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Microcystis colonies can overwinter in sediment and may inoculate the water column through recruitment, promoting the annual recurrence of Microcystis blooms. Through microcosm experiments, the survivability of benthic Microcystis was quantitatively investigated by elucidating the dynamics of its cell numbers, photosynthetic activity, and toxin content under various sediment conditions. The abundance of Microcystis colonies in the sediment samples did not decrease significantly over the 22-week experiment at 5 °C, whereas more than 90% of the benthic population died within 3 months at 25 °C. The survivability of the Microcystis colonies under the aerobic conditions of surface sediments was significantly lower than under the anaerobic conditions of deep sediments. Toxic M. aeruginosa and non-toxic M. wesenbergii exhibited similar survivability, although the final survival efficiency of M. aeruginosa was higher than that of M. wesenbergii at 15 and 25 °C. Microcystin quotas remained stable at 5 and 15 °C but decreased significantly at 25 °C. The photosynthetic activity of the benthic Microcystis colonies decreased gradually, with a larger decline rate at higher temperatures. Our study suggests that most benthic Microcystis colonies can overwinter successfully, with microcystins preserved and photosynthetic activity maintained, significantly increasing the risk of bloom formation. However, they were unable to accumulate in the sediments of subtropical shallow lakes over a period of years. [ABSTRACT FROM AUTHOR]

Aphanizomenon flos-aquae ( A. flos-aquae), a cyanobacterium frequently encountered in water blooms worldwide, is source of neurotoxins known as PSPs or aphantoxins that present a major threat to the environment and to human health. Although the molecular mechanism of PSP action is well known, many unresolved questions remain concerning its mechanisms of toxicity. Aphantoxins purified from a natural isolate of A. flos-aquae DC-1 were analyzed by high-performance liquid chromatography (HPLC), the major component toxins were the gonyautoxins1 and 5 (GTX1 and GTX5, 34.04% and 21.28%, respectively) and the neosaxitoxin (neoSTX, 12.77%). The LD50 of the aphantoxin preparation was determined to be 11.33 μg/kg (7.75 μg saxitoxin equivalents (STXeq) per kg) following intraperitoneal injection of zebrafish ( Danio rerio). To address the neurotoxicology of the aphantoxin preparation, zebrafish were injected with low and high sublethal doses of A. flos-aquae DC-1 toxins 7.73 and 9.28 μg /kg (5.3 and 6.4 μg STXeq/kg, respectively) and brain tissues were analyzed by electron microscopy and RT-PCR at different timepoints postinjection. Low-dose aphantoxin exposure was associated with chromatin condensation, cell-membrane blebbing, and the appearance of apoptotic bodies. High-dose exposure was associated with cytoplasmic vacuolization, mitochondrial swelling, and expansion of the endoplasmic reticulum. At early timepoints (3 h) many cells exhibited characteristic features of both apoptosis and necrosis. At later timepoints apoptosis appeared to predominate in the low-dose group, whereas necrosis predominated in the high-dose group. RT-PCR revealed that mRNA levels of the apoptosis-related genes encoding p53, Bax, caspase-3, and c-Jun were upregulated after aphantoxin exposure, but there was no evidence of DNA laddering; apoptosis could take place by pathways independent of DNA fragmentation. These results demonstrate that aphantoxin exposure can cause cell death in zebrafish brain tissue, with low doses inducing apoptosis and higher doses inducing necrosis. © 2011 Wiley Periodicals, Inc. Environ Toxicol, 2013. [ABSTRACT FROM AUTHOR]

Abstract: This work aims to compare the droplet size distribution features of DME/diesel blended fuels and conventional diesel oil by using a high-resolution digital camera in combination with image processing techniques. Based on the acquired size distribution data, microscopic spray characteristics including the mean diameter, the characteristic diameter, and the relative span factor can be thereby calculated to evaluate the spray quality of the test fuels. According to the experimental results, finer spray droplets can be observed for blended fuels compared with diesel spray, which probably owes to the flash boiling effect of DME in diesel when injected out of the nozzle exit. In addition, when the mass fraction of DME increases from 10% to 20%, the corresponding droplet size distribution curve moves toward smaller diameters and the number of large droplets reduces simultaneously, indicating that the spray quality can be improved by DME addition. As for microscopic spray characteristics, it is found that blending DME in diesel causes considerable reduction in the mean diameter and the characteristic diameter. Meanwhile, the result shows an increased relative span factor as the mass fraction of DME increases, which is mainly because large droplets still exist for blended fuel cases, although the absolute number is reduced by DME addition. [Copyright &y& Elsevier]

