Microcystis Blooms Research Articles

Microcystis Bloom in an Urban Lake after River Water Diversion—A Case Study

To improve the water quality of Lake Yuehu, a water diversion from the Han River was conducted in July 2008. However, an unexpected Microcystis bloom occurred in the lake after water introduction. Water and sediment samples were collected from Lake Yuehu and the variation of chemical and biochemical parameters, as well as the phytoplankton community, were analyzed during the water diversion to assess its effect and to clarify the mechanism leading to the Microcystis bloom. The nitrogen (N) concentration was increased and phosphorus (P) concentration decreased in Lake Yuehu after receiving water from the Han River, which had a high loading of N and a low loading of P. These conditions may benefit the growth and dominance of non-N2 fixing Microcystis, as it may not have suffered from P limitation during our study because it did not produce extracellular phosphatase, which worked as an indicator of P deficiency, as evidenced by the in situ enzyme-labelled fluorescence. Notably, the sediment Fe (OOH)~P content significantly decreased in Lake Yuehu; this pulsed release of P from the sediment might have sustained the Microcystis bloom. Based on our results, algal blooms may occur as a consequence of conducting water diversion projects to improve water quality.

Water flow and temperature as main factors that regulate phytoplankton and cyanobacterial blooms in a large subtropical river

Seasonal variations and interannual changes (2006-2019) of the phytoplankton community, related to variations in water quality and river discharge, in the lower part of the Uruguay River in South America are presented. In total, 422 microalgae and cyanobacterial taxa were identified. Cryptophytes, cyanobacteria, and diatoms were the most important groups. Although nanoflagellates and cryptophytes were always present in plankton, statistical differences were found in seasonal assemblages of phytoplankton. According to the similarity analysis (SIMPER), the typical species for each season were identified: Aulacoseira spp. in winter, Dolichospermum uruguayense, Durinskia baltica and Ankistrodesmus arcuatus in spring, Microcystis aeruginosa, M. wesenbergii, Dolichospermum uruguayense and D. circinale in summer and Ceratium cf. furcoides, A. arcuatus, Raphidiopsis and Jaaginema sp. in autumn. Under lentic river conditions (<2000 m3 s-1) and above 22ºC, high biomass was recorded due to the blooms of Microcystis and Dolichospermum. In 2010, M. panniformis reached 10.4 µg l-1 microcystin-LR. Raphidiopsis mediterranea and R. raciborskii began to be registered in Spring (2009 and 2014 respectively) reaching 1041 cell ml-1 in Spring 2017. This paper shows that flow, transparency and temperature are the main factors that regulate phytoplankton biomass and cyanobacterial blooms in the Uruguay River. In the summer, when the Uruguay River is in low flow conditions, cyanobacteria remain in the river. When flow increases, cyanobacteria are transported downstream and could reach the estuary of the Rio de la Plata, impacting its beaches.

Nitrogen Stimulates Microcystis-Dominated Blooms More than Phosphorus in River Conditions That Favor Non-Nitrogen-Fixing Genera.

Despite the implementation of intensive phosphorus reduction measures, periodic outbreaks of cyanobacterial blooms in large rivers remain a problem in Korea, raising the need for more effective solutions to reduce their occurrence. This study sought to evaluate whether phosphorus or nitrogen limitation is an effective approach to control cyanobacterial (Microcystis) blooms in river conditions that favor this non-nitrogen-fixing genus. These conditions include nutrient enrichment, high water temperature, and thermal stratification during summer. Mesocosm bioassays were conducted to investigate the limiting factors for cyanobacterial blooms in a river reach where severe Microcystis blooms occur annually. We evaluated the effect of five different nitrogen (3, 6, 9, 12, and 15 mg/L) and phosphorus (0.01, 0.02, 0.05, 0.1, and 0.2 mg/L) concentrations on algae growth. The results indicate that nitrogen treatments stimulated cyanobacteria (mostly Microcystis aeruginosa) more than phosphorus. Interestingly, phosphorus additions did not stimulate cyanobacteria, although it did stimulate Chlorophyceae and Bacillariophyceae. We conclude that phosphorus reduction might have suppressed the growth of Chlorophyceae and Bacillariophyceae more than that of cyanobacteria; therefore, nitrogen or at least both nitrogen and phosphorus control appears more effective than phosphorus reductions alone for reducing cyanobacteria in river conditions that are favorable for non-nitrogen-fixing genera.

