[Nitrogen Removal and the Characteristics of Denitrification Bacteria Using NUA-DAS Ecofilter].

A small-scale combined ecofilter was constructed using neutralized-used acid residue (NUA) and dewatered alum sludge (DAS), and the nitrogen removal for wastewater treatment and characteristics of denitrification bacteria using the NUA-DAS ecofilter were studied. After the system was stabilized, the average removal rates of COD, TN, NO3--N in the final effluents were 60%, 70% and 95%, respectively, and the range of NO3--N concentration in the effluents was only 0.02-0.55 mg·L-1. Furthermore, the richness and similarity of three types of functional genes (nirS, nirK and nosZ) for denitrification in different substrates during the operation period were analyzed using PCR-DGGE method. These results showed that the richness of all denitrification bacteria at NUA and DAS increased remarkably after operation for 30 and 60 days compared to that in fresh substrate, and the richness was basically the same for the same kind of gene at the identical substrate regardless of depth gradient and operation period. The richness of nirS, nirK and nosZ detected in the NUA and DAS followed the order of nosZ > nirK > nirS. It was also revealed that spatial location had an apparent influence on the community structure of denitrifying bacteria (nirS, nirK and nosZ) but operation time had no obvious effect. Finally, nirK might be the most suitable for the environment in the system, and the adaptive capacity of denitrification bacteria (nirS, nirK and nosZ) in NUA could be superior to that in DAS.

Prevalence of antibiotic resistance genes in antibiotic-resistant Escherichia coli isolates in surface water of Taihu Lake Basin, China.

The rapid development of antibiotic-resistant bacteria (ARB) has been of concern worldwide. In this study, antibiotic resistance genes (ARGs) were investigated in antibiotic-resistant Escherichia coli isolated from surface water samples (rivers, n = 17; Taihu Lake, n = 16) and from human, chicken, swine, and Egretta garzetta sources in the Taihu Basin. E. coli showing resistance to at least five drugs occurred in 31, 67, 58, 27, and 18% of the isolates from surface water (n = 665), chicken (n = 27), swine (n = 29), human (n = 45), and E. garzetta (n = 15) sources, respectively. The mean multi-antibiotic resistance (MAR) index of surface water samples (0.44) was lower than that of chicken (0.64) and swine (0.57) sources but higher than that of human (0.30) and E. garzetta sources (0.15). Ten tetracycline, four sulfonamide, four quinolone, five ß-lactamase, and two streptomycin resistance genes were detected in the corresponding antibiotic-resistant isolates. Most antibiotic-resistant E. coli harbored at least two similar functional ARGs. Int-I was detected in at least 57% of MAR E. coli isolates. The results of multiple correspondence analysis and Spearman correlation analysis suggest that antibiotic-resistant E. coli in water samples were mainly originated from swine, chicken, and/or human sources. Most of the ARGs detected in E. garzetta sources were prevalent in other sources. These data indicated that human activities may have contributed to the spread of ARB in the aquatic environment.

Nitric oxide supplementation alleviates ammonium toxicity in the submerged macrophyte Hydrilla verticillata (L.f.) Royle.

The likely protective effects of nitric oxide (NO) against ammonium toxicity were investigated in the submerged macrophyte Hydrilla verticillata. The plants were subjected to ammonium stress (3mM ammonium chloride) in the presence of sodium nitroprusside (SNP, 10 µM), an NO donor. Treatment with SNP significantly increased the NO content and partially reversed the ammonium-induced negative effects, including membrane damage and the decrease in levels of chlorophyll, malondialdehyde, glutathione and ascorbic acid. Further, SNP application increased the catalytic activities of ascorbate peroxidase, superoxide dismutase, guaiacol peroxidase, catalase and glutathione S-transferase, but decreased that of NADH-oxidase. Histochemical staining showed that SNP application caused a significant decrease in the levels of superoxides and hydrogen peroxide. In contrast, application of other breakdown products of SNP (10 µM sodium ferrocyanide, 10 µM sodium nitrite and 10 µM sodium nitrate) failed to show any protective effect. The results suggest that the increased intracellular NO, resulting from SNP application, improved the antioxidant capacity of H. verticillata plants in coping with ammonium-induced oxidative stress.

Effects of ammonium on the antioxidative response in Hydrilla verticillata (L.f.) Royle plants.

To investigate ammonium toxicity, the submerged plant Hydrilla verticillata (L.f.) Royle was treated with 0.1-3.0mM ammonium for 12h and 4d. After exposure to ammonium for 4d, content of O2(-) and H2O2 increased in leaves of H. verticillata exposed to 3mM ammonium compared with control (0mM NH4Cl), while the malondialdehyde content decreased. The chlorophyll (a+b) and carotenoid concentrations decreased in H. verticillata plants exposed to 1.5-3mM ammonium for 12h and 4d. Compared with controls, the activity of superoxide dismutase, peroxidase, catalase, glutathione reductase, ascorbate peroxidase, and glutathione S-transferase increased in plants treated with ammonium for 12h, and the activity of most enzymes was further enhanced at 4d. The changes in nonprotein thiols, total glutathione, ascorbic acid, and dehydroascorbate content were also assayed. Our results suggest that ammonium induced the oxidative stress and the heated antioxidant response in H. verticillata.

Excess Zn alters the nutrient uptake and induces the antioxidative responses in submerged plant Hydrilla verticillata (L.f.) Royle.

