Microcystis Wesenbergii Research Articles

Phytoplankton from a brackish lagoon in the central region of Veracruz, Mexico

Introduction: The brackish lagoons are ecosystems with great diversity and possibilities for human use. Therefore, the knowledge about phytoplankton needs to be improved to understand its real impact. Objective: To relate the Mandinga's Lagoon phytoplankton to the limnological conditions during the dry and wet seasons. Methods: The material was collected in three stations: Isla Conchas (ICO), Mandinga Chica (MCH) and Isla del Amor (IA) during the dry (March 2018) and wet (September 2017 and 2018) seasons. The limnological analysis included ten abiotic variables, and the phytoplankton was analyzed by the Utermöhl method. Data was analyzed with the Shannon index (H´) and Canonical Correspondence Analysis (CCA). Results: 136 species were identified: 68.4 % Heterokontophyta, 22.8 % Dinoflagellata, and 5.9 % Cyanobacteriota; with 40 euryhaline and 96 stenohaline. The most abundant species were: Bacillaria paxillifera, Chaetoceros compressus, Coscinodiscus rothii, and Chaetoceros atlanticus. The highest abundance was in ICO (dry) and the lowest in MCH (wet), with 307 x 103 and 76 x 103 cells/ml, respectively; the H´ ranged from 1.31 to 0.70 bits/ind. The CCA showed a relationship between salinity and dissolved oxygen with C. rothii and Ceratoneis closterium. The phosphates were associated with B. paxillifera, C. atlanticus, and Podosira stelligera. The nitrate, water temperature and pH were related to Tripos hircus, T. furca, Diploneis bombus, and Merismopedia elegans. In contrast, Skeletonema costatum, Cocconeis scutelum, and Nitzschia bicapitata did not correlate with the limnological variables. Conclusions: The Mandinga's Lagoon is a shallow, euryhaline and well-oxygenated ecosystem. The dominance of diatoms and dinoflagellates was evidenced by their ability to survive in different salinities and temperatures. It is recommended monitor phytoplankton, in particular Microcystis wesenbergii, B. quinquecornis, Pseudo-nitzschia cf. pungens, and P. cf. pseudodelicatissima as they are harmful algae.

A non-microcystin-producing Microcystis wesenbergii strain alters fish food intake by disturbing neuro-endocrine appetite regulation

Cyanobacterial harmful algal blooms (cHABs) are pervasive sources of stress resulting in neurotoxicity in fish. A member of the widely distributed Microcystis genus of bloom-forming cyanobacteria, Microcystis wesenbergii can be found in many freshwater lakes, including Dianchi Lake (China), where it has become one of the dominant contributors to the lake's recurrent blooms. However, unlike its more well-known counterpart M. aeruginosa, the effects of dense non-microcystin-containing M. wesenbergii blooms are seldom studied. The disturbance of appetite regulation and feeding behaviour can have downstream effects on the growth of teleost fish, posing a significant challenge to aquaculture and conservation efforts. Here we examined the effects of M. wesenbergii blooms on the food intake of Acrossocheilus yunnanensis, a native cyprinid in southern China. This fish species has disappeared in Dianchi Lake, and its reintroduction might be negatively affected by the presence of this newly-dominant Microcystis species. We co-cultured juvenile A. yunnanensis with a non-microcystin-producing strain of M. wesenbergii at initial densities between 5 × 104 and 1 × 106 cells/mL and monitored fish feeding behaviour and changes in neurotransmitter and hormone protein levels. High-density M. wesenbergii cultures increased the feeding rate of co-cultured fish, elevating concentrations of appetite-stimulating signalling molecules (Agouti-related protein and γ-aminobutyric acid), while decreasing inhibitory ones (POMC). These changes coincided with histopathological alterations and reduced somatic indices in brain and intestinal tissues. Given this potential for detrimental effects and dysregulation of food intake, further studies are necessary to determine the impacts of chronic exposure of M. wesenbergii in wild fish.

Rapid flotation of Microcystis wesenbergii mediated by high light exposure: implications for surface scum formation and cyanobacterial species succession.

