Microcystis Blooms Research Articles

Biological and Chemical Investigations of Water Quality and Contamination Study After a Suspicious Algal Bloom in a Coastal Lagoon, Jeddah, Saudi Arabia

The General Authority of Meteorology and Environmental Protection (GAMEP) started an investigation about suspicion of microcystis bloom with toxin production in lagoon near Obhour, Jeddah. Water samples were collected from different spots covering all lagoon directions. The samples were analyzed for salinity, coliforms, toxin producing microalgae using MPN, and microscopic examination. LC/MS-MS analysis was used to identify and quantify the extra-cellular microcystins (MCs) in the lagoon water. The results revealed complete absence of the toxic algae or its secreted toxins. The results revealed the presence of Dunaliella salina with rich ?-carotene production responsible for brown or pink color in the lagoon.

Urea dynamics during Lake Taihu cyanobacterial blooms in China

Lake Taihu, the third largest freshwater lake in China, suffers from harmful cyanobacteria blooms caused by Microcystis spp., which do not fix nitrogen (N). Reduced N (i.e., NH4+, urea and other labile organic N compounds) is an important factor affecting the growth of Microcystis. As the world use of urea as fertilizer has escalated during the past decades, an understanding of how urea cycling relates to blooms of Microcystis is critical to predicting, controlling and alleviating the problem. In this study, the cycling rates of urea-N in Lake Taihu ranged from non-detectable to 1.37 μmol N L−1 h−1 for regeneration, and from 0.042 μmol N L−1 h−1 to 2.27 μmol N L−1 h−1 for potential urea-N removal. The fate of urea-N differed between light and dark incubations. Increased 15NH4+ accumulated and higher quantities of the removed urea-15N remained in the 15NH4+ form were detected in the dark than in the light. A follow-up incubation experiment with 15N-urea confirmed that Microcystis can grow on urea but its effects on urea dynamics were minor, indicating that Microcystis was not the major factor causing the observed fates of urea under different light conditions in Lake Taihu. Bacterial community composition and predicted functional gene data suggested that heterotrophic bacteria metabolized urea, even though Microcystis spp. was the dominant bloom organism.

Phytoplankton diversity and trophic status of Lake Maninjau, West Sumatra, Indonesia

Abstract. Sulastri, Henny C, Nomosatryo S. 2019. Phytoplankton diversity and trophic status of Lake Maninjau, West Sumatra, Indonesia. Pros Sem Nas Masy Biodiv Indon 5: 242-250. Microcystis blooms have been recorded in Lake Maninjau in 2000, October 2011 and recently on April 2018. Microcystis bloom was characterized by green color enhancement in the column water due to high concentration of chlorophyll-a reach to > 100 µg.L-1. The occurrence of phytoplankton bloom in this lake was not recorded all the year but Microcystis was disappeared and the water is clear again in a certain period. This study was aimed to reveal phytoplankton diversity and relation to trophic status in Lake Maninjau. Phytoplankton diversity and water quality include water transparency, temperature, DO, pH, conductivity, and nutrient were observed in 2009, 2014, 2015, 2016 dan 2018. Phytoplankton sample and water quality parameters were measured in the euphotic zone at nine stations. Three variable chlorophyll-a, Secchi depth (transparency) and total phosphorus concentration used to calculate the trophic state index. There are 121 species of phytoplankton belong to phylum Chlorophyta (74 species), Cyanophyta (23 species), Pyrrhophyta (7 species) dan Euglenophyta (4 species). The trophic status in Lake Maninjau showed variability temporally; it was mesotrophic, meso-eutrophic, eutrophic and hiper-eutrophic. Hypereutrophic status was characterized by low phytoplankton diversity (27 species), high chlorophyll-a, nutrient concentration, and Microcystis aeruginosa abundance (4180.932 x 103 individual.L-1). Mesotrophic was characterized by high phytoplankton diversity (63 species) belong to phylum Chlorophyta especially family Desmidiaceae, Oocyataceae, Scenedesmusceae, and low nutrient concentration. The higher trophic status is more decrease phytoplankton diversity.

