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Algicidal bacteria can inhibit the growth of algae or lyse algal cells, thus playing roles in shaping aquatic microbial communities and maintaining the functions of aquatic ecosystems. Nevertheless, our understanding of their diversities and distributions remains limited. In this study, we collected water samples from 17 freshwater sites in 14 cities in China and screened a total of 77 algicidal bacterial strains using several prokaryotic cyanobacteria and eukaryotic algae as target strains. According to their target-specificities, these strains were classified into three subgroups, cyanobacterial algicidal bacteria, algal algicidal bacteria, and broad-target algicidal bacteria, each displaying distinctive compositions and geographical distribution patterns. They are assigned to Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes bacterial phyla, of which Pseudomonas and Bacillus are the most abundant gram-negative and gram-positive genus, respectively. A number of bacterial strains, such as Inhella inkyongensis and Massilia eburnean, are suggested as new algicidal bacteria. The diverse taxonomies, algal-inhibiting abilities and distributions of these isolates have suggested that there are rich algicidal bacterial resources in these aquatic environments. Our results provide new microbial resources for algal-bacterial interaction studies, and shed new insights into how algicidal bacteria can be used in the control of harmful algal blooms, as well as in algal biotechnology. [ABSTRACT FROM AUTHOR]

Since 2007, Ulva prolifera, a green macroalgal species that blooms periodically in the Yellow Sea of China, has caused the world's biggest green tide, which induced harmful ecological impacts and economic losses. When the alga is subject to prolonged exposure to air, it suffers abiotic stresses. To explore the physiological and molecular mechanisms of salt stress, the transcriptome data of U. prolifera at different salinities (30, 50, and 90 psu) were obtained by high-throughput sequencing using the Illumina HiSeq platform, and photosynthetic physiological parameters were also measured. The results showed that a total of 89,626 unigenes were obtained after de novo assembly, of which 60,441 unigenes were annotated in the databases (NR, NT, KO, SWISS-PROT, PFAM, GO, and KOG). GO functional enrichment analysis revealed that the enrichment of differentially expressed genes (DEGs) was mainly in cellular, cell, and binding processes. KEGG metabolic pathway enrichment analysis showed that the most frequently enriched pathways of DEGs included glycolysis, pyruvate metabolism, peroxisome, and fatty acid biosynthesis. In addition, resistance-associated proteins, such as heat-shock proteins, microtubule-associated proteins, ubiquitin-associated proteins, abscisic-acid-signaling-pathway-associated proteins, and antioxidant-related proteins are upregulated under salt stress. Genes associated with photosynthesis and carbon fixation pathways are also upregulated, accompanied by an increase in photosynthetic oxygen release rates. These findings provide a basis for understanding the molecular mechanisms of the response of U. prolifera to salinity change, thus providing a theoretical basis for the analysis of the green tide outbreak mechanism. [ABSTRACT FROM AUTHOR]

Simple Summary: High light stress is one of the main factors affecting the normal growth of Ulva prolifera. The response mechanism of U. prolifera to 12 h of high light stress was explored by the multi-omics method. We found that short-term high light could inhibit the assimilation process of U. prolifera, destroy the cellular structure, and inhibit respiration. Moreover, it was raised by the genes associated with photosynthetic pigment synthesis, optical system I, and electronic transport, and may be able to make up the ATP defects by circulating electronic transport. At the same time, it reduced NADPH production by attenuating photosystem II synthesis. The carbon fixed approach was also transformed from the C3 pathway to the C4 pathway. Revealing the response mechanism of U. prolifera to high light can provide a more theoretical basis for studying the outbreak of green tide of U. prolifera in the Yellow Sea. The main algal species of Ulva prolifera green tide in the coastal areas of China are four species, but after reaching the coast of Qingdao, U. prolifera becomes the dominant species, where the light intensity is one of the most important influencing factors. In order to explore the effects of short-term high light stress on the internal molecular level of cells and its coping mechanism, the transcriptome, proteome, metabolome, and lipid data of U. prolifera were collected. The algae were cultivated in high light environment conditions (400 μmol·m−2·s−1) for 12 h and measured, and the data with greater relative difference (p < 0.05) were selected, then analyzed with the KEGG pathway. The results showed that the high light stress inhibited the assimilation of U. prolifera, destroyed the cell structure, and arrested its growth and development. Cells entered the emergency defense state, the TCA cycle was weakened, and the energy consumption processes such as DNA activation, RNA transcription, protein synthesis and degradation, and lipid alienation were inhibited. A gradual increase in the proportion of the C4 pathway was recorded. This study showed that U. prolifera can reduce the reactive oxygen species produced by high light stress, inhibit respiration, and reduce the generation of NADPH. At the same time, the C3 pathway began to change to the C4 pathway which consumed more energy. Moreover, this research provides the basis for the study of algae coping with high light stress. [ABSTRACT FROM AUTHOR]

