Undibacterium cyanobacteriorum sp. nov., an auxin-producing bacterium isolated from fresh water during cyanobacterial bloom period.

A novel Gram-negative, white-pigmented, and auxin-producing strain, 20NA77.5T, was isolated from fresh water during cyanobacterial bloom period. Pairwise comparison of the 16S rRNA gene sequences showed that strain 20NA77.5T belonged to the genus Undibacterium and exhibited the highest sequence similarity to the type strains of Undibacterium danionis (98.00%), Undibacterium baiyunense (97.93%), Undibacterium macrobrachii (97.92%), and Undibacterium fentianense (97.71%). The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain 20NA77.5T and its related type strains were below 79.93 and 23.80%, respectively. The predominant fatty acids (> 10% of the total fatty acids) were C16:0 and summed feature 3 (C16:1ω7c and/or C16:1ω6c). The genomic DNA G + C content of strain 20NA77.5T was found to be 48.61%. Based on the phylogenetic distinctness, chemotaxonomic features, and phenotypic features, strain 20NA77.5T is considered to represent a novel species of the genus Undibacterium, for which the name Undibacterium cyanobacteriorum sp. nov is proposed. The type strain is 20NA77.5T (= KCTC 8005T = LMG 33136T).

Reservoir regulation-induced variations in water level impacts cyanobacterial bloom by the changing physiochemical conditions.

Gaining insight into the impact of reservoir regulation on algal blooms is essential for comprehending the dynamic changes and response mechanisms in the reservoir ecosystem. In this study, we conducted a comprehensive field investigation linking physiochemical parameters, and phytoplankton community to different water regimes in the Three Gorges Reservoir. Our aim was to explore the effects of reservoir regulation on the extinction of cyanobacterial blooms. The results showed that during the four regulatory events, the water levels decreased by 2.02-4.33 m, and the average water velocity increased 68 % compared to before. The average total phosphorus and total nitrogen concentrations reduced by up to 20 %, and the cyanobacterial biomass correspondingly declined dramatically, between 66.94 % and 75.17 %. As the change of water level decline increasing, there was a significant increase of algal diversity and a notable decrease of algal cell density. Additionally, a shift in the dominant phytoplankton community from Cyanobacteria to Chlorophyceae was observed. Our analysis indicated that water level fluctuations had a pronounced effect on cyanobacterial extinction, with hydrodynamic changes resulting in a reduction of cyanobacterial biomass. This research underlined the potential for employing hydrodynamic management as a viable strategy to mitigate the adverse ecological impacts of cyanobacterial blooms, providing a solution for reservoir's eco-environmental management.

Satellite Tracking Reveals the Speed Up of the Lacustrine Algal Bloom Drift in Response to Climate Change.

Satellite evidence indicates a global increase in lacustrine algal blooms. These blooms can drift with winds, resulting in significant changes of the algal biomass spatial distribution, which is crucial in bloom formation. However, the lack of long-term, large-scale observational data has limited our understanding of bloom drift. Here, we have developed a novel method to track the drift using multi-source remote sensing satellites and presented a comprehensive bloom drift data set for four typical lakes: Lake Taihu (China, 2011-2021), Lake Chaohu (China, 2011-2020), Lake Dianchi (China, 2003-2021), and Lake Erie (North America, 2003-2021). We found that blooms closer to the water surface tend to drift faster. Higher temperatures and lower wind speeds bring blooms closer to the water surface, therefore accelerating drift and increasing biomass transportation. Under ongoing climate change, algal blooms are increasingly likely to spread over larger areas and accumulate in downwind waters, thereby posing a heightened risk to water resources. Our research greatly improves the understanding of algal bloom dynamics and provides new insights into the driving factors behind the global expansion of algal blooms. Our bloom-drift-tracking methodology also paves the way for the development of high-precision algal bloom prediction models.

Insights into cyanobacterial blooms through the lens of omics.

