In this study, the distribution, transfer and fate of both polychlorinated biphenyls (PCBs) and cyanotoxins via phytoplankton routes were systematically investigated in two Chinese lakes. Results indicated that PCB adsorption/bioaccumulation dynamics has significantly positive correlations with the biomass of green alga and diatoms. Total lipid content of phytoplankton is the major factor that influences PCB adsorption/bioaccumulation. Cyanobacterial blooms with relatively lower lipid content could also absorb high amount of PCBs due to their high cell density in the water columns, and this process was proposed as major route for the transfer of PCBs in Chinese eutrophic freshwater. According to these findings, a novel route on fates of PCBs via phytoplankton and a green bioadsorption concept were proposed and confirmed. In the practice of mechanical collections of bloom biomass from Lake Taihu, cyanotoxin/cyanobacteria and PCBs were found to be removed simultaneously very efficiently followed this theory.Download high-res image (72KB)Download full-size image

The succession amongst different cyanobacteria genera remains understudied and poorly understood as much of the focus has been on mono-specific blooms. The spring–summer succession between Aphanizomenon flos-aquae and Microcystis and its underlying mechanism were investigated from 2009 to 2012 in hypereutrophic Dianchi Lake in China. Regularly, A. flos-aquae grows rapidly and forms bloom in March at water temperatures around 15°C, followed by Microcystis blooming around 18°C in April. Since 2010, the pattern of succession has changed, featuring an increase of Microcystis but decrease of A. flos-aquae biovolume, leading to near disappearance of A. flos-aquae in 2012. Coincidently, there was a sharp increase of nitrogen concentration in 2010, going up to 5.67 mg/l in 2011, and a big increase in the mass ratio of TN to TP from 13.6 in 2009 to 21.1 in 2011. We hypothesized that temperature is the most influential factor governing the initiation of rapid growth and succession between A. flos-aquae and Microcystis, while increase of TN and/or ratio of TN to TP may trigger the decline and disappearance of A. flos-aquae, time of recruitment, and the population dynamics of Microcystis. Our findings are not only meaningful to the understanding of the cyanobacterial bloom mechanism but also to the management of shallow eutrophic lakes.

The cyanobacterium Pseudanabaena sp. FACHB 1277, a 2-methylisoborneol (2-MIB) producer isolated from Xionghe Reservoir, was identified by molecular biological methods based on the 16S rDNA sequence. Pseudanabaena sp. FACHB 1277 is a planktonic freshwater species with relatively high 2-MIB per cell density value (7.76 × 10−6 ng cell−1) and specific growth rate (0.25 ± 0.01 d−1). The effects of temperature and light intensity on 2-MIB production of Pseudanabaena sp. FACHB 1277 were investigated. Of the six temperatures tested, 10, 15, 20, 25, 30, and 35 °C, the maximum total 2-MIB per cell density and minimum cell density were observed at 10 °C, while the total 2-MIB and dissolved 2-MIB (including extracellular and dissolved intracellular 2-MIB) increased with increasing temperature. Among the six tested light intensities (10, 25, 40, 55, 70, and 85 μmol photons m−2 s−1), the minimum total 2-MIB per cell density and maximum cell density were observed at 25 μmol photons m−2 s−1. The total 2-MIB and extracellular 2-MIB increased with light intensity increasing from 10 to 40 μmol photons m−2 s−1, while no significant increase was observed when the light intensity was higher than 40 μmol photons m−2 s−1. The maximum intracellular 2-MIB (including dissolved and bound) occurred at 25 μmol photons m−2 s−1. The present study indicates that increasing temperature could favor the conversion of bound intracellular to dissolved 2-MIB, while increasing light intensity stimulates the release of dissolved intracellular 2-MIB into the environment.

