Ciming Hu

Apoptotic responses of Carassius auratus lymphocytes to nodularin exposure in vitro

Nodularin, a metabolite of Nodularin spumigena, is widely detected in water blooms worldwide and causes serious negative effects on fish. The apoptosis-related cytotoxic effects and mechanisms of nodularin on Carassius auratus lymphocytes were investigated. Transmission electron microscopy results showed that nodularin-treated lymphocytes display a series of morphological changes, including condensed cytoplasm, nuclear chromatin agglutination and marginalization. DNA fragmentation was verified by the DNA-ladder and formation of sub-G1 DNA peaks. These cell characteristics confirmed the occurrence of apoptosis in lymphocytes. Flow cytometric results showed that the percentages of apoptotic cells incubated with 1, 5, 10, and 100 μg/L nodularin for 12 h reached 15.76%, 17.36%, 20.34% and 44.21%, respectively; controls showed low rates of apoptosis (2.4%). The mechanism of apoptosis induced by nodularin was determined, and results showed that nodularin exposure caused a significant increase in intracellular reactive oxygen species (ROS), loss of mitochondrial transmembrane potential in a dose-dependent manner, upregulation of intracellular Ca²⁺, downregulation of Bcl-2 and upregulation of Bax expression at the mRNA and protein levels, and activation of caspase-3 and caspase-9 without caspase-8. In summary, all the results suggest that nodularin induces lymphocyte apoptosis via the mitochondrial apoptotic pathway and destroys the immune response of fish.

Characteristics of γ-hexachlorocyclohexane biodegradation by a nitrogen-fixing cyanobacterium, Anabaena azotica

Biodegradation of γ-hexachlorocyclohexane (lindane) by a nitrogen-fixing cyanobacterium isolated from Chinese paddy soils, Anabaena azotica 118, was investigated. Lindane with an initial concentration of 0.2xa0mgxa0L−1 in the cultures had no negative effect on the chlorophyll a concentration of A. azotica after 5xa0d exposure. The tolerance of this cyanobacterium to lindane indicates that it has the potential to biodegrade lindane. The degradation experiments show that the percentage of lindane removal efficiency by A. azotica was 48.8% after 5xa0d, at an initial lindane concentration of 0.2xa0mgxa0L−1 and initial A. azotica chlorophyll a concentration of 50xa0mgxa0L−1. The calculated half-life was 4.78xa0d. Elevated culture temperature, irradiation, and usage of nitrate as the nitrogen source in the cultures could increase the biodegradation efficiency of lindane. γ-Pentachlorocyclohexene was detected as a metabolite of lindane. The ability of A. azotica to biodegrade lindane has potential use in the bioremediation for this organochlorine pesticide.

Removal of microcystin-LR from drinking water using a bamboo-based charcoal adsorbent modified with chitosan

A new kind of low-cost syntactic adsorbent from bamboo charcoal and chitosan was developed for the removal of microcystin-LR from drinking water. Removal efficiency was higher for the syntactic adsorbent when the amount of bamboo charcoal was increased. The optimum dose ratio of bamboo charcoal to chitosan was 6:4, and the optimum amount was 15 mg/L; equilibrium time was 6 hr. The adsorption isotherm was non-linear and could be simulated by the Freundlich model (R2 = 0.9337). Adsorption efficiency was strongly affected by pH and natural organic matter (NOM). Removal efficiency was 16% higher at pH 3 than at pH 9. Efficiency rate was reduced by 15% with 25 mg/L NOM (UV254 = 0.089 cm(-1)) in drinking water. This study demonstrated that the bamboo charcoal modified with chitosan can effectively remove microcystin-LR from drinking water.

Environmental Factors Influencing Seasonal Variation of Microcystin-RR Concentrations in Baoyang River, a Shallow City River in Changxing of China

The shallow city river of Baoyang located in China had been eutrophicating with nutrients from domestic sewages for many years. A heavy bloom of Microcystis.aeruginosa in Baoyang River was recorded in 2004 and microcystin-RR (MCRR), the most popular cyanobacterial hepatotoxin microcystins in China, could be detected in the river in the next several years in the filtered waters. To determine the environmental variable factors associated with concentrations of MCRR, samples taken from the beginning of April 2008 to the end of March 2009, were analyzed by high-performance liquid chromatography with photodiode array detection. MCRR, the main microcystins found in the filtered water samples from spring to winter, ranged from undetectable to 4.37µg/L. The highest concentrations of MCRR were found in the late summer in October 2008, and the concentrations of MCRR at the bottom waters were higher than that at the aquatic surfaces. Significant positive relationships (p<0.01) were observed between MCRR and NO3-N; but significant negative relationships (p<0.01) were observed between MCRR and pH, COD, NO2-N and TN. This research indicated NO3-N would be very important for the biosynthesis of MCRR. The relationships between MCRR concentrations and environmental factors were complicated and further researches should be focused on the prediction methods of microcystins by the nonlinear models for their potential health risks.