To investigate the effects of zinc (Zn) on aquatic macrophyte, the submerged plant Hydrilla verticillata (L.f.) Royle was cultured in control solution or together with 0.05-30 mg L(-1) Zn(2+) for 7 d. The alterations in nutrient uptake and antioxidative response were assayed. Zn stress increased the uptake of Cu, Fe, Mn, Mg, and Zn while decreased that of P. Compared with control plants, the synthesis of chlorophyll was stimulated at 0.05-0.5 mg L(-1) Zn but inhibited at concentrations >5 mg L(-1), while the activity of NADH oxidase was suppressed at low level of Zn(2+) (0.05-5 mg L(-1)) but activated at concentrations of 30 mg L(-1). There were not significant changes in the content of malondialdehyde and activity of lipoxygenase, catalase, and glutathione S-transferase in the presence of Zn concentrations up to 0.5 mg L(-1) Zn, while at high concentrations significant increase in these parameters was observed. Meanwhile, activity of total superoxide dismutase increased in all treatments compared with control plants. The activity of guaiacol peroxidase and ascorbate peroxidase increased at 0.5-30 mg L(-1) Zn, and that of glutathione reductase increased at concentration of 0.05-0.5 mg L(-1) Zn but decreased significantly at 5-30 mg L(-1). In addition, some important antioxidative metabolites such as ascorbate, dehydroascorbate, glutathione and oxidized glutathione increased significantly in leaves treated with 10-30 mg L(-1) Zn when compared with control plants. These results suggested that Zn induced the nutrient imbalance and oxidative damage and the accelerated operation of antioxidative reactions might provide H. verticillata (L.f.) Royle with the enhanced Zn-stress tolerance.

The effect of excess Zn on mineral nutrition and antioxidative response in rapeseed seedlings.

Zinc (Zn) is a necessary element for plants, but excess Zn can be detrimental. To investigate Zn toxicity, rapeseed (Brassica napus) seedlings were treated with 0.07-1.12 mM Zn for 7d. Inhibition of plant growth along with root damage, chlorosis and decreased chlorophyll (a and b) content in newly expanded leaves (the second and third leaves formed following cotyledons) were found under Zn stress. The Zn content increased in plants under external Zn stress, while concentrations of phosphorus, copper, iron, manganese and magnesium reduced significantly, especially in roots. Meanwhile, increased lipid peroxidation was detected biochemically and histochemically. Compared with controls, NADH oxidase and peroxidase (POD) activity increased in leaves and roots of plants under high Zn, but superoxide dismutase (SOD), catalase and ascorbate peroxidase activities decreased. The changes in glutathione S-transferase activity and in ascorbic acid, dehydroascorbate, non-protein thiols and glutathione contents were also measured under Zn stress. Isoforms of SOD and POD were separated using non-denaturing polyacrylamide gel electrophoresis and their activities were analyzed. Our results suggested that excess Zn exerts its toxicity partially through disturbing nutrient balance and inducing oxidative stress in plants. These data will be helpful for better understanding of toxicity of Zn and the adaptive mechanism in Zn non-hyperaccumulator plants.

Metabolic adaptations to ammonia-induced oxidative stress in leaves of the submerged macrophyte Vallisneria natans (Lour.) Hara.

Ammonia (i.e. the total of NH(3) and NH(4)(+)) has been one of the main causes of the decline of macrophytes in fresh water. In order to study the effects of ammonia toxicity, plants of the submersed macrophyte Vallisneria natans (Lour.) Hara were treated with various concentrations of NH(4)Cl (0.1, 0.4, 1.2, 2 and 2.8mM) for 4 days or with 2mM NH(4)Cl for different lengths of time (12h, 1, 2, 4 and 8 days). The toxic effect and oxidative stress caused by NH(4)Cl resulted in a reduction of total chlorophyll (chlorophyll a and b) and an increase in the levels of reactive oxygen species (ROS) O(2)(-) and H(2)O(2), with an increased concentration of NH(4)Cl and duration of exposure. Meanwhile, weak chlorosis and water-soaked symptoms were observed in older leaves exposed to 2.8mM NH(4)Cl for 4 days. The activity of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) was up-regulated in leaves treated with 1.2, 2 and 2.8mM NH(4)Cl for 4 days or with 2mM NH(4)Cl for 1, 2 and 4 days, when compared with controls. Among these enzymes, the activity of superoxide dismutase, ascorbate peroxidase and glutathione reductase was significantly up-regulated in plants treated with 0.4mM NH(4)Cl for 4 days, while they were down-regulated at 4 and 8 days from their peak values in leaves treated with 2mM NH(4)Cl. The content of ascorbic acid decreased significantly in leaves treated with 0.4-2.8mM NH(4)Cl for 4 days or with 2mM NH(4)Cl for 2-8 days. The content of total glutathione (tGSH; reduced and oxidized glutathione) increased in leaves treated with NH(4)Cl at 0.4, 1.2 and 2mM for 4 days or with 2mM NH(4)Cl at 1, 2 and 4 days, while tGSH was decreased below the level of controls by treatment with 2.8mM NH(4)Cl for 4 days or to the level of controls by treatment with 2mM NH(4)Cl for 8 days. However, the content of malondialdehyde (MDA) decreased with increased concentration of NH(4)Cl and duration of exposure. Results from staining with 3,3'-dimethoxybenzidine (DAB) further indicated that the level of H(2)O(2) and the activity of guaiacol peroxidase increased significantly in plants exposed to 2mM NH(4)Cl for 4 days. These results suggested that ammonia exerted its toxic effect on the growth of V. natans (Lour.) Hara, at least in part, by induction of oxidative stress and inhibition of photosynthesis. The decrease in the content of malondialdehyde is discussed.