In China, mechanical collection of cyanoblooms followed by soil-based treatments has been widely used as emergency strategies in many eutrophicated freshwaters. This study was to evaluate both efficiencies and potential risks of typical soil-based technologies. Results from this study indicated that over 90% of cyanobacterial biomass and 96% of dissolved microcystins (MCs) could be restrained in soils via three-level systems, which were much better than single-level systems. High concentrations of MCs, ranged from 65 to 276 ng g–1 and from 2.12 to 6.6 ng g–1, were found in soils around treatment systems and croplands, respectively. In the soil solutions, MCs ranged from 0.35 to 2.0 μg L–1, showing a potentially high leaching risk. In the samples from shallow groundwater near the treatment systems, MC concentrations were detected as high as 1.2 μg L–1. Moreover, bioaccumulations of MCs varied between 22 and 365 μg kg–1, and 19–222 μg kg–1 were found in 13 kinds of crops and 7 kinds of wild grass, respectively. Our results indicated for the first time that current soil-based technologies were effective but could pose potential environmental, ecological, and public health risks. Further improvements of these technologies were also proposed based on our findings.

Previous investigations suggested that buoyancy state in response to light differed between individuals within natural populations of cyanobacteria. To understand the mechanisms of heterogeneity of buoyancy in different species/strains in relation to light, two types of colonial Microcystis in different buoyancy behavior were selected and used to compare their photosynthetic activity, gas vesicle volume, ballast mass, and migration at varying light regime. The photosynthesis–irradiance curve and Fv/Fm examination indicated that negatively buoyant strains were more adapted at high irradiance than buoyant ones. Transcription levels of gvp gene and gas vesicle volume decreased in buoyant strains, but increased in negatively buoyant ones at high irradiance. The results indicated that the combination effect of decrease in gas vesicle buoyancy and increase in carbohydrate contributed to the downward migration of buoyant strains, while the significant increase of gas vesicles provided sufficient buoyancy to negate ballast mass, resulting in the upward migration of negatively buoyant ones at high irradiance. In addition, either sinking or floating velocities were elevated in buoyant and negatively buoyant strains, coincidently with the colony enlargement of all strains at high irradiance, respectively. These findings suggest that this heterogeneity was associated with the interplay between gas vesicles, ballast, and colony size. The fact that different species/strains of Microcystis respond diversely to light depending on their physiological conditions presents a good example to understand heterogeneity of buoyancy in the field, and the presence of heterogeneity of buoyancy may be implicated in the dominancy and persistence of Microcystis bloom in ever-changing environment.

The cyanobacterium Microcystis is the most common bloom-forming species in eutrophicated water bodies. Known eco-physiological advantages of this organism help it to compete effectively with other algae and cyanobacteria; however, little is known about the physiological characteristics competence of colonial Microcystis. In the present study, carbonic anhydrase (CA) activity, the affinity for dissolved inorganic carbon (DIC), and the transcription of CA genes were examined in unicellular and colonial Microcystis strains. In comparison with unicellular strains, colonial Microcystis exhibited dramatically higher inorganic carbon affinity at 25 and 35°C, but no significant differences were observed at 15°C. The relative transcription levels of the CA genes icfA1, icfA2, ecaA, and ecaB in all colonial Microcystis were significantly higher than those in unicellular Microcystis at 25 and 35°C. In addition, CA activities of Microcystis increased with temperature, but no significant difference was observed between the unicellular and colonial Microcystis. These results suggest that temperature and phenotypes probably play important roles in the utilization of DIC and trigger the expression of CA genes of Microcystis. The present results may indicate that the capacity for utilizing inorganic carbon plays a role in the persistence or/and succession of different Microcystis blooms.

AbstractTo identify some desirable algal strains for our future research and/or the production of algae-based biofuel, 43 green algal strains were successfully isolated from Chinese freshwaters, and then incubated in the laboratory bioreactors for the growth and oil accumulation investigations. During a 15 d incubation experiment, the accumulations of their biomass and total lipids, together with the lipid productivities for these green algal strains were systematically investigated and compared. Results indicated that the accumulations of biomass for the 43 algal strains ranged from 0.53 g/L to 6.07 g/L during the experiments, with the highest biomass of 6.07 g/L for green algae Scenedesmus bijuga. The lipid content for the tested algal strains varied from 20% to 51% of the dry biomass at the end of cultivation experiments. Green algae Chlorella pyrenoidosa was one of the best oil producers based on our investigations, with the total lipid content of 51% of dry biomass. Taking the growth rates and the accumulations of intracellular lipids into the consideration, 10 strains were considered to have significant potential for biofuel applications. In addition, the lipid productivities of the selected strains were further investigated.