Changing the ratio of light-harvesting pigments was regarded as an efficient way to improve the photosynthesis rate in microalgae, but the underlying mechanism is still unclear. In the present study, a mutant of Anabeana simensis (called SP) was selected from retrieved satellite cultures. Several parameters related with photosynthesis, such as the growth, photosynthesis rate, the content of photosynthetic pigment, low temperature fluorescence spectrum (77K) and electron transport rate, were compared with those of the wild type. It was found that the change in the ratio of light-harvesting pigments in the mutant led to more efficient light energy transfer and usage in mutant than in the wild type. This may be the reason why the mutant had higher photosynthesis and growth rates. [ABSTRACT FROM AUTHOR]

A lysing-bacterium DC10, isolated from Dianchi Lake of Yunnan Province, was characterized to be Pseudomonas sp. It was able to lyse some algae well, such as Microcystis viridis, Selenastrum capricornutum, and so on. In this study, it was shown that the bacterium lysed the algae by releasing a substance; the best lytic effects were achieved at low temperatures and in the dark. Different concentrations of CaCl2 and NaNO3 influenced the lytic effects; the ability to lyse algae decreased in the following order: pH 4 > pH 9 > pH 7 > pH 5.5. It was significant to develop a special technology with this kind of bacterium for controlling the bloomforming planktonic microalgae. [ABSTRACT FROM AUTHOR]

Liquid breakup intensity in the near-nozzle region and droplet size fluctuations at different downstream positions of an internal-mixing twin-fluid (IMTF) atomizer were studied by using a high-speed camera and a Malvern Spraytec diffractometer, and the effect of operating conditions on spray steadiness was analyzed. The results show that under the operating conditions of this study, the primary breakup process of IMTF atomization is affected by various breakup modes, and the characteristic droplet diameters at a given position exhibit different degrees of fluctuation, which can be considered to be inherently unsteady. The primary breakup process at medium gas/liquid mass flow ratio (GLR) is more unsteady than that at either small GLR or large GLR. At different downstream positions, the steadiness of larger droplets is significantly lower than that of smaller droplets. Compared with the near-nozzle region, the spray steadiness is significantly improved in the fully developed region. Moreover, frequency spectrum analysis performed on the time-resolved data of various droplet characteristic diameters in the near-nozzle region shows the presence of a pulsation frequency in the spectrum diagrams. This pulsation frequency can be used for evaluating the influence of GLR on the spray steadiness. • Using laser diffraction technique to study the steadiness of IMTF spray is feasible. • Primary breakup process at medium GLR is more unsteady than at either small GLR or large GLR. • Pulsation frequency of time-resolved droplet sizes in the near-nozzle region is a signature of IMTF spray steadiness. [ABSTRACT FROM AUTHOR]

Harmful cyanobacterial blooms frequently occur in shallow eutrophic lakes and usually cause the decline of submerged vegetation. Therefore, artificial aquatic plants (AAPs) were introduced into enclosures in the eutrophic Dianchi Lake to investigate whether or not they could reduce cyanobacterial blooms and promote the growth of submerged macrophytes. On the 60th day after the AAPs were installed, the turbidity, total nitrogen (TN), total phosphorous (TP), and the cell density of phytoplankton (especially cyanobacteria) of the treated enclosures were significantly reduced as compared with the control enclosures. The adsorption and absorption of the subsequently formed periphyton biofilms attached to the AAPs effectively decreased nutrient levels in the water. Moreover, the microbial diversity and structure in the water changed with the development of periphyton biofilms, showing that the dominant planktonic algae shifted from Cyanophyta to Chlorophyta. The biodiversity of both planktonic and attached bacterial communities in the periphyton biofilm also gradually increased with time, and were higher than those of the control enclosures. The transplanted submerged macrophyte (Elodea nuttallii) in treated enclosures recovered effectively and reached 50% coverage in one month while those in the control enclosures failed to grow. The application of AAPs with incubated periphyton presents an environmentally-friendly and effective solution for reducing nutrients and controlling the biomass of phytoplankton, thereby promoting the restoration of submerged macrophytes in shallow eutrophic waters. [ABSTRACT FROM AUTHOR]