The genus Omphalina is an ideal genus for studying the evolutionary mechanism of lichenization. Based on molecular phylogeny using ITS and nuLSU sequences by means of Bayesian and maximum likelihood analyses and morphological examination, combining the existence of green algae in basidiomata stipe and a Botrydina-type vegetative thallus, we described a bryophilous new basidiolichen species, Omphalina licheniformis, from a residential area of Jiangxi Province, China. This finding of unusual new basidiolichen species updated our understanding of the delimitation of Omphalina, indicating that both non-lichen-forming and lichen-forming fungal species are included simultaneously. The presence of algal cells in the basidiomata should receive more attention, as this would be helpful to distinguish more potential basidiolichens and explore the cryptic species diversity. This work provides new insights and evidence for understanding the significance of lichenization during the evolution of Agaricomycetes. [ABSTRACT FROM AUTHOR]

• HCA grouped 7 sampling sites into two groups. • MLR, SVR, RF, XGBoost model predict phytoplankton biomass (ACD) in the MRP. • The RF model outperformed MLR, SVR and XGBoost model in predicting ACD of the MRP. • SHAP method was used to interpret the RF model. • Effect of input variable on model output was analyzed using SHAP in the MRP. The water quality of the Middle Route of the South-to-North Water Diversion Project (MRP) of China is related to the health and safety of about 8500w people. In recent years, multiple occurrences of abnormal algal proliferation in water conveyance channels have posed potential risks to the water quality of diverted water. To clarify the growth situation of phytoplankton and evaluate the response relationships between water environmental parameters and phytoplankton in the MRP, in this study, a long-term monitoring dataset was collected from seven monitoring sites from May 2015 to December 2020 to statistically analyse the spatiotemporal characteristics of planktonic algal cell density (ACD). Based on this, four machine learning models, including multiple linear regression (MLR), support vector regression (SVR), random forest (RF), and extreme gradient boosting (XBGoost), were constructed to predict the ACD, and the SHapely Additive exPlanations (SHAP) method was used to interpret the best prediction model for identifying the response relationship between water environmental parameters and ACD. The results showed that (1) the seven monitoring sites could be divided into two significant groups (i.e., Group I and Group II) by hierarchical clustering analysis (HCA), among which the ACD of Group II was higher than that of Group I. (2) the performance of four prediction models using different evaluation metrics indicated that the RF model surpassed in prediction accuracy compared with the other three models in predicting ACD variations in Group I and Group II. (3) SHAP analysis revealed that the key factors affecting ACD variations in Group I were water temperature (WT), water depth (WD), permanganate index (PI), flow rate (Q) and dissolved oxygen (DO), and the ACD were inhibited when WT was below 23 °C, WD exceeded 6.5 m, and Q was between 100 and 250 m3/s. Additionally, WT, PI, and DO were the most important predictors of ACD in Group II, and ACD were inhibited when WT was below 24 °C, PI was lower than 2.4 mg/L and DO was higher than 9 mg/L. This research provides a theoretical basis and reference for water quality management and algal ecological control of water transfer projects with high spatial heterogeneity. [ABSTRACT FROM AUTHOR]

