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ABSTRACT The cyanobacterial genusMicrocystisis globally distributed and known for its ability to produce microcystins, a structurally diverse group of cyanotoxins. However, the biosynthetic capacity ofMicrocystisis vast; its diverse genomes contain a variety of biosynthetic gene clusters (BGCs) encoding the synthesis of metabolites that may be toxic, have important ecological function, or have applications for biotechnology or drug discovery. Recent studies illustrate that these BGCs vary significantly acrossMicrocystisstrains, can be highly expressed in environmental conditions, and may play key roles in cellular physiology, grazer deterrence, and microbial interactions. However, many of these BGCs and metabolites remain poorly characterized or completely uncharacterized, having been identified only through genome sequencing or mass spectrometry, respectively, leaving no knowledge of their structure, bioactivity, or physiological or ecological functions. Here, we synthesize the current body of knowledge regarding the secondary metabolism ofMicrocystisin terms of genetic and chemical diversity, potential drivers of synthesis, and physiological and ecological functions. This review highlights the need for further research to characterize the largely unexplored genetic and chemical diversity ofMicrocystisin communities in the environment and discusses the challenges and opportunities of integrating high-throughput multiomic approaches to link uncharacterized gene clusters with their corresponding metabolites.Microcystiswill continue to be a rich source for secondary metabolite research as its genetic and chemical potential likely plays a critical role in the persistence and observed dynamics of harmful algal blooms and may harbor uncharacterized toxins and metabolites. 

ABSTRACT Cyanobacterial harmful algal blooms (cyanoHABs) threaten human, animal, and ecosystem health and safety through production of toxic secondary metabolites.Microcystis,a cosmopolitan bloom‐forming cyanobacterial genus, is well‐known for producing hepatotoxic microcystins (MCs), but it can produce many other bioactive cyanopeptides, such as anabaenopeptins (APs), that occur at high levels in blooms. The toxicological and ecological impacts of such co‐occurring cyanopeptides in the natural environment remain understudied. Here we evaluated the effects of pure MCs and APs individually and in combination, as well as extracts ofMicrocystiscultures producing diverse suites of cyanopeptides, including strains with and without MCs and APs, on human lung (A549), kidney (HK2), and liver (Hep‐3B) cell viability. Individual MC and AP congeners exhibited a gradient of toxic effects across cell lines; MC‐LA caused the most toxic effects, MC‐LR had comparable effects to AP‐A and AP‐B, and MC‐RR caused the least toxicity. Combined exposure to MC‐LA and AP‐B produced dose‐dependent synergistic effects across all three cell lines.Microcystisculture extracts significantly reduced cell viability in dose‐ andMicrocystisstrain‐dependent patterns that could not be explained by microcystin or anabaenopeptin content alone, suggesting a role of other metabolites and their interactions within the mixtures. These findings demonstrate that mixtures of environmentally relevant cyanopeptides can have greater toxic threats than individual compounds and underscore the importance of considering metabolites beyond MCs and their potential interactions in public health, future risk assessments, and management strategies for cyanoHAB‐impacted waters. 

ABSTRACT Here, we report on the raw and coassembled metatranscriptomes of 39 Lake Erie surface (1.0 m) water samples collected over a 2-day diel period encompassing episodic weather and bloom events. Preliminary taxonomic annotations and read mappings revealed thatMicrocystisspp. accounted for up to ~47% of the transcriptionally active community. 

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. 

ABSTRACT We report 40 metagenomic libraries collected from the Winam Gulf of Lake Victoria during May–July of 2022–2023 and an additional eight opportunistic libraries from adjacent Lakes Simbi, Naivasha, and regional river systems. The sampling period captured cyanobacterial bloom events – shedding insight onto community composition and genomic potential.