The Composition and Function of Microbiomes Within Microcystis Colonies Are Significantly Different Than Native Bacterial Assemblages in Two North American Lakes.

The toxic cyanobacterium Microcystis is one of the most pervasive harmful algal bloom (HAB) genera and naturally occurs in large colonies known to harbor diverse heterotrophic bacterial assemblages. While colony-associated microbiomes may influence Microcystis blooms, there remains a limited understanding of the structure and functional potential of these communities and how they may be shaped by changing environmental conditions. To address this gap, we compared the dynamics of Microcystis-attached (MCA), free-living (FL), and whole water (W) microbiomes during Microcystis blooms using next-generation amplicon sequencing (16S rRNA), a predictive metagenome software, and other bioinformatic approaches. Microbiomes were monitored through high resolution spatial-temporal surveys across two North American lakes, Lake Erie (LE) and Lake Agawam (LA; Long Island, NY, United States) in 2017, providing the largest dataset of these fractions to date. Sequencing of 126 samples generated 7,922,628 sequences that clustered into 7,447 amplicon sequence variants (ASVs) with 100% sequence identity. Across lakes, the MCA microbiomes were significantly different than the FL and W fractions being significantly enriched in Gemmatimonadetes, Burkholderiaceae, Rhizobiales, and Cytophagales and depleted of Actinobacteria. Further, although MCA communities harbored > 900 unique ASVs, they were significantly less diverse than the other fractions with diversity inversely related to bloom intensity, suggesting increased selection pressure on microbial communities as blooms intensified. Despite taxonomic differences between lakes, predicted metagenomes revealed conserved functional potential among MCA microbiomes. MCA communities were significantly enriched in pathways involved in N and P cycling and microcystin-degradation. Taxa potentially capable of N2-fixation were significantly enriched (p < 0.05) and up to four-fold more abundant within the MCA faction relative to other fractions, potentially aiding in the proliferation of Microcystis blooms during low N conditions. The MCA predicted metagenomes were conserved over 8 months of seasonal changes in temperature and N availability despite strong temporal succession in microbiome composition. Collectively, these findings indicate that Microcystis colonies harbor a statistically distinct microbiome with a conserved functional potential that may help facilitate bloom persistence under environmentally unfavorable conditions.

Simultaneous Microcystin Degradation and Microcystis aeruginosa Inhibition with the Single Enzyme Microcystinase A.

Harmful Microcystis blooms (HMBs) seriously threaten the ecology of environments and human health. Microcystins (MCs) produced by Microcystis are powerful mediators of HMB induction and maintenance. In this study, microcystinase A (MlrA), an enzyme with MC-degrading ability, was successfully obtained at over 90% purity for the first time through overexpression in Escherichia coli K12 TB1. The obtained MlrA exhibited high stability at high temperature and under alkaline conditions, while also exhibiting a long half-life. MlrA selectively inhibited MC-producing Microcystis cultures, but had no effect on MC-nonproducing Synechocystis cultures. The inhibition mechanism of MlrA against Microcystis was investigated by evaluating the morphological and physiological characteristics of cultures. MlrA effectively degraded extracellular MCs and decreased the synthesis of intracellular MCs by causing downregulation of genes involved in the microcystin biosynthesis pathway. Concomitantly, MlrA inhibited Microcystis photosynthesis by causing the downregulated expression of important photosynthesis pathway genes and interrupting electron transport chain activities and pigment synthesis. Thus, MlrA achieved the inhibition of Microcystis growth by reducing its photosynthetic capacity and intracellular MC contents, while also degrading extracellular MCs. On the basis of these results, we propose a new paradigm to achieve the simultaneous removal of MCs and HMBs using the single enzyme characterized here.