Cyanobacteria are oxygen-producing photosynthetic bacteria that convert carbon dioxide into biomass upon exposure to sunlight. However, favorable conditions cause harmful cyanobacterial blooms (HCBs), which are the dense accumulation of biomass at the water surface or subsurface, posing threats to freshwater ecosystems and human health. Understanding the mechanisms underlying cyanobacterial bloom formation is crucial for effective management. In this regard, recent advancements in omics technologies have provided valuable insights into HCBs, which have raised expectations to develop more effective control methods in the near future. This literature review aims to present the genomic architecture, adaptive mechanisms, microbial interactions, and ecological impacts of HCBs through the lens of omics. Genomic analysis indicates that the genome plasticity of cyanobacteria has enabled their resilience and effective adaptation to environmental changes. Transcriptomic investigations have revealed that cyanobacteria use various strategies for adapting to environmental stress. Additionally, metagenomic and metatranscriptomic analyses have emphasized the significant role of the microbial community in regulating HCBs. Finally, we offer perspectives on potential opportunities for further research in this field.

Wind-driven post-bloom dispersion of Microcystis in a large shallow eutrophic lake: A case study in Lake Taihu.

To clarify the wind-driven post-bloom dispersion range of Microcystis, which originally clustered on the water surface, an Individual-Based Model (IBM) of Microcystis movement considering the combined effects of wind and light was developed based on actual hydrodynamic data and Microcystis biomass. After calibrating the effects of hydrodynamics and light, 66 cases of short-term (within a week) post-bloom with satellite images from 2011 to 2017 were simulated. The results showed that there were three short-term post-bloom types: vertical reduction (VR), horizontal reduction (HR) and mixed reduction (MR). For VR type, the cyanobacterial bloom reduction rate was rapid (>160 km2/day), but the dispersion range of Microcystis was limited (<2 km/day), and a larger bloom area was likely to form in the original location when wind speed decreased. For HR type, the cyanobacterial bloom reduction rate was slow (<10 km2/day), but Microcystis exhibited a broad dispersion range (>4 km/day), often leading to smaller, thicker, and longer-lasting cyanobacterial blooms downwind, albeit with a lower probability of occurrence. The characteristics of MR lay between the two aforementioned types.

Succession of particle-attached and free-living bacterial communities in response to microalgal dynamics induced by the biological cyanocide paucibactin A.

Microalgae, including cyanobacteria and eukaryotic algae, are hotspots of primary production and play a critical role in global carbon cycling. However, these species often form blooms that poses a threat to aquatic ecosystems. Although the use of bacteria-derived cyanocides is regarded as an environmentally friendly method for controlling cyanobacterial blooms, only a few studies have examined their potential impact on ecosystems. This study is the first to explore the response of particle-attached (PA) and free-living (FL) bacteria to the dynamics of microalgal communities induced by the biological cyanocide paucibactin A. The microalgal community dynamics were divided into two distinct phases [phase I (days 0-2) and phase II (days 3-7)]. In phase I, paucibactin A caused a sudden decrease in the cyanobacterial concentration. Phase II was characterized by increased growth of eukaryotic microalgae (Scenedesmus, Pediastrum, Selenastrum, and Coelastrum). The stability of the bacterial community and the contribution of stochastic processes to community assembly were more pronounced in phase II than in phase I. The microalgal dynamics triggered by paucibactin A coincided with the succession of the PA and FL bacterial communities. The lysis of cyanobacteria in phase I favored the growth of microbial organic matter degraders in both the PA (e.g., Aeromonas and Rheinheimera) and FL (e.g., Vogesella) bacterial communities. In phase II, Lacibacter, Phycisphaeraceae, and Hydrogenophaga in the PA bacterial community and Lacibacter, Peredibacter, and Prosthecobacter in the FL bacterial community showed increased relative abundances. Overall, the FL bacterial community exhibited greater sensitivity to the two sequential processes compared with the PA bacterial community. These results highlight the need for studies evaluating the impact of biological cyanocides on aquatic ecosystems when used to control natural cyanobacterial blooms.

Biological and Chemical Approaches for Controlling Harmful Microcystis Blooms.