Bloom-Cyanobacteria can release phosphorus (P) into overlying water during their decline period, thus inevitably providing available P for the next round of bloom. In order to quantitatively evaluate the contribution of cyanobacterial bloom decline to P amounts in Caohai, a typical cyanobacteria-dominated sub-lake in northern Dianchi Lake, the P concentrations in algae during the peak and bottom of cyanobacterial bloom were measured and calculated. Remote sensing monitoring analysis and monthly monitoring data showed that the cyanobacterial bloom in Caohai developed from June, reached its peak in July to August and then declined to its bottom from December to February. The concentrations of different phosphorus forms contained in algal cells were different between the peak and bottom of the cyanobacterial bloom. Total phosphorus (TP) concentration in algae (TP-A) were higher in summer than in winter, while the TP content per unit Chl-a in winter was much larger than in summer. The annual released TP was approximately 24.12 tons in 2016, and its potential contribution to TP and Ortho-P in water body of Caohai was around 0.958 and 0.647 mg·L-1, respectively. The P release amount was 303.30 and 20.57 tons in 2011 and 2014, respectively. For Caohai of Dianchi Lake, the P released from bloom-cyanobacteria could provide adequate P for the next year's bloom recovery. [ABSTRACT FROM AUTHOR]

Multi-factor risk assessment is an important prerequisite for water quality protection and the safe operation of mega hydro-projects. As the largest long-distance inter-basin water diversion project in the world, the Middle Route of the South-to-North Water Diversion Project of China (MRSNWDPC) has been in operation for 8 years and has benefited 79 million people along the canal. However, concerns have been raised in recent years about the potential negative effects of abnormal algal proliferation in the MRSNWDPC. It is very important for the safety of water supply to carry out relevant risk analysis and formulate regulatory management. In order to quantitatively evaluate the risk of algal proliferation in the MRSNWDPC under the influence of multiple factors, a multivariate risk assessment method based on Vine Copula theory and Monte Carlo simulation was proposed. Five key factors (water temperature, flow velocity, flow rate, algal cell density, and dissolved oxygen) were used and multiple dependency models in each section of the MRSNWDPC from January 2016 to January 2019 were established to study the risk of algal proliferation under multiple scenarios. The results demonstrate that water temperature can be used as an appropriate early-warning indicator of algal proliferation. The early-warning interval (unit: °C) of water temperature in the upper, middle, and lower reaches are 26–29°C, 23–26°C, and 21–23°C, respectively. Unlike bivariate analysis, the multiple dependency model describes the relationship between variables more accurately and enriches the scenarios of multiple conditional probabilities. When the water temperature fluctuates in the early-warning interval, regulating the upstream, midstream, and downstream flow velocity to be higher than 0.6 m/s, 0.5 m/s, and 0.6 m/s, respectively, can effectively reduce the risk of algal proliferation. This research not only provides a reference for the ecological control of algae in the MRSNWDPC and similar mega hydro-projects but also enriches the application of the Vine Copula theory coupled with the random sampling method for multi-variable risk analysis. [Display omitted] • ●The risk of algal proliferation under multiple scenarios is comprehensively analyzed. • Algal early-warning thresholds of water temperature and flow rate are determined. • The regulation strategy of algal control in water diversion project is proposed. • The Vine Copula-based Model is effectively applied in multi-scenario risk analysis. [ABSTRACT FROM AUTHOR]

