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PubMed2024

Transcriptional profiles of Microcystis reveal gene expression shifts that promote bloom persistence in in situ mesocosms.

Harmful algal blooms caused by cyanobacteria threaten aquatic ecosystems, the economy, and human health. Previous work has tried to identify the mechanisms that allow blooms to form, focusing on the role of nutrients. However, little is known about how introduced nutrients influence gene expression in situ. To address this knowledge gap, we used in situ mesocosms initiated with water experiencing a Microcystis bloom. We added pulses of nutrients that are commonly associated with anthropogenic sources to the mesocosms for 72 hours and collected samples for metatranscriptomics to examine how the physiological function of Microcystis and bloom status changed. The addition of nitrogen (N) as urea, but not the addition of PO4, resulted in conspicuous bloom persistence for at least 9 days after the final introduction of nutrients. The addition of urea initially resulted in the upregulation of photosynthesis machinery, as well as phosphate, carbon, and N transport and metabolism. Once Microcystis presumably became N-replete, upregulation of amino acid metabolism, microcystin biosynthesis, and other processes associated with biomass generation occurred. These capacities coincided with the upregulation of toxin-antitoxin systems, CRISPR-cas genes, and transposases suggesting that phage defense and genome rearrangement are critical in bloom persistence. Overall, our results show the stepwise transcriptional response of a Microcystis bloom to the introduction of nutrients, specifically urea, as it is sustained in a natural setting. The transcriptomic shifts observed herein may serve as markers of the longevity of blooms while providing insight into why Microcystis blooms over other cyanobacteria.IMPORTANCEHarmful algal blooms represent a threat to human health and ecosystems. Understanding why blooms persist may help us develop warning indicators of bloom persistence and create novel mitigation strategies. Using mesocosm experiments initiated with water with an active bloom, we measured the stepwise transcription changes of the toxin-producing cyanobacterium Microcystis in response to the addition of nutrients that are important in causing blooms. We found that nitrogen (N), but not phosphorus, promoted bloom longevity. The initial introduction of N resulted in the upregulation of genes involved in photosynthesis and N import. At later times in the bloom, upregulation of genes involved in biomass generation, phage protection, genomic rearrangement, and toxin production was observed. Our results suggest that Microcystis first fulfills nutritional requirements before investing energy in pathways associated with growth and protection against competitors, which allowed bloom persistence more than a week after the final addition of nutrients.

Microcystis↗
PubMed2026

Metabolomics and genomics reveal high diversity and concentrations of cyanopeptides during a Microcystis bloom.

Cyanobacterial blooms are an immense global problem that release complex mixtures of poorly characterized biologically active cyanopeptides into freshwater. In this study, metabolomics and genomics were used to assess the diversity and concentrations of cyanopeptides during a dense Microcystis bloom during the late summer of 2023 in Lake Champlain, a large transboundary lake situated between Canada and the United States. Despite the relatively low genetic diversity of the bloom determined by 16S rRNA metabarcoding, 151 cyanopeptides were detected by non-targeted metabolomics. This represents the most recorded cyanopeptides from a single lake plankton bloom event to date. Fifty-two cyanopeptides were previously reported and 99 represent putative new structures. Standards from the microcystin, cyanopeptolin, microginin, and anabaenopeptin groups were used to either quantify or approximate respective cyanopeptide concentrations over the sampling period. Cyanopeptolins were the most diverse (n = 68) cyanopeptides and the second most abundant, reaching 12,892 μg/L. Microginins were the second most diverse (n = 24) and reached the highest concentrations (18,262 μg/L). Anabaenopeptins were the third most diverse (n = 17) cyanopeptides, reaching 4,818 μg/L. Only 8 microcystins were detected, reaching 4,935 μg/L, where MC-LR was the dominant congener. Target cyanopeptide biosynthesis genes for microcystins (mcyE), cyanopeptolins (mcnC), anabaenopeptins (apnD), microviridins (mdnC), and aeruginosins (aerA) were also quantified using digital droplet PCR (ddPCR). The gene copy numbers for mcyE, mcnC, and apnD were highly correlated with their corresponding cyanopeptide concentrations. Overall, the studied Microcystis bloom produced a very diverse cyanopeptide mixture with high cyanopeptide concentrations including non-microcystin groups.

Microcystis↗
PubMed2025

Intraspecific divergence within Microcystis aeruginosa mediates the dynamics of freshwater harmful algal blooms under climate warming scenarios.

