Development of a bioavailable Hg(II) sensing system based on MerR-regulated visual pigment biosynthesis.

Engineered microorganisms have proven to be a highly effective and robust tool to specifically detect heavy metals in the environment. In this study, a highly specific pigment-based whole-cell biosensor has been investigated for the detection of bioavailable Hg(II) based on an artificial heavy metal resistance operon. The basic working principle of biosensors is based on the violacein biosynthesis under the control of mercury resistance (mer) promoter and mercury resistance regulator (MerR). Engineered biosensor cells have been demonstrated to selectively respond to Hg(II), and the specific response was not influenced by interfering metal ions. The response of violacein could be recognized by the naked eye, and the time required for the maximum response of violacein (5 h) was less than that of enhanced green fluorescence protein (eGFP) (8 h) in the single-signal output constructs. The response of violacein was almost unaffected by the eGFP in a double-promoter controlled dual-signals output construct. However, the response strength of eGFP was significantly decreased in this genetic construct. Exponentially growing violacein-based biosensor detected concentrations as low as 0.39 µM Hg(II) in a colorimetric method, and the linear relationship was observed in the concentration range of 0.78-12.5 µM. Non-growing biosensor cells responded to concentrations as low as 0.006 µM Hg(II) in a colorimetric method and in a Hg(II) containing plate sensitive assay, and the linear relationship was demonstrated in a very narrow concentration range. The developed biosensor was finally validated for the detection of spiked bioavailable Hg(II) in environmental water samples.

[Microstructure and spectral property of Er3+ doped transparent oxyfluoride glass ceramics with high fluorine contents].

The microstructure and spectral properties of Er3+ doped transparent oxyfluoride glass ceramics with high fluorine content were reported. Two samples with the same initial contents (50SiO2-45PbF2-5PbO-1ErF3) were prepared under the different preparation parameters. The final fluorine contents were detected by a fluoride ion selective electrode. The results shows that the final fluorine contents increase by covering crucibles with corundum lid during melt. The samples were characterized by X-ray diffraction, transmission electron microscopy (TEM), absorption spectra and upconversion luminescence spectra. The results show that PbF2 crystals were precipitated in the sample with high fluorine content before heat treatment. And the PbF2 crystals precipitated inside the glass matrix are spherical with diameters of approximately 10-15 nm in size from the high resolution TEM micrograph. The absorption spectra, J-O parameters and the upconversion spectra show that the Er3+ ions were located in crystalline and vitreous mixed states. It is different from the sample with low fluorine content which is completely amorphous. After heat treatment, Er3+ ions that remain in the glassy phase entered into fluoride nanocrystals in the sample with high fluorine content. The fluorine environment decreases non-radiative transfer which eases the upconversion processes. Hence, the upconversion luminescence intensity of Er3+ ions in the high fluorine content sample after heat treatment is much stronger than that in the precursor sample.

[Inventory of regional surface nutrient balance and policy recommendations in China].

By applying OECD surface soil nitrogen balance methodology, the framework, methodology and database for nutrient balance budget in China are established to evaluate the impact of nutrient balance on agricultural production and water environment. Results show that nitrogen and phosphorus surplus in China are 640 x 10(4) t and 98 x 10(4) t respectively, and nitrogen and phosphorus surplus intensity in China are 16.56 kg/hm2 and 2.53 kg/hm2 respectively. Because of striking spatial difference of nutrient balance across the country, China is seeing a dual-challenge of nutrient surplus management as well as nutrient deficit management. Chemical fertilizer and livestock manure are best targets to perform nutrient surplus management due to their marked contributions to nutrient input. However, it is not cost-effective to implement a uniform management for all regions since nutrient input structures of them vary considerably.

[Nitrogen flow in farming-feeding system and its environmental impact in China].

By applying nitrogen flow model for farming-feeding system (NFM-FFS) which integrates soil full nitrogen balance model with inventory analysis for agricultural pollution, nitrogen flow in China farming-feeding systems and its environmental impact are analyzed. In 2003, although surface nitrogen surpluses, nitrogen deficit in agricultural soil system in China is estimated to be 623.9 x 10(4) t, and 13.7 kg/hm2 averagely, which implies that soils in China farming-feeding systems are at the risk of nitrogen content decline and potential soil degradation as a whole. With a intense nutrient input in arable land and no extra fertilizer input in grassland in China, there is a nitrogen surplus of 1761.9 x 10(4) t, averagely 142.8 kg/hm2, while grassland has a deficit of 2,385.7 x 10(4) t, averagely 90.7 kg/hm2. As a result, existing negative impact of cropping activities on water environment as well as grassland degradation may be effectively abated by balancing nitrogen input between arable land and grassland. Total nitrogen loss from China farming-feeding system is 2,266 x 10(4) t, including 495.8 x 10(4) t exported into surface water by drainage and surface runoff, and 102.4 x 10(4) t into groundwater by leaching. Lost nitrogen is to be deposited in rivers, lakes and marine system, and is less likely to return to farming-feeding system. Fertilizer should be the priority of rural pollution control and management because of its dominant contribution to nitrogen exported into water environment from farming-feeding system.