Cultivation and Characterization of the MaMV-DC Cyanophage that Infects Bloom-forming Cyanobacterium Microcystis aeruginosa

The MaMV-DC cyanophage,which infects the bloom-forming cyanobacterium Microcystis aeruginosa,was isolated from Lake Dianchi,Kunming,China.Twenty-one cyanobacterial strains were used to detect the host range of MaMV-DC.Microcystic aeruginosa FACHB-524 and plaque purification were used to isolate individual cyanophages,and culturing MaMV-DC with cyanobacteria allowed us to prepare purified cyanophages for further analysis.Electron microscopy demonstrated that the negatively stained viral particles are tadpole-shaped with an icosahedral head approximately 70 nm in diameter and a contractile tail approximately 160 nm in length.Using one-step growth experiments,the latent period and burst size of MaMV-DC were estimated to be 24–48 hours and approximately 80infectious units per cell,respectively.Restriction endonuclease digestion and agarose gel electrophoresis were performed using purified MaMV-DC genomic DNA,and the genome size was estimated to be approximately 160 kb.Sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE)analysis revealed four major structural proteins.These results support the growing interest in using freshwater cyanophages to control bloom-forming cyanobacterium.

去除藻毒素的水处理方法

蓝-绿藻水华及其所含毒素已成为我国许多富营养化水源的主要问题.蓝-绿藻所含的毒素是复杂的有机化合物,其中包括神经毒素、肝毒素和皮肤毒素.在水处理时如能有效去除藻类,则藻毒素将随之减少.除藻措施可在水源地或水厂内同时进行.在水源处可采取的措施是预氧化、投加除藻剂和防止水源水因水质或水温而引起的上下分层.一般水厂常规处理工艺不能有效去除藻毒素,可以采用强化混凝、优化粉末活性炭和臭氧以及氯的投加量、用生物活性炭过滤或组合工艺.其中生物预处理、臭氧氧化、粉末或颗粒活性炭吸附有较好去除效果.但是在藻类大量繁殖时,须慎重采用预氧化,否则当用氯或臭氧进行预氧化时,如投药量不当,会使藻细胞破裂,反而析出较多的毒素到水中.蓝-绿藻毒素的最佳去除工艺是臭氧和活性炭相结合的生物活性炭法.

Effects of Microcystis aeruginosa on life history of water flea Daphnia magna

Cyanobacterial blooms in eutrophic freshwater systems are a worldwide problem, creating adverse effects for many aquatic organisms by producing toxic mierocystins and deteriorating water quality. In this study, microcystins （MCs） in Microcystis aeruginosa, and Daphnia magna exposed to M. aeruginosa, were analyzed by HPLC-MS, and the effects of M. aeruginosa on D. magna were investigated. When D. magna was exposed to M. aeruginosa for more than 2 h, Microcystin-LR （MC-LR） was detected. When exposed to 1.5× 10^6, 3× 10^6, 0.75× 10^7, and 1.5× 10^7 cell/mL of M. aeruginosa for 96 h, average survival of D. magna for treatments were 23.33%, 33.33%, 13.33%, 16.67%, respectively, which were significantly lower than the average 100% survival in the control group （P 〈 0.05）. The adverse effects ofM. aeruginosa on body length, time for the first brood, brood numbers, gross fecundity, lifespan, and population growth olD. magna were density-dependent. These results suggest that the occurrence of M. aeruginosa blooms could strongly inhibit the population growth of D. magna through depression of survival, individual growth and gross fecundity. In the most serious situations, M. aeruginosa blooms could undermine the food web by eliminating filter-feeding zooplankton, which would destroy the ecological balance of aquaculture water bodies.

Oxidative stress responses of submerged macrophyte Vallisneria asiatica to different concentrations of cyanobacteria

In a 10-day aquarium experiment, this investigation examines macrophyte restoration in eutrophic Lake Taihu, the physiological effects of different plant biomass levels and of increasing natural cyanobacterial concentrations on a submerged macrophyte, Vallisneria asiatica. Cyanobacterial stress suppressed the superoxide dismutase （SOD） activity of the plant＇s leaves and induced the catalase （CAT） and peroxidase （POD） activities of its roots. The soluble protein content in V. asiatica decreased with an increase in natural cyanobacterial concentrations, whereas the malonaldehyde （MDA） increased significantly at chlorophyll a （Chl a） concentrations of 222 and 262 μg/L in water. V. asiatica adapted to the stress caused by cyanobacterial concentrations by adjusting its antioxidant defense system to remove the excessive reactive oxygen species when the algal Chl a concentration was 〉109 μg/L. Additionally, high biomass of V. asiatica （2 222 g FW/m^2） can inhibit the reproduction of cyanobacteria more significantly than low biomass （1 111 g FW/m^2）. High biomass of V. asiatica increased the oxidative stress in an individual plant when the initial Chl a concentration in the water reached 222 and 262 μg/L, as expressed by the increased MDA in leaves, compared with low biomass of K asiatica. This provides a basis for controlling cyanobacterial concentrations and V. asiatica biomass for the recovery of V. asiatica in eutrophic Lake Taihu.

Factors Affecting the Occurrence and Growth of Toxic Cyanobacteria Microcystis Aeruginosa in Laguna De Bay, Philippines

Cyanobacteria is one of the major sources of toxins in freshwater. These microorganisms are highly adaptive to changing environmental conditions. In this study, the occurrence of toxin producing cyanobacteria in Laguna de Bay and factors affecting its occurrence and growth were determined. The presence ofMicrocystis aeruginosa was positively correlated with nitrate （NO3） and iron （Fe^2＋） with correlation coefficient of ＋0.72972 and ＋0.91063, respectively. It is negatively correlated with occurrence of sunshine （in days） and turbidity with correlation -0.79055 and -0.93531, respectively.

