taxonomy, but converged in function with evidence of metabolic interdependence between the host and its microbiome. Divergence corresponded with a physiological trade‐off between fitness in low‐phosphorus environments and growth rate in phosphorus‐rich conditions. Co‐occurrence of genotypes adapted to different nutrient environments in phosphorus‐rich lakes may have critical implications for understanding howM. aeruginosablooms persist after initial nutrient depletion. Ultimately, we demonstrate that the intertwined effects of genome evolution, host life history strategy and ecological interactions between a host and its microbiome correspond with an intraspecific niche shift with important implications for whole ecosystem function. 

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3. Sulfolipid substitution ratios of Microcystis aeruginosa and planktonic communities as an indicator of phosphorus limitation in Lake Erie

   https://doi.org/10.1002/lno.12333  

   Martin, Robbie M.; Denney, Maddie K.; Pound, Helena L.; Chaffin, Justin D.; Bullerjahn, George S.; McKay, R. Michael L.; Zastepa, Arthur; Jones, Katarina A.; Castro, Hector F.; Campagna, Shawn R.; et al (March 2023, Limnology and Oceanography)

   Abstract Phosphorus (P) availability frequently limits primary production in lakes, influences the physiology of phytoplankton, shapes community structure, and can stimulate or constrain the formation of cyanobacterial blooms. Given the importance of P, numerous methods are available to assess P stress in phytoplankton communities. Marine phytoplankton are known to substitute sulfolipids for phospholipids in response to P limitation. We asked whether sulfolipid substitution might serve as an additional indicator of P stress in freshwater phytoplankton communities. The question was addressed using cultures ofMicrocystis aeruginosa, Lake Erie microcosms, and surveys of lipid profiles in Lake Erie during aMicrocystisspp. bloom. Peak area response ratios of the intact polar lipids sulfoquinovosyldiacylglycerol (SQDG) to phosphatidylglycerol (PG) were used as the metric of lipid substitution. In cultures ofM. aeruginosaNIES‐843, the SQDG : PG ratio increased from ~ 0.9 to ~ 3.3 with decreasing P concentration. In P‐limited communities, the SQDG : PG ratio increased from ~ 6 to ~ 11 after 48 h in microcosm controls, while P amendments reduced the ratio to ~ 3. In Lake Erie surveys, the SQDG : PG ratio ranged from ~ 0.4 to ~ 7.4 and was negatively correlated (Pearsonr = −0.62) with total dissolved P. The SQDG : PG ratio was not correlated with concentrations of chlorophylla, soluble reactive P, or N : P molar ratios. These results demonstrated thatM. aeruginosaandMicrocystis‐dominated communities remodel lipid profiles in response to P scarcity, providing a potential short‐term, time‐integrated biomarker of nutrient history and P stress in fresh waters. 

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4. Mobilome impacts on physiology in the widely used non-toxic mutant Microcystis aeruginosa PCC 7806 ΔmcyB and toxic wildtype

   https://doi.org/10.1186/s12864-024-10839-5  

   Stark, Gwendolyn F; Truchon, Alexander R; Wilhelm, Steven W (December 2024, BMC Genomics)

   Abstract TheMicrocystismobilome is a well-known but understudied component of this bloom-forming cyanobacterium. Through genomic and transcriptomic comparisons, we found five families of transposases that altered the expression of genes in the well-studied toxigenic type-strain,Microcystis aeruginosaPCC 7086, and a non-toxigenic genetic mutant,Microcystis aeruginosaPCC 7806 ΔmcyB. Since its creation in 1997, the ΔmcyBstrain has been used in comparative physiology studies against the wildtype strain by research labs throughout the world. Some differences in gene expression between what were thought to be otherwise genetically identical strains have appeared due to insertion events in both intra- and intergenic regions. In our ΔmcyBisolate, a sulfate transporter gene cluster (sbp-cysTWA) showed differential expression from the wildtype, which may have been caused by the insertion of a miniature inverted repeat transposable element (MITE) in the sulfate-binding protein gene (sbp). Differences in growth in sulfate-limited media also were also observed between the two isolates. This paper highlights howMicrocystisstrains continue to “evolve” in lab conditions and illustrates the importance of insertion sequences / transposable elements in shaping genomic and physiological differences betweenMicrocystisstrains thought otherwise identical. This study forces the necessity of knowing the complete genetic background of isolates in comparative physiological experiments, to facilitate the correct conclusions (and caveats) from experiments. 

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5. Bifurcation Analysis of a New Aquatic Ecological Model with Aggregation Effect and Harvesting

   https://doi.org/10.1142/S0218127423501808  

   Liang, Chenyu; Zhang, Hangjun; Xu, Yancong; Rong, Libin (December 2023, International Journal of Bifurcation and Chaos)

   In this paper, we investigated the dynamics of the interaction between Microcystis aeruginosa and filter-feeding fish in a new aquatic ecological model and considered the effects of aggregation and harvesting and focused on studying the critical threshold conditions through the analysis of saddle-node bifurcation, Hopf bifurcation, and Bogdanov–Takens bifurcation. We also conducted numerical simulations to illustrate our findings and provided biological interpretations. The results obtained indicate that the aggregation effect or harvesting can disrupt the coexistence of Microcystis aeruginosa and filter-feeding fish. The filter-feeding fish population may go extinct while the Microcystis aeruginosa population could survive. We identified the importance of finding an appropriate timing for harvesting Microcystis aeruginosa in order to promote the growth of the filter-feeding fish population. This optimal timing may be influenced by the carrying capacity of Microcystis aeruginosa. Taken together, our study sheds light on the dynamics of Microcystis aeruginosa and filter-feeding fish in an aquatic ecosystem, highlighting the critical role of aggregation, harvesting, and timing in determining the coexistence and survival of these species. 

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