Intraspecific biodiversity can have ecosystem-level consequences and may affect the accuracy of ecological forecasting. For example, rare genetic variants may have traits that prove beneficial under future environmental conditions. The cyanobacterium responsible for most freshwater harmful algal blooms worldwide, Microcystis aeruginosa, occurs in at least three types. While the dominant type occurs in eutrophic environments and is adapted to thrive in nutrient-rich conditions, two additional types have recently been discovered that inhabit oligotrophic and eutrophic environments and have genomic adaptations for survival under nutrient limitation. Here, we show that these oligotrophic types are widespread throughout the Eastern USA. By pairing an experimental warming study with gene expression analyses, we found that the eutrophic type may be most susceptible to climate warming. In comparison, oligotrophic types maintained their growth better and persisted longer under warming. As a mechanistic explanation for these patterns, we found that oligotrophic types responded to warming by widespread elevated expression of heat shock protein genes. Reduction of nutrient loading has been a historically effective mitigation strategy for controlling harmful algal blooms. Our results suggest that climate warming may benefit oligotrophic types of M. aeruginosa, potentially reducing the effectiveness of such mitigation efforts. In-depth study of intraspecific variation may therefore improve forecasting for understanding future whole ecosystem dynamics.

Microcystis↗
PubMed1978

Isolation, characterization and pathology of the toxin from a Microcystis aeruginosa (= Anacystis cyanea) bloom.

The nature of the toxicity of a bloom of blue-green alga, M. aeruginosa (= Anacystis cyanea), that occurred in a man-made lake was investigated. Crude algal bloom extracts were toxic to laboratory mice when injected intraperitoneally. The lethal dose (LD100) of these extracts was 15-30 mg of lyophilized algal bloom per kilogram body weight. The toxin was purified by a procedure that included ammonium sulphate fractionation, solvent extraction, acid precipitation, Sephadex G25 and DEAE-Sephadex chromatography, and high-voltage electrophoresis at pH 6.5. The preparation gave a single spot on high-voltage electrophoresis at pH 9.0, had no free amino group, and was characterized by a simple amino acid composition of equimolar quantities of L-methionine, L-tyrosine, D-alanine, D-glutamic acid, erythro beta-methyl aspartic acid and methylamine. The LD50 for the purified toxin was estimated to be 0.056 mg/kg of mice, and the approximate LD100 is 0.070 mg/kg, based on the total material found from amino acid analysis. Parenteral administration of the purified toxin to mice produced extensive liver lobular haemorrhage and death within 1-3 h. Repeated inoculation of sublethal doses daily over some weeks produced progressive hepatocyte degeneration and necrosis and the development of fine hepatic fibrosis.

Amino Acids↗
PubMed2026

Nitrogen sources and concentrations shape algal odor compounds: Key drivers of β-cyclocitral and β-ionone in water bodies of the lower Yangtze River.

Taste and odor (T&O) compounds derived from cyanobacterial blooms pose escalating threats to freshwater security worldwide, yet the drivers of specific T&O metabolites remain poorly constrained. Here, we investigated the dual effects of nitrogen (N) sources and concentrations on the production of β-cyclocitral and β-ionone, two algal-derived T&O compounds, through integrated field surveys (54 sites across lakes and rivers) in the eutrophic lower Yangtze River, China, and laboratory cultivation of typical cyanobacteria (Microcystis aeruginosa and Pseudanabaena cinerea). Our field data revealed that the concentrations of β-cyclocitral and β-ionone in lakes and rivers were not significantly different, but increased with the trophic level index. Redundancy analysis and Mantel analysis showed that Microcystis and Pseudanabaena were potentially dominant contributors to β-cyclocitral and β-ionone in the water column. Structural equation modeling and variation partitioning analysis showed that enhanced nitrate (NO3--N) significantly promoted the production of these compounds. Laboratory experiments demonstrated that inorganic N (NaNO₃) maximized total T&O yields by promoting algal biomass, whereas organic N (urea and glutamic acid) elevated the T&O production per unit biomass by 1.5- to 9.5-fold. Notably, Pseudanabaena exhibited a 2.3-fold higher β-ionone yield than Microcystis, with greater sensitivity to N concentrations. Our study highlights the critical role of nitrogen pollution, both source and concentration, in the production of T&O compounds by phytoplankton and provides reference data for managing T&O issues in rivers and shallow lakes.

Norisoprenoids↗
PubMed1978

A Zoogloea sp. associated with blooms of Anabaena flos-aquae.