Increasing occurrences of Microcystis surface scum have been observed in the context of global climate change and the increase in anthropogenic pollution, causing deteriorating water quality in aquatic ecosystems. Previous studies on scum formation mainly focus on the buoyancy-driven floating process of larger Microcystis colonies, neglecting other potential mechanisms. To study the non-buoyancy-driven rapid flotation of Microcystis, we here investigate the floating processes of two strains of single-cell species (Microcystis aeruginosa and Microcystis wesenbergii), which are typically buoyant, under light conditions (150 μmol photons s-1 m-2). Our results showed that M. wesenbergii exhibited fast upward migration and formed surface scum within 4 hours, while M. aeruginosa did not form visible scum throughout the experiments. To further explore the underlying mechanism of these processes, we compared the dissolved oxygen (DO), extracellular polymeric substance (EPS) content, and colony size of Microcystis in different treatments. We found supersaturated DO and the formation of micro-bubbles (50-200 µm in diameter) in M. wesenbergii treatments. M. aeruginosa produces bubbles in small quantities and small sizes. Additionally, M. wesenbergii produced more EPS and tended to aggregate into larger colonies. M. wesenbergii had much more derived-soluble extracellular proteins and polysaccharides compared to M. aeruginosa. At the same time, M. wesenbergii contains abundant functional groups, which was beneficial to the formation of agglomerates. The surface scum observed in M. wesenbergii is likely due to micro-bubbles attaching to the surface of cell aggregates or becoming trapped within the colony. Our study reveals a species-specific mechanism for the rapid floatation of Microcystis, providing novel insights into surface scum formation as well as succession of cyanobacterial species.

Phosphorus Threshold for the Growth of Microcystis wesenbergii, Microcystis aeruginosa, and Chlorella vulgaris Based on the Monod Formula

The outbreak of algae in freshwater bodies poses an important threat to aquatic ecosystems, making finding an effective method for controlling algal blooms imperative. Numerous key factors influence algal bloom outbreaks, with nutrient levels in the water body being the decisive factor. Current research regarding the effect of nutrient levels on algal growth shows that phosphorus is a nutrient that influences algal blooms. Herein, we propose the concept of a modified Monod model for the relationship between algal specific growth rate and phosphorus concentration. Through this improved Monod model, we inferred that the phosphorus concentration at a specific growth rate of zero is the lower threshold of phosphorus concentration that limits algal growth and can effectively control algal outbreaks. This lower threshold is denoted as S′. On the basis of this concept, we designed algal growth experiments. Our results provided an equation that effectively describes the relationship between algal growth and nutrient concentration. When three algal species grow under phosphorus-limited conditions, the corresponding phosphorus concentrations at which they maintain a growth rate of 0 are 0.0565, 0.0386, and 0.0205 mg/L as reflected by the following order of their S′ values: Microcystis wesenbergii S′ < Microcystis aeruginosa S′ < Chlorella vulgaris S′. Furthermore, with the increase in phosphorus concentration, the growth of M. aeruginosa becomes faster than that of M. wesenbergii and C. vulgaris. Consequently, M. aeruginosa becomes the dominant population in the water, leading to its predominance in algal blooms. This situation explains the common occurrence of cyanobacterial blooms. Our findings provide a theoretical basis for regulating the concentration of phosphorus to control algal outbreaks. Therefore, our study is of great importance for controlling the eutrophication of water bodies.

The extracellular polysaccharide determine the physico-chemical surface properties of Microcystis.

Microcystis possesses the capacity to form colonies and blooms in lakes and reservoirs worldwide, causing significant ecological challenges in aquatic ecosystems. However, little is known about the determining factors of physico-chemical surface properties that govern the competitive advantage of Microcystis. Here, The physico-chemical surface properties of Microcystis wesenbergii and Microcystis aeruginosa, including specific surface area (SSA), hydrophobicity, zeta potential, and functional groups were investigated. Additionally, the extracellular polysaccharide (EPS) were analyzed. Laboratory-cultured Microcystis exhibited hydrophilic, a negative zeta potential and negatively charged. Furthermore, no significant relationship was shown between these properties and the cultivation stage. Microcystis wesenbergii exhibited low free energy of cohesion, high surface free energy, high growth rate, and high EPS content during the logarithmic phase. On the other hand, M. aeruginosa displayed lower free energy of cohesion, high surface free energy, high EPS content, and high growth rate during the stationary phase. These characteristics contribute to their respective competitive advantage. Furthermore, the relationship between EPS and surface properties was investigated. The polysaccharide component of EPS primarily influenced the SSA and total surface energy of Microcystis. Likewise, the protein component of EPS influenced hydrophobicity and surface tension. The polysaccharide composition, including glucuronic acid, xylose, and fructose, mainly influenced surface properties. Additionally, hydrophilic groups such as O-H and P-O-P played a crucial role in determining hydrophobicity in Microcystis. This study elucidates that EPS influenced the SSA, hydrophobicity, and surface free energy of Microcystis cells, which in turn impact the formation of Microcystis blooms and the collection.