Microcystin-LR (MC-LR) is a potent heptapeptide hepatotoxin at high doses, but its underlying mechanism of promoting liver cell proliferation at low doses is unclear. The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) is key in mediating the protective antioxidant response against various environmental toxicants, but emerging data suggest that constitutive activation of Nrf2 contributes to a malignant phenotype. The purpose of this study was to characterize the interactions and effects of Nrf2 activation on cell proliferation induced by MC-LR treatment. Treatment of HepG2 and Hep3B cells with MC-LR resulted in significant increases in Nrf2-ARE binding activities in the nuclear fractions and upregulation of its downstream genes HO-1 and NQO1. A possible mechanism may be that MC-LR binds to the cytosolic regulator protein Keap1 to liberate Nrf2. Nrf2 knockdown inhibited MC-LR-induced cell proliferation and cell cycle progression. Together, these results indicate that MC-LR-induced upregulation of Nrf2 in cancer cells promotes liver cancer cell growth and suggest a positive role of Nrf2 in tumorigenesis.

Toxic cyanobacterial blooms constitute a threat to human safety because Microcystis sp. releases microcystins during growth, and particularly during cell death. Therefore, analysis of toxic and nontoxic Microcystis in natural communities is required in order to assess and predict bloom dynamics and toxin production by these organisms. In this study, an analysis combining fluorescence in situ hybridization (FISH) with flow cytometry (FCM) was used to discriminate between toxic and nontoxic Microcystis and also to quantify the percentage of toxic Microcystis present in blooms. The results demonstrate that the combination of FISH and flow cytometry is a useful approach for studying the ecology of Microcystis toxin production and for providing an early warning for toxic Microcystis blooms.

An indirect inhibitive surface plasmon resonance (SPR) immunoassay was developed for the microcystins (MCs) detection. The bioconjugate of MC-LR and bovine serum albumin (BSA) was immobilized on a CM5 sensor chip. A serial premixture of MC-LR standards (or samples) and monoclonal antibody (mAb) were injected over the functional sensor surface, and the subsequent specific immunoreaction was monitored on the BIAcore 3000 biosensor and generated a signal with an increasing intensity in response to the decreasing MCs concentration. The developed SPR immunoassay has a wide quantitative range in 1–100 μg L−1. Although not as sensitive as conventional enzyme-linked immunosorbent assay (ELISA), the SPR biosensor offered unique advantages: (1) the sensor chip could be reusable without any significant loss in its binding activity after 50 assay-regeneration cycles, (2) one single assay could be accomplished in 50 min (including 30-min preincubation and 20-min BIAcore analysis), and (3) this method did not require multiple steps. The SPR biosensor was also used to detect MCs in environmental samples, and the results compared well with those obtained by ELISA. We conclude that the SPR biosensor offers outstanding advantages for the MCs detection and may be further developed as a field-portable sensor for real-time monitoring of MCs on site in the near future.

•We exhibited growth inhibition of Microcystis on Aphanizomenon.•Different Microcystis inhibited the growth of Aphanizomenon to various degrees.•The allelopathic effect of some Microcystis strains was inducible.•Microcystin-LR was not the allelochemical which inhibited Aphanizomenon.Severe eutrophication of freshwater ecosystem promotes frequent and long-lasting cyanobacteria blooms. In many lakes, the population dynamics of the dominant cyanobacteria species follows seasonal shifts. In Lake Dianchi, a plateau lake in China, blooms involve the alternating seasonal succession of two dominant cyanobacteria species, Aphanizomenon and Microcystis. In this study, we investigated the inhibitory effects of five Microcystis strains on a strain of Aphanizomenon flos-aquae, all isolated during blooms in Lake Dianchi. We used dialysis tubing involved batch and semi-continuous co-culture bioassays to investigate the interaction between these two genera. Our results revealed that different Microcystis inhibited the growth of A. flos-aquae to various degrees, with the strains Microcystis ichthyoblabe kutz 1313 and Microcystis aeruginosa 905 (Ma905) exhibiting the strongest inhibitory effects. The axenic Ma905 did not differ from a non-axenic strain in the inhibitory effect, demonstrating that the growth inhibitory effects we observed were due to Microcystis rather than bacteria. Filtrate of most Microcystis monoculture in different growth phases had a negligible effect on A. flos-aquae. However, the filtrate of Microcystis viridis 1337 (Mv1337) and Ma905 co-cultured with A. flos-aquae from day 21 and day 28, respectively, exhibited stronger inhibitory effects than did their corresponding monoculture filtrates, suggesting that the allelopathic effect of some Microcystis strains is inducible. Results of experiments using solid phase extraction (SPE) fractions of Microcystis monoculture were similar to those from the dialysis tubing bioassays. The microcystin content of the SPE fractions of Ma905 and Mv1337 from day 28 contained 380 μg L−1 and 290 μg L−1 microcystin-LR (MC-LR), respectively. However, a further bioassay with pure MC-LR with concentrations of 250 μg L−1 and 500 μg L−1 did not inhibit A. flos-aquae, and further excluded MC-LR as a candidate allelochemical. In summary, our research demonstrates that some Microcystis strains are able to suppress the growth of A. flos-aquae. This finding indicates that allelopathic effects likely play a role in driving the alternating seasonal succession of these dominant cyanobacteria blooms in Lake Dianchi.