The proliferation of harmful cyanobacterial blooms dominated by Microcystis aeruginosa has become an increasingly serious problem in freshwater ecosystems due to climate change and eutrophication. Microcystis-blooms in freshwater generate compounds with unpleasant odors, reduce the levels of dissolved O2, and excrete microcystins into aquatic ecosystems, potentially harming various organisms, including humans. Various chemical and biological approaches have thus been developed to mitigate the impact of the blooms, though issues such as secondary pollution and high economic costs have not been adequately addressed. Red clays and H2O2 are conventional treatment methods that have been employed worldwide for the mitigation of the blooms, while novel approaches, such as the use of plant or microbial metabolites and antagonistic bacteria, have also recently been proposed. Many of these methods rely on the generation of reactive oxygen species, the inhibition of photosynthesis, and/or the disruption of cellular membranes as their mechanisms of action, which may also negatively impact other freshwater microbiota. Nevertheless, the underlying molecular mechanisms of anticyanobacterial chemicals and antagonistic bacteria remain unclear. This review thus discusses both conventional and innovative approaches for the management of M. aeruginosa in freshwater bodies.

Sphingobium cyanobacteriorum sp. nov., isolated from fresh water.

A novel Gram-stain-negative, yellow-pigmented, short rod-shaped bacterial strain, HBC34T, was isolated from a freshwater sample collected from Daechung Reservoir, Republic of Korea. The results of 16S rRNA gene sequence analysis indicated that HBC34T was affiliated with the genus Sphingobium and shared the highest sequence similarity to the type strains of Sphingobium vermicomposti (98.01 %), Sphingobium psychrophilum (97.87 %) and Sphingobium rhizovicinum (97.59 %). The average nucleotide identity (ANI) and digital DNA-DNA hybridisation (dDDH) values between HBC34T and species of the genus Sphingobium with validly published names were below 84.01 and 28.1 %, respectively. These values were lower than the accepted species-delineation thresholds, supporting its recognition as representing a novel species of the genus Sphingobium. The major fatty acids (>10 % of the total fatty acids) were identified as summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c). The main polar lipids were phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, two phospholipids and two unidentified polar lipids. The respiratory quinone was Q-10. The genomic DNA G+C content of HBC34T was 64.04 %. The polyphasic evidence supports the classification of HBC34T as the type strain of a novel species of the genus Sphingobium, for which the name Sphingobium cyanobacteriorum sp. nov is proposed. The type strain is HBC34T (= KCTC 8002T= LMG 33140T).

Sustainable control of Microcystis aeruginosa, a harmful cyanobacterium, using Selaginella tamariscina extracts.

Eco-friendly reagents derived from plants represent a promising strategy to mitigate the occurrence of toxic cyanobacterial blooms. The use of an amentoflavone-containing Selaginella tamariscina extract (STE) markedly decreased the number of Microcystis aeruginosa cells, thus demonstrating significant anti-cyanobacterial activity. In particular, the Microcystis-killing fraction obtained from pulverized S. tamariscina using hot-water-based extraction at temperatures of 40 °C induced cell disruption in both axenic and xenic M. aeruginosa. Liquid chromatographic analysis was also conducted to measure the concentration of amentoflavone in the STE, thus supporting the potential M. aeruginosa-specific killing effects of STE. Bacterial community analysis revealed that STE treatment led to a reduction in the relative abundance of Microcystis species while also increasing the 16S rRNA gene copy number in both xenic M. aeruginosa NIBR18 and cyanobacterial bloom samples isolated from a freshwater environment. Subsequent testing on bacteria, cyanobacteria, and algae isolated from freshwater revealed that STE was not toxic for other taxa. Furthermore, ecotoxicology assessment involving Aliivibrio fischeri, Daphnia magna, and Danio rerio found that high STE doses immobilized D. magna but did not impact the other organisms, while there was no change in the water quality. Overall, due to its effective Microcystis-killing capability and low ecotoxicity, aqueous STE represents a promising practical alternative for the management of Microcystis blooms.

Modular catalytic activity of nonribosomal peptide synthetases depends on the dynamic interaction between adenylation and condensation domains.