Species composition of Cyanoprokaryota in the summer phytoplankton of 55 lakes and reservoirs, sampled in Bulgaria in the years 2018, 2019, 2021 and 2023

The paper presents detailed results on cyanoprokaryote diversity in the summer phytoplankton of 55 lakes, small and large reservoirs sampled in Bulgaria in the frame of three joined projects related to algal blooms threat to human health and national security. The phytoplankton of twenty from these selected waterbodies was sampled for first time. In total, 185 species and one variety from 55 genera have been identified, 54 of which (29%) were novel for the country. The average contribution of cyanophytes to the phytoplankton per site was 8 species (or 44% of the total biodiversity), reaching in some sites 80%. According to the morphology, the recorded algae were distributed as follows: 83 coccal, 52 non-heterocytous filamentous and 51 heterocytous filamentous cyanoprokaryotes. Their average contribution to the phytoplankton diversity was estimated as 4 coccal, 2 non-heterocytous and 2 heterocytous species per site. Most of the cyanoprokaryote species (94, or 51%) were recorded only once, even in the case of wetlands and sites which have been repeatedly visited during all sampling campaigns. These 96 species embrace 39 coccal, 23 non-heteroctous and 32 heterocytous forms. No species was found in all studied waterbodies. The most widely spread species were Microcystis aeruginosa (19 records), Planktolyngbya limnetica (17 records), Aphanizomenon klebahnii (16 records), Microcystis wesenbergii (16 records), Aphanocapsa delicatissima (13 records), Cuspidothrix issatschenkoi (12 records), Coelomoron pusillum (11 records), Pseudanabaena limnetica (11 records), Anagnostidinema amphibium (10 records), Raphidiopsis raciborskii (10 records), Limnococcus limneticus (10 records), and separate cells of Microcystis as well (15 records). The record of the chytrid parasite Rhizosiphon anabaenae on separate trichomes of Sphaerospermopsis aphanizomenoides is described.

Genome sequence of the novel freshwater Microcystis cyanophage Mwe-Yong1112-1.

The freshwater cyanophage Mwe-Yong1112-1 was isolated using Microcystis wesenbergii as a host and found to have an icosahedral head, about 45 nm in diameter, and a flexible tail, approximately 133 nm in length and 4.5 nm in width. The complete genome of the cyanophage is 39,679 bp in length with a G+C content of 66.6%. Mwe-Yong1112-1 shared the highest pairwise average nucleotide identity (ANI) value of 67.7% (below the ≥95% boundary to define a species) and the highest nucleotide sequence similarity of 17.48% (below the >70% boundary to define a genus) with the most closely related phage. In a proteomic tree, Mwe-Yong1112-1 and three unclassified phages formed a monophyletic clade between the families Saparoviridae and Pyrstoviridae, but Mwe-Yong1112-1 occupied a separate branch from the other three phages, suggesting that it represents a new evolutionary lineage. This study enriches the available information about freshwater cyanophages.

The Effects of Algaecides and Herbicides on a Nuisance Microcystis wesenbergii-Dominated Bloom

Microcystis-dominated cyanobacterial harmful algal blooms (cyanoHABs) are a reoccurring problem globally, resulting in widespread economic and health impacts. As public awareness of the risks of blooms increases, there is an urgent need for studies on both short-term and long-term management of cyanoHABs. In order to provide science-based best management practices and treatment options, we tested various concentrations and combinations of USEPA-registered algaecides and herbicides on a Microcystis wesenbergii-dominated bloom. The bloom material was exposed to fifteen different algaecides, herbicides, or combinations, using four different concentrations. Cell abundance and morphology as well as microscopic analyses were undertaken at the time of collection and 72 h post-treatment. Overall, the effectiveness of the chemicals varied with the most efficacious treatments being SeClear®, and a combination of Hydrothol® 191 and GreenClean® Liquid 5.0, both of which resulted in a significant decrease at all tested concentrations after 72 h. Interestingly, Microcystis wesenbergii is more resistant to algaecides than M. aeruginosa. Results from this study provide valuable data for treating cyanoHABs and show the varied efficacy of different algaecidal formulations.

A new sandwich hybridization assay method to identify and quantify Microcystis spp.

AbstractCyanobacteria are responsible for the largest number of harmful algal blooms (HABs) worldwide. HABs caused by the genus Microcystis are health threats because they often occur within close proximity to humans and produce phycotoxins such as microcystins that can contaminate drinking water and recreational areas. Molecular techniques enable accurate and rapid (~ 1 h) HAB detection that facilitates monitoring, “early warnings” of blooms, and corresponding management responses. Sandwich hybridization assay (SHA), the technique considered here, directly (no amplification) identifies and quantifies plankton species using ribosomal RNA (rRNA)‐targeted oligonucleotides. This project focused on the development of a new SHA method for the detection of Microcystis (16S rRNA) using laboratory cultures. Assay calibration curve and limits of detection were determined using Microcystis aeruginosa, though signal intensity differed significantly (p < 0.05) between three species (M. aeruginosa, Microcystis botrys, Microcystis wesenbergii). SHA results for M. aeruginosa raised under three light intensities (40, 60, and 100 μmol photons m−2 s−1) and two temperatures (25°C and 32°C) were greatest at the highest irradiance for both temperatures, but otherwise variable, yielding an overall significant (p < 0.05) interaction between light and temperature. The 32°C treatment also resulted in significantly lower (p < 0.05) Photosystem II quantum efficiency (Fv/Fm) and microcystins concentrations per light intensity. Spiked field experiments showed that SHA signal was not significantly affected (p > 0.05) by a mixed phytoplankton assemblage. The assay speed, wide detection range, and specificity indicate that this method has promise for additional field studies and HAB monitoring.