Removal of Microcystis blooms using enhanced colony formation and buoyancy by controlling extracellular polysaccharides and cation concentrations

This study attempted to promote the colony formation and enlarge the colony size of wild Microcystis strain by adjusting extracellular polysaccharides and cationic ion concentrations in culture medium, and then, using the enhanced floating velocity (Stokes’ law), wild Microcystis at the water surface was removed. In order to examine the difference between extracellular polysaccharides mixture and tightly cell-bound extracellular polysaccharides used in this study, the component composition and physical properties were also examined. The results showed that tightly cell-bound extracellular polysaccharides contained the greater amounts of cations (Ca2+ and Mg2+), phosphorus, carboxy group and monosaccharides than extracellular polysaccharides mixture. There were greater amounts of carboxy groups and mannose residue in tightly cell-bound extracellular polysaccharides than extracellular polysaccharides mixture, which would contribute to the stronger cell–cell adhesion of wild Microcystis to make colony formation and expand colony size. The adjustment of extracellular polysaccharides and cationic ion concentrations was effective method to promote the colony formation and enlarge the colony size of wild Microcystis, and that the control of Microcystis buoyancy by enhancing the colony size would be one of the options for the suppression of Microcystis blooms from the viewpoint of cost-effective, low-energy, environmentally-friendly, and non-destructive of Microcystis cells.

Increased algicidal activity of Aeromonas veronii in response to Microcystis aeruginosa: interspecies crosstalk and secondary metabolites synergism.

Toxic Microcystis spp. blooms constitute a serious threat to water quality worldwide. Aeromonas veronii was isolated from Microcystis sp. colonies collected in Lake Kinneret. Spent Aeromonas media inhibits the growth of Microcystis aeruginosa MGK isolated from Lake Kinneret. The inhibition was much stronger when Aeromonas growth medium contained spent media from MGK suggesting that Aeromonas recognized its presence and produced secondary metabolites that inhibit Microcystis growth. Fractionations of the crude extract and analyses of the active fractions identified several secondary metabolites including lumichrome in Aeromonas media. Application of lumichrome at concentrations as low as 4 nM severely inhibited Microcystis growth. Inactivation of aviH in the lumichrome biosynthetic pathway altered the lumichrome level in Aeromonas and the extent of MGK growth inhibition. Conversely, the initial lag in Aeromonas growth was significantly longer when provided with Microcystis spent media but Aeromonas was able to resume normal growth. The longer was pre-exposure to Microcystis spent media the shorter was the lag phase in Aeromonas growth indicating the presence of, and acclimation to, secondary MGK metabolite(s) the nature of which was not revealed. Our study may help to control toxic Microcystis blooms taking advantage of chemical languages used in the interspecies communication.

Nitrogen\u2013phosphorus-associated metabolic activities during the development of a cyanobacterial bloom revealed by metatranscriptomics

The efforts towards reduction of nutrient contamination of surface waters have greatly gained attention to mitigate increasing incidences of harmful cyanobacterial blooms (CyanoHABs), but little attention has been paid on the roles and importance of cyanobacterial N2-fixation and phosphorus (P) scavenging pathways during cyanoHABs. Meta-transcriptomic analyses revealed that expressions of genes involved in N2-fixation (nifDKH) and P-scavenging were significantly upregulated during the bloom compared to pre-bloom in Harsha Lake. The activities of N2-fixation occurred during early summer after a late spring phytoplankton bloom, and were associated with high phosphorus and low nitrogen. The highly active cyanobacterial N2-fixers were dominated by Nostoc and Anabaena. Following the activities of N2-fixation and production of new nitrogen, an early summer Microcystis-dominated bloom, a shift of dominance from Nostoc and Anabaena to Microcystis and an increase of microcystin and saxitoxin occurred. By contrast, P-scavenging activities dominated also by Nostoc and Anabaena were associated with low P and the Microcystis bloom. This information can be used to aid in the understanding the impact that nitrogen and phosphorus have on the early summer CyanoHAB and the functional activities of Nostoc- and Anabaena-dominated or Microcystis-dominated communities, and aid in making management decisions related to harmful algal blooms.