Nonribosomal peptide synthetases (NRPSs) are large multidomain enzymes for the synthesis of a variety of bioactive peptides in a modular and pipelined fashion. Here, we investigated how the condensation (C) domain and the adenylation (A) domain cooperate with each other for the efficient catalytic activity in microcystin NRPS modules. We solved two crystal structures of the microcystin NRPS modules, representing two different conformations in the NRPS catalytic cycle. Our data reveal that the dynamic interaction between the C and the A domains in these modules is mediated by the conserved "RXGR" motif, and this interaction is important for the adenylation activity. Furthermore, the "RXGR" motif-mediated dynamic interaction and its functional regulation are prevalent in different NRPSs modules possessing both the A and the C domains. This study provides new insights into the catalytic mechanism of NRPSs and their engineering strategy for synthetic peptides with different structures and properties.

Field and laboratory studies of fluorescence-based technologies for real-time tracking of cyanobacterial cell lysis and potential microcystins release.

Elevated levels of dissolved microcystins (MCs) in source water due to rapid cell lysis of harmful cyanobacterial blooms may pose serious challenges for drinking water treatment. Catastrophic cell lysis can result from outbreaks of naturally-occurring cyanophages - as documented in Lake Erie during the Toledo water crisis of 2014 and in 2019, or through the application of algaecides or water treatment chemicals. Real-time detection of cyanobacterial cell lysis in source water would provide a valuable tool for drinking water plant and reservoir managers. In this study we explored two real-time fluorescence-based devices, PhycoSens and PhycoLA, that can detect unbound phycocyanin (uPC) as a potential indication of cell lysis and MCs release. The PhycoSens was deployed at the Low Service pump station of the City of Toledo Lake Erie drinking water treatment plant from July 15 to October 19, 2022 during the annual cyanobacteria bloom season. It measured major algal groups and uPC in incoming lake water at 15-min intervals during cyanobacteria dominant and senescence periods. Intermittent uPC detections from the PhycoSens over a three-month period coincided with periods of increasing proportions of extracellular MCs relative to total (intracellular and extracellular) MCs, indicating potential for uPC use as an indicator of cyanobacterial cell integrity. Following exposures of laboratory-cultured MCs-producing Microcystis aeruginosa NIES-298 (120 µg chlorophyll/L) to cyanophage Ma-LMM01, copper sulfate (0.5 and 1 mg Cu/L), sodium carbonate peroxyhydrate (PAK® 27, 6.7 and 10 mg H2O2/L), and potassium permanganate (2.5 and 4 mg/L), appearance of uPC coincided with elevated fractions of extracellular MCs. The PhycoLA was used to monitor batch samples collected daily from Lake Erie water exposed to algaecides in the laboratory. Concurrence of uPC signal and surge of dissolved MCs was observed following 24-h exposures to copper sulfate and PAK 27. Overall results indicate the appearance of uPC is a useful indicator of the onset of cyanobacterial cell lysis and the release of MCs when MCs are present.

Nanoparticles for Mitigation of Harmful Cyanobacterial Blooms.

With the rapid advancement of nanotechnology and its widespread applications, increasing amounts of manufactured and natural nanoparticles (NPs) have been tested for their potential utilization in treating harmful cyanobacterial blooms (HCBs). NPs can be used as a photocatalyst, algaecide, adsorbent, flocculant, or coagulant. The primary mechanisms explored for NPs to mitigate HCBs include photocatalysis, metal ion-induced cytotoxicity, physical disruption of the cell membrane, light-shielding, flocculation/coagulation/sedimentation of cyanobacterial cells, and the removal of phosphorus (P) and cyanotoxins from bloom water by adsorption. As an emerging and promising chemical/physical approach for HCB mitigation, versatile NP-based technologies offer great advantages, such as being environmentally benign, cost-effective, highly efficient, recyclable, and adaptable. The challenges we face include cost reduction, scalability, and impacts on non-target species co-inhabiting in the same environment. Further efforts are required to scale up to real-world operations through developing more efficient, recoverable, reusable, and deployable NP-based lattices or materials that are adaptable to bloom events in different water bodies of different sizes, such as reservoirs, lakes, rivers, and marine environments.