Arsenic Accumulation and Biotransformation Affected by Nutrients (N and P) in Common Blooming-Forming Microcystis wesenbergii (Komárek) Komárek ex Komárek (Cyanobacteria)

Arsenic accumulation and biotransformation in algae was mostly carried out in a medium that contained far higher nutrient concentrations than that in natural freshwaters. The obtained results might have limited environmental validity and result in a failure to describe authentic arsenic biogeochemical cycles in natural freshwater systems. To validate the assumption, arsenic accumulation, and biotransformation in common bloom forming Microcystis wesenbergii was performed under a high nutrient concentration in BG11 medium (N = 250 mg/L, P = 7.13 mg/L), and adjusted low nutrients that mimicked values in natural freshwaters (N = 1.5 mg/L, P = 0.3 mg/L). The growth rate and maximum M. wesenbergii cell density were much lower in the high nutrient set, but more inhibition was shown with increasing ambient iAs(V) concentrations both in the high and low nutrient sets. The proportion of intracellular contents in total arsenicals decreased with increasing iAs(V) concentrations in both high and low nutrient sets but increased with incubation time. Intracellular iAs(III) was not found in the high nutrient set, while it formed high concentrations that could be comparable to that of an extracellular level in the low nutrient set. M. wesenbergii could methylate arsenic, and a higher proportion of organoarsenicals was formed in the low nutrient set. Lower intracellular MMA(V) and DMA(V) concentrations were found in the high nutrient set; contrarily, they presented a higher concentration that could be comparable to the extracellular ones in the low nutrient set. The results demonstrated that different nutrient regimes could affect arsenic accumulation and biotransformation in M. wesenbergii, and low nutrient concentrations could inhibit the excretion of iAs(III), MMA(V) and DMA(V) out of cells. Further investigations should be based on natural freshwater systems to obtain an authentic arsenic accumulation and biotransformation in cyanobacteria.

Differential Effect of Hydroxen Peroxide οn Toxic Cyanobacteria of Hypertrophic Mediterranean Waterbodies

Cyanobacterial blooms have been known since ancient times; however, they are currently increasing globally. Human and ecological health risks posed by harmful cyanobacterial blooms have been recorded around the world. These risks are mainly associated with their ability to affect the ecosystem chain by different mechanisms like the production of cyanotoxins, especially microcystins. Their expansion and their harmful effects have led many researchers to seek techniques and strategies to control them. Among them, hydrogen peroxide could be a promising tool against cyanobacteria and cyanotoxins and it is well-established as an environmentally friendly oxidizing agent because of its rapid decomposition into oxygen and water. The aim of the present study was to evaluate the effect of hydrogen peroxide on phytoplankton from two hypertrophic waterbodies in Greece. The effect of hydrogen peroxide on concentration of microcystins found in the waterbodies was also studied. Treatment with 4 mg/L hydrogen peroxide was applied to water samples originated from the waterbodies and Cyanobacterial composition and biomass, phycocyanin, chlorophyll-a, and intra-cellular and total microcystin concentrations were studied. Cyanobacterial biomass and phycocyanin was reduced significantly after the application of 4 mg/L hydrogen peroxide in water treatment experiments while chlorophytes and extra-cellular microcystin concentrations were increased. Raphidiopsis (Cylindrospermopsis) raciborskii was the most affected cyanobacterial species after treatment of the water of the Karla Reservoir in comparison to Aphanizomenon favaloroi, Planktolyngbya limnetica, and Chroococcus sp. Furthermore, Microcystis aeruginosa was more resistant to the treatment of Pamvotis lake water in comparison with Microcystis wesenbergii and Microcystis panniformis. Our study showed that hydrogen peroxide differentially impacts the members of the phytoplankton community, affecting, thus, its overall efficacy. Different effects of hydrogen peroxide treatment were observed among cyanobacerial genera as well as among cyanobacterial species of the same genus. Different effects could be the result of the different resistance mechanisms of each genus or species to hydrogen peroxide. Hydrogen peroxide could be used as a treatment for the mitigation of cyanobacterial blooms in a waterbody; however, the biotic and abiotic characteristics of the waterbody should be considered.

