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Algal organic matter (AOM) released from microalgae has high potential effects for water treatment. In response to the complex problem of algal-laden water treatment, this study investigated the characteristics of AOM of Microcystis aeruginosa under long-term exposure to pharmaceuticals and personal care products (PPCPs). The results indicated that algae under low carbamazepine (10 µg/L), and/or diclofenac at any concentration treatment promoted the release of total organic matter, whereas they were inhibited at high carbamazepine and low naproxen exposure. Macromolecular organics of AOM were inhibited when algae were subjected to long-term exposure to carbamazepine at any concentration (0.25–1000 µg/L), and the higher the carbamazepine concentration was, the more seriously macromolecular organics were inhibited. For naproxen and diclofenac treatment, macro- and medium-molecular-weight organics were promoted under high concentration treatment (>1 µg/L), yet they were inhibited under low concentration 10 µg/L). This research had significant effects on algal-laden water treatment containing various PPCPs concentrations as well as the risk assessment of PPCPs in water.

Myriophyllum aquaticum has shown potential allelopathic effects for the biocontrol of cyanobacteria and cyanotoxins. However, the composition of allelochemicals and their biological effects may be influenced by seasonal changes. In this study, we investigated the impact of aqueous extracts of M. aquaticum collected in different seasons on the growth of Microcystis aeruginosa and the concentration of microcystin-LR. Plant samples were extracted using ultrasound cycles in aqueous solutions, and extracts at varying concentrations (0.1, 10, and 100 mg/L) and a control treatment were inoculated with M. aeruginosa, and cell growth was analyzed using a Neubauer chamber. Photosynthetic pigment quantification was used to measure physiological effects and liquid chromatography was used to evaluate the microcystin-LR concentrations. The extracts of plants collected during autumn and winter exhibited higher inhibition of M. aeruginosa growth and a reduction in photosynthetic pigments compared to those collected during spring and summer. These results can be explained by the higher presence of phenolic compounds in the composition of extracts from autumn and winter. Microcystin-LR concentrations were decreased at 10 and 100 mg/L, with the highest efficiency observed in autumn, while spring showed lower efficiency. Our findings suggest that M. aquaticum extracts have inhibitory potential on M. aeruginosa, particularly during the autumn season, making them a promising nature-based solution for the biocontrol of harmful algal blooms.

Atlantic Salmon (Salmo salar) and Chinook Salmon (Oncorhynchus tshawytscha) develop a severe liver disease called net-pen liver disease (NPLD), which is characterized by hepatic lesions that include megalocytosis and loss of gross liver structure. Based on studies where salmonids have been exposed to microcystin (MC) via intraperitoneal injection, NPLD is believed to be caused by MC exposure, a hepatotoxin produced by cyanobacteria. Despite the link between MC and NPLD, it remains uncertain if environmentally relevant MC exposure is responsible for NPLD. To determine if we could produce histopathology consistent with NPLD, we compared the response of Atlantic and Chinook Salmon sub-lethal MC exposure. Salmon were orally gavaged with saline or MC containing algal paste and sampled over 2 weeks post-exposure. Liver lesions appeared by 6 h but were resolved 2-weeks post-exposure; histopathological changes observed in other tissues were not as widespread, nor was their severity as great as those in the liver. There was no evidence for NPLD due to the absence of hepatic megalocytosis. These results indicate that the development of NPLD is not due to acute MC exposure but may be associated with higher MC concentration occurring in food, long-term exposure through drinking of contaminated seawater and/or interactions with other marine toxins.

The utilization of allelochemicals to inhibit algal overgrowth is a promising approach for controlling harmful algal blooms (HABs). Quercetin has been found to have an allelopathic effect on algae. However, its responsive mechanism needs to be better understood. In the present study, the inhibitory effects of different quercetin concentrations on M. aeruginosa were evaluated, and the inhibition mechanisms were explored. The results demonstrated that quercetin significantly inhibited M. aeruginosa growth, and the inhibitory effect was concentration-dependent. The inhibition rate of 40 mg L−1 quercetin on algal density reached 90.79% after 96 h treatment. The concentration of chlorophyll-a (chl-a) in treatment groups with quercetin concentrations of 10, 20, and 40 mg L−1 decreased by 59.74%, 74.77%, and 80.66% at 96 h, respectively. Furthermore, quercetin affects photosynthesis and damages the cell membrane, respiratory system, and enzyme system. All photosynthetic fluorescence parameters, including the maximum photochemical quantum yield (Fv/Fm), the actual photochemical quantum yield (YII), the maximum relative electron transfer rate (rETRmax), and light use efficiency (α), exhibited a downtrend after exposure. After treatment with 20 mg L−1 quercetin, the nucleic acid and protein content in the algal solution increased, and the respiration rate of algae decreased significantly. Additionally, superoxide dismutase (SOD) activities significantly increased as a response to oxidative stress. In comparison, the activities of ribulose 1,5-biphosphate carboxylase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) decreased significantly. These results revealed that quercetin could inhibit M. aeruginosa by affecting its photosynthesis, respiration, cell membrane, and enzymic system. These results are promising for controlling M. aeruginosa effectively.

The eutrophication of aquatic ecosystems caused by rapid human urbanization has led to an increased production of potentially hazardous bacterial populations, known as blooms. One of the most notorious forms of these aquatic blooms are cyanobacteria, which in sufficiently large quantities can pose a hazard to human health through ingestion or prolonged exposure. Currently, one of the greatest difficulties in regulating and monitoring these potential hazards is the early detection of cyanobacterial blooms, in real time. Therefore, this paper presents an integrated microflow cytometry platform for label-free phycocyanin fluorescence detection, which can be used for the rapid quantification of low-level cyanobacteria and provide early warning alerts for potential harmful cyanobacterial blooms. An automated cyanobacterial concentration and recovery system (ACCRS) was developed and optimized to reduce the assay volume, from 1000 mL to 1 mL, to act as a pre-concentrator and subsequently enhance the detection limit. The microflow cytometry platform utilizes an on-chip laser-facilitated detection to measure the in vivo fluorescence emitted from each individual cyanobacterial cell, as opposed to measuring overall fluorescence of the whole sample, potentially decreasing the detection limit. By applying transit time and amplitude thresholds, the proposed cyanobacteria detection method was verified by the traditional cell counting technique using a hemocytometer with an R2 value of 0.993. It was shown that the limit of quantification of this microflow cytometry platform can be as low as 5 cells/mL for Microcystis aeruginosa, 400-fold lower than the Alert Level 1 (2000 cells/mL) set by the World Health Organization (WHO). Furthermore, the decreased detection limit may facilitate the future characterization of cyanobacterial bloom formation to better provide authorities with ample time to take the appropriate actions to mitigate human risk from these potentially hazardous blooms.

Cyanobacteria are rich sources of secondary metabolites and have the potential to be excellent industrial enzyme producers. β-glucosidases are extensively employed in processing biomass degradation as they mediate the most crucial step of bioconversion of cellobiose (CBI), hence controlling the efficiency and global rate of biomass hydrolysis. However, the production and availability of these enzymes derived from cyanobacteria remains limited. In this study, we evaluated the β-glucosidase from Microcystis aeruginosa CACIAM 03 (MaBgl3) and its potential for bioconversion of cellulosic biomass by analyzing primary/secondary structures, predicting physicochemical properties, homology modeling, molecular docking, and simulations of molecular dynamics (MD). The results showed that MaBgl3 derives from an N-terminal domain folded as a distorted β-barrel, which contains the conserved His–Asp catalytic dyad often found in glycosylases of the GH3 family. The molecular docking results showed relevant interactions with Asp81, Ala271 and Arg444 residues that contribute to the binding process during MD simulation. Moreover, the MD simulation of the MaBgl3 was stable, shown by analyzing the root mean square deviation (RMSD) values and observing favorable binding free energy in both complexes. In addition, experimental data suggest that MaBgl3 could be a potential enzyme for cellobiose-hydrolyzing degradation.