Insights into the relationship between colony formation and extracellular polymeric substances (EPS) composition of the cyanobacterium Microcystis spp

Extracellular polymeric substances (EPS) were considered as fundamental substances in colony formation; however, the understanding of EPS composition remains limited. This study analyzed the content and composition of EPS fractions (soluble EPS, loosely bound EPS, and tightly bound EPS) of four Microcystis species from laboratory cultures in both unicellular and colonial morphologies, as well as colonies collected during Microcystis blooms, using fluorescence excitation - emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC). This method enables to make insight into protein-like and humic acid-like components but cannot detect polysaccharides. The EPS was successfully categorized into three humic acid-like components (C1 – C3) and a protein-like component (C4). Component C1 was discovered to be involved in colony formation and colony size growth of Microcystis. EPS content varied among Microcystis morphospecies, such as M. aeruginosa, M. wesenbergii and M. ichthyoblabe, and this was significantly affected by the environmental constraints rather than the morphospecies. The proportion of C1 relating to larger colony size was negatively correlated to temperature and concentrations of TN and TP. The tightly bound EPS directly promoted colony formation, but the soluble EPS or loosely bound EPS alone did not induce colony formation in Microcystis. These results advanced the current knowledge on the chemical materials involved in the colony formation of Microcystis and provided new clues in unicellular-multicellular transformation as well as colonial morphology changes in Microcystis.

Nitrogen limitation affects the sinking property of Microcystis by promoting carbohydrate accumulation

Nitrogen limitation has been proven to inhibit Microcystis proliferation, and the significant decline in Microcystis blooms in late summer or autumn has been considered to be related to the nitrogen depletion in water. Sinking loss is another factor that influences the dynamics of cyanobacteria in lakes. However, to date, it is still unclear how the sinking property of Microcystis responds to nitrogen availability. Our results suggest that nitrogen limitation would directly influence sinking property of Microcystis, through a significant increase in the specific density of cells. In the short term, carbohydrate accumulation was mainly responsible for the high specific density, showing a high correlation among the NO3−-N concentration, specific density and carbohydrate content. Furthermore, carbohydrates could rapidly accumulate after one light/dark cycle, which was mainly due to the reduction in carbohydrate consumption in the darkness under nitrogen limitation. Under nitrogen-light coupling conditions, the specific density ranged from 1.060 to 1.068, except for the treatment with high-nitrogen plus low-light, which showed the value of 1.032. More importantly, when coupled with low nitrogen, the low light did not decrease the carbohydrate content and the specific density, which implied that the sinking cells could not migrate back to the surface. Accordingly, a hypothesis was proposed that the carbohydrate accumulation induced by low nitrogen availability caused an increase in specific density, which invalidates the buoyancy regulation, and cells sink continually out of the water column. This study explores a new understanding on the disappearance mechanisms of Microcystis blooms in the late summer and fall.

Preliminary evaluation of ecological effects of silver and bighead carps to control cyanobacterial blooms in the early eutrophication lakes