Development of thermal treatment for the extraction of extracellular polymeric substances from Microcystis: Evaluating extraction efficiency and cell integrity

Extracellular polymeric substances (EPS) play a crucial role in processes associated with the growth and survival of microorganisms, such as in colony formation of cyanobacterium Microcystis. Thermal treatment is an effective method for EPS extraction. However, intracellular materials, however, often contaminate EPS extracts, possibly owing to cell lysis during thermal extraction. In this study, EPS samples were extracted using boric acid buffer under different temperatures (45–75 °C) and extraction periods (15–30 min), and evaluated with respect to both extraction efficiency and cell integrity. Moreover, the method developed in this study was compared to two widely employed methods (thermal extraction with 0.05% NaCl or NaOH (pH = 10)) with respect to EPS yield and composition, cell integrity or the release of cellular inclusions, and changes in cell size and morphology. Results indicated that thermal extraction with the boric acid buffer achieved the highest EPS yield and the lowest cell lysis. The optimal results were achieved by treatment at 65 °C for 30 min. However, a large quantity of cell debris and released cellular inclusions were detected when the other thermal methods were used, which suggests that stabilizing the cellular osmotic pressure and pH can effectively improve EPS yield and minimize cell lysis during thermal extraction. The findings of this study improve the EPS extraction from Microcystis, which can foster further investigations on the functions of these substances in the formation of Microcystis blooms.

Use statistical machine learning to detect nutrient thresholds in Microcystis blooms and microcystin management

The frequency of toxin-producing cyanobacterial blooms has increased in recent decades due to nutrient enrichment and climate change. Because Microcystis blooms are related to different environmental conditions, identifying potential nutrient control targets can facilitate water quality managers to reduce the likelihood of microcystins (MCs) risk. However, complex biotic interactions and field data limitations have constrained our understanding of the nutrient-microcystin relationship. This study develops a Bayesian modelling framework with intracellular and extracellular MCs that characterize the relationships between different environmental and biological factors. This model was fit to the across-lake dataset including three bloom-plagued lakes in China and estimated the putative thresholds of total nitrogen (TN) and total phosphorus (TP). The lake-specific nutrient thresholds were estimated using Bayesian updating process. Our results suggested dual N and P reduction in controlling cyanotoxin risks. The total Microcystis biomass can be substantially suppressed by achieving the putative thresholds of TP (0.10 mg/L) in Lakes Taihu and Chaohu, but a stricter TP target (0.05 mg/L) in Dianchi Lake. To maintain MCs concentrations below 1.0 μg/L, the estimated TN threshold in three lakes was 1.8 mg/L, but the effect can be counteracted by the increase of temperature. Overall, the present approach provides an efficient way to integrate empirical knowledge into the data-driven model and is helpful for the management of water resources.

The "Neglected Viruses" of Taihu: Abundant Transcripts for Viruses Infecting Eukaryotes and Their Potential Role in Phytoplankton Succession.

Drivers of algal bloom dynamics remain poorly understood, but viruses have been implicated as important players. Research addressing bloom dynamics has generally been restricted to the virus-infection of the numerically dominant (i.e. bloom forming) taxa. Yet this approach neglects a broad diversity of viral groups, limiting our knowledge of viral interactions and constraints within these systems. We examined hallmark virus marker genes in metatranscriptomic libraries from a seasonal and spatial survey of a Microcystis aeruginosa bloom in Lake Tai (Taihu) China to identify active infections by nucleocytoplasmic large DNA viruses (NCLDVs), RNA viruses, ssDNA viruses, bacteriophage, and virophage. Phylogenetic analyses revealed a diverse virus population with seasonal and spatial variability. We observed disproportionately high expression of markers associated with NCLDVs and ssRNA viruses (consistent with viruses that infect photosynthetic protists) relative to bacteriophage infecting heterotrophic bacteria or cyanobacteria during the height of the Microcystis bloom event. Under a modified kill-the-winner scheme, we hypothesize viruses infecting protists help suppress the photosynthetic eukaryotic community and allow for the proliferation of cyanobacteria such as Microcystis. Our observations provide a foundation for a little considered factor promoting algal blooms.

Seasonal changes in the bacterial community structure of three eutrophicated urban lakes in Mexico city, with emphasis on Microcystis spp.