Gut microbes play a critical role in helping hosts adapt to external environmental changes and are becoming an important phenotype for evaluating the response of aquatic animals to environmental stresses. However, few studies have reported the role that gut microbes play after the exposure of gastropods to bloom-forming cyanobacteria and toxins. In this study, we investigated the response pattern and potential role of intestinal flora in freshwater gastropod Bellamya aeruginosa when exposed to toxic and non-toxic strains of Microcystis aeruginosa, respectively. Results showed that the composition of the intestinal flora of the toxin-producing cyanobacteria group (T group) changed significantly over time. The concentration of microcystins (MCs) in hepatopancreas tissue decreased from 2.41 ± 0.12 on day 7 to 1.43 ± 0.10 μg·g−1 dry weight on day 14 in the T group. The abundance of cellulase-producing bacteria (Acinetobacter) was significantly higher in the non-toxic cyanobacteria group (NT group) than that in the T group on day 14, whereas the relative abundance of MC-degrading bacteria (Pseudomonas and Ralstonia) was significantly higher in the T group than that in the NT group on day 14. In addition, the co-occurrence networks in the T group were more complex than that in the NT group at day 7 and day 14. Some genera identified as key nodes, such as Acinetobacter, Pseudomonas, and Ralstonia, showed different patterns of variation in the co-occurrence network. Network nodes clustered to Acinetobacter increased in the NT group from day 7 to day 14, whereas the interactions between Pseudomonas and Ralstonia and other bacteria almost changed from positive correlations in the D7T group to negative correlations in the D14T group. These results suggested that these bacteria not only have the ability to improve host resistance to toxic cyanobacterial stress by themselves, but they can also further assist host adaptation to environmental stress by regulating the interaction patterns within the community. This study provides useful information for understanding the role of freshwater gastropod gut flora in response to toxic cyanobacteria and reveals the underlying tolerance mechanisms of B. aeruginosa to toxic cyanobacteria.

Freshwater salinization is a growing environmental issue caused by various anthropic or natural factors that lead to changes in water chemistry and physical conditions, affecting the survival and diversity of phytoplankton. In this study, we tested the physiological, morphological and interspecific competition of the freshwater cyanobacterium Microcystis aeruginosa and the green algae Scenedesmus obliquus to salinity stress. Results demonstrated that increasing salinity had a significant negative effect on the growth of M. aeruginosa and S. obliquus. M. aeruginosa showed a decline in growth rate with increasing salinity, while S. obliquus showed a lower growth rate under salinity stress but with no significant difference between the two salinity groups. In cocultures, S. obliquus outcompeted M. aeruginosa, and the displacement was accelerated with increasing salinity. The photosynthetic performance of both algae was affected by salinity, the presence of competitors, and the cultivation time. S. obliquus showed morphological variations under salinity stress and the presence of a competitor. The study suggests that salinity stress and competition can have a significant impact on the growth and performance of algae species. The findings of our study suggest that the salinization of freshwater can impact the interspecific interactions among phytoplankton, which play a crucial role in the functioning of freshwater ecosystems.

Harmful cyanobacterial blooms occur worldwide and pose a great threat to aquatic ecosystems and public health. The application of algicidal bacteria represents an eco-friendly strategy for controlling harmful cyanobacterial blooms; thus, searching for a high efficiency of algicidal bacteria has been becoming an important and continuous task in science. Herein, we identified a bacterial strain coded Streptomyces sp. HY with a highly algicidal activity, and investigated its algicidal efficiency and mechanism against Microcystis aeruginosa. The strain HY displayed high algicidal activity toward Microcystis aeruginosa cells, with a removal rate of 93.04% within 2 days via indirect attack. Streptomyces sp. HY also showed the ability to lyse several genera of cyanobacterial strains, including Dolichospermum, Pseudanabaena, Anabaena, and Synechocystis, whereas it showed a minor impact on the green alga Scenedesmus obliquus, demonstrating its selectivity specially for targeting cyanobacteria. Its algicidal mechanism involved damages to the photosynthesis system, morphological injury of algal cells, oxidative stress, and dysfunction of the DNA repair system. Furthermore, HY treatment reduced the expression levels of genes (mcyB and mcyD) related to microcystin biosynthesis and decreased the total content of microcystin-leucine-arginine by 79.18%. Collectively, these findings suggested that the algicidal bacteria HY is a promising candidate for harmful cyanobacterial bloom control.

Occurrence of large-scale harmful algal blooms (HABs) in our reservoirs and water bodies threaten both quality of our drinking water and economy of aquaculture immensely. Hence, rapid removal of HAB biomass during and after a bloom is crucial in protecting the quality of our drinking water and preserve our water resources. We reported here a rapidly deployable algae cleaning system based on a high-capacity high-throughput (HCHT) spiral blade continuous centrifuge connected with inlet and effluent water tanks and a series of feed-in and feed-out pumps as well as piping, all fitted into a standard 20 feet metal shipping container. The system separates algal biomass from algae-laden water with a maximum flow rate of 4000 L/h and a centrifugal force of 4500× g. Cells collected by the system are still intact due to the low centrifugal force used. We showed that after HCHT centrifugation, cellular contents of HAB biomass were not found in the effluent water, and hence, could be discharged directly back to the water body. Furthermore, the addition of flocculants and chemicals prior to the separation process is not required. The system could operate continuously with proper programmed procedures. Taken overall, this system offered a much better alternative than the traditional flocculation- and sonication-based methods of HAB removal in a freshwater environment. This deployable system is the first of its kind being built and had been field-tested successfully.

In the present study, the effects of nitrogen (N) and phosphorus (P) on the growth of Microcystis aeruginosa and the production of microcystins (MCs) were investigated. The results showed that the growth of M. aeruginosa was not merely determined by N or P, but both nutrients were limiting for the species. Moreover, an excess of N and constant P in the culture medium could stimulate the growth of M. aeruginosa, whereas the growth of the species was inhibited in the culture medium containing excess of P and constant N. The optimal growth of M. aeruginosa was at an N:P ratio of 0.1 with the maximal optical density of 1.197 at 680 nm (OD680), whereas the maximal microcystin-LR (MC-LR) content of 228.2 μg·L−1 observed in the culture medium with an N:P ratio of 5. Interestingly, MC-LR production occurred under conditions of N starvation, thereby suggesting that the growth rate of M. aeruginosa was not related to MC-LR production under conditions of nutrient stress.

Cyanobacterial blooms and their toxigenic potential threaten freshwater resources worldwide. In Atlantic Canada, despite an increase of cyanobacterial blooms in the last decade, little is known about the toxigenic potential and the taxonomic affiliation of bloom-forming cyanobacteria. In this study, we employed polymerase chain reaction (PCR) and metagenomic approaches to assess the potential for cyanotoxin and other bioactive metabolite production in Harvey Lake (oligotrophic) and Washademoak Lake (mesotrophic) in New Brunswick, Canada, during summer and early fall months. The PCR survey detected the potential for microcystin (hepatotoxin) and anatoxin-a (neurotoxin) production in both lakes, despite a cyanobacterial bloom only being visible in Washademoak. Genus-specific PCR associated microcystin production potential with the presence of Microcystis in both lakes. The metagenomic strategy provided insight into temporal variations in the microbial communities of both lakes. It also permitted the recovery of a near-complete Microcystis aeruginosa genome with the genetic complement to produce microcystin and other bioactive metabolites such as piricyclamide, micropeptin/cyanopeptolin, and aeruginosin. Our approaches demonstrate the potential for production of a diverse complement of bioactive compounds and establish important baseline data for future studies of understudied lakes, which are frequently affected by cyanobacterial blooms.

