Fate of selenate metabolized by Enterobacter taylorae isolated from rice straw

Rice straw has been successfully tested as an effective organic source and a carrier of selenate [Se(VI)]-reducing bacteria to remove Se(VI) from agricultural drainage water. In this study, an Se(VI)-reducing bacterium identified as Enterobacter taylorae was isolated from rice straw and used to remove Se(VI) from a 0.5% tryptic soy broth (TSB) and high-salt (15.5 dS m(-)(1)) synthetic agricultural drainage water containing Se(VI) in a range of 500-5000 microg/L. Results showed that E. taylorae reduced 81-94% of the added Se(VI) to elemental Se [Se(0)] in the 0.5% TSB solution during a 5-day experiment. In the high-salt drainage water, Se(VI) reduction was rapid during a 9-day experiment. On the final day of the experiment, Se(0) [75%] and Se(-II) [19%] were the major forms of Se in the drainage water with small amounts of Se(VI), Se(IV), and volatile Se released. The pathway of Se(VI) reduction in the drainage water followed the order Se(VI) --> selenite [Se(IV)] --> Se(0) --> selenide [Se(-II)]. This study suggests that E. taylorae may be used to remediate high-salt Se(VI)-contaminated agricultural drainage water.     

硅钙复混肥对玉米抗倒性及产量的影响

据报道 ,水稻施用硅肥后 ,能提高植株体内ＳｉＯ2 含量 ,提高细胞壁的强度 ,进而株形挺拔、抗倒伏。小麦试验亦表明 ,施硅增加冬小麦表皮细胞壁厚度和硅化细胞数量 ,提高茎秆刚性。但到目前为止 ,关于施硅钙肥对玉米抗倒性能及产量影响的报导甚少。为此 ,我们探讨了在正常密度条件下 ,施用硅钙复混肥对玉米抗倒伏及其产量的影响 ,为科学施用硅钙肥提供理论依据。1　材料与方法本项目于 1 996年布置在辽宁省农业科学院土肥所试验地上 ,土壤为壤质草甸土 ,其理化性质为有机质 2 8.45ｇ/ｋｇ ,全氮 0 .0 93%,全磷 0 .8ｇ/ｋｇ ,全钾 2 8.1 5ｇ/…     

Transition-State Spectroscopy of Cyclooctatetraene

The 351-nanometer photoelectron spectrum of the planar cyclooctatetraene radical anion (COT·-) shows transitions to two electronic states of cyclooctatetraene (COT). These states correspond to the D4h 1A1g state, which is the transition state for COT ring inversion, and the D8h 3A2u state. The electron binding energy of the 1A1g transition state is 1.099 ± 0.010 electron volts, which is lower by 12.1 ± 0.3 kilocalories per mole than that of the 3A2u state. The photoelectron spectrum shows that the singlet lies well below the triplet in D8h COT and confirms ab initio predictions that the molecule violates Hund's rule. Vibrational structure is observed for both features and is readily assigned by use of a simple potential energy surface.     

Characteristics of an amidase isolated from a soil bacterium

Amidase was extracted from a bacterium isolated from soil, and its properties were compared with those of amidase in soil. Amidase activity of the bacterial protein was lower than that of soil amidase, respectively, in its optimal pH (7.0 vs 8.5), optimal temperature (50 vs 60°C), K_m constant calculated by the Lineweaver-Burk plot (5.6 vs 17.9 mm), activation energy (18.9 vs 43.3 kJmol^?) and Q₁₀ (av. = 1.28 vs 1.75). Bacterial amidase was stable at temperatures ranging from 10 to 50°C and denatured at 55°C. Toluene inhibited both bacterial and soil amidase.When the inhibitions by 21 trace elements were compared by using 2 μmol 0.1 mg^?1 protein, the most effective inhibitors of bacterial amidase (> 25% inhibition) were: Ag(I), Cd(II), Cu(II), Hg(II), Ni(II), Pb(II), Zn(II), Al(III) and Se(IV). The effect of 16 pesticides on bacterial amidase varied considerably. By using 2 μg of active ingredient of pesticide 0.1 mg^?1 protein, the inhibition of bacterial amidase ranged from 7 to 49% with Dinitroamine and Butylate, respectively. The results show that soil constituents have a considerable influence on the reaction catalyzed by this enzyme.     