Evaluation of Impact of Cadmium and Mercury on Cyanobacteria Fluorescence Emission Using Flow Cytometry： Preliminary Studies

Heavy metals currently pose one of the most serious problems in terms of environmental protection. We analysed the effect of cadmium and mercury salts upon chlorophyll fluorescence emision of Microcystis aeruginosa, Cylindrospermopsis raciborskii and Aphanizomenon gracile. Time of incubation （3, 12 and 24 h） and salts concentration（1 μM, 10 μM, 100μM） influenced the emision. The higher the salt concentration and the longer the time of incubation, the greater the influence on inhibition of chlorophyll fluorescence was observed. Our results might indicate that nontoxic strains of M. aeruginosa MAKR0205 can have a high tolerance to heavy metal ions and ability of their detoxication. Further studies are necessary to confirm their potential ability in the water purification.

Aquatic Toxicities of Three Aryloxyphenoxypropanoic Acid Herbicides on Cyanobacterium Microcystis aeruginosa

Pesticides will be released into aquatic systems after application in agriculture or industry. AOPPs （aryloxyphenoxypropanoic acids） herbicides, including fenoxaprop, quizalofop-P-ethyl and haloxyfop-methyl, can pose aquatic toxicity on cyanobacterium M. aeruginosa （Microcystis aeruginosa）. The inhibition percentages of the biomass of M. aeruginosa exposure to 10 mg＇L-I fenoxaprop, quizalofop-P-ethyl and haloxyfop-methyl on day 7 were 23.13%, 7.55%, and 7.56%, respectively. Protein content was also inhibited by the three AOPPs to fenoxaprop is the most toxic, followed by quizalofop-P-ethyl varying degrees. The growth and protein content results showed that and haloxyfop-methyl. It indicates that both the biomass and the protein content can be served as an indicator for evaluating the toxicity of the three chemicals. Growth rates of M. aeruginosa exposure to fenoxaprop are also the most significantly different compared to the control, which means that fenoxaprop is the most toxic among the three compounds. Results from this study may provide insights for evaluation of environmental risks of AOPPs. In addition, such insights will be helpful for guiding the application of AOPPs in agriculture.

Characterization of 1,4-dihydroxy-2-naphthoyl-coenzyme A synthase(MenB) in phylloquinone biosynthesis of Synechocystis sp.PCC 6803

The gene product Sll1127 is a predicted 1,4-dihydroxy-2-naphthoyl-CoA synthase catalyzing an intramolecular Claisen condensation in the phylloquinone biosynthesis of the cyanobacterium Synechocystis sp.PCC 6803.This predicted catalytic function has been verified and the enzyme has been characterized for the first time with kcat = 0.013 s-1 and KM = 9μM.Its catalytic activity is found to strictly depend on externally added bicarbonate with an apparent KD = 0.60 mM.In addition,this enzyme is inhibited by its 1,4-dihydroxy-2-naphthoyl-CoA product through high-affinity binding,which causes a 18 nm shift of the inhibitor absorption at 392 to 410 nm and engenders a new absorption peak at 345 nm.All these properties of the cyanobacterial enzyme are closely similar to those of the Escherichia coli orthologue from the menaquinone biosynthetic pathway.These results provide additional supporting evidence for the essential role of bicarbonate as a catalytic base in the enzymatic reaction and the eubacterial origin of the enzymes in the cyanobacterial biosynthesis of phylloquinone.

Conformational changes in photosynthetic pigment proteins on thylakoid membranes can lead to fast non-photochemical quenching in cyanobacteria

A high non-photochemical quenching(NPQ) appeared below the phase transition temperature when Microcystis aeruginosa PCC7806 cells were exposed to saturated light for a short time.This suggested that a component of NPQ,independent from state transition or photo-inhibition,had been generated in the PSII complex;this was a fast component responding to high intensity light.Glutaraldehyde(GA),commonly used to stabilize membrane protein conformations,resulted in more energy transfer to PSII reaction centers,affecting the energy absorption and dissipation process rather than the transfer process of phycobilisome(PBS).In comparison experiments with and without GA,the rapid light curves(RLCs) and fluorescence induction dynamics of the fast phase showed that excess excitation energy was dissipated by conformational change in the photosynthetic pigment proteins on the thylakoid membrane(PPPTM).Based on deconvolution of NPQ relaxation kinetics,we concluded that the fast quenching component(NPQ f) was closely related to PPPTM conformational change,as it accounted for as much as 39.42% of the total NPQ.We hypothesize therefore,that NPQ f induced by PPPTM conformation is an important adaptation mechanism for Microcystis blooms under high-intensity light during summer and autumn.

Inhibitory effects of the extracts with different solvents from three compositae plants on cyanobacterium Microcystis aeruginosas

The algicidal activity of the terrestrial plants is a novel and promising means for alga control of eutrophic waters. In this study, three compositae plants-Artemisia annua （A. annua）, Conyza canadensis （ C. canadensis）, and Erigeron annuus （E. annuus） were selected and antialgal activity of petroleum ether （PE）, ethyl acetate （EA） and ethanol extracts of these plants on blue algae Microcystis aeruginosa was investigated. The result shows the EA extracts of these plants present the stronger inhibitory effects. The results of the further separation of PE and EA extracts according to water-solubility and acidity or alkalinity show that fatty acids and telpenoids in A. annua, terpenoids and organic acid in C. Canadensis and E. Annuus may be the main antialgal active constituents. This study suggested that the EA extracts of these plants could become the potential algicide to prevent water blooming.