In the paper, to better understand the dynamic relationship between Microcystis aeruginosa and filter-feeding fish, we have constructed a new aquatic ecological model to describe the aggregation effect of Microcystis aeruginosa. Mathematical theory works mainly investigated the critical threshold condition through the discovery of transcritical bifurcation, saddle–node bifurcation, Hopf bifurcation and Bogdanov–Takens bifurcation. The numerical simulation works mainly revealed that Microcystis aeruginosa aggregation effect has played an important role in the dynamic relationship with the aid of bifurcation analysis, which also in turn proved the validity of theoretical derivation. The results showed that if the Microcystis aeruginosa aggregation area became larger and larger, and exceeded a critical threshold, the filter-feeding fish would eventually go extinct. Furthermore, it should be stressed that Microcystis aeruginosa aggregation can effectively control the feeding dynamic behavior of filter-feeding fish and provide shelter from predators. Finally, all these results were expected to be useful in studying population dynamics of some aquatic ecosystems.

Microcystis aeruginosa is predicted to interact and coexist with diverse broad- and narrow-host-range viruses within a bloom; however, little is known about their affects on Microcystis population dynamics. Here, we developed a real-time PCR assay for the quantification of these viruses that have different host ranges. During the sampling period, total Microcystis abundance showed two peaks in May and August with a temporary decrease in June. The Microcystis population is largely divided into three phylotypes based on internal transcribed sequences (ITS; ITS types I to III). ITS I was the dominant phylotype (66% to 88%) except in June. Although the ITS II and III phylotypes were mostly less abundant, these phylotypes temporarily increased to approximately equivalent abundances of the ITS I population in June. During the same sampling period, the abundances of the broad-host-range virus MVGF_NODE331 increased from April to May and from July to October with a temporary decrease in June, in which its dynamics were in proportion to the increase of total Microcystis abundances regardless of changes in host ITS population composition. In contrast, the narrow-host-range viruses MVG_NODE620 and Ma-LMM01 were considerably less abundant than the broad-host-range virus and generally did not fluctuate in the environment. Considering that M. aeruginosa could increase the abundance and sustain the bloom under the prevalence of the broad-host-range virus, host abundant and diverse antiviral mechanisms might contribute to coexistence with its viruses., アオコ感染性広域・狭域宿主ウイルスの動態 --アオコとウイルスはいかに共存するか--. 京都大学プレスリリース. 2023-02-24.

Current trends in cyanobacterial harmful algal blooms (cHABs) demonstrate increasing risks to human health and the health of aquatic ecosystems around the globe. Expansion of algal blooms, both geographically and temporally, serve to place increasing numbers of freshwater species, including fish, in peril. Microcystis aeruginosa, one of the most common species of bloom-causing cyanobacteria, is capable of producing a vast diversity of biologically active compounds, however Microcystis studies are often dominated by microcystins. How non-microcystin metabolites contribute to Microcystis toxicity, particularly in freshwater fish, has been the subject of a limited, but growing, body of research. To contribute to the bridging of this knowledge gap, my thesis examined the effects of extracellular metabolites produced by M. aeruginosa on in vitro fish cell lines derived from multiple tissues of the freshwater salmonid rainbow trout (Oncorhynchus mykiss), incorporating not only changing metabolite production over the lifespan of a bloom, but also toxicity in the absence of microcystins. I found that non-microcystin-producing strains of M. aeruginosa, commonly referred to as ‘non-toxic,’ were capable of producing and releasing metabolites that significantly reduced the viability of cell lines derived from the brain, gills, and milt of fish. Impairment of reproduction can seriously impact the sustainability of a population. In examining the effects of ‘non-toxic’ extracellular metabolites on gene expression, I found that these cyanobacterial mixtures were able to dysregulate genes associated with reproduction and steroidogenesis in brain and gonadal tissue-derived cell lines. While the correlation between in vitro cytotoxic and sub-lethal effects and in vivo ramifications requires further investigation, overall, this thesis highlights the need to integrate non-microcystin metabolites into risk assessments for freshwater systems and fish species impacted by Microcystis algal blooms.

Murray-Darling Freshwater Research CentreMDFRC item.The properties of Daphnia carinata King as a grazer for use in biomanipulation trials were investigated. Mesocosm experiments suggested that in water from a lake where D. carinata was scarce, phytoplankton was nutrient-limited and the manipulated biomass of zooplankton had no effect on total chlorophyll a, whereas in water from a lake where D. carinata was dominant, nutrients were not limiting and total chlorophyll a was negatively correlated with the manipulated biomass of zooplankton. When offered lake phytoplankton in feeding trials, D. carinata consumed all items present, including colonies of cyanobacteria and long filaments of diatoms. In large outdoor tanks with natural plankton, the biovolume of prokaryotic ultraplankton (possible predecessors of cyanobacterial blooms) was consistently reduced in the presence of D. carinata. There was no evidence of an adverse effect of single-celled Microcystis aeruginosa containing the peptide toxin microcystin-LR on D. carinata grazing rates or survival. Different concentrations of microcystin-LR in solution covering the range of toxicities observed during M. aeruginosa blooms (5-500 nM) had no effect on D. carinata grazing. The suppression of phytoplankton biomass by D. carinata grazing is one of several possible mechanisms that might be considered for biomanipulation in Australia.

Attached bacteria of Microcystis play important roles in the occurence, outbreak and decline of Microcystis water blooms. In this study, a novel actinobacterium, designated strain JXJ CY 38 T, was isolated from the culture mass of Microcystis aeruginosa FACHB-905 (MAF), collected from Lake Dianchi, south-west, China. The strain was found to be a Gram-stain positive, short rod, catalase positive and oxidase negative. The isolate was found to be able to grow at 5.0-38.0 °C (optimum, 28.0 °C), pH 4.0-11.0 (optimum, 7.0-8.0) and 0-3.0% (w/v, optimum, 0%) NaCl. Based on 16S rRNA gene sequences, strain JXJ CY 38 T shows high similarities to Nocardioides furvisabuli JCM 13813 T (99.0%) and Nocardioides alpinus JCM 18960 T (98.7%), and less than 98.2% similarities to other members of the genus. The major cellular fatty acids (> 10.0%) were identified as iso-C16:0 (23.6%), C18:1ω9c (18.2%) and C17:1ω8c (16.4%), while the predominant menaquinone was found to be MK-8 (H4). The diagnostic diamino acids in the cell wall peptidoglycan were identified as aspartic acid, glutamic acid, glycine and alanine, with mannose, ribose and arabinose as whole cell sugars. The polar lipids were found to be diphosphatidylglycerol, phosphatidylglycerol, a phospholipid, phosphatidylcholine and an unidentified lipid. The DNA G + C content was determined to be 71.3%. The digital DNA-DNA hybridization and average nucleotide identity values between strain JXJ CY 38 T and the type strains N. furvisabuli JCM 13813 T and N. alpinus JCM 18960 T were 49.4% and 37.7%, and 92.0% and 83.4%, respectively. On the basis of the above taxonomic data and differences in physiological characteristics from the closely related type strains, strain JXJ CY 38 T was determined to represent a novel species of genus Nocardioides, for which the name Nocardioides lacusdianchii sp. nov. is proposed. The type strain is JXJ CY 38 T (= KCTC 49381 T = CGMCC 4.7665 T). Strain JXJ CY 38 T apparently exhibits complex effects on the interactions between MAF and other attached bacteria, including the promotion or inhibition of the growth of MAF and bacteria, and the synthesis and release of microcystins by MAF.