Projected climate change impact on cyanobacterial bloom phenology in temperate rivers based on temperature dependency.

Climate warming is linked to earlier onset and extended duration of cyanobacterial blooms in temperate rivers. This causes an unpredictable extent of harm to the functioning of the ecosystem and public health. We used Microcystis spp. cell density data monitored for seven years (2016-2022) in ten sites across four temperate rivers of the Republic of Korea to define the phenology of cyanobacterial blooms and elucidate the climatic effect on their pattern. The day of year marking the onset, peak, and end of Microcystis growth were estimated using a Weibull function, and linear mixed-effect models were employed to analyze their relationships with environmental variables. These models identified river-specific temperatures at the beginning and end dates of cyanobacterial blooms. Furthermore, the most realistic models were employed to project future Microcystis bloom phenology, considering downscaled and quantile-mapped regional air temperatures from a general circulation model. Daily minimum and daily maximum air temperatures (mintemp and maxtemp) primarily drove the timing of the beginning and end of the bloom, respectively. The models successfully captured the spatiotemporal variations of the beginning and end dates, with mintemp and maxtemp predicted to be 24℃ (R2 = 0.68) and 16℃ (R2 = 0.35), respectively. The beginning and end dates were projected to advance considerably in the future under the Representative Concentration Pathway 2.6, 4.5, and 8.5. The simulations suggested that the largest uncertainty lies in the timing of when the bloom ends, whereas the timing of when blooming begins has less variation. Our study highlights the dependency of cyanobacterial bloom phenology on temperatures and earlier and prolonged bloom development.

ß-cyclocitral, a novel AChE inhibitor, contributes to the defense of Microcystis aeruginosa against Daphnia grazing.

ß-cyclocitral is one of the major compounds in cyanobacterial volatile organic compound (VOCs) and can poison other aquatic organisms. To investigate the effect of ß-cyclocitral on cyanobacterial-grazer interactions, Daphnia sinensis was fed Microcystis aeruginosa and exposed to ß-cyclocitral. Our present study demonstrated that M. aeruginosa could significantly inhibit D. sinensis grazing. And the grazing inhibition by Microcystis aeruginosa results from the suppression of feeding rate, heart rate, thoracic limb activity and swimming speed of D. sinensis. In addition, M. aeruginosa could also induce intestinal peristalsis and emptying in D. sinensis. Interestingly, our present study found that the exposure to ß-cyclocitral could mimic a range of phenotypes induced by M. aeruginosa in D. sinensis. These results suggested that M. aeruginosa could release ß-cyclocitral to inhibit Daphnia grazing. To further examine the toxic mechanism of ß-cyclocitral in Daphnia, several in vivo and in vitro experiments displayed that ß-cyclocitral was a novel inhibitor of acetylcholinesterase (AChE). It could induce the accumulation of acetylcholine (ACh) by inhibiting AchE activity in D. sinensis. High level of endogenous Ach could inhibit feeding rate and induce intestinal peristalsis and emptying in D. sinensis.

Dynamics of the benthic and planktic microbiomes in a Planktothrix-dominated toxic cyanobacterial bloom in Australia.

Cyanobacterial blooms are a concerning issue that threaten ecosystems, ecology and animal health. Bloom frequency has increased tremendously in recent times due to pollution, eutrophication of waterways, climate change, and changes in microbial community dynamics within the aquatic environment. Information about the spatiotemporal variation in microbial communities that drive a cyanobacterial bloom is very limited. Here, we analysed the spatiotemporal diversity and composition of bacterial communities, with a focus on cyanobacteria, during the bloom phase in a natural reservoir in Eastern Australia using high throughput amplicon sequencing. Sampling points and season had no influence on the richness and evenness of microbial communities during the bloom period, however some compositional differences were apparent across the seasons. Cyanobacteria were highly abundant during summer and autumn compared to winter and spring. The dominant cyanobacterial taxa were Planktothrix, Cyanobium and Microcystis and were found to be significantly abundant during summer and autumn. While cyanobacterial abundance soared in summer (25.4 %), dominated by Planktothrix (12.2 %) and Cyanobium (8.0 %), the diversity was highest in autumn (24.9 %) and consisted of Planktothrix (7.8 %), Nodularia (5.3 %), Planktothricoides (4.6 %), Microcystis (3.5 %), and Cyanobium (2.3 %). The strongly correlated non-photosynthetic Gastranaerophilales found in the sediment and water, suggested vertical transmission from the animal gut through faeces. To our knowledge, this is the first report of Planktothrix-driven toxic cyanobacterial bloom in Australia. Our study expands current understanding of the spatiotemporal variation in bacterial communities during a cyanobacterial bloom and sheds light on setting future management strategies for its control.