Novel Algicides against Bloom-Forming Cyanobacteria from Allelochemicals: Design, Synthesis, Bioassay, and 3D-QSAR Study.

Simple SummaryDue to the frequent outbreaks of cyanobacteria bloom worldwide, research on novel algicides has attracted more and more attention. At present, allelochemicals have been reported as promising natural algicides. However, current studies mainly focus on the parent compounds, and the structural modification of original allelochemicals has been rarely involved. In this study, phenolic acid derivatives were innovatively synthesized as potential algicides, and lead compounds with excellent activity were found. For instance, upon the algicidal activity on Aphanizomenon flos-aquae, the EC50 of the best active compound 18 reached 0.63 µM (0.17 mg/L), while the EC50 values of previously reported allelochemicals have been basically at the mg/L level. The result indicates that the algicides reported in this study are more efficient at inhibiting cyanobacteria with lower effective concentrations than most previously reported compounds. Moreover, 3D-QSAR models were constructed and provided a theoretical guidance for further structure optimization of compounds to achieve better algicidal activity.Cyanobacteria bloom caused by water eutrophication has threatened human health and become a global environmental problem. To develop green algicides with strong specificity and high efficiency, three series of ester and amide derivatives from parent allelochemicals of caffeic acid (CA), cinnamic acid (CIA), and 3-hydroxyl-2-naphthoic acid (HNA) were designed and synthesized. Their inhibitory effects on the growth of five harmful cyanobacterial species, Microcystis aeruginosa (M. aeruginosa), Microcystis wesenbergii (M. wesenbergii), Microcystis flos-aquae (M. flos-aquae), Aphanizomenon flos-aquae (Ap. flos-aquae), and Anabaena flos-aquae (An. flos-aquae), were evaluated. The results revealed that CIA esters synthesized by cinnamic acid and fatty alcohols showed the best inhibition effect, with EC50 values ranging from 0.63 to >100 µM. Moreover, some CIA esters exhibited a good selectivity in inhibiting cyanobacteria. For example, the inhibitory activity of naphthalen-2-yl cinnamate was much stronger on Ap. flos-aquae (EC50 = 0.63 µM) than other species (EC50 > 10 µM). Three-dimensional quantitative structure–activity relationship (3D-QSAR) analysis was performed and the results showed that the steric hindrance of the compounds influenced the algicidal activity. Further mechanism study found that the inhibition of CIA esters on the growth of M. aeruginosa might be related to the accumulation of malondialdehyde (MDA).

Diversity, seasonal succession and host specificity of bacteria associated with cyanobacterial aggregates in a freshwater lake

Cyanobacterial blooms are threatening our global freshwater ecosystem due to eutrophication and global warming. The heterotrophic Bacteria Associated with Cyanobacterial Aggregates (BACA) are known to provide adaptative support to cyanobacterial species which outcompete the microorganisms during the period of bloom formation. In this study, diversity, seasonal succession, spatial, and host specificity of BACA were explored by analyzing their diversity in time-series samples from a eutrophic freshwater lake, Lake Taihu. Diversity analysis using high-throughput sequencing of the samples investigated here revealed that four Microcystis species including Microcystis aeruginosa , Microcystis wesenbergii , Microcystis panniformis, and Microcystis flos-aquae tend to exhibit host specificity. However, no obvious differences between the BACA of floating and sinking samples were observed in this study. Water temperature was found as a key factor driving the succession of BACA in Taihu Lake. BACA was not only observed, exhibiting long term seasonal succession but intra-seasonal succession in response to steep environmental changes was also observed. This study provides detailed insights into the diversity, seasonal succession, spatial and host specificity of BACA in Lake Taihu. • Diversity and succession of Bacteria Associated with Cyanobacterial Aggregates. • Water temperature was found as a key factor driving the succession of BACA. • No significant difference between BACA of floating and sinking samples were observed. • Bacteria Associated with Microcystis Aggregates exhibit host specificity.

Cyanobacteria, cyanotoxins, and their histopathological effects on fish tissues in Feh\xe9rv\xe1rcsurg\xf3 reservoir, Hungary

Cyanobacteria are important members of lake plankton, but they have the ability to form blooms and produce cyanotoxins and thus cause a number of adverse effects. Freshwater ecosystems around the world have been investigated for the distribution of cyanobacteria and their toxins and the effects they have on the ecosystems. Similar research was performed on the Fehérvárcsurgó reservoir in Hungary during 2018. Cyanobacteria were present and blooming, and the highest abundance was recorded in July (2,822,000 cells/mL). The species present were Aphanizomenon flos-aquae, Microcystis flos-aquae, Microcystis wesenbergii, Cuspidothrix issatschenkoi, Dolichospermum flos-aquae, and Snowella litoralis. In July and September, the microcystin encoding gene mcyE and the saxitoxin encoding gene sxtG were amplified in the biomass samples. While a low concentration of microcystin-RR was found in one water sample from July, analyses of Abramis brama and Carassius gibelio caught from the reservoir did not show the presence of the investigated microcystins in the fish tissue. However, several histopathological changes, predominantly in gills and kidneys, were observed in the fish, and the damage was more severe during May and especially July, which coincides with the increase in cyanobacterial biomass during the summer months. Cyanobacteria may thus have adverse effects in this ecosystem.