Although Microcystis-based toxins have been intensively studied, previous studies using laboratory cultures of Microcystis strains are difficult to explain the phenomenon that microcystin concentrations and toxin variants in natural blooms differ widely and frequently within a short-term period. The present study was designed to unravel the mechanisms for the frequent variations of intracellular toxins related to the differences in cyanobacterial colonies during bloom seasons in Lake Taihu, China. Monitoring of Microcystis colonies during warm seasons indicated that the variations in microcystins in both concentrations and toxin species were associated with the frequent alteration of Microcystis colonies in Lake Taihu. High concentration of microcystins in the blooms was always associated with two Microcystis colonies, Microcystis flos-aquae and Microcystis aeruginosa, whereas when Microcystis wesenbergii was the dominant colonial type, the toxin production of the blooms was low. Additionally, environmental factors such as temperature and nutrition were also shown to have an effect on the toxin production of the blooms, and may also potentially influence the Microcystis species present. The results of the present study provides insight into a new consideration for quick water quality monitoring, assessment and risk alert in cyanobacterium- and toxin-contaminated freshwaters, which will be beneficial not only for water agencies but also for public health.

•Potential anoxic biodegradation of both dissolved and intracellular microcystins (MCs) was evaluated.•Dissolved MCs in sediments were significantly reduced under anoxic condition.•Intracellular MCs were not rapidly degraded in unruptured fresh cyanobacteria.•The addition of soluble organic matter enhanced anoxic biodegradation of MCs.The kinetics of the anoxic biodegradation of intracellular and dissolved microcystin (MCs) and the effects of soluble organic materials on the process were investigated via a series of well-controlled microcosm experiments. The potential for the removal of intracellular and dissolved MCs from lake sediment differed. The dissolved MCs could be degraded to below the detection limit at 20 °C within one to 3 days after a lag phase of 2–6 days under anoxic conditions. The levels of intracellular MCs were also significantly reduced in the sun-dried cyanobacterial samples but not rapidly reduced in fresh cyanobacterial samples until the cells were ruptured. The addition of soluble organic matter enhanced the anoxic biodegradation of MCs. These results indicate that the application of anoxic biodegradation via lake sediments is an effective method to remove dissolved and intracellular MCs and that this process exhibits significant bioremediation potential for the further treatment of cyanobacteria.Download full-size image