Artificial urban lakes commonly have physicochemical conditions that contribute to rapid anthropogenic eutrophication and development of cyanobacterial blooms. Microcystis is the dominat genus in most freshwater bodies and is one of the main producter of microcystins. Using 454-pyrosequencing we characterized the bacterial community, with special emphasis on Microcystis, in three recreational urban lakes from Mexico City in both wet and dry seasons. We also evaluated some physicochemical parameters that might influence the presence of Microcystis blooms, and we associated the relative abundance of heterotrophic and autotrophic bacterial communities with their possible metabolic capacities. A total of 14 phyla, 18 classes, 39 orders, 53 families and 48 bacterial genera were identified in both seasons in the three urban lakes. Cyanobacteria had the highest relative abundance followed by Proteobacteria and Actinobacteria. Microcystis was the dominant taxon followed by Arthrospira, Planktothrix and Synechococcus. We also found heterotrophic bacteria associated with the blooms, such as Rhodobacter, Pseudomonas, Sphingomonas and, Porphyrobacter. The highest richness, diversity and dominance were registered in the bacterial community of the Virgilio Uribe Olympic Rowing-Canoeing Track in both seasons, and the lowest values were found in the Chapultepec Lake. The canonical correspondence analysis showed that dissolved oxygen and NO3–N concentrations might explain the presence of Microcystis blooms. The metabolic prediction indicated that these communities are involved in photosynthesis, oxidative phosphorylation, methane metabolism, carbon fixation, and nitrogen and sulfur metabolism. The lakes studied had a high prevalence of Microcystis, but average values of microcystins did not exceed the maximum permissible level established by the United States Environmental Protection Agency for recreational and cultural activities. The presence of cyanobacteria and microcystins at low to moderate concentrations in the three lakes could result in ecosystem disruption and increase animal and human health risks.

Nitrogen availability affects the dynamics of Microcystis blooms by regulating the downward transport of biomass

Nitrogen availability is one of the key factors affecting the dynamics of non-diazotrophic cyanobacterial blooms in eutrophic lakes. While previous studies mainly focused on the promoting effect of nitrogen on the growth of cyanobacteria, this study aimed to investigate the role of nitrogen availability in the downward transport of biomass and its effects on the dynamics of Microcystis blooms. We performed field enclosure experiments which demonstrated that nitrogen availability negatively affects the downward transport of biomass. With a nitrogen loading of 0.02 g N m−2 d−1, the Microcystis biomass in the water column decreased by 56.2% over a 4-day period. During the same period of time, the average sinking ratio was 0.23 d−1; moreover, the termination of biomass growth was detected. At the notably higher nitrogen loading of 0.5 g N m−2d−1, the downward transport of biomass could still compensate for the biomass growth, although the average sinking ratio was lower at 0.16 d−1. Additional laboratory culture experiments demonstrated that the increase in the downward transport of Microcystis occurred in parallel to an increase in the carbohydrate content and a decrease in gas vesicle content. Further proteomic analysis indicated that the carbohydrate accumulation induced by nitrogen deficiency was a result of the slowing down of catabolic consumption, especially the downregulation of glycolysis. Thus, our study suggests that increased intracellular carbohydrate accumulation at low nitrogen availability causes a higher sinking ratio of Microcystis, indicating that nitrogen limits the duration of Microcystis blooms; thus, decreased nitrogen availability may lead to increased sinking of biomass out of the water column, accelerating the dissipation of Microcystis blooms.

Determining the Exposure Pathway and Impacts of Microcystis on Threadfin Shad, Dorosoma petenense, in San Francisco Estuary.

Blooms of the cyanobacterium Microcystis spp. could affect fish health through the ingestion of colonies as well as exposure to dissolved microcystins in the water column. The goal of the present study was to evaluate the dietary exposure pathway through which Microcystis spp. blooms may affect liver function and nutritional status using a novel approach involving multiple analytical methods to assess the potential risk. Our study was conducted using threadfin shad, Dorosoma petenense, which is a pelagic fish commonly exposed to Microcystis spp. blooms in the upper San Francisco Estuary. The approach incorporated published and optimized methods that offer multiple lines of evidence including in situ hybridization, immunohistochemistry, histopathology, condition factor indices, and nutritional profiles. Measurements of threadfin shad health and tissue condition were conducted at sites where Microcystis was present or absent during the 2007 bloom season. The results showed that dietary exposure to fish from Microcystis blooms resulted in the accumulation of microcystin in the gut and liver tissues of threadfin shad collected from the sites with blooms. Although toxicity endpoints were likely confounded by antecedent conditions, our findings demonstrate dietary exposure of Microcystis toxins to fish using a novel approach with multiple lines of evidence. Environ Toxicol Chem 2020;39:787–798. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Harvesting colonial Microcystis flos-aquae using two-stage filtration: Influence of pre-filtration on harvesting performance