放养鲢（Hypophthalmichthys molitrix）、鳙（Aristichthys mobilis）控制富营养化湖泊蓝藻水华暴发是当前最有效的手段之一.为评估富营养化初期湖泊鲢、鳙控藻的生态效果，2016年在洱海红山湾开展原位围栏鲢、鳙控藻实验，对围栏内外的浮游生物群落结构及水环境因子的变化进行对比分析，同时测定了围栏内鲢、鳙的生长及摄食节律.结果表明：围栏内鲢、鳙呈现匀速生长，围栏生存环境适宜.根据Egger's模型估算鲢、鳙的日摄食量分别为24.96%和18.18%，鲢的日粮高于鳙；滤食率结果表明，鲢对浮游植物的摄食率高于鳙（分别为3.01和2.19 L/（g·h），而鳙对浮游动物的滤食率高于鲢（分别为18.61和13.54 L/（g·h））.研究期间，围栏内外水体理化因子无显著差异；但围栏内外微囊藻生物量差异明显，并且在7月达到生物量峰值（围栏内为1.7 mg/L，围栏外为2.4 mg/L）.鲢、鳙对浮游植物的优势种类——微囊藻和隐藻有明显的削减效果，6-8月逐渐上升并在8月达到最高（64%）；当浮游植物优势种由微囊藻替换为硅藻门和绿藻门的种类时，鲢、鳙的削减效率不明显（10-11月为负值）.此外，鲢、鳙放养显著降低了浮游甲壳动物的总生物量和枝角类生物量.因此，结合实验结果得出，鲢具有更高的控藻能力，尤其对微囊藻水华，但同时具备了较高对浮游甲壳动物的削减能力，需要进一步分析富营养化初期湖泊——洱海中实施非经典生物操纵的适宜性.;It is one of the most effective ways to control the outbreak of cyanobacteria blooms in eutrophic lakes by stocking silver and bighead carps. In order to evaluate the ecological effects of controlling algae by silver and bighead carps in early eutrophication lakes. In 2016, a little biomanipulation in-situ pen with the stock of silver and bighead carps was built to control cyanobacterial blooms in Hongshan Bay of Lake Erhai. The changes of plankton community structure and water environmental factors were compared and analyzed within and outside the pen. Meanwhile, the growth and feeding rhythm of silver and bighead carps were measured. The pen-cultured silver and bighead carp all displayed normal growth, the survival environment of the pen is suitable. Daily rations of silver and bighead carp were estimated by Egger's model in the main growing season. Filtration rate was calculated from the daily ration and the density plankton in the lake. Daily rations of silver and bighead carp was 24.96% and 18.18%. The daily rations silver carp is higher than that of bighead carp. Filtration rates of silver and bighead carp for phytoplankton were 3.01 L/(g·h) and 2.19 L/(g·h), respectively, and filtration rates for zooplankton were 13.54 L/(g·h) and 18.61 L/(g·h), respectively. Silver carp had a stronger ability of eliminating phytoplankton than bighead carp. Bighead carp had a stronger ability of eliminating zooplankton than silver carp. During the study, there was no significant difference in the environmental parameters within and outside the pen. The biomass of Microcystis reached its peak in July (1.7 mg/L in the fish pen and 2.4 mg/L in the surrounding lake water). The Microcystis biomass was significantly lower in the pen. The present stocking density of silver and bighead carp(about 20 g/m³ in June)was effective to control Microcystis. From June to August, the reduction rate of the phytoplankton in the silver and bighead carp gradually increased, and the rate of reduction was up to 64% in August. When phytoplankton's dominant species Chlorophyta and diatom replace Microcystis, the rate of reduction decreased gradually, with negative values in October and November. Furthermore, the biomass of crustacean zooplankton biomass and cladocerans biomass were significantly lower in the pen. Therefore, in combination with several experimental results, silver carp had a stronger ability of eliminating phytoplankton than bighead carp. Especially for Microcystis blooms, silver carp at the same time have the higher on the reduction ability of crustacean zooplankton. We need to further analyze the suitability of non-traditional biological manipulation in the early stage of eutrophication Lake Erhai.

Effects of the cultivable bacteria attached to Microcystis colonies on the colony size and growth of Microcystis

The interactions between bacteria and algae may play a significant part in the formation and development of algal blooms. The bloom-forming cyanobacterium Microcystis occurs mainly as colonial form in natural waters, and thus it is necessary to study the interaction between bacteria and colonial Microcystis. This paper aimed to investigate effects of the cultivable bacteria attached to Microcystis colonies on the colony size and growth of colonial Microcystis aeruginosa. Eleven bacterial strains were isolated from M. aeruginosa colonies collected from Lake Taihu. Among these bacteria, seven bacterial isolates significantly influenced the colony size of M. aeruginosa, and four bacterial isolates significantly influenced the growth rate of M. aeruginosa. Four isolates, related to the Exiguobacterium, Delftia, Bacillus and Stenotrophomonas, significantly decreased the colony size of M. aeruginosa by 36-51%, and two isolates, assigned to the Chryseobacterium and Pseudomonas chengduensis, significantly increased the M. aeruginosa colony size by 89% and 63%, respectively, while these isolates had no effect on the cyanobacterial growth rate. Two isolates, belonged to the Rheinheimera and Pseudomonas, significantly decreased the growth rate of M. aeruginosa by 47% and 36%, respectively, and one bacterial strain related to Aeromonas increased the cyanobacterial growth rate by 22%, while these isolates had no effect on the cyanobacterial colony size. One isolate belonged to Sphingomonas was found to significantly increase the colony size of M. aeruginosa by 80% and significantly decrease the growth rate of M. aeruginosa by 21%. PCR-denaturing gradient gel electrophoresis (PCR-DGGE) analysis showed that all of the bacterial isolates were able to colonize M. aeruginosa colonies. Our data suggested that the bacteria attached to Microcystis colonies might influence the cyanobacterial colony size and growth, and thus influence the formation and development of Microcystis blooms.

