Studies On Microbial Physiological And Ecological Characteristics In Paddy Soil Polluted By Cd And Its Clonning And Expression Of The Resistant Gene CzcC

In this paper, soil microbial physiological and ecological characteristics in submerged paddy soil contaminated by heavy metal Cd were studied using traditional incubation and modern molecule biology methods. A bacterium (designated strain KDC1) capable of growing in the high concentration of Cd was isolated from soil contaminated metal Cd. The full-length czcC gene encoding the structure modified protein in cadmium- resistant system of Ralstonia eutropha was cloned and expressed successfully. The results will be useful reference for building up alert index systems in paddy soil polluted by Cd, environmental quality evaluation and available for using Cd-resistant bacteria. Here are presented the main result of this study:1. Influence of Cd2+ on change processes of culturable microbial populations, the biological activities and the enzyme activities in submerged Red paddy soil from Jiangxi province was studied using traditional incubation method. The results showed that there are different effectives on the soil microbial population and the biochemical process in soils contaminated by different concentration of Cd, the lower concentratuion of cadmium was helpful to increase most of microbial population, but the higher concentrations of Cd caused a great inhibitory effect on microbial activities. The order of aerobic microorganisms inhibited by Cd was actinomycetes, fungi and bacteria. The methanogenic bacteria were the most sensitive one to Cd2+, compared with other anaerobic populations among the soil bacteria populations. The second was the anaerobic nitrogen-fixing bacteria and the hydrogen-producing acetogenic bacteria. The inhibition of Cd2+ was slightly weaker to both of the denitrifying and the hydrolytic-fermentative