Cyanobacterial blooms are increasingly common in aquatic environments worldwide. These microorganisms cause concern due to their ability to produce cyanotoxins. Aquatic organisms, especially zooplankton, are exposed to cyanobacterial toxins by different routes, depending on the bloom phase. During cyanobacterial dominance, zooplankton is exposed to cyanotoxins through the ingestion of cyanobacterial cells, while at the bloom senescence, dissolved toxins are the most representative route. In this study, we assessed the effects of a microcystin-producing strain of Microcystis aeruginosa (NPLJ-4) on clones of the tropical small cladocerans Macrothrix spinosa (two clones) and Ceriodaphnia cornuta (one clone) exposed to intact cells and aqueous cell crude extracts. Short-term toxicity assays and life-table experiments were performed to assess the effects of the toxic M. aeruginosa on the survival and life history of the cladocerans. In the short-term toxicity assay, we found that cladocerans were more affected by intact cells. Both clones of M. spinosa were more affected when exposed to intact cells, while C. cornuta displayed about 5-fold more resistance. On the other hand, crude extracts had a low impact on cladocerans’ survival. Also, we observed a significant decrease in survival, fecundity, and growth of animals exposed to sublethal and environmentally relevant concentrations of M. aeruginosa cellular biomass. However, even at high concentrations of dissolved microcystins, the crude extract did not have significant effects on the life history parameters of the cladocerans. Although they can be found during cyanobacterial bloom events, small-bodied cladocerans are still affected by toxic Cyanobacteria depending on the exposure route.

Hydroclimatic and anthropogenic factors in climate change scenarios contribute to ecological changes of harmful cyanobacterial algal blooms in lakes. This study describes the variability of the bathymetric and temporal distribution of cyanobacterial communities in a deep oligotrophic lake. An increase of two to nine in the detection of CyanoHABs potential was observed, likely linked to nitrogen contributions to Lake Rupanco during the last 36 years related to changes in land use and the cultivation of salmonids. We recorded an unusual bloom of Microcystis aeruginosa in winter, 2017 at 30 m during the total mixing period of the lake, associated with the highest N/P index (16.24), the increase of total nitrogen (75 μg/L) and climatic conditions that favored the availability of nitrogen of this cyanobacterium. This study provides information on the causes of increased cyanobacteria in a deep oligotrophic lake. Long-term information on the composition of cyanobacterial communities is very helpful in determining ecological changes.

Increasing temperature and varying light quality can favor the formation of blooms of toxin-producing cyanobacteria. With respect to light quality, increasing type-B ultraviolet radiation (UV-B) causes cellular damage with cascading effects at different levels of biological systems. This study aimed to evaluate the combined effects of light intensity, UV-B, and increasing temperature on the circadian rhythm of production and release of microcystins (MCs) as well as the expression of mcy genes (mcyA, mcyD, and mcyE) and internal H2O2 formation of Microcystis aeruginosa. Microcystis aeruginosa was exposed to UV-B (0.8 W m−2) in 24-h cycles (12 h light:12 h dark) at 23, 25, and 30 °C combined with 30 or 50 µmol photons m−2 s−1. Samples were collected every 4 h during each 24-h cycle for MC analyses, evaluation of mcy gene expression by RT-qPCR, and internal H2O2 formation. The combination of 23 and 30 °C with UV-B changed the circadian rhythm of MC production and release and reduced the cyanotoxin concentration per cell quota. mcyD gene expression was 10.75-fold higher at 23 °C and 50 µmol photons m−2 s−1 treatment. However, a 7.55-fold decline in the expression of the mcyE gene occurred at 12 h (light period). The combination of 23 °C with UV-B caused the highest intracellular H2O2 formation. The enhanced expression of genes involved in MC synthesis at midday demonstrated that there is a critical period of stress that signals the toxin-production, which has significant implications for the general well-being of aquatic ecosystems.

Toxic cyanobacteria blooms have been reported in freshwater sources worldwide and may lead to aquatic biota toxin accumulation and trophic chain transfer, resulting in ecological and public health concerns. To assess cyanobacteria effects on microcystin uptake and accumulation and on phosphatase, acethylcholinesterase (AChE) and carboxylesterase (CarbE) enzymatic activities, an in vivo experiment was carried out employing the golden mussel Limnoperna fortunei. These mussels were exposed to a Microcystis aeruginosa NPLJ-4 strain (NPLJ-4) for 48 hours at different cell densities. Subsequently, algal cell counts were carried out and enzymatic activities were assayed. All three enzymes (Phosphatase, AChE and CarbE) were inhibited at the end of the exposure experiment. Mussels exposed to higher in vivo M. aeruginosa densities exhibited microcystin uptake and accumulation. In vitro assays were also carried out, exposing soluble L. fortunei enzyme fractions to M. aeruginosa extracts containing microcystin, and phosphatase inhibition was observed, whereas acetylcholinesterase and carboxylesterase were not inhibited. The results indicate that metabolites other than mycrocystin probably caused the observed in vivo esterase inhibitions, requiring further investigations.

Selective inhibition of photosynthesis is a fundamental strategy to solve the global challenge caused by harmful cyanobacterial blooms. However, there is a lack of specificity of the currently used cyanocides, because most of them act on cyanobacteria by generating nontargeted oxidative stress. Here, for the first time, we find that the simplest β-diketone, acetylacetone, is a promising specific cyanocide, which acts on Microcystis aeruginosa through targeted binding on bound iron species in the photosynthetic electron transport chain, rather than by oxidizing the components of the photosynthetic apparatus. The targeted binding approach outperforms the general oxidation mechanism in terms of specificity and eco-safety. Given the essential role of photosynthesis in both natural and artificial systems, this finding not only provides a unique solution for the selective control of cyanobacteria but also sheds new light on the ways to modulate photosynthesis.

Microcystis is a well-known toxic cyanobacterium in eutrophic environments, and an increasing number of Microcystis blooms have emerged in salty reservoirs and coastal rivers. This study observed that many Microcystis were identified in a coastal river in June 2020. The relative abundance of Microcystis decreased from 81.2 to 10.2% in the sampling sites from a salinity of 0 (Sal. 0) to a salinity of 12 (Sal. 12). Hepatotoxic microcystins (MCs) were identified in the coastal river and its estuary. Of the samples, those with a salinity of 5 (Sal. 5) had the highest concentration of MCs at 7.81 ± 0.67 μg L−1. In a saline water simulation experiment, the results showed that salt inhibited Microcystis (M.) aeruginosa growth, enhanced the activity levels of superoxide dismutase (SOD) and catalase (CAT) and stimulated microcystin production. Transcription analysis showed that the expression levels of the psaB and rbcL genes controlling photosymbiotic processes were downregulated, and capD and csaBgene-related polysaccharide productions were upregulated by salt incubation. Notably, metabolism analysis showed that the total polysaccharides, proteins and small molecular matter, such as sucrose, methionine and N-acetyl-D-glucosamine, in the Microcystis cells increased substantially to resist the extracellular hyperosmotic pressure caused by the high salinity levels in culture. These findings indicate that increased salt in a natural aquatic body shifts the phytoplankton community by influencing the physiological metabolism of cyanobacteria and poses a high risk of microcystin exposure during cyanobacterial blooms in coastal rivers.

Cyanobacteria are photosynthetic microorganisms that compose phytoplankton and therefore have a trophic relationship with zooplankton, which represent an important link for energy flux in aquatic food webs. Several species can form blooms and produce bioactive metabolites known as cyanotoxins. However, the ecological and adaptative role of these toxins are still under debate. Many studies have addressed the cyanotoxins’ function in defense against herbivory when grazing pressure by zooplankton plays a role in phytoplankton top-down control. Thus, the present study evaluated the ecophysiological responses of the cyanobacterial strain Microcystis aeruginosa NPLJ-4 underlying the chemical induced defense against the cladoceran Daphnia gessneri. Exposure to predator infochemicals consisted of cultures established in ASM-1 medium prepared in a filtrate from a culture of adults of D. gessneri at an environmentally relevant density. Daphnia infochemicals promoted a significant increase in toxin production by M. aeruginosa. However, no differences in growth were observed, despite a significant increase in both maximum photosynthetic efficiency and electron transport rate in response to zooplankton. Additionally, there was no significant variation in the production of exopolysaccharides. Overall, although a grazer-induced defense response was demonstrated, there were no effects on M. aeruginosa fitness, which maintained its growth in the presence of Daphnia alarm cues.