Effects of disturbance modes on the size of <i>Microcystis flos-aquae</i> colonies

风浪扰动是影响湖泊生态系统的重要环境因素之一.为了解扰动方式对微囊藻群体大小的影响，在实验室可控条件下，模拟不同扰动方式（持续扰动和间歇扰动）对太湖水华微囊藻（Microcystis flos-aquae）群体大小的影响.结果显示，间歇扰动组水华微囊藻群体从35.09 μm迅速增大至43.73 μm，实验第17天时为59.00 μm；而持续扰动组水华微囊藻群体大小先从35.07 μm增大到43.51 μm，实验第17天时减小至13.95 μm；不扰动组整个实验期间群体大小相对稳定，实验初为35.38 μm，实验第17天时为33.67 μm.方差分析显示，间歇扰动组群体大小显著大于持续扰动组和不扰动组，持续扰动组显著小于不扰动组.实验第17天时间歇扰动组藻细胞密度（1.675×10⁶ cells/ml）显著高于持续扰动组（0.344×10⁶ cells/ml）和不扰动组（1.461×10⁶ cells/ml）.研究结果表明，适当强度下的间歇扰动能促使水华微囊藻群体显著增大和生长，而长时间的持续扰动则会抑制水华微囊藻群体的聚集和生长，该结果有助于人们对太湖微囊藻水华暴发机理的认识.;Disturbance induced by wind-wave is one of the important environmental factors that affect the lake ecosystem. To understand the effect of disturbance modes on the size of Microcystis flos-aquae colonies in lakes, one experiment on the effects of different simulated disturbance modes (continuous disturbance and intermittent disturbance) on the size of Microcystis flos-aquae colonies from Lake Taihu was conducted under controlled conditions in laboratory. The experiment results showed that the size of Microcystis flos-aquae colony increased rapidly from 35.09 μm to 43.73 μm in the intermittent disturbance groups, and to 59.00 μm on the 17th day of the experiment. However, the size of Microcystis flos-aquae colony in the continuous disturbance groups increased from 35.07 μm to 43.51 μm, and decreased to 13.95 μm on the 17th day of the experiment. The size of Microcystis flos-aquae colony in the non-disturbance groups was relatively stable throughout the experiment, which was 35.38 μm, 33.67 μm at the beginning and on the 17th day of the experiment, respectively. Variance analysis showed that the size of Microcystis flos-aquae colony in the intermittent disturbance groups was significantly greater than that in the continuous disturbance groups and the non-disturbance groups. Also, the size of Microcystis flos-aquae colony in the continuous disturbance groups was significantly smaller than that in the non-disturbance group. On the 17th day of the experiment, the algal cell density (1.675×10⁶ cells/ml) was significantly higher in the intermittent disturbance groups than that in the continuous disturbance groups (0.344×10⁶ cells/ml) and the non-disturbance groups (1.461×10⁶ cells/ml). The results showed that intermittent disturbances at appropriate intensities could significantly increase the size and the growth of Microcystis flos-aquae colony, but continuous disturbance could inhibit their aggregation and growth over long time, which is valuable for understanding the breakout mechanism of Microcystis blooms in Lake Taihu.