Lake Avernus Has Turned Red: Bioindicator Monitoring Unveils the Secrets of "Gates of Hades".

Lake Avernus is a volcanic lake located in southern Italy. Since ancient times, it has inspired numerous myths and legends due to the occurrence of singular phenomena, such as coloring events. Only recently has an explanation been found for them, i.e., the recurring color change over time is due to the alternation of cyanobacterial blooms that are a consequence of natural nutrient inputs as well as pollution resulting from human activities. This current report specifically describes the red coloring event that occurred on Lake Avernus in March 2022, the springtime season in this region of Italy. Our innovative multidisciplinary approach, the 'Fast Detection Strategy' (FDS), was devised to monitor cyanobacterial blooms and their toxins. It integrates remote sensing data from satellites and drones, on-site sampling, and analytical/bioinformatics analyses into a cohesive information flow. Thanks to FDS, we determined that the red color was attributable to a bloom of Planktothrix rubescens, a toxin-producing cyanobacterium. Here, we report the detection and identification of 14 anabenopeptins from this P. rubescens strain, seven of which are known and seven are newly reported herein. Moreover, we explored the mechanisms and causes behind this cyclic phenomenon, confirming cyanobacteria's role as reliable indicators of environmental changes. This investigation further validates FDS's effectiveness in detecting and characterizing cyanobacterial blooms and their associated toxins, expanding its potential applications.

Cyanosphere Dynamic During Dolichospermum Bloom: Potential Roles in Cyanobacterial Proliferation.

Under the effect of global change, management of cyanobacterial proliferation becomes increasingly pressing. Given the importance of interactions within microbial communities in aquatic ecosystems, a handful of studies explored the potential relations between cyanobacteria and their associated bacterial community (i.e., cyanosphere). Yet, most of them specifically focused on the ubiquitous cyanobacteria Microcystis, overlooking other genera. Here, based on 16s rDNA metabarcoding analysis, we confirmed the presence of cyanosphere representing up to 30% of the total bacterial community diversity, during bloom episode of another preponderant cyanobacterial genus, Dolichospermum. Moreover, we highlighted a temporal dynamic of this cyanosphere. A sPLS-DA model permits to discriminate three important dates and 220 OTUs. With their affiliations, we were able to show how these variations potentially imply a turnover in ecological functions depending on bloom phases. Although more studies are necessary to quantify the impacts of these variations, we argue that cyanosphere can have an important, yet underestimated, role in the modulation of cyanobacterial blooms.

Long-term acclimation to warming improves the adaptive ability of Microcystis aeruginosa to high temperature: Based on growth, photosynthetic activity, and microcystin production.