Microcystins (MCs), the products of blooming algae Microcystis, are waterborne environmental toxins that have been implicated in the development of liver cancer, necrosis, and even fatal intrahepatic bleeding. Alternative protective approaches in addition to complete removal of MCs in drinking water are urgently needed. In our previous work, we found that sulforaphane (SFN) protects against microcystin-LR (MC-LR)-induced cytotoxicity by activating the NF-E2-related factor 2 (Nrf2)-mediated defensive response in human hepatoma (HepG2) and NIH 3T3 cells. The purpose of this study was to investigate and confirm efficacy the SFN-induced multi-mechanistic defense system against MC-induced hepatotoxicity in an animal model. We report that SFN protected against MC-LR-induced liver damage and animal death at a nontoxic and physiologically relevant dose in BALB/c mice. The protection by SFN included activities of anti-cytochrome P450 induction, anti-oxidation, anti-inflammation, and anti-apoptosis. Our results suggest that SFN may protect mice against MC-induced hepatotoxicity. This raises the possibility of a similar protective effect in human populations, particularly in developing countries where freshwaters are polluted by blooming algae.Download high-res image (89KB)Download full-size imageResearch Highlights► SFN protected against MC-LR-induced liver damage and animal death in BALB/c mice. ► The dose of SFN is at a nontoxic and physiologically relevant dose. ► The protection included activities of anti-oxidation, anti-inflammation, and anti-apoptosis. ► SFN may protect mice against MC-induced hepatotoxicity.

•Single and combined toxic effect of MCLR and copper on V. Natans was evaluated.•Bioaccumulations of MCLR and copper in the seedlings were determined.•Synergistic effect was elicited at low concentration of MCLR and copper interaction.•Interaction of MCLR and copper increased the bioaccumulation of MCLR and copper.•Ecological risks of MCLR and copper were increased in their coexist environment.Microcystin-LR (MCLR) and copper are commonly found in eutrophic water bodies because of eutrophic run-offs, cyanobacterial blooms, and copper algicide applications. However, the ecotoxicological risk of their combination remains unknown. This study investigated the effect of MCLR, Cu, and their mixture on the growth and physiological responses of Vallisneria natans. Results showed that the combined toxicity of them was concentration dependent. Synergistic effects were elicited at low concentrations of MCLR and Cu exposure (≤0.25 + 0.64 mg/L). Additive or antagonistic effects were induced at higher concentrations. Single and combined exposures could induce oxidative stress, such as increased superoxide anion radical levels. To cope with oxidative stress, V. natans could activate their antioxidant defense systems, such as enhanced superoxide dismutase production and changes in peroxidase activities. Exposure to combined MCLR and Cu (even only with 0.005 + 0.041 mg/L) adversely affected their antioxidant defense systems. As a consequence, malondialdehyde levels significantly increased. The interaction of MCLR and Cu could also significantly increase the bioaccumulations of MCLR and Cu. This increase could be accounted for their synergistic toxic effects on V. natans. Our results suggested that the exacerbated ecological hazard of MCLR and Cu with environmental concentrations may harm aquatic ecosystems.Download high-res image (220KB)Download full-size image

•An Ecopath model of Dianchi Lake with heavy cyanobacterial bloom was first built.•Dianchi Lake was detritus-driven ecosystem with short cut on the whole food chain.•Dianchi Lake ecosystem could use positive feedback to maintain high biomass.•Heavy cyanobacterial blooms can be explained by the characteristics of food web.•Exotic zooplanktivore and filter-feeding fishes should be cautiously managed.Lake Dianchi is the largest shallow lake in Yunnan-Guizhou plateau and the sixth largest one in China. The lake has been experiencing cyanobacterial blooms in the last two decades. Although a few studies have investigated the tempo-spatial dynamics of cyanobacterial blooms and their underlying mechanisms, knowledge regarding the food web structure and trophic interactions in bloom-dominated ecosystems is scarce. In the present study, an Ecopath model was developed to assess the entire lake ecosystem on the basis of historical and survey data obtained between 2009 and 2010 at Lake Dianchi. The results showed that the aggregation of flows sensu Lindeman refers to six trophic levels (TLs), and most biomasses and trophic flows were primarily concentrated at the first three levels. About 77.5% of the trophic flows from TLI to TLII originated from detritus, whereas high proportions of under-utilised zooplankton biomass returned to the detritus because of low transfer efficiencies (2.9%) in TLII. The microbial loop was considered to be involved in linking the transfer between detritus and TLII. In addition, low values of connectance index and average mutual information implied that the food web tended to be lost in information diversity and had a less complicated structure. High cycling flows concentrated in the microbial loop reflected that the ecosystem enhanced recycling to forms positive feedback by which ecosystem locked the nutrients and promoted the inflation of biomass in plankton communities. Thus, Dianchi Lake was clearly thought to be a bottom-up control ecosystem. These characteristics of the food web partly explained why cyanobacterial blooms were exceptionally heavy and durable in this lake. Finally, the implications of artificially stocking filter-feeding fish (bighead and silver fish) and exotic zooplantivorous icefish on the ecosystem structure and function are discussed herein.