Phosphorus (P) has an important role in eutrophication and it is essential to explore the processes and mechanisms of P mobility in natural waters. In this study, laboratory experiments were conducted to simulate the SW system (sediment and water) and SAW system (sediment, algae and water) under four hydrodynamic intensity conditions (static control, 50 rpm, 125 rpm and 200 rpm treatments), to investigate P mobility. Results in SW system showed that, sediment was an important source of P for overlying water, and the released total P (TP) increased with stronger hydrodynamic intensity, when P associated with metal pools (redox-sensitive P [BD-P] and meta-oxides bound P [NaOH-P]) were the most unstable and easier to migrate into the overlying water. Stronger hydrodynamic disturbances could enhance the processes including sediment resuspension, dissolution of particles, and release of P, when P mobility had a close relationship with redox conditions near sediment-water interface (SWI). Therefore, the release of TP, BD-P and NaOH-P from sediment increased and decreased in the control and 50-200 rpm treatments over time. In SAW system, the release of TP significantly increased from sediment comparing to SW system, and the growth of Microcystis aeruginosa could selectively enhance the release of BD-P, NaOH-P, and organic P (OP). Meanwhile, the released P from sediment was quickly accumulated by algal cells. The maximum accumulation ability of P by cells, the highest photosynthetic efficiency and the best growth of M. aeruginosa were observed in 125 rpm treatment. But with excessively strong hydrodynamic intensity (200 rpm treatment), the accumulation ability of P and alkaline phosphatase activity (APA) of M. aeruginosa was suppressed, which might hinder algal utilization of P and inhibit algal growth. Overall, our findings demonstrated the patterns of P mobility in natural ecosystems and could contribute to the understanding of P cycling.

Blooms of Microcystis aeruginosa occur frequently in many freshwater ecosystems around the world, but the mechanism of recovery has not been fully understood. In our previous study, three benthic bacterial species (E.sp013, Ba.spD06, and Ba.spD24) were identified capable of promoting the recruitment of M. aeruginosa. Here, we further investigated the transcriptional response of M. aeruginosa to the benthic bacteria in early phase of recruitment by means of RNA-Seq analysis. In total, 5 803 803 unigenes on average length of 404 bp were obtained from the transcriptome of M. aeruginosa. There were 54 982 unigenes identified as benthic bacteria-responsive unigenes based on the expression level analysis. Results of the protein-protein interaction analysis (PPI) show that the hub genes of the benthic bacteria responsive unigenes mediated network were ribosomal proteins of 30S and 50S, and the most significant functional module of the network was related to the ribosome. Both the unigenes encoding the translation initiation factors (IF-2, IF-3) and elongation factors (lepA, fusA, and tufA) were up-regulated to respond benthic bacteria. Therefore, it indicates that the benthic bacteria have a positive influence on activating the ribosome during the early recovery stage of M. aeruginosa.

Microcystin, a cyanotoxin produced by Microcystis aeruginosa growing in eutrophic waters, can promote liver tumors in people ingesting contaminated water. To date, water treatment systems have not been effective in removing or degrading these cyanotoxins. In this work, we investigated the inhibitory activity of surfactants on the growth of M. aeruginosa and their application to extract the intracellular produced cyanotoxins. The experiments involving growth inhibition and extraction of cyanotoxins were carried out using the non-biodegradable surfactant cetyl trimethyl ammonium bromide (CTAB) in addition to other biodegradable surfactants. These were Tween 80 and surfactants derived from amino acids and peptides, respectively, from arginine, SDA, and hydrolyzed peptone, SDP. We demonstrated that the tested surfactants could be used to inhibit the growth of M. aeruginosa. At this point, CTAB and SDA proved to be the most competent surfactants in reducing cyanobacterial growth. Moreover, microcystins have been successfully removed from the water employing a cloud point extraction protocol based on the use of these surfactants and ammonium sulfate.

To investigate the treatment effect of algae biosorbent on heavy metal wastewater, in this paper, the adsorption effect of M. aeruginosa powder on heavy metal ions copper, cadmium and nickel was investigated using the uniform experimental method, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and TG-DSC comprehensive thermal analysis. The experimental results showed that the initial concentration of copper ion solution was 25 mg/L, the temperature was 30 °C, the pH value was 8 and the adsorption time was 5 h, which was the best condition for the removal of copper ions by algae powder adsorption, and the removal rate was 83.24%. The initial concentration of cadmium ion solution was 5 mg/L, the temperature was 35 °C, the pH value was 8 and the adsorption time was 4 h, which was the best condition for the adsorption of cadmium ion by algae powder, and the removal rate was 92.00%. The initial nickel ion solution concentration of 15 mg/L, temperature of 35 °C, pH value of 7 and adsorption time of 1 h were the best conditions for the adsorption of nickel ions by algae powder, and the removal rate was 88.67%. The spatial structure of algae powder changed obviously before and after adsorbing heavy metals. The functional groups such as amino and phosphate groups on the cell wall of M. aeruginosa enhanced the adsorption effect of heavy metal ions copper, cadmium and nickel. Additionally, M. aeruginosa adsorption of heavy metal ions copper, cadmium, nickel is an exothermic process. The above experiments show that M. aeruginosa can be used as a biological adsorbent to remove heavy metals, which lays a theoretical foundation for the subsequent treatment of heavy metal pollution by algae.

The occurrence of cyanobacterial species, especially toxic ones, poses a great threat to coastal and estuary areas. In this study, the toxigenic Microcystis aeruginosa (M. aeruginosa) FACHB-905 was exposed to BG-11 medium with different salinities (1, 4, 7, 10 and 15 ppt) to investigate the physiological responses of this species in terms of oxidative stress, chl a fluorescence and microcystins (MCs) contamination. The results showed that low salinity (≤7 ppt) favored the electron transfer of photosystem II, which promoted the growth and photosynthesis of M. aeruginosa and induced MCs production. However, increased salinity (≥10 ppt) suppressed the growth and photosynthesis of M. aeruginosa and aggravated the oxidative stress of the strain. Salinity of 15 ppt reduced MCs contamination and caused irreversible damage to the photosynthetic system of M. aeruginosa, leading to the lysis and death of algal cells. These results indicated that changes in salinity exerted important regulations on the growth and MCs contamination of the toxic M. aeruginosa, which may provide a reference for the risk assessment of the harmful cyanobacterial species in the coastal and estuary areas.