Production and stability of ethylene in soil

Summary One of the major factors affecting the production and stability of ethylene (C₂H₄) in soil is its water content. This study was conducted to determine the effect of unsaturated vs. saturated conditions on the production and stability of C₂H₄ in soil. L-Methionine and D-glucose were added alone and in combination at 1.0 and 5.0 g kg^-1 soil, respectively. The addition of l-methionine significantly promoted C₂H₄ production at field capacity to a much greater extent than under waterlogged conditions. Glucose was equally effective under both moisture regimes, while the combined application of both amendments (l-methionine and d-glucose) led to the release of significantly higher amounts of C₂H₄ under saturated conditions. Antibiotic experiments revealed that under aerobic conditions, l-methionine may be more efficiently converted to C₂H₄ by soil fungi, while in glucose-amended soil, both bacteria and fungi are active in generating C₂H₄. C₂H₄ was more stable under saturated conditions. The magnitude of C₂H₄ removal from the headspace after 3 days of incubation under unsaturated conditions (25.7%) was comparable to that after 6 days under saturated conditions (24.1%). The loss of C₂H₄ was approximately 10-fold greater in non-sterilized soil than in sterilized (autoclaved) soil, both maintained at field capacity, indicating that a biotic component has a major influence on C₂H₄ stability. Kinetic analysis revealed that the C₂H₄ loss/degradation in nonautoclaved soil under aerobic conditions followed a firstorder reaction, with a rate constant (k) of 0.115 day^-1 and a half-life (t _1/2) of 6.0 days.     

Temperature and pH effects on biodegradation of hexachlorocyclohexane isomers in water and a soil slurry

This study was conducted to monitor the biodegradation of alpha-, beta-, gamma-, and delta-hexachlorocyclohexane (HCH) isomers in liquid culture by a Pandoraea species and determine the influence of pH and temperature on the biodegradation of alpha- and gamma-HCH in liquid as well as in soil slurry cultures. The Pandoraea species degraded 79.4% delta-HCH and 34.3% gamma-HCH in liquid culture at 4 weeks of incubation. alpha- and beta-HCH exhibited almost identical rates (41.6 and 42.4%, respectively) of degradation. The highest degradation of alpha- and gamma-HCH (67.1 and 60.2%, respectively) was observed at an initial pH of 8.0 in liquid; 58.4 and 51.7% rates of degradation of alpha- and gamma-HCH, respectively, at an initial pH of 9.0 were found in soil slurry cultures. An incubation temperature of 30 degrees C was optimum for effective degradation of alpha- and gamma-HCH isomers (62.5 and 57.7%, respectively) in liquid culture, and 54.3 and 51.9% rates of degradation of alpha- and gamma-HCH isomers, respectively, were found in a soil slurry. Increasing the soil/water ratio decreased the extent of degradation of both HCH isomers. Degradation of HCH isomers occurred concomitant with bacterial growth. Byproducts of growth from Pandoraea species significantly decreased the pH of the liquid and the soil slurry during the growth on HCH isomers. The results of this study suggest that this bacterial strain may effectively be used for remediating polluted sites and water contaminated with different HCH isomers over a range of environmental conditions.     

Urease activity in sewage sludge-amended soils

Three diverse field-moist soil samples were treated with five sewage sludges (applied at five loading rates) containing high concentrations of heavy metals. Urease activity was assayed after 0, 3, 7, 14 and 30 days of incubation. Results showed that when soils were treated with the sewage sludges, urease activity was often inhibited at the lower loading rates (2.2 and 8.9mg sludge g^?1 soil), but was enhanced substantially with the higher application rates (22.2, 44.4 and 100 mg sludge g^?1 soil). Inhibition of urease activity in the sewage sludge amended-soils ranged from 4 to 37% (Domino soil), 8–27% (Hesperia soil), and 3–49% (Ramona soil) at various times of incubation. Inhibition of the enzyme activity was attributed to the presence of heavy metals in the sludges. The increased activity of urease in the sludge-amended soils at the highest application rate (100 mg sludge g^?1 soil) ranged from 1.13 to 5.00-fold (Domino soil), 1.20–4.04-fold (Hesperia soil), and 1.13–5.40-fold (Ramona soil). Enhanced urease activity was believed to be due to the additional source of organic matter and nutrients supplied by the sludge which stimulated microbial activity and subsequent urease synthesis.