In our investigation, the fluoride content of surface water in northern China exceeds the standard, and accompanied by the problem of eutrophication. At present, there have been many studies on the coagulation treatment of pure fluoride-polluted waters, but the removal of fluoride in the waters containing algae has received little attention. In this paper, a typical type of cyanobacteria, M. aeruginosa , was chosen, and two coagulants (AlCl 3 and FeCl 3) were selected to explore the difference and mechanism of algae on the coagulation removal of fluoride. Results indicated that when AlCl 3 dosage was between 1.0 mmol/L and 1.5 mmol/L, M. aeruginosa contributed to efficient fluoride removal because algae promoted the adsorption of F by increasing the distribution of Al(OH) 3. In particular, M. aeruginosa increased the F removal rate by 50.22% at 1.5 mmol/L AlCl 3 dosage. However, FeCl 3 showed unsatisfactory effects on fluoride removal. The residual Al/Fe in the coagulated effluent showed that M. aeruginosa fixed large quantities of Fe, same with AlCl 3 , manifesting no selectivity in adhering metals. Besides, FeCl 3 had appeared to be more advantageous in removing organic matters. In particular, the high complexation capacity between HA and FeCl 3 caused the blockage and competition of the adsorption sites, which was why the presence of algal cells had no obvious promoting effect on fluoride removal by FeCl 3. In addition, the HA flocs formed by using AlCl 3 also had an excellent ability to adsorb F-, suggesting that other substances in waters could promote the fluoride removal, not just M. aeruginosa. [Display omitted] • Algae significantly promoted defluorination of AlCl 3 but not FeCl 3. • Algae had no selectivity in fixing Al or Fe, but only the Al efficiently removed F. • FeCl 3 combined with algae organic matters more strongly than AlCl 3. • F- adsorption on algal and HA flocs formed by AlCl 3 was identified. [ABSTRACT FROM AUTHOR]

• Natural product cercosporin has great photoinactivation effects on M. aeruginosa. • Bifunctional cercosporin inactivates algae through ROS generation and cell adsorption. • Scalable algae from Taihu Lake were inactivated under natural sunlight. Harmful cyanobacterial blooms (HCBs), mainly caused by eutrophication, have deleterious impacts on water resources and pose a great threat to human health and natural ecosystems. Thus, an environmentally-friendly method to inhibit HCBs is urgently needed. Learning from nature, herein, natural product cercosporin, produced by the fungi Cercospora to damage plant cells under natural sunlight, was developed as a powerful photosensitive algicidal reagent to inhibit HCBs. Microcystis aeruginosa could be severely inactivated by 20 μM cercosporin in 36 h with 95% inhibition ratio under 23 W compact fluorescent light irradiation. Further mechanism investigation showed that algal cell walls and membranes along with the antioxidant and photosynthetic systems were damaged via two mechanisms, those being, reactive oxygen species generation and cell adsorption. More importantly, the practical applicability of cercosporin was demonstrated by its effectiveness in a 2 L-scale photoinactivation experiment using cyanobacterial blooms from Taihu Lake, China under natural sunlight with a lower dosage of cercosporin (7.5 μM). This study established the bifunctional mechanisms by which cercosporin inactivates HCBs, opening design possibilities for the development of novel photosensitive algicidal reagents to control HCBs. [Display omitted] [ABSTRACT FROM AUTHOR]

Nowadays, the ubiquitous distribution and increasing abundance of P+III in waterbodies have caused serious concerns regarding its bioavailability and potential toxicity. However, our knowledge on these issues is relatively limited. We addressed previously unknown effects of P+III on three dominate algae species i.e. Microcystic aeruginosa (M. aeruginosa), Chlorella pyrenoidesa (C. pyrenoidesa) and Cyclotella. sp in eutrophic waterbodies in China. Remarkable declines in biomass, specific growth rate and Chl-a of algae cells treated with 0.01–0.7 mg/L P+III as sole or an alternative P source were observed, indicating P+III had an inhibitory effect on the algal growth. Besides, the intracellular enzyme activities e.g superoxide dismutase (SOD) and malondialdehyde (MDA) were significantly increased with P+III stress. M. aeruginosa and Cyclotella. sp cells seemed to be more sensitive to P+III toxicity than C. pyrenoidesa since cell membrane suffered more serious stress and destruction. These findings combined, it confirmed P+III could not be utilized as bioavailable P, but had certain toxicity to the tested algae. It indicated that the increased P+III abundance in eutrophic waterbodies would accelerate the algal cell death, which could have a positive effect against algal blooms. Our results provide new insights into assessing the ecological risks of P+III in aquatic environments. [Display omitted] • Responses of three dominant algae under various P+III regimes were investigated. • P+III was unable to support any growth of three tested algae as a P source. • M. aeruginosa and Cyclotella. sp were more sensitive to P+III toxicity. • Increased P+III in waterbodies could have a positive effect against algal blooms. [ABSTRACT FROM AUTHOR]