Global climate warming and human activities have increased the magnitude and frequency of Microcystis surface blooms, posing significant threats to freshwater ecosystems and human health over recent decades. Heavy rainfall events have been reported to cause the disappearance of these blooms. Although some studies have employed turbulence models to analyze the movement characteristics of Microcystis colonies, the impact of rainfall is complex, comprehensive investigations on their vertical migration induced by short-term rainfall are still necessary. Utilizing monitoring data from eutrophic ponds and controlled simulation experiments, this study examines the short-term impacts of rainfall on the vertical distribution of Microcystis in the water column. Our findings indicate that rainfall contributes to the disappearance of Microcystis blooms by reducing the quantity of small to medium-sized colonies (0–100 μm) at the surface, subsequently decreasing the overall Microcystis biomass. As rainfall intensity increases, larger colonies migrate deeper into the water column. At a rainfall threshold of 666 mm, the difference in the median volume diameter (DV50) of Microcystis colonies between the surface and bottom reaches a minimal value of 3.09%. Post-rainfall, these colonies rapidly ascend, aggregate into larger formations, and re-establish surface blooms. The greater the rainfall, the smaller the resultant Microcystis biomass, albeit with larger aggregated colony sizes. When rainfall exceeds 222 mm, the recovery rate of surface Microcystis biomass remains below 100%, decreasing to 19.48% at 666 mm of rainfall, while the median volume diameter (DV50) of the colonies increases to 139.07% of its pre-rainfall level. Furthermore, compared to pre-rainfall conditions, the photosynthetic activity of the surface Microcystis colonies was enhanced and the secretion of EPS was increased under heavy rainfall conditions. Our results identify a critical response time of 30 min for Microcystis colonies to rainfall, after which the response ceases to intensify. These insights are crucial for predicting post-rain Microcystis bloom dynamics and aiding management authorities in timely interventions. [Display omitted] • Microcystis colonies of different sizes respond differently to rainfall. • Smaller colonies migrate upwards, forming larger colonies to reform blooms. • The scale of blooms reformation depends on rainfall magnitude. • Rainfall enhances the photosynthetic activity of Microcystis cells. [ABSTRACT FROM AUTHOR]

Summary: Environmental factors that affect the growth and microcystin production of microcystis have received worldwide attention because of the hazards microcystin poses to environmental safety and public health. Nevertheless, the effects of organic anthropogenic pollution on microcystis are rarely discussed. Gibberellin A3 (GA3) is a vegetable hormone widely used in agriculture and horticulture that can contaminate water as an anthropogenic pollutant. Because of its common occurrence, we studied the effects of GA3 on growth and microcystin production of Microcystis aeruginosa (M. aeruginosa) PCC7806 with different concentrations (0.001–25mg/L) in batch culture. The control was obtained without gibberellin under the same culture conditions. Growth, estimated by dry weight and cell number, increased after the GA3 treatment. GA3 increased the amounts of chlorophyll a, phycocyanin and cellular-soluble protein in the cells of M. aeruginosa PCC7806, but decreased the accumulation of water-soluble carbohydrates. In addition, GA3 was observed to affect nitrogen absorption of the test algae, but to have no effect on the absorption of phosphorus. The amount of microcystin measured by enzyme-linked immunosorbent assay (ELISA) increased in GA3 treatment groups, but the stimulatory effects were different in different culture phases. It is suggested that GA3 increases M. aeruginosa growth by stimulating its absorbance of nitrogen and increasing its ability to use carbohydrates, accordingly increasing cellular pigments and thus finally inducing accumulation of protein and microcystin. [Copyright &y& Elsevier]

Cladophora represents a microscopic forest that provides many ecological niches and fosters a diverse microbiota. However, the microbial community on Cladophora in brackish lakes is still poorly understood. In this study, the epiphytic bacterial communities of Cladophora in Qinghai Lake were investigated at three life stages (attached, floating, and decomposing). We found that in the attached stage, Cladophora was enriched with chemoheterotrophic and aerobic microorganisms, including Yoonia - Loktanella and Granulosicoccus . The proportion of phototrophic bacteria was higher in the floating stage, especially Cyanobacteria . The decomposing stage fostered an abundance of bacteria that showed vertical heterogeneity from the surface to the bottom. The surface layer of Cladophora contained mainly stress-tolerant chemoheterotrophic and photoheterotrophic bacteria, including Porphyrobacter and Nonlabens . The microbial community in the middle layer was similar to that of floating-stage Cladophora . Purple oxidizing bacteria were enriched in the bottom layer, with Candidatus Chloroploca , Allochromatium , and Thiocapsa as the dominant genera. The Shannon and Chao1 indices of epibiotic bacterial communities increased monotonically from the attached stage to the decomposing stage. Microbial community composition and functional predictions indicate that a large number of sulfur cycle-associated bacteria play an important role in the development of Cladophora . These results suggest that the microbial assemblage on Cladophora in a brackish lake is complex and contributes to the cycling of materials. IMPORTANCE Cladophora represents a microscopic forest that provides many ecological niches fostering a diverse microbiota, with a complex and intimate relationship between Cladophora and bacteria. Many studies have focused on the microbiology of freshwater Cladophora , but the composition and succession of microorganisms in different life stages of Cladophora , especially in brackish water, have not been explored. In this study, we investigated the microbial assemblages in the life stages of Cladophora in the brackish Qinghai Lake. We show that heterotrophic and photosynthetic autotrophic bacteria are enriched in attached and floating Cladophora , respectively, whereas the epiphytic bacterial community shows vertical heterogeneity in decomposing mats.