The harvesting of bloom-forming colonial Microcystis flos-aquae using filtration helps with bloom control, the acquisition of a biomass resource and nutrient removal from eutrophic lakes. In this study, two-stage filtration of three combinations for M. flos-aquae harvesting was investigated, and the main factors affecting two-stage filtration performance were analysed. The results showed that compared with filtration with a 5 μm membrane alone, pre-filtration with a 20 μm screen improved biomass harvesting rate by 25.03% while 200 μm and 550 μm screens pre-filtrations resulted in decreases of 26.90% and 42.20%, respectively. The influences of colony size distribution and cellular concentration on filtration performance were predicted well using a multiple linear regression model (MLR). According to the model analysis, filtrate with larger colony size and narrower size distribution resulted higher harvesting performance. As the cellular concentration increased, the averaged flux decreased, while biomass harvesting rate increased initially, reached the highest value and then decreased. These results could be applied for the development of efficient filtration harvesting strategies for Microcystis bloom control.

Anticyanobacterial process and action mechanism of Streptomyces sp. HJC‐D1 on Microcystis aeruginosa

AbstractEutrophication of environmental waters and occurrence of harmful cyanobacterial blooms have drawn much attention all over the world. For controlling cyanobacteria overgrowth, biological control methods such as anticyanobacterial process by microorganisms have been recently explored. In this study, a Streptomyces strain named HJC‐D1 is isolated from an eutrophic pond in China, which exhibited anticyanobacterial activity against a representative bloom‐forming cyanobacterium Microcystis aeruginosa. Based on its morphology and 16S rRNA sequence, the isolated strain is identified as Streptomyces sp. Results show that the M. aeruginosa is biodegraded by the isolated strain HJC‐D1, and the Chl a removal efficiency is 53.5 ± 4.3%–62.6 ± 3.3% at the initial Chl a concentration of 0.2713–0.6375 mg L−1. The anticyanobacterial mechanism of Streptomyces sp. on M. aeruginosa is that the growth of cyanobacterial cell is destroyed by the active substances secreted by strain HJC‐D1, and TEM results demonstrate the degradation processes are divided into three steps: cell breakage, organelle release, and cell death. The isolated microorganism may be a potential environment‐friendly strain and provides a possible approach for Microcystis bloom control in lakes and reservoirs.

Impact of extreme wet and dry years on the persistence of Microcystis harmful algal blooms in San Francisco Estuary

Cyanobacteria harmful algal blooms (CHABs) became a concern in the upper San Francisco Estuary, California beginning in 1999, when yearly blooms of Microcystis began in the Delta region. Subsequent research identified that the increase in the magnitude, duration and toxicity of Microcystis blooms was associated with drought related conditions of elevated water temperature and low streamflow. However, the impact of extreme conditions on the resilience of the bloom was unknown. The 2014 and 2017 water years provided a unique opportunity to determine the effect of climatic “whiplash” produced by the occurrence of extreme wet conditions following extreme dry conditions on the Microcystis bloom. We hypothesized that the period of record wet conditions in 2017 (1906-2018) would eliminate the Microcystis bloom for that year and perhaps revert the estuary phytoplankton community back to pre-bloom conditions due to extreme flushing, despite the increase in magnitude and spatial and temporal distribution of the Microcystis bloom during the 2014 extreme dry year. Field sampling was conducted at 2-week or 4-week intervals between July and November at stations throughout the Delta for both years and included a suite of physical, chemical and biological factors. Using PRIMER-e DISTLM, we determined that retention time in the upper estuary and water temperature were key environmental correlates with the Microcystis bloom amplitude and in regression models described 58-78% of the variation of the bloom surface biovolume or subsurface abundance. The period of record high streamflow in 2017 was not enough to eliminate the Microcystis bloom. However, the bloom was small in 2017, with a low abundance, late initiation, short duration, narrow distribution and low toxin production. Warm water temperature enabled the bloom to flower in late summer despite streamflow many times those measured previously. In addition, although conditions early in the summer of 2017 favored diatoms, the summer was characterized by an abundance of other non-Microcystis cyanobacteria. We conclude that once established, Microcystis is likely to be resistant to extreme wet conditions, as long as water temperature and other key water quality conditions are favorable.