Gradually warming of water bodies caused by climate change is expected to intensify the expansion of Microcystis blooms causing a series of severe problems in waters. However, most predictions about global warming further promoting the dominance of Microcystis are dependent on the strains only experiencing short-term acclimation to high temperature. It still remains unknown whether long-term warming acclimation improves the adaptive ability of Microcystis to high temperature. The present study used Microcysits aeruginosa maintained at 25 °C, short- and long -term acclimated at 30 °C to explore the above knowledge gaps. The results showed that: (1) The growth rate of long-term warming acclimated M. aeruginosa was significantly enhanced, compared with those of low temperature cultured and short-term warming acclimated ones; (2) A faster decline rate of photosynthetic activity during growth phase and a higher ultimately stable photosynthetic activity during stationary phase of M. aeruginosa were caused by longer warming acclimation time; (3) high temperature reduced the microcystin production of long-term warming acclimated M. aeruginosa compared to that of low temperature cultured M. aeruginosa; (4) Warming acclimation time improved the driving effect of photosynthetic activity on the growth of M. aeruginosa but decreased the restriction ability of growth state to microcystin production of M. aeruginosa at high temperature; (5) Compared to low temperature cultured M. aeruginosa, high temperature improved the driving effect of photosynthetic activity on the growth of long-term warming acclimated M. aeruginosa, but decreased the sensitivity of photosynthetic activities to environmental resources and the regulative ability of microcystin production to photosynthetic activity. These findings indicated that long-term warming acclimation enhanced M. aeruginosa adaptive ability to high temperature and demonstrated the necessity of applying long-term warming acclimated strains in the future studies about the impact of global warming on cyanobacteria.

Damage mechanism of calcium peroxide on Microcystis aeruginosa PCC7806 and its potential application.

Calcium peroxide (CP) is an oxidizing agent that can gradually release hydrogen peroxide (HP) to achieve selective killing of cyanobacteria in water blooms, and reduce the phosphorus content in the water column. Despite the potential of CP for use in cyanobacterial water bloom disposal, there is a lack of research on the mechanism of oxidative damage on cyanobacterial cells by calcium peroxide. Further studies are required to comprehend the underlying scientific principles and potential risks and benefits of applying this approach to cyanobacteria disposal. In this investigation, we employed varying doses of CP for the treatment of Microcystis aeruginosa (M. aeruginosa), which resulted in the following findings: (1) the HP released from CP can damage the photosystem II of M. aeruginosa, reduce cell photosynthetic pigment content, intensify the degree of membrane lipid peroxidation, and increase the extracellular protein content; (2) CP significantly increased the soluble extracellular polysaccharide (sEPS) and bound extracellular polysaccharide (bEPS) content of cells (p < 0.05), causing the cells to exist as agglomerates and effectively allowing them to flocculate and precipitate, reducing the turbidity of the water body; (3) The increased dose elevated the pH and calcium ions significantly decreased the orthophosphate content, resulting in an increase in extracellular alkaline phosphatase activity, but possibly increasing the total extracellular nitrogen content. These results suggested that CP is an effective chemical algaecide for cyanobacteria, and has the potential to be applied to dispose of cyanobacterial blooms while reducing the phosphorus content of the water column and further inhibiting the growth and proliferation of cells.

Comparative Genome analysis of the Genus Curvibacter and the Description of Curvibacter microcysteis sp. nov. and Curvibacter cyanobacteriorum sp. nov., Isolated from Fresh Water during the Cyanobacterial Bloom Period.

The three Gram-negative, catalase- and oxidase-positive bacterial strains RS43T, HBC28, and HBC61T, were isolated from fresh water and subjected to a polyphasic study. Comparison of 16S rRNA gene sequence initially indicated that strains RS43T, HBC28, and HBC61T were closely related to species of genus Curvibacter and shared the highest sequence similarity of 98.14%, 98.21%, and 98.76%, respectively, with Curvibacter gracilis 7-1T. Phylogenetic analysis based on genome sequences placed all strains within the genus Curvibacter. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between the three strains and related type strains supported their recognition as two novel genospecies in the genus Curvibacter. Comparative genomic analysis revealed that the genus possessed an open pangenome. Based on KEGG BlastKOALA analyses, Curvibacter species have the potential to metabolize benzoate, phenylacetate, catechol, and salicylate, indicating their potential use in the elimination of these compounds from the water systems. The results of polyphasic characterization indicated that strain RS43T and HBC61T represent two novel species, for which the name Curvibacter microcysteis sp. nov. (type strain RS43T =KCTC 92793T=LMG 32714T) and Curvibacter cyanobacteriorum sp. nov. (type strain HBC61T =KCTC 92794T =LMG 32713T) are proposed.