Phytoplankton community structure and driving factors in typical reservoirs of arid region of northwest China

为了解西北干旱区水库浮游植物群落结构特征，并进一步探究浮游植物与环境因子之间的相关关系，于2017年对张掖境内不同分布区域的8座典型水库进行为期4个季度的采样调查.结果显示，调查期间共计检出浮游植物8门106属294种，其中硅藻门、绿藻门和蓝藻门占比分别为48.35%、26.64%和14.47%.浮游植物密度在0.3×10⁴~4.38×10⁷ cells/L之间，夏、秋季较高，冬季最低，且随着海拔的降低浮游植物密度呈现显著升高的趋势.Shannon-Wiener多样性指数、Simpson指数、Pielou均匀度指数和Margalef指数年均值分别为2.26、0.77、1.20和0.86，综合浮游植物细胞密度和物种组成对水质进行评价可知，K1、K2、K3和K5水库为贫营养，K4、K6、K7和K8水库为中营养-富营养.Spearman相关性分析和典范对应分析发现，总氮、电导率、温度和海拔是水库浮游植物密度大小及优势种分布的主要影响因子，低海拔水库中细小平裂藻（Merismopedia minima）、史密斯微囊藻（Microcystis smithii）和惠氏微囊藻（Microcystis wesenbergii）等水华蓝藻随着水温升高而占据绝对优势，尤其史密斯微囊藻密度在夏季超过水华阈值（10⁷ cells/L），值得引起注意.;In order to explore the structural characteristics of phytoplankton community in the main reservoirs in arid climate area, northwest China, and to further study the correlation between phytoplankton and environmental factors, 8 major reservoirs in different distribution areas were surveyed for 4 quarters in 2017. The results reveled that a total 294 species belonging to 8 phyla and 106 genera were identified to be mainly composed of the Bacillariophyta, Chlorophyta and Cyanophyta and in the proportions of 48.35%, 26.64% and 14.47%, respectively. During the survey period, the density of phytoplankton was between 0.3×10⁴-4.38×10⁷ cells/L, which was higher in Summer and Autumn than in Winter and Spring, with the existence of a significant increasing trend with decreasing altitude. The Shannon-Wiener diversity index, Simpson index, Pielou evenness index, and Margalef index were 2.26, 0.77, 1.20, and 0.86, respectively. The comprehensive evaluation combining the density of phytoplankton, indicator species and four diversity indices showed that K1, K2, K3 and K5 reservoirs were oligotrophic, while K4, K6, K7 and K8 reservoirs were meso-trophic to trophic. Spearman correlation analysis of phytoplankton density and environmental factors found that phytoplankton density was extremely significantly correlated with total nitrogen (TN), electrical conductivity (Spc), and altitude, and significantly correlated with temperature, pH, and Sal. Spearman correlation analysis and CCA analysis found that TN, Spc, temperature, and altitude were the main factors influencing phytoplankton density and dominant species distribution in reservoirs. Water-blooming cyanobacteria such as Merismopedia minima, Microcystis smithii and Microcystis wesenbergii had an absolute advantage in low-altitude reservoir as temperature rise. It was worth noting that the density of Microcystis smithii increased with temperature rise and exceeded the bloom threshold (10⁷ cells/L) in Summer.

Summer cyanoprokaryote blooms in eleven reservoirs in South Bulgaria (2019)

Forty taxa from the Cyanoprokaryota division were identified in eleven reservoirs in South Bulgaria, and seventeen of them dominated by biomass in 2019. The potential producers of cyanotoxins Microcystis aeruginosa, Microcystis wesenbergii, Dolichospermum spiroides and Planktothrix agardhii caused intense blooms. Cyanoprokaryote blooms persisted throughout the summer, and their contribution to the total phytoplankton biomass varied from 15 to 100%. In September, in the Sinyata Reka reservoir, the biomass of Microcystis aeruginosa reached 35.3 mg L-1, and of Microcystis wesenbergii - 10.5 mg L-1. In Novo Zhelezare reservoir in July the biomass of Dolichospermum spiroides reached 18.81 mg L-1, and Planktothrix agardhii in August - 16.8 mg L-1.

