[Effects of long-term application of pig manure containing residual tetracycline on the formation of drug-resistant bacteria and resistance genes].

The effect of residual veterinary tetracycline on the formation of drug-resistant bacteria and corresponding resistance genes was investigated. During the research, the soil with long-term application of pig manure containing residual tetracycline was collected in autumn and summer respectively in the farmland around a certain pig farm in Shuyang City, Huang Huai area, north of Jiangsu province. At the same time, soils without application of pig manure in the farmland of this area were collected as the reference sample. Composition of drug-resistant bacteria in all soil samples was analyzed and three common tetracycline-resistance genes (tetA, tetC, tetE) were studied by PCR as well. During the research, 59 drug-resistant bacteria belonging to 13 bacterial genus respectively were separated from the soil sample collected in autumn while 35 drug- resistant bacteria belonging to 10 bacterial genus respectively were separated from the soil sample collected in summer and as for the reference sample, 3 drug-resistant bacteria belonging to 1 bacterial genus (Streptomyces) were separated with pathogenic bacteria up to 38.14% of total drug-resistant bacteria. PCR result showed that resistance genes were detected in all drug-resistant bacteria and tetC accounted for the most. At the same time, the residual tetracycline in the soil which was in a range of 41.1-61.9 microg x kg(-1) correlated with the amount of resistance genes (4.63 x 10(5)-37.42 x 10(5) copies x g(-1)). Besides, the climate was found accelerating the formation of drug-resistant bacteria and resistance genes.

[Effect of environmental factors on the formation of several typical tetracycline resistance genes in soil].

The extensive use of veterinary tetracycline in the stock husbandry has led to the increasingly serious environmental pollution, the tetracycline resistance genes induced by which could bring more hazardous environmental risk than veterinary tetracycline. This study investigated the effects of environmental factors on the formation of several typical tetracycline resistance genes (tetA, tetC). The results showed that temperature, light and pH could have impacts on the formation of tetracycline resistance genes in soil, the amounts of the tetracycline resistance bacteria and resistance genes induced in different treatments all reached the maximum in the proper environmental condition (25 degrees C, 500 lx, pH7.5), which were all significantly higher than those in other environmental conditions (P < 0.05). In contrast, the adverse condition such as high temperature, strong light and high pH could effectively inhibit the formation of tetracycline resistance genes, probably due to the reduction of tetracycline residues or the direct influence on the formation of tetracycline resistance genes. And the results also showed that environmental factors could affect the growth of tetracycline resistance bacteria. Further analysis proved that the content of tetracycline resistance gene in soil had a positive correlation with the number of tetracycline resistance bacteria in the studied samples, therefore an inferred result was concluded that the growth of tetracycline resistance bacteria played a key role in the formation of the tetracycline resistance genes.

[Effect of submerging and wetting-redrying on Cd speciation and uptake by Sorghum hybrid Sudangrass in two paddy soils under spiked Cd].

Effect of continuous submerging and wetting-redrying on cadmium speciation and uptake by Sorghum hybrid Sudangrass in a Ferric-accumulic Stagnic Anthrosol and a Tipical Hapludult collected from the Taihu Lake region and the rolling downs of Yingtan, Jiangxi, China respectively, was studied by pot experiment with Cd spike in 2003. Compared to that under wetting-redrying treatment, the MgCl2-extracted pool of Cd in Huangnitu with spiked Cd of 5mg x kg(-1) and 10mg x kg(-1) was decreased from 21.8% and 28.5% to 8.0% and 16.9% while NH2OH x HCl-extracted pool increased from 17.7% and 17.3% to28.1% and 37.5% under continuous submerging. However, in the Typical Halpudult, NaAC-extracted pool of Cd decreased from 20.8% and 29.6% to 11.6% and 12.6%. Cd uptake by Sorghum hybrid Sudangrass was found in negative correlation with the MgCl2 extracted pool of Cd. Total Cd uptake was significantly reduced by the pretreatment of continuously submerging in Huangnitu.