In this study, bismuth oxyhalide (BiOXs (XCl, Br, I)) semiconductors were prepared by a simple solvothermal method, with ethanol serving as solvent and a series of tetrabutylammonium halide surfactants as halogen sources. Under identical synthetic conditions, BiOBr was more readily constructed into regular flower-like hierarchical architectures. The photocatalytic properties of the materials were studied by monitoring the degradation of rhodamine B (RhB), with visible light absorption, and colorless salicylic acid (SA). It was found that both RhB and SA were rapidly degraded on the surface of BiOBr. BiOCl was rather active for the degradation of RhB, but ineffective toward the degradation of SA. However, neither RhB nor SA could be degraded effectively in the case of BiOI. Further experiments such as UV–visible spectroscopy and detection of OH and O2− radicals suggest that the electronic structure of the BiOX photocatalysts is responsible for the difference in their activities.Download high-res image (291KB)Download full-size image

Microcystins (MCs), a cyclic heptapeptide hepatotoxins, are mainly produced by the bloom-forming cyanobacerium Microcystis, which has become an environmental hazard worldwide. Long term consumption of MC-contaminated water may induce liver damage, liver cancer, and even human death. Therefore, in addition to removal of MCs in drinking water, novel strategies that prevent health damages are urgently needed. Sulforaphane (SFN), a natural-occurring isothiocyanate from cruciferous vegetables, has been reported to reduce and eliminate toxicities from xenobiotics and carcinogens. The purpose of the present study was to provide mechanistic insights into the SFN-induced antioxidative defense system against MC-LR-induced cytotoxicity. We performed cell viability assays, including MTS assay, colony formation assay and apoptotic cell sorting, to study MC-LR-induced cellular damage and the protective effects by SFN. The results showed that SFN protected MC-LR-induced damages at a nontoxic and physiological relevant dose in HepG2, BRL-3A and NIH 3 T3 cells. The protection was Nrf2-mediated as evident by transactivation of Nrf2 and activation of its downstream genes, including NQO1 and HO-1, and elevated intracellular GSH level. Results of our studies indicate that pretreatment of cells with 10 μM SFN for 12 h significantly protected cells from MC-LR-induced damage. SFN-induced protective response was mediated through Nrf2 pathway.

Lake Dianchi is a shallow and turbid lake, located in Southwest China. Since 1985, Lake Dianchi has experienced severe cyanabacterial blooms (dominated by Microcystis spp.). In extreme cases, the algal cell densities have exceeded three billion cells per liter. To predict and elucidate the population dynamics of Microcystis spp. in Lake Dianchi, a neural network based model was developed. The correlation coefficient (R2) between the predicted algal concentrations by the model and the observed values was 0.911. Sensitivity analysis was performed to clarify the algal dynamics to the changes of environmental factors. The results of a sensitivity analysis of the neural network model suggested that small increases in pH could cause significantly reduced algal abundance. Further investigations on raw data showed that the response of Microcystis spp. concentration to pH increase was dependent on algal biomass and pH level. When Microcystis spp. population and pH were moderate or low, the response of Microcystis spp. population would be more likely to be positive in Lake Dianchi; contrarily, Microcystis spp. population in Lake Dianchi would be more likely to show negative response to pH increase when Microcystis spp. population and pH were high. The paper concluded that the extremely high concentration of algal population and high pH could explain the distinctive response of Microcystis spp. population to + 1 SD (standard deviation) pH increase in Lake Dianchi. And the paper also elucidated the algal dynamics to changes of other environmental factors. One SD increase of water temperature (WT) had strongest positive relationship with Microcystis spp. biomass. Chemical oxygen demand (COD) and total phosphorus (TP) had strong positive effect on Microcystis spp. abundance while total nitrogen (TN), biological oxygen demand in five days (BOD5), and dissolved oxygen had only weak relationship with Microcystis spp. concentration. And transparency (Tr) had moderate positive relationship with Microcystis spp. concentration.