The application of hydrogen peroxide (H 2 O 2) to control harmful algal blooms is affected by algal density and species. In the present study, a simulation field study was carried out to evaluate the removal of cyanobacteria with high algal density (chlorophyll a of approximately 220–250 μg/L) and low algal density (chlorophyll a of approximately 30–50 μg/L) using 10, 20 mg/L H 2 O 2 and 5 mg/L H 2 O 2. The dynamics of algal biomass, nutrients, microcystins, phytoplankton, and zooplankton were measured within 7 d. The results showed that 5 mg/L H 2 O 2 effectively eliminated algal biomass (measured as chlorophyll a and phycocyanin) and inhibited 50% of the photosynthetic activity of the cyanobacteria at 7 d in the low algal cell density group, while the same inhibition rate was observed in the high algal cell density group when the H 2 O 2 was 20 mg/L. However, using a high dosage of H 2 O 2 , such as 10 mg/L, to suppress cyanobacteria with high biomass could result in a dramatic increase in nutrients and microcystins in the water column. The portion of eukaryotic algae, such as Chlorophyta, Bacillariophyta and Euglenophyta, in the phytoplankton community increased with increasing H 2 O 2 concentrations; moreover, the dominant species of cyanobacteria changed from the nontoxic genus Dactylococcopsis to the toxic genus Oscillatoria, which may result in acute toxicity to zooplankton. Our results demonstrated that the application of H 2 O 2 to control cyanobacterial blooms at the early stage when algal cell density was low posed less potential ecological risks and may have increased the diversity of the phytoplankton community. Image 1 • Low-dose of H 2 O 2 can suppress cyanobacteria growth when algal density was low. • The release of microcystins and nutrients increased with H 2 O 2 concentration. • Using H 2 O 2 to control HABs shifted dominant species of phytoplankton community. • Number of toxic cyanobacteria increased with increasing H 2 O 2 concentration. Main findings: (1) Low-dose H 2 O 2 was sufficient to suppress cyanobacteria when algal density was relatively low. (2) Number of toxic cyanobacteria increased with increasing H 2 O 2 concentration. [ABSTRACT FROM AUTHOR]

• The ciliate communities showed a clear variation among five algal cell concentrations; • Taxonomic breadths maintained at stable levels at concentrations of 102–104 cells ml−1; • The sharp drop in taxonomic breadth was found at the concentration of 105 cells ml−1; • Periphytic ciliates may be used to indicate influence of harmful algae on water quality. Our study focused on ciliates grazing potential against harmful algal blooms, because ciliates are considered as voracious feeders of toxic phytoplankton and major herbivores in marine food webs. Ciliates are major contributors to control the flux of harmful algal blooms by lessen the magnitude of their biomass from top to bottom by high consumption on these blooms. Keeping an eye on harmful algal blooms as common pollutant of marine ecosystem the community-based method was used to test the potential effects of two harmful algal species Alexandrium tamarense and Gymnodinum catenatum on the community patterns of the ciliates. For this purpose, the 14-day (mature) samples of ciliate communities were collected using glass slides as an artificial substratum at a depth of 1 m in coastal waters of the Yellow Sea, northern China. A series of algal cell concentrations of both species was prepared as 100 (control), following 102, 103, 104 and 105 cell ml−1, respectively. The study results indicated that both algal species showed strong effects on the community patterns of the ciliates at high concentration. Species abundance, relative species number and taxonomic distinctness indices of ciliate communities generally increased by increasing the concentration whereas, sharply decreased at the concentration level of (105 cells ml−1) for both algal species. Canonical analysis of principal coordinates demonstrated the variations in community structures of the ciliates driven by the concentrations of both algal species. Ellipse test showed an increased pattern in species departure from an expected breadth of species contour with increasing the algal cell concentrations. Based on our findings, it is suggested that extended studies on community-based bioassay is a valuable tool to strengthen the information about the effects of microalgae on the ciliate community structures. [ABSTRACT FROM AUTHOR]