We compared the demographic variables and bacterivory of two strains of Diaphanosoma mongolianum from two water bodies in Spain, one without Microcystis (Maidevera in Zaragoza) and the other with dense Microcystis (La Albufera of Valencia). We hypothesized that the strain rarely exposed to Microcystis would be unable to grow on this cyanobacterial diet. We fed both strains Monoraphidium caribeum and Microcystis aeruginosa, together and separately, and compared their demographic variables. Monoraphidium caribeum was cultured in the laboratory on a defined medium, while the cyanobacteria were collected from La Albufera and sonicated before feeding the cladocerans (at 0.5 × 106 cells ml−1). We also tested the growth of D. mongolianum on bacterial diets by using seston (0–15 µm), bacterioplankton (0–3 µm) and mixed fractions (3–15 µm), from sieving Lake Albufera. We conducted population growth and life table demography experiments at 25 °C, using the two strains of D. mongolianum. Both strains had r (population growth rate) ranging from 0.05 to 0.3 d−1, on all diets. The r was higher (0.18 d−1) on the 0–15 µm seston compared to the mixed fraction (0.12 d−1) although D. mongolianum also grew well on bacterioplankton (0.16 d−1) alone. The response of the strains collected from two different water bodies was different to the test diets. We found that both strains of D. mongolianum could effectively utilize Microcystis for survival and growth, regardless of previous exposure to the cyanobacteria. The tested cladocerans could also grow well on small sized food particles (0–3 µm and 0–15 µm). Our results explain why D. mongolianum is common in eutrophic water bodies

Aeration is an important measure to prevent cyanobacterial growth in eutrophic lakes and reservoirs. The purpose of this study is to clarify the influence of aeration induced turbulence on growth and competition of Microcystis and Scenedesmus in the presence of sediments with varying particle sizes. Microcystis aeruginosa and Scenedesmus obliquus were selected as the model organisms. Sediments with varying particle sizes were added into mono and mixed cultures of the organisms. In the absence of sediment, both low, and high-intensity aerations (the turbulent dissipation rates were 1.60×10−6 and 1.16×10−5 m2/s3, respectively) promoted the growth of Scenedesmus, but the growth of Microcystis was inhibited particularly obvious under the high-intensity aeration conditions. In the presence of sediment, Scenedesmus was promoted under all aeration conditions, while Microcystis was inhibited. The inhibition rate of Microcystis decreased with the increase of sediment size when treated with low-intensity aeration in the nighttime. The highest inhibition rate of M. aeruginosa (89.2%) was identified under the condition of low-intensity aeration in the nighttime with small sediment addition. Furthermore, our results indicated that the impacts of sediment-induced light intensity reduction on algal growth were insignificant. In the mixed culture, the growth of Microcystis was inhibited by Scenedesmus in all treatments with aeration. Our results provided a theoretical basis for the practice in controlling cyanobacteria by aeration.

The allelochemical 5,4′-dihydroxyflavone (DHF) exerts a strong inhibitory effect against Microcystis aeruginosa TY001. In this study, the effects of DHF on growth, full photosynthetic performance, gene expression, and the antioxidant system of M. aeruginosa were examined to explore the possible damage mechanism. Quantitative real-time polymerase chain reaction analysis revealed downregulated expression of prx and fabZ, two photosynthesis-related genes (psaB and psbA), and a DNA repair gene (recA) on days 3 and 5. The levels of antioxidant enzymes also decreased, including superoxide dismutase, catalase, and peroxidase. Additionally, DHF significantly increased malondialdehyde and reactive oxygen species levels in cells. In conclusion, inhibited photosynthesis and oxidative damage were the main mechanisms by which DHF inhibited M. aeruginosa TY001. This study provides evidence that polyphenolic compounds, such as DHF, may be effective components of aquatic management strategies.

Occurrence of Harmful Algal Blooms (HABs) creates a threat to aquatic ecosystem affecting the existing flora and fauna. Hence, the mitigation of HABs through an eco-friendly approach remains a challenge for environmentalists. The present study provides the genomic insights of Rhizobium strain AQ_MP, an environmental isolate that showed the capability of degrading Microcystis aeruginosa (Cyanobacteria) through lytic mechanisms. Genome sequence analysis of Rhizobium strain AQ_MP unraveled the algal lytic features and toxin degradative pathways in it. Functional genes of CAZymes such as glycosyltransferases (GT), glycoside hydrolases (GH), polysaccharide lyases (PL) which supports algal polysaccharide degradation (lysis) were present in Rhizobium strain AQ_MP. Genome analysis also clarified the presence of the glutathione metabolic pathway, which is the biological detoxification pathway responsible for toxin degradation. The conserved region mlrC, a microcystin toxin-degrading gene was also annotated in the genome. The study illustrated that Rhizobium strain AQ_MP harbored a wide range of mechanisms for the lysis of Microcystis aeruginosa cells and its toxin degradation. In future, this study finds promiscuity for employing Rhizobium strain AQ_MP species for bioremediation, based on its physiological and genomic analysis.

Environment-friendly sound measures with high algal growth inhibition efficiency are required to control and eliminate CyanoHABs. This study examined the effects of protopine on growth, gene expression, and antioxidant system of the M. aeruginosa TY001 and explored possible damage mechanism. The results revealed that higher concentrations of protopine seriously inhibited the growth of M. aeruginosa. Quantitative real-time PCR analysis showed downregulated expression of stress response genes (prx and fabZ), and DNA repair gene (recA) on days 3 and 5. The activities of antioxidant enzymes were also decreased markedly, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Additionally, protopine stress can significantly increase the malondialdehyde (MDA) level in cells. In conclusion, oxidative damage and DNA damage are the main mechanisms of protopine inhibition on M. aeruginosa TY001. Our studies provide evidence that alkaloid compounds such as protopine may have a potential use value as components of aquatic management strategies.

Phytoplankton allelopathic studies have mostly been restricted methodologically, leading to very limited quantitative physiological data. In the present study, investigations were carried out to determine physiological changes that occur during allelopathic interactions between chlorophytes (Chlamydomonas reinhardtii P.A. Dangeard 1888; Selenastrum sp.) and cyanobacteria (Microcystis aeruginosa (Kutzing) Kutzing, Microcystis sp. SR, Anabaena variabilis Kutzing ex Bornet & Flahault 1886) using nylon membrane partitioned chambers. The growth of the cyanobacteria and chlorophytes were both stimulated and inhibited in a species-dependent manner. Among the chlorophytes, the Fv/Fm values of Selenastrum were significantly inhibited by Microcystis LE3 and Anabaena UTEX B377 during co-cultivation. There was a significant change in the Fv/Fm values of Anabaena UTEX B377 during co-cultivation with Chlamydomonas CC-503 and Selenastrum. Total microcystins content of Microcystis LE3 significantly declined during co-cultivation with Chlamydomonas CC-503 and Selenastrum. Nitrogen fixation by Anabaena UTEX B377 was significantly lowered in the presence of Microcystis LE3, Microcystis SR, Chlamydomonas CC-503, and Selenastrum. Antioxidant enzyme activities of the investigated chlorophytes and cyanobacteria were altered during allelopathic interactions with each other. These results revealed that phytoplankton species undergo various physiological changes during allelopathic interactions.

The global expansion of toxic Microcystis blooms, and production of cyanotoxins including microcystins, are an increasing risk to freshwater fish. Differentiating intracellular and extracellular microcystin toxicity pathways (i.e., within and outside of cyanobacterial cells) in fish is necessary to assess the severity of risks to populations that encounter harmful algal blooms in pre-to-postsenescent stages. To address this, adult and juvenile Rainbow Trout (Oncorhynchus mykiss) were, respectively, exposed for 96 h to intracellular and extracellular microcystins (0, 20, and 100 μg L-1) produced by Microcystis aeruginosa. Fish were dissected at 24 h intervals for histopathology, targeted microcystin quantification, and nontargeted proteomics. Rainbow Trout accumulated intracellular and extracellular microcystins in all tissues within 24 h, with greater accumulation in the extracellular state. Proteomics revealed intracellular and extracellular microcystins caused sublethal toxicity by significantly dysregulating proteins linked to the cytoskeletal structure, stress responses, and DNA repair in all tissues. Pyruvate metabolism in livers, anion binding in kidneys, and myopathy in muscles were also significantly impacted. Histopathology corroborated these findings with evidence of necrosis, apoptosis, and hemorrhage at similar severity in both microcystin treatments. We demonstrate that sublethal concentrations of intracellular and extracellular microcystins cause adverse effects in Rainbow Trout after short-term exposure.