Bacteria were found attached to the heterocysts of Aphanizomenon flos-aquae and embedded within the mucilage of both anabaena flos-aquae and Microcystis aeruginosa in freshwater plankton. Electron microscopy of thin sections preceding the peak of an Anabaena flos-aquae bloom showed that the density of bacterial cells was 7.4 X 10(5) cells/ml in the planktonic macroenvironment and 2.6 X 10(11) cells/ml within the microenvironment of cyanobacterial mucilage. The bacteria occurred in aggregates and isolation required that these be dispersed by homogenizing at 50 000 rpm with glass beads. This procedure yielded a single bacterial isolate from blooms of Anabaena flos-aquae during 2 consecutive years. The isolate was flagellated, catalase- and oxidase-positive. Gram-negative, and rod-shaped to pleomorphic. Observation that the isolate required a pH greater than 8 for consistent growth, could not grow alone on liquid media but could grow alone on the corresponding solid media, could grow in liquid media only in the presence of Anabaena, formed tough mucilagenous colonies on solid media only in the presence of Anabaena extract, and rapidly assimilated but did not respire extracellular 14C-labelled organic matter produced by Anabaena suggested that the occurrence of the bacterium in cyanobacterial mucilage was not coincidental but reflected an obligatory bacterial requirement for the biological or physicochemical microenvironment of the mucilage. The bacterial isolate occurred in three growth forms. Either as a planktonic swarmer cell (which showed a positive chemotactic response to the cyanobacterium) embedded in cyanobacterial mucilage, or embedded in its own mucilage derived, in part, from a low molecular weight (below 1300) carbohydrate secreted by the cyanobacterium. These cultural, biochemical, and ecological characteristics suggest that the isolate is a new species in the genus Zoogloea and of potential importance in phytoplankton ecology.

Cyanobacteria↗
PubMed1979

[Immunostimulating activity of the lipopolysaccharides of blue-green algae].

The whole cells of blue-gree algae and lipopolysaccharides isolated from these cells were shown to stimulate the production of macro-(mainly) and microglobulin antibodies in rabbits. The macro- and microphage indices in rabbits increased significantly after the injection of LPS isolated from blue-green algae 24--48 hours before infecting the animals with a virulent Y. pseudotuberculosis strain. Besides, the inhibiting action of this strain on the migration of phagocytes to the site of infection was abolished immediately after the injection. The use of the indirect hemagglutination test allowed to prove the absence of close antigenic interrelations between blue-green algae and the following organisms: Spirulina platensis, Microcystis aeruginosa, Phormidium africanum and P. uncinatum.

Adjuvants, Immunologic↗
PubMed1975

[Biolgical problems of a manmade small lake (author's transl)].

In connection with an intensive hygienic supervision of public bathing facilities and the attempts to draw up a law on bathing hygiene, the lack of contamination standards for small lakes available to the public for bathing was particularly conspicuous. In addition to the current chemical and bacteriological routine examinations, a small bathing lake with a surface area of 3000 square metres containing about 7000 m3 of water and which has been in existence for over 10 years was objected to extensive biological investigations during the months July to September. The results of the analysis show a relatively constant hydrogen ion concentration (pH 8.2), small variations in electrolytic conductivity and 8 German degrees of hardness. The mean phosphourus level was 60 mug/L. the orthophosphate levels ranged between 5.2 and 18.5 mug/L. Oxygen saturation during the entire summer months was more than 100%. Altogether, 49 different kinds of phytoplankton- and 12 kinds of zooplancton-organisms were identified. The total biological mass of phytoplancton organisms was between 8.5 and 16 mg fresh weight per litre, bacterial biomass varied between 4.5 and 9.5 mg/l. Particularly striking for summer conditions was the high proportion of Cyclotella- and Synedra species among the phytoplancton mass, while the algal-bloom producing Microcystis flos aquae attained a maximum proportion of 15%. In spite of the great variety of its forms, green algae were present in small numbers only. The comparison of the described findings with the trophic-systems of HUTCHINSON, NYGAARD and RAWSON indicated an eutrophic type of lake; classification according to the types of the various saprobic systems of NAUMANN, KOLKWITZ and LIEBMANN yielded a predominantly beta-mesosaprobic type of lake. The investigations described show, however, that this is probably a lake rich in nutrients, but that there is a relatively stable biological equilibrium and that, consequently, there is no further threat of progressive eutrophism. Special hygienic parameters, contamination due to visitors and phytoplancton production will be reported in a second communication.

Animals↗