Rice sheath blight causes serious damage to rice crops in China. The most common practice for rice sheath blight control is still chemical treatment, an environmentally unfriendly way. Studies have demonstrated the use of nitrogen-fixing cyanobacteria to prevent crop diseases as well as to improve soil fertility and crop productivity. However, little information is available on the biocontrol of rice sheath blight using cyanobacteria. Therefore, the objective of the present study was to screen and evaluate the biocontrol effect of nitrogen-fixing cyanobacteria against the disease through microchamber and microarea experiments. Based on the results of the microchamber experiment, three strains (SCAU04, SCAU15, and SCAU26) out of nine nitrogen-fixing cyanobacterial strains with a significant inhibition (>80%) on rice sheath blight were selected. Further, microarea experiments during two seasons demonstrated the highest disease control efficacy (54.5%) on day 20 with SCAU26 treatment. Moreover, the algal treatments significantly promoted root length, underground biomass, and number of grains per panicle. SCAU04 and SCAU26 treatments significantly improved the rice theoretical yield and significantly (P < 0.05) enhanced soil potassium content compared with the control group without algal treatment. The extract of SCAU04, SCAU15, and SCAU26 algal cells inhibited the mycelial growth of R. solani (inhibition rate; 90.12%, 78.33%, and 89.87%, respectively). Based on gas chromatography–mass spectrometry results, eight metabolites were selected and evaluated for their activity against R. solani. Among them, seven inhibited R. solani growth; diisooctyl adipate showed the highest inhibitory effect. All three cyanobacteria produced the phytohormones salicylic acid, auxins, and cytokines. The salicylic acid and trans-zeatin-riboside contents of SCAU04 were 3654.74 ng g−1 and 5266.67 ng g−1, respectively. The isopentenyladenine content of SCAU26 reached 2839.98 ng g−1. Morphological and molecular analysis identified the best two strains SCAU04 and SCAU26 as Nostoc piscinale and Anabaena variabilis , respectively. To conclude, our findings indicate that cyanobacteria produce bioactive substances to inhibit R. solani , secrete phytohormones to promote plant growth and induce plant disease resistance, and improve soil nutrient content to support plant growth. • Two cyanobacteria showed high disease control efficacy on rice sheath blight. • Algal treatments promoted root length, underground biomass, and yield of rice. • The extract of algal cells inhibited the mycelial growth of Rhizoctonia solani. • Several antifungal substances and phytohormones were identified in the algae. • The two cyanobacteria were identified as Nostoc piscinale and Anabaena variabilis. [ABSTRACT FROM AUTHOR]

As the largest inland sea of China, the Bohai Sea has confronted significant environmental changes in recent decades, and a shift of phytoplankton community from diatoms to dinoflagellates was observed by microscopic method in previous studies. However, the counting of some small-sized non-diatoms (e.g., flagellates and cyanobacteria) have long been neglected due to the limitation of this method. In this study, we measured the phytoplankton community structure and abundance in the central Bohai Sea in summer and autumn of 2015 by employing both microscopic method and high-performance liquid chromatography (HPLC) pigments – CHEMTAX analysis. The results of microscopic counting showed that the phytoplankton community was characterized by diatoms, dinoflagellates, and chrysophytes, which contained a total of 107 species. Dinoflagellates and diatoms co-dominated in summer while the latter became the dominant group in autumn. Compared with microscopic counting, CHEMTAX analysis allowed identification of a larger number of phytoplankton groups (including 8 phyla). The results of CHEMTAX analysis showed that besides diatoms and dinoflagellates, the small-sized non-diatoms (i.e., flagellates and cyanobacteria) also played an important role. Diatoms and cyanobacteria dominated the total Chl a (contributing 32.5% and 17.1%, respectively), followed by cryptophytes, dinoflagellates, and prasinophytes in the summer. A short-term summer to autumn variability of phytoplankton abundance and community was observed. Temperature and nutrient availability affected the succession of the phytoplankton community from diatoms and non-diatoms co-dominance in the summer to absolute diatoms dominance in the autumn. A direct comparison of algal cell abundance and CHEMTAX biomass showed that a significant positive correlation was observed only for dinoflagellates (P < 0.01) in the autumn. Our work provides some basic information on the dynamics of small-sized flagellates and cyanobacteria in this area, and also suggests that a combination of both the methods is needed in future investigations to better understand the current status as well as the future changes of phytoplankton community. • Microscopic analysis showed diatoms, dinoflagellates and chrysophytes in seawater. • CHEMTAX analysis allowed identification of a larger number of phytoplankton groups. • Variation of phytoplankton community from summer to autumn was observed. • Temperature and nutrients affected the variation of the phytoplankton community. [ABSTRACT FROM AUTHOR]