Community dynamics of free-living and particle-attached bacteria following a reservoir Microcystis bloom

The composition of microbial communities can vary at the microspatial scale between free-living (FL) and particle-attached (PA) niches. However, it remains unclear how FL and PA bacterial communities respond to cyanobacterial blooms across water depths. Here, we examined the community dynamics of the FL (0.2–3 μm) and PA (>3 μm) bacterioplankton based on 16S rRNA gene high-throughput sequencing in a subtropical stratified reservoir under Microcystis aeruginosa bloom and non-bloom conditions. Both FL and PA bacterioplankton communities showed different responses in alpha- and beta-diversities to the bloom, suggesting the idea that the responses of bacterial community could depend on lifestyle. Specifically, abundant PA subcommunities showed a greater variation between bloom and non-bloom groups than abundant FL ones. In contrast, rare FL subcommunities exhibited a stronger response to water depth than rare PA ones. Furthermore, the rare taxa exhibited a preference for PA status, shaped and stimulated by the M. aeruginosa bloom. Our analyses also showed that PA bacterial communities were generally more diverse and appeared to be more responsive to routinely measured environmental variables than FL bacteria. Microcystis blooms had a facilitative influence on specific bacteria by mediating the transitions from free-living to particle-attached lifestyles. Altogether, these findings highlight the importance of bacterial lifestyle and abundance in understanding the dynamics of microbial community in cyanobacterial bloom aquatic ecosystem.

Hindcasting eutrophication and changes in temperature and storage volume in a semi-arid reservoir: a multi-decadal Landsat-based assessment.

In situ monitoring of freshwater systems is often constrained by cost and accessibility, particularly in developing countries and in remote areas. Satellite remote sensing is therefore increasingly being integrated with existing in situ water quality monitoring programs. In this study, we use the Landsat TM/ETM+ image record collected between 1984 and 2015 to track temporal changes in trophic status, chlorophyll-a levels, algal bloom incidences, water clarity, water temperature, and reservoir water volume in a poorly monitored hypereutrophic semi-arid reservoir. Historical reservoir water quality data are inferred from calibrated Landsat-based empirical algorithms. The results show that, although the reservoir has existed in a eutrophic to hypereutrophic state over the past 30years, its water quality has significantly deteriorated in the most recent decade. Mean summer chlorophyll-a concentrations were found to have increased by around 163% between 1984 and 2015, while water clarity dropped by more than 58% over the same period. Statistically significant changes in surface water temperatures were also apparent for the month of August, with a cumulative increase of 1.24°C over the 31-year study period. The rise in temperature appears to correlate with the incidence of Microcystis blooms observed in the reservoir over the past decade. On the other hand, the water volume in the reservoir was found to have been fairly stable over time, likely as a result of adaptive reservoir management. This study demonstrates the strength of using Landsat data to hindcast and quantify changes in water quality and quantity in poorly monitored freshwater systems.

Unique Biosynthetic Pathway in Bloom-Forming Cyanobacterial Genus Microcystis Jointly Assembles Cytotoxic Aeruginoguanidines and Microguanidines.

The cyanobacterial genus Microcystis is known to produce an elaborate array of structurally unique and biologically active natural products, including hazardous cyanotoxins. Cytotoxic aeruginoguanidines represent a yet unexplored family of peptides featuring a trisubstituted benzene unit and farnesylated arginine derivatives. In this study, we aimed at assigning these compounds to a biosynthetic gene cluster by utilizing biosynthetic attributes deduced from public genomes of Microcystis and the sporadic distribution of the metabolite in axenic strains of the Pasteur Culture Collection of Cyanobacteria. By integrating genome mining with untargeted metabolomics using liquid chromatography with mass spectrometry, we linked aeruginoguanidine (AGD) to a nonribosomal peptide synthetase gene cluster and coassigned a significantly smaller product to this pathway, microguanidine (MGD), previously only reported from two Microcystis blooms. Further, a new intermediate class of compounds named microguanidine amides was uncovered, thereby further enlarging this compound family. The comparison of structurally divergent AGDs and MGDs reveals an outstanding versatility of this biosynthetic pathway and provides insights into the assembly of the two compound subfamilies. Strikingly, aeruginoguanidines and microguanidines were found to be as widespread as the hepatotoxic microcystins, but the occurrence of both toxin families appeared to be mutually exclusive.