The inhibitory mechanisms of artemisinin anti-algae sustained-release granules (AASG) on algal cells at cytoplasmic level were investigated. The results showed that 0.2 g L−1 AASG could effectively inhibit the growth of Microcystis aeruginosa (M.aeruginosa). The stress of 0.2 g L−1 AASG changed the excitation energy distribution pattern of Photosystem II (PSII) of algal cells, which showed the increase of heat dissipation share and the inhibition of physiological activities related to PSII. At the same time, AASG induced a large amount of reactive oxygen species (ROS), which aggravated the membrane lipid peroxidation and caused serious damage to algae cell membrane. AASG also resulted in the decrease of esterase activity and alkaline phosphatase activity (APA) in algal cells. Results showed that AASG inhibited algal growth by exerting adverse effects on PSII, ROS and metabolic activity of M.aeruginosa.

Two immobilization methods (i.e., ice water-soaked using a digital temperature controller vs. freeze-dried using liquid nitrogen) were applied for mass production techniques of TiO2-embedded expanded polystyrene (TiEPS) balls with nanoscale TiO2 particles embedded on EPS balls. No significant changes in crystalline structure of TiO2 nanoparticles embedded on the TiEPS balls were observed during the mass production of TiEPS balls. Greater residuals of freeze-dried TiEPS balls suggested the improved immobilization methods for mass production procedures of TiEPS balls. Although similar growth inhibition between TiEPS balls using two immobilization methods was observed within 10 hrs, both growth and reproduction of M. aeruginosa can be more significantly inhibited by applying the freeze-dried TiEPS balls after 10 hrs. These results were mainly attributed to the difference in exposed surface area of embedded TiO2 nanoparticles which generated various reactive oxygen species peroxidizing and leading to the inactivation and degradation of M. aeruginosa. Relatively greater k value (0.207 day-1) was estimated from freeze-dried TiEPS balls than that (0.089 day-1) from ice water-soaked TiEPS balls, suggesting that both growth and reproduction of M. aeruginosa were effectively inhibited with greater amounts of reactive oxygen species generated from freeze-dried TiEPS balls. Consequently, self-floating freeze-dried TiEPS balls can be readily applied to inhibit the excessive growth of harmful algae in the stagnant water body without the recovery process for long time.

The presence and status of harmful algal blooms (HABs) in Japan are reviewed, revealing a decrease in red tides; however, toxic blooms are found to be increasing in western Japan. Environmentally friendly control strategies against HABs are also compared with integrated agricultural pest management. Very high densities (105–108 CFU/g) of algicidal and growth-inhibiting bacteria were found in biofilm on seagrass and seaweed surfaces and in surrounding coastal seawater. The situation in freshwater ecosystems is similar to coastal seas for toxic cyanobacterium,Microcystis aeruginosa, and aquatic plants. These findings offer new insights into the ecology of influential bacteria and harmful algae, suggesting that protection and restoration of native seagrasses and seaweeds in coastal marine environments should be implemented to suppress HABs. Diatom blooms were successfully induced with bottom sediment perturbation to prevent the occurrence of harmful flagellates such asChattonellaspp. andAlexandrium catenellain the Seto Inland Sea; however, this method requires robust and reproducible verification. “Sato-Umi” is a helpful concept for HAB control in the sea and freshwater ecosystems when adequately managed by people (e.g., appropriate bottom perturbation; protection and restoration of seaweeds, seagrasses, and aquatic plants; application of polycultures of fish, seaweeds, etc.).

Agriculture runoffs and discharge of wastewaters are the major causes of eutrophication. Although eutrophication could promote the thriving of any phytoplankter, harmful algal blooms (HABs) are dominated frequently by cyanobacteria. Currently, HABs dominated by the toxigenic cyanobacterium Microcystis aeruginosa in lakes and reservoirs are the main environmental concerns worldwide. This study aimed to determine how M. aeruginosa (Ma) modifies the population growth of Pseudokirchneriella subcapitata (Ps) and Ankistrodesmus falcatus (Af). Growth kinetics were determined for each species and in the combinations: Ps-Ma, Af-Ma, Af-Ps, and Ps-Af-Ma. At the end of experiments, photosynthetic pigments, phycobiliproteins, and microcystins were quantified. A logistic equation significantly described the growth trend for all of the tested species, enabling the identification of negative effects on early stages in the population growth of co-cultures with the cyanobacterium; in addition, the interaction effects on the growth rate and in the maximum attainable population density were determined. The biomasses of A. falcatus and P. subcapitata were significantly higher when cultured individually than in all of the combinations with the cyanobacterium. The concentrations of chlorophyll a and b, as well as carotenoids, were lower in combined cultures, but phycobiliprotein content in the cultures with M. aeruginosa was not significantly affected. Microcystis aeruginosa negatively affected the growth of the microalgae, but A. falcatus was significantly more inhibited than P. subcapitata; however, microcystin concentrations were significantly reduced in the co-cultures with microalgae. These results could help to explain the displacements of microalgae when cyanobacteria are present, giving rise to cyanobacterial blooms in eutrophic freshwaters.

Many studies have attempted to find measures for control of cyanobacterial harmful algal blooms (cyanoHABs) caused by Microcystis, Anabaena, and other bloom-forming plankton species. We have investigated allelopathic inhibition of the submerged macrophyte Myriophyllum spicatum on four phytoplankton species of two taxonomic groups: Chlorophyta Selenastrum capricornutum, Scenedesmus obliquus, and cyanobacteria Microcystis aeruginosa (different strains for toxic, non-toxic, the North Han River originated (NHR) and colonies) and Anabaena circinalis. Inhibitions of unicellular cyanobacteria M. aeruginosa were over 50% for three consecutive days from the 3rd to the 5th day of the coexistence. M. spicatum even inhibited M. aeruginosa at a high initial concentration (1.1 mg L−1 Chl-a). Moreover, M. aeruginosa in a mixture of four phytoplankton species (S. capricornutum, S. obliquus, M. aeruginosa and A. circinalis) was selectively inhibited by M. spicatum. The inhibition of toxic, non-toxic, and NHR of Microcystis by M. spicatum were not significantly different. Colonial cyanobacteria strains were mostly not inhibited by M. spicatum.

To elucidate the mechanism of succinic acid (SA) inhibition of Microcystis aeruginosa, the chlorophyll fluorescence transients, photosynthesis, photosynthetic electron transport activity, and gene expression of M. aeruginosa were evaluated under various doses of SA. The results demonstrated that, after treatment with 60 mg L-1 SA for 1 h, the chlorophyll fluorescence transients and related parameters changed significantly, indicating that the function and structure of photosynthetic apparatuses of Microcystis were seriously damaged. The initial quantum efficiency α, maximum net photosynthetic rate Pnmax, dark respiration rate Rd, and gross photosynthetic rate decreased to 57%, 49%, 49%, and 46%, respectively, relative to the control. Furthermore, photosystem II (PSII) activity (H2O→p-BQ) and the electron transport activity of H2O→MV and DPC→MV significantly decreased. Real-time PCR analysis revealed that, following incubation with 60 mg L-1 SA for 24 h, the expression level of core protein genes (psbA, psaB, psbD, and psbO) of the photosynthesis centers photosystem I (PSI) and PSII decreased significantly. However, the transcription of gene nblA encoding phycobilisome degradation protein was elevated. The downregulation of the rbcL gene, which encodes the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), resulted in the suppression of CO2 fixation and assimilation. High concentration (60 mg L-1) of SA resulted in damage to oxygen-evolving complex (OEC) and reaction center of PSII, blocking photosynthetic electron transport, thereby lowering the rate photosynthesis and inhibiting the growth of Microcystis. We concluded that inhibition of photosynthesis is an important mechanism of SA inhibition in M. aeruginosa.