Freshwater phytoplankton communities can be classified into a variety of functional groups that are based on physiological, morphological, and ecological characteristics. This classification method was used to study the temporal and spatial changes in the phytoplankton communities of Gaozhou Reservoir, which is a large municipal water source in South China. Between January 2015 and December 2017, a total of 155 taxa of phytoplankton that belong to seven phyla were identified. The phytoplankton communities were classified into 28 functional groups, nine of which were considered to be representative functional groups (relative biomass > 10%). Phytoplankton species richness was greater in the summer and autumn than in the winter and spring; cyanobacterial blooms occurred in the spring. The seasonal succession of phytoplankton functional groups was characterized by the occurrence of functional groups P (Staurastrum sp. and Closterium acerosum) and Y (Cryptomonas ovata and Cryptomonas erosa) in the winter and spring, and functional groups NA (Cosmarium sp. and Staurodesmus sp.) and P (Staurastrum sp. and Closterium acerosum) in the summer and autumn. The temperature, nitrogen, and phosphorus levels were the main factors driving seasonal changes in the phytoplankton communities of Gaozhou Reservoir. The functional group M (Microcystis aeruginosa) dominated the community during the cyanobacterial blooms in spring 2016, with the maximum algal cell density of 3.12 × 108 cells L−1. Relatively low temperature (20.8 °C), high concentrations of phosphorus (0.080–0.110 mg L−1), suitable hydrological and hydrodynamic conditions (e.g., relatively long retention time), and relatively closed geographic location in the reservoir were the key factors that stimulated the cyanobacterial blooms during the early stages. [ABSTRACT FROM AUTHOR]

Eastern China is a typical region that suffers from harmful cyanobacterial blooms. Numerous studies have focused on bloom formation mechanisms; however, the detailed mechanisms remained unclear. Our study explored the influence of four metal ions (Ca, Cu, Pb and Cd) on Microcystis aeruginosa to determine their effects on bloom formation. We found that Ca concentrations higher than 100 mg L−1 contributed to cyanobacterial bloom formation. The presence of Ca triggered the anti-oxidation process and promoted the secretion of extracellular polysaccharides, thus inducing aggregation of algal cells and enhancing their buoyancy 2.1-fold more than the control (p ＜0.05). The reverse regulation of dissolved CO 2 to bicarbonate by carbonic anhydrase formed a large amount of carbonate and decreased the growth rate by 38–56%. Cu (>0.1 mg L−1) presented significant toxicity to algal cells while Pb (>1 mg L−1) suppressed the algal growth rate due to the acidic condition. Cd (<0.1 mg L−1) exhibited no apparent toxicity to the algae. Furthermore, as the buoyancy increased, Cd was likely to facilitate the formation of cyanobacterial blooms, which needs further research. These findings can provide a theoretical basis for eutrophic lake management and contribute to the development of water quality and wastewater discharge standards. • The buoyancy of algal cell increased with increasing cell aggregation proportion. • Four metal ions stimulate SOD, POD, CA and MDA in M. aeruginosa. • The regulation of CA in algal cells promoted the precipitation with metal ions. • Calcium higher than 100 mg L−1 was beneficial for bloom formation. [ABSTRACT FROM AUTHOR]