Dynamic Changes of Nitrogen-Transforming and Phosphorus-Accumulating Bacteria Along with the Formation of Cyanobacterial Blooms

In order to reveal the dynamic changes of nitrogen-transforming and phosphorus-accumulating bacteria in the process of cyanobacterial bloom formation, bacterial community structure and functional genes associated with nitrogen cycling were analyzed using high-throughput sequencing and real-time quantitative PCR (qPCR). The high-throughput sequencing results showed that the diversity of bacterial communities decreased during cyanobacterial blooms, and the lacustrine free-living and bloom-attached bacterial communities varied with increased bloom density. With increasing density of cyanobacteria, the relative abundance of Actinobacteria and Bacteroidetes decreased, whereas that of Firmicutes increased. Moreover, the growth of phosphate-accumulating organisms was increased in the phycosphere of cyanobacterial blooms, while that of nitrifiers was inhibited. Denitrifiers increased significantly under moderate blooms. The qPCR data also revealed that the abundance of nitrification and denitrification genes decreased or disappeared with the development of cyanobacterial blooms, indicating that the nitrogen transformation process might be inhibited, which showed a positive feedback of bacterial community to the development of Microcystis blooms by satisfying the needs of the nutrients budget.

Analysis of free and metabolized microcystins in samples following a bird mortality event

In the summer of 2012, over 750 dead and dying birds were observed at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island, Maryland, USA (Chesapeake Bay). Clinical signs suggested avian botulism, but an ongoing dense Microcystis bloom was present in an impoundment on the island. Enzyme-linked immunosorbent assay (ELISA) analysis of a water sample indicated 6000 ng mL−1 of microcystins (MCs). LC-UV/MS analysis confirmed the presence of MC-LR and a high concentration of an unknown MC congener (m/z 1037.5). The unknown MC was purified and confirmed to be [D-Leu1]MC-LR using NMR spectroscopy, LC-HRMS and LC–MS2, which slowly converted to [D-Leu1,Glu(OMe)6]MC-LR during storage in MeOH. Lyophilized algal material from the bloom was further characterized using LC-HRMS and LC–MS2 in combination with chemical derivatizations, and an additional 24 variants were detected, including MCs conjugated to Cys, GSH and γ-GluCys and their corresponding sulfoxides. Mallard (Anas platyrhynchos) livers were tested to confirm MC exposure. Two broad-specificity MC ELISAs and LC–MS2 were used to measure free MCs, while ‘total’ MCs were estimated by both MMPB (3-methoxy-2-methyl-4-phenylbutyric acid) and thiol de-conjugation techniques. Free microcystins in the livers (63–112 ng g−1) accounted for 33–41% of total microcystins detected by de-conjugation and MMPB techniques. Free [D-Leu1]MC-LR was quantitated in tissues at 25–67 ng g−1 (LC–MS2). The levels of microcystin varied based on analytical method used, highlighting the need to develop a comprehensive analysis strategy to elucidate the etiology of bird mortality events when microcystin-producing HABs are present.

The ecological risks of hydrogen peroxide as a cyanocide: its effect on the community structure of bacterioplankton

Microcystis blooms are an environmental and ecological concern that has received a serious attention. Hydrogen peroxide (H2O2) is an environment-friendly cyanocide that is commonly used to control Microcystis blooms. While the ecological safety of H2O2 has been previously studied, its influence on bacterioplankton has not been investigated to date. In this study, we used mesocosm experiments to determine the influence of H2O2 on the dynamic changes of the community structure of bacterioplankton. By using deep-sequencing and metagenomics strategy we determined the community structures of phytoplankton and bacterioplankton assemblages that were dominated by Microcystis at a highly eutrophic Dianchi Lake, China. The results showed that Microcystis was more sensitive to H2O2 than other eukaryotic algae. More interestingly, application of H2O2 changed the community structure of bacterioplankton, evidenced by the emergence of Firmicutes as the dominant species in place of Bacteroidetes and Proteobacteria. The H2O2 treatment resulted in the community of bacterioplankton that was primarily dominated by Exiguobacterium and Planomicrobium. Our results show that the abundance changed and the bacterioplankton diversity did not recover even after the concentration of H2O2 reached to the background level. Thus, the response of bacterioplankton must be considered when assessing the ecological risks of using H2O2 to control Microcystis blooms, because bacterioplankton is the key player that forms the basis of food web of aquatic environment.

Biodiversity of cyanobacteria and other aquatic microorganisms across a freshwater to brackish water gradient determined by shotgun metagenomic sequencing analysis in the San Francisco Estuary, USA.