Assessment of Constructed Wetlands’ Potential for the Removal of Cyanobacteria and Microcystins (MC-LR)

Microcystis blooms and the subsequent release of hepatotoxic microcystins (MCs) pose a serious threat to the safety of water for human and livestock consumption, agriculture irrigation, and aquaculture worldwide. Microcystin-LR (MC-LR), the most toxic variant of MCs, has been widely detected in a variety of environments such as water, sediments, plants, and many aquatic organisms. Conventional solutions of water treatment are costly, requiring specific infrastructure, as well as specialized personnel and equipment. Therefore, these solutions are not feasible in many rural areas or in the treatment of large reservoirs. In this regard, low-cost and low-technology solutions, such as constructed wetlands (CWs), are attractive solutions to treat surface waters contaminated with toxic cyanobacteria blooms from lakes, ponds, reservoirs, and irrigation systems. In line with this, the main aim of this work was to evaluate the potential of CWs for the treatment of water contaminated with MC-LR produced by Microcystis aeruginosa—LEGE 91094. For that, microcosms (0.4 × 0.3 × 0.3 m) simulating CWs were assembled with Phragmites australis to treat lake water contaminated with Microcystis aeruginosa cells and MCs. Results showed removal percentages of M. aeruginosa cells above 94% and about 99% removal of MC-LR during 1 week treatment cycles. CWs maintained their functions, regardless the presence of MC-LR in the system, and also showed significant removal of nutrients (ammonium ion removal up to 86%) and organic matter (removal reaching 98%). The present work indicates that CWs have the potential for removal of cyanobacterial cells and cyanotoxins, which can be useful for the treatment of eutrophic waters and provide water of sufficient quality to be used, for instance, in agriculture.

Insight Into the Molecular Mechanisms for Microcystin Biodegradation in Lake Erie and Lake Taihu.

Microcystins are potent hepatotoxins that are frequently detected in fresh water lakes plagued by toxic cyanobacteria. Microbial biodegradation has been referred to as the most important avenue for removal of microcystin from aquatic environments. The biochemical pathway most commonly associated with the degradation of microcystin is encoded by the mlrABCD (mlr) cassette. The ecological significance of this pathway remains unclear as no studies have examined the expression of these genes in natural environments. Six metatranscriptomes were generated from microcystin-producing Microcystis blooms and analyzed to assess the activity of this pathway in environmental samples. Seventy-eight samples were collected from Lake Erie, United States/Canada and Lake Tai (Taihu), China, and screened for the presence of mlr gene transcripts. Read mapping to the mlr cassette indicated transcripts for these genes were absent, with only 77 of the collective 3.7 billion reads mapping to any part of the mlr cassette. Analysis of the assembled metatranscriptomes supported this, with only distantly related sequences identified as mlrABC-like. These observations were made despite the presence of microcystin and over 500,000 reads mapping to the mcy cassette for microcystin production. Glutathione S-transferases and alkaline proteases have been previously hypothesized to be alternative pathways for microcystin biodegradation, and expression of these genes was detected across space and time in both lakes. While the activity of these alternative pathways needs to be experimentally confirmed, they may be individually or collectively more important than mlr genes in the natural environment. Importantly, the lack of mlr expression could indicate microcystin biodegradation was not occurring in the analyzed samples. This study raises interesting questions about the ubiquity, specificity and locality of microcystin biodegradation, and highlights the need for the characterization of relevant mechanisms in natural communities to understand the fate of microcystin in the environment and risk to public health.