Wind induced turbulence caused colony disaggregation and morphological changes in the cyanobacterium <i>Microcystis</i>

微囊藻群体大小和形态决定其垂向迁移能力，从而影响着水华的形成.为了探讨湖泊中风生紊流对微囊藻群体大小和形态的影响，本研究于2012年8月26日至9月7日在太湖梅梁湾的围隔内进行了12 d的昼夜不间断的高频采样（采样间隔每2小时一次）.研究期间，水面微囊藻密度呈现4次周期性消涨，藻密度变化范围为4×10⁴~2671×10⁴ cells/mL.而整个水柱中的藻密度变化范围仅为3×10⁴~18×10⁴ cells/mL.皮尔逊相关性分析表明微囊藻的原位生长速率与表面藻密度呈负相关而与风速呈正相关.强风速使微囊藻在水柱中均匀分散，增强了透光性，促进了微囊藻的生长.微囊藻群体粒径随着风速的增大逐渐减小，反之亦然.其中值粒径（D₅₀）变化范围为66.2~768.0 μm.在此期间微囊藻群体形态主要以鱼害微囊藻、不规则的惠氏微囊藻、球状的惠氏微囊藻和铜绿微囊藻群体形态为主，其占比也呈现出波动状态.皮尔逊相关分析结果显示微囊藻群体大小与风速呈负相关，说明湖泊中风生紊流会影响微囊藻群体大小.当紊流强度为2.33×10^-5 m²/s³时，微囊藻群体会发生破碎现象，该紊流强度相当于5 m/s的风在30 m深的水库或湖泊中所产生的紊流强度.微囊藻群体被风生紊流破碎后最大粒径与该风速下紊流的最小涡旋尺度相近，表明紊流的最小涡旋尺度决定了微囊藻所能形成群体的最终大小.监测期间，整水柱中不同群体形态的微囊藻占比发生了明显变化，在监测初期以鱼害微囊藻群体形态为主，随后不规则的惠氏微囊藻和铜绿微囊藻群体形态的比例不断增加，最后鱼害微囊藻群体形态又占据主导地位.球状的惠氏微囊藻群体形态在整个监测期中的比例随时间的增加而逐渐降低.不同群体形态微囊藻之间比例的大幅变化无法用微囊藻生长演替来解释.而皮尔逊相关分析结果显示鱼害微囊藻与惠氏微囊藻（不规则的和球状的惠氏微囊藻之和）群体形态之间存在负相关，且惠氏微囊藻与铜绿微囊藻群体形态呈负相关.但在今后研究中需进一步关注在微囊藻群体形态的动态变化过程中细胞大小、胶被、产毒特性和基因序列等特征，从而验证不同种微囊藻群体是否存在形态转换这一猜想.总而言之，普通强度的风生紊流能够破碎微囊藻群体，而气候变化导致的内陆湖泊周边风速下降会促使微囊藻形成更大的群体，从而有利于水华的形成.;Colony size and morphology influence the vertical migration capacity of Microcystis and therewith the occurrence of surface accumulations or blooms. To explore the influence of wind-induced turbulence on the colony size and morphology of Microcystis in field conditions, a high-frequency field investigation was conducted in an enclosure in Meiliang Bay, Lake Taihu, China, from 26 August to 7 September 2012. A Pearson's correlation analysis indicated that the in situ growth rate of Microcystis was negatively related to surface cell density and positively related to wind speed. Strong wind speed stimulated Microcystis growth by enhancing light transmission due to the homodispersion of Microcystis in the water column. The Microcystis colony size was negatively correlated with wind speed, suggesting that wind-induced turbulence could break up colonies in shallow lakes. The results indicated that Microcystis colonies could be broken up by a turbulence intensity of 2.33×10^-5 m²/s³, which corresponds to an average wind speed of 5.00 m/s in a reservoir with 30-m depth. Different Microcystis morphotypes were present and negative relationships were detected between the proportion of Microcystis ichthyoblabe and the proportion of Microcystis wesenbergii and between the proportion of Microcystis aeruginosa and the proportion of Microcystis wesenbergii out of all Microcystis throughout the water column, but more evidence is need to support the hypothesis that the morphology of Microcystis colonies changes over time. Altogether, the results suggest that declining wind speed, driven by climate change, will promote surface blooms of Microcystis due to the formation of larger colonies.

Tracing the active genetic diversity of Microcystis and Microcystis phage through a temporal survey of Taihu.