The combined effects of increased temperature and solar ultraviolet radiation (UVR, 280–400 nm) on M. aeruginosa cultures was analyzed in terms of cell abundance, reactive oxygen and nitrogen species (ROS/RNS), antioxidant activity of catalase (CAT), superoxide dismutase (SOD), glutathione S transferase (GST), fatty acids (FA) content and lipid damage. After 12 days exposure to high temperature (29 °C), cells were exposed to solar UVR (4 h). Ultraviolet-B radiation (UVBR, 280–315 nm) resulted into low cell abundance, high ROS/RNS and a significant increase in SOD activity with no changes in GST and a decreased CAT activity at control temperature (26 °C). A significant increase in the analyzed enzymatic antioxidants was observed at 29 °C, as a response to avoid ultraviolet-A radiation (UVAR, 315–400 nm) damage. The relative abundance of ω6 FAs was not affected by UVAR while ω3 FA were highly sensitive at 29 °C but unsaturated fatty acids (UFA) peroxidation did not occur. The differential response in FA to high temperature and UVAR results in differences in lipid damage and antioxidants. It was evident that selected UFAs (mostly ω6) play an important role in high temperature adaptation in addition to enzymatic antioxidant increased activity shifting the temperature growth from 26 to 29 °C. Thus, cell death and UFA damage were avoided at high temperature and low solar irradiance thanks to an increased enzymatic antioxidant activity.

Induced water hyacinth with purple roots (PRWH) exerts a significant inhibitory effect on the growth of blue-green algae. Interestingly, its chemical constituents differ from those of wild-type water hyacinth and have not yet been reported. This study aimed to explore the chemical constituents of PRWH and its bioactive components serving as allelopathic agents against blue-green algae. Phytochemical investigation of the bioactive ethyl acetate fraction of a crude methanol extract from PRWH led to the isolation of 56 compounds, including 11 new phenylphenalene derivatives. The structures of these compounds were elucidated by comprehensive analyses through NMR, HRMS, and X-ray techniques. Bioactivity evaluation against Microcystis aeruginosa indicated that compounds 7, 12, 15, 37, 39, 45, and 47 potently inhibited blue-green algae growth.

With the increasing eutrophication of the aquatic environments, cyanobacteria blooms caused certain damage to the animals and plants in the aquatic environments. In this experiment, two species were selected from six species of submerged macrophytes, the experimental conditions were changed to achieve the best inhibitory effect on Microcystis aeruginosa, and oxidative damage analysis was carried out. The experiment results demonstrated that the inhibition rate of Vallisneria natans and Ceratophyllum demersum was nearly 100% at the concentration of 3 g/L after 15 days of anaerobic soaking extract. In addition, the longer the soaking time of the two submerged macrophytes, the weaker the photosynthesis effect, and the lower the chlorophyll fluorescence parameters, the more obvious the inhibition effect on M. aeruginosa. Lipid peroxidation injury of M. aeruginosa could be reflected by malondialdehyde (MDA) concentration. The MDA concentration in the experimental group was significantly higher than the control group. Results showed that V. natans and C. demersum could induce oxidative damage in M. aeruginosa. It was also observed that the secondary metabolites produced by V. natans were mainly fatty acids (e.g., the oxidative acid was 6.92 w/%, and the successful acid was 9.85 w/%) which inhibited M. aeruginosa in gas chromatography-mass spectrometry (GC-MS). The main secondary metabolites in C. demersum were hydroxyl acids (e.g., the 4-hydroxy-3-methoxyphenylacetic acid was 24.33 w/%), which could inhibit the algae through allelopathy. This study provided reference for submerged macrophytes to inhibit M. aeruginosa under different conditions.

The increased production, consumption, and release of antibiotics account for their frequent contamination of aquatic ecosystems and detection in different biological matrices. Several antibiotics affect non-target organisms such as algae, cyanobacteria, zooplankton, and fish, making investigations on them very crucial for the health and maintenance of biodiversity. The impact of broad-spectrum antibiotics like ciprofloxacin (CPX) on toxin-producing and non-toxin-producing cyanobacteria has been poorly investigated. Therefore, the present study investigated the physiological and toxicological effects of CPX on Microcystis aeruginosa EAWAG 198, Microcystis aeruginosa LE3, and Microcystis flos-aquae UTEX-LB 2677. CPX caused a significant (p < 0.05) decrease in the cell densities and chlorophyll-a of the three strains. The antibiotic caused oxidative stress in all the strains, as demonstrated by a significant rise in the levels of intracellular hydrogen peroxide (H2O2) of the treated cultures at 96 h post-exposure. Lipid peroxidation and the activity of the antioxidant enzyme—peroxidase (POD) and glutathione-S-transferase (GST)—of the cultures were significantly (p < 0.05) altered. Exposure to CPX generally stimulated the production of biomolecules such as total proteins, lipids, and total carbohydrates as a function of increasing exposure concentration. The exception to the general trend was M. aeruginosa EAWAG 198, a non-toxin-producing strain, which suffered a significant decline in carbohydrate content during exposure to CPX. This study revealed that environmentally relevant levels of CPX could alter the population dynamics, photosynthesis, biochemical composition, and the general physiology of Microcystis species/strains in aquatic ecosystems.

The cell membrane permeability, morphology, metabolomics, and gene expression of Microcystis aeruginosa under various concentrations of succinic acid (SA) were evaluated to clarify the mechanism of SA inhibition of M. aeruginosa. The results showed that SA caused intracellular protein and nucleic acid extravasation by increasing the cell membrane permeability. Scanning electron microscopy suggested that a high dose of SA (60 mg L−1) could damage the cell membrane and even cause lysis in some cells. Metabolomics result demonstrated that change in intracellular lipids content was the main reason for the increase of cell membrane permeability. In addition, SA could negatively affect amino acids metabolism, inhibit the biosynthesis of nucleotides, and interfere with the tricarboxylic acid (TCA) cycle of algal cells. Furthermore, SA also affected N assimilation and caused oxidative damage to Microcystis. In conclusion, SA inhibits the growth of M. aeruginosa through multisite action.

Secondary metabolites of cyanobacteria and algae released during algal blooms often exhibit toxic effects, but only a small number of the metabolites are the subject of routine analytical screenings. Alternatively, ecotoxicological assays offer a better representation of the overall negative effects. The aim of this work was to compare multiple assays in their sensitivity towards cellular algal organic matter (COM) of the toxin-producing cyanobacterium Microcystis aeruginosa. Multiple endpoints were investigated: mortality, growth inhibition, bioluminescence inhibition, genotoxicity, endocrine-disrupting effects, oxidative stress, and the induction of ethoxyresorufin-O-deethylase (EROD). Three rainbow trout (Oncorhynchus mykiss) cell lines as well as representatives of bacteria, yeasts, algae, vascular plants, and crustaceans were employed, and the results were expressed per mg of dissolved organic carbon (DOC) in the COM. M. aeruginosa COM was toxic to the RTgill-W1, RTG-2, and RTL-W1 cell lines (EC50 values ranging from 0.48 ± 0.02 to 1.9 ± 0.1 mgDOC/L), to the crustacean Thamnocephalus platyurus (LC50 = 20 ± 1 mgDOC/L), and to Lepidium sativum (IC50 = 241 ± 13 mgDOC/L). In contrast, no effect was observed for bacteria and yeasts, and the growth of the alga Desmodesmus subspicatus was even stimulated. No genotoxicity, endocrine-disrupting effects or increase in oxidative stress or EROD activity was detected. The content of six microcystins (MC-LR, MC-RR, MC-YR, MC-LY, MC-LW, and MC-LF), anatoxin-a, cylindrospermopsin, and nodularin in the M. aeruginosa COM was determined by liquid chromatography–tandem mass spectrometry. An artificially prepared mixture of the detected cyanotoxins in the corresponding concentrations did not induce response in the O. mykiss cell lines and T. platyurus, suggesting that other cyanobacterial metabolites are responsible for the toxicity of M. aeruginosa.