Multiannual variations in Microcystis bloom episodes – Temperature drives shift in species composition

Cyanobacteria are notorious for producing water blooms and for toxin formation. Toxic cyanobacterial blooms present an ever-increasing serious threat to both the quality of drinking water and recreational uses and severely disrupt aquatic ecosystems, worldwide. In many cases, such blooms are dominated by toxic Microcystis sp. that produce a family of structurally similar hepatotoxins, known as microcystins (MCs). Here we present a retrospective analysis of Microcystis seasonal blooms from Lake Kinneret (Sea of Galilee, Israel) indicating that the population is composed of at least 25 different genotypes and two different chemo-types, whose relative abundance changes over decades. Based on a long-term record of biotic and abiotic parameters and laboratory experiments we propose that minor increase in water temperature, but not in salinity, may affect Microcystis community structure by changing the relative abundance of species/strains from toxic to less or non-toxic species.

Network analysis reveals succession of Microcystis genotypes accompanying distinctive microbial modules with recurrent patterns

Every member of the ecological community is connected via a network of vital and complex relationships, called the web of life. To elucidate the ecological network and interactions among producers, consumers, and decomposers in the Daechung Reservoir, Korea, during cyanobacterial harmful algal blooms (cyanoHAB), especially those involving Microcystis, we investigated the diversity and compositions of the cyanobacterial (16S rRNA gene), including the genotypes of Microcystis (cpcBA-IGS gene), non-cyanobacterial (16S), and eukaryotic (18S) communities through high-throughput sequencing. Microcystis blooms were divided into the Summer Major Bloom and Autumn Minor Bloom with different dominant genotypes of Microcystis. Network analysis demonstrated that the modules involved in the different phases of the Microcystis blooms were categorized into the Pre-Bloom, Bloom, Post-Bloom, and Non-Bloom Groups at all sampling stations. In addition, the non-cyanobacterial components of each Group were classified, while the same Group showed similarity across all stations, suggesting that Microcystis and other microbes were highly interdependent and organized into cyanoHAB-related module units. Importantly, the Microcystis genotype-based sub-network uncovered that Pirellula, Pseudanabaena, and Vampirovibrionales preferred to interact with specific Microcystis genotypes in the Summer Major Bloom than with other genotypes in the Autumn Minor Bloom, while the copepod Skistodiaptomus exhibited the opposite pattern. In conclusion, the transition patterns of cyanoHAB-related modules and their key components could be crucial in the succession of Microcystis genotypes and to enhance the understanding of microbial ecology in an aquatic environment.

Programmed Cell Death-Like and Accompanying Release of Microcystin in Freshwater Bloom-Forming Cyanobacterium Microcystis: From Identification to Ecological Relevance.

Microcystis is the most common freshwater bloom-forming cyanobacterium. Its massive blooms not only adversely affect the functionality of aquatic ecosystems, but are also associated with the production of microcystins (MCs), a group of potent toxins that become a threat to public health when cell-bound MCs are significantly released from the dying Microcystis into the water column. Managing Microcystis blooms thus requires sufficient knowledge regarding both the cell death modes and the release of toxins. Recently, more and more studies have demonstrated the occurrence of programmed cell death-like (or apoptosis-like) events in laboratory and field samples of Microcystis. Apoptosis is a genetically controlled process that is essential for the development and survival of metazoa; however, it has been gradually realized to be an existing phenomenon playing important ecological roles in unicellular microorganisms. Here, we review the current progress and the existing knowledge gap regarding apoptosis-like death in Microcystis. Specifically, we focus first on the tools utilized to characterize the apoptosis-related biochemical and morphological features in Microcystis. We further outline various stressful stimuli that trigger the occurrence of apoptosis and discuss the potential mechanisms of apoptosis in Microcystis. We then propose a conceptual model to describe the functional coupling of apoptosis and MC in Microcystis. This model could be useful for understanding both roles of MC and apoptosis in this species. Lastly, we conclude the review by highlighting the current knowledge gap and considering the direction of future research. Overall, this review provides a recent update with respect to the knowledge of apoptosis in Microcystis and also offers a guide for future investigations of its ecology and survival strategies.

The global Microcystis interactome.

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 with Microcystis aeruginosa during blooms in 12 lakes spanning four continents as an initial test of the hypothesized Microcystis interactome. We predicted that microbiome composition and functional potential would be similar across blooms globally. Our results, as revealed by 16S rRNA sequence similarity, indicate that M. aeruginosa is 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, like Microcystis, 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. While Microcystis and 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 global Microcystis blooms, thereby providing initial support for the hypothesized Microcystis interactome.