Harmful algal blooms are commonly thought to be dominated by a single genus, but they are not homogenous communities. Current approaches, both molecular and culture-based, often overlook fine-scale variations in community composition that can influence bloom dynamics. We combined homology-based searches (BLASTX) and phylogenetics to distinguish and quantify Microcystis host and phage members across a summer season during a 2014 Microcystis- dominated bloom that occurred in Lake Tai (Taihu), China. We found 47 different genotypes of the Microcystis-specific DNA-dependent RNA polymerase (rpoB), which included several morphospecies. Microcystis flos-aquae and Microcystis wesenbergii accounted for ~86% of total Microcystis transcripts, while the more commonly studied Microcystis aeruginosa only accounted for ~7%. Microcystis genotypes were classified into three temporal groups according to their expression patterns across the course of the bloom: early, constant and late. All Microcystis morphospecies were present in each group, indicating that expression patterns were likely dictated by competition driven by environmental factors, not phylogeny. We identified three primary Microcystis-infecting phages based on the viral terminase, including a novel Siphoviridae phage that may be capable of lysogeny. Within our dataset, Myoviridae phages consistent with those infecting Microcystis in a lytic manner were positively correlated to the early host genotypes, while the Siphoviridae phages were positively correlated to the late host genotypes, when the Myoviridae phages express putative genetic markers for lysogeny. The expression of genes in the microcystin-encoding mcy cassette was estimated using mcyA, which revealed 24 Microcystis-specific genotypes that were negatively correlated to the early host genotypes. Of all environmental factors measured, pH best described the temporal shift in the Microcystis community genotypic composition, promoting hypotheses regarding carbon concentration mechanisms and oxidative stress. Our work expounds on the complexity of HAB events, using a well-studied dataset to highlight the need for increased resolution of community dynamics.

Dosage and pH dependence of coagulation with polytitanium salts for the treatment of Microcystis aeruginosa-laden and Microcystis wesenbergii-laden surface water: The influence of basicity

Polytitanium coagulants have been recently developed and have received wide attention due to both strong coagulation capability and sludge recycling to produce valuable by-products, titanium dioxide (TiO2). This study reports the performance of coagulation with emerging polytitanium salts, polytitanium chloride (PTC) and polytitanium sulfate (PTS), for the treatment of two common cyanobacteria (Microcystis aeruginosa, MA and Microcystis wesenbergii, MW)-laden surface water, which has been barely reported. Of particular concern is the coagulant dosage and solution pH dependence of polytitanium coagulation, which are the main parameters influencing coagulation efficiency. The influence of basicity (B) of PTC and PTS on coagulation performance was simultaneously included. Results show the optimized B value of 1.5 with coagulant dosage of 30 mg/L and initial solution pH between 7–9 for both PTC and PTS coagulation, wherein obvious advantage of PTC was observed over PTS regardless of MA- or MW-laden surface water treatment. The PTC coagulation could achieve almost complete removal of algae (about 99.0 %) with synergic removal of organic matter with high-efficiency. Both PTC and PTS were more capable at alkaline solution pH conditions for turbidity and algae removal through sweep flocculation, while satisfied removal of the humic acid-representative organic matters was observed at acidic to neutral pH conditions by charge neutralization. Satisfied flocculation zones were determined according to synergic removal of algae, turbidity and organic matters, with most of the satisfied points distributed at solution pH 7–9 conditions. This study will provide theoretical basis and facilitate wide application of the polytitanium coagulation for algae-loaded surface water treatment.

Identification and enumeration of cyanobacteria species using a deep neural network

Cell classification and cell counting are essential for the detection, monitoring, forecasting, and management of harmful algae populations. Conventional methods of algae classification and cell counting are known to be time-consuming, labor-intensive, and subjective, depending on the expertise of the observers. The objectives of this study were to classify and quantify five cyanobacteria using the deep learning techniques of a fast regional convolutional neural network (R-CNN) and convolutional neural network (CNN). Water samples taken from the Haman weir of Nakdong River and Baekje weir of the Geum River were observed under the optical microscope. The images captured by the microscope were used to classify cyanobacteria species using the fast R-CNN model. Post-processing of the classified images generated by the model reduced the noises of the cell features, thereby improving the accuracy of the CNN model in quantifying cyanobacteria cells. The distinctive morphological features of the five species were extracted by the fast R-CNN model. This model was able to achieve a reasonable agreement with the manual classification results, yielding average precision (AP) values of 0.929, 0.973, 0.829, 0.890, and 0.890 for Microcystis aeruginosa, Microcystis wesenbergii, Dolichospermum, Oscillatoria, and Aphanizomenon, respectively. The CNN model for the Microcystis species obtained an R2 value of 0.775 and RMSE value of 26 cells for training, and an R2 of 0.854 and RMSE of 23 cells for validation. A minor underestimation and overestimation for a population with <50 cells and >250 cells were observed, respectively, which are due to the overlapping of cells and the presence of blurry regions in the input images. In conclusion, this study was able to demonstrate the reliable performance of cyanobacteria classification and cell counting using deep learning approaches.