Blooms of Microcystis and other harmful cyanobacteria can degrade water quality by producing cyanotoxins or other toxic compounds. The goals of this study were (1) to facilitate understanding of community structure for various aquatic microorganisms in brackish water and freshwater regions with emphasis on cyanobacteria, and (2) to test a hypothesis that Microcystis genotypes that tolerate higher salinity were blooming in brackish water environments during the severe drought, 2014. Shotgun metagenomic analysis revealed that cyanobacteria dominated the brackish water region while bacteria dominated the freshwater region. A group of cyanobacteria (e.g., Aphanizomenon, Microcystis, Planktothrix, Pseudanabaena), bacteria (e.g., Bacillus, Porphyrobacter), and diatoms (Phaeodactylum and Thalassiosira) were abundant in the brackish water region. In contrast, Hassallia (cyanobacteria) and green algae (Nannochloropsis, Chlamydomonas, and Volvox) were abundant in the landward freshwater region. Station variation was also apparent. One landward sampling station located downstream of an urbanized area differed substantially from the other stations in terms of both water chemistry and community structure, with a higher percentage of arthropods, green algae, and eukaryotes. Screening of the Microcystis internal transcribed spacer region revealed six representative genotypes, and two of which were successfully quantified using qPCR (Genotypes I and VI). Both genotypes occurred predominantly in the freshwater region, so the data from this study did not support the hypothesis that salinity tolerant Microcystis genotypes bloomed in the brackish water region in 2014.

Grazing of the copepod Cyclops vicinus on toxic Microcystis aeruginosa: potential for controlling cyanobacterial blooms and transfer of toxins

Abstract Grazing of zooplankton on phytoplankton may contribute to a reduction of harmful cyanobacteria in eutrophic waters. However, the feeding capacity and interaction between zooplankton and toxic cyanobacteria vary among grazer species. In this study, laboratory feeding experiments were designed to measure the grazing rate of the copepod Cyclops vicinus on Microcystis aeruginosa and the potential microcystin (MC) accumulation in the grazer. Copepods were fed a mixed diet of the edible green alga Ankistrodesmus falcatus and toxic M. aeruginosa for 10 days. The results showed that C. vicinus efficiently ingested toxic Microcystis cells with high grazing rates, varying during the feeding period (68.9–606.3 Microcystis cells animal-1 d-1) along with Microcystis cell density. Microcystis cells exhibited a remarkable induction in MC production under grazing conditions with concentrations 1.67–12.5 times higher than those in control cultures. Furthermore, C. vicinus was found to accumulate MCs in its body with concentrations increasing during the experiment (0.05–3.21 μg MC animal-1). Further in situ studies are needed to investigate the ability of Cyclops and other copepods to assimilate and detoxify MCs at environmentally relevant concentrations before deciding on the biocontrol of Microcystis blooms by copepods.

Transcriptomic Analysis Reveals the Pathways Associated with Resisting and Degrading Microcystin in Ochromonas.

Toxic Microcystis bloom is a tough environment problem worldwide. Microcystin is highly toxic and is an easily accumulated secondary metabolite of toxic Microcystis that threatens water safety. Biodegradation of microcystin by protozoan grazing is a promising and efficient biological method, but the mechanism in this process is still unclear. The present study aimed to identify potential pathways involved in resisting and degrading microcystin in flagellates through transcriptomic analyses. A total of 999 unigenes were significantly differentially expressed between treatments with flagellates Ochromonas fed on microcystin-producing Microcystis and microcystin-free Microcystis. These dysregulated genes were strongly associated with translation, carbohydrate metabolism, phagosome, and energy metabolism. Upregulated genes encoding peroxiredoxin, serine/threonine-protein phosphatase, glutathione S-transferase (GST), HSP70, and O-GlcNAc transferase were involved in resisting microcystin. In addition, genes encoding cathepsin and GST and genes related to inducing reactive oxygen species (ROS) were all upregulated, which highly probably linked with degrading microcystin in flagellates. The results of this study provided a better understanding of transcriptomic responses of flagellates to toxic Microcystis as well as highlighted a potential mechanism of biodegrading microcystin by flagellate Ochromonas, which served as a strong theoretical support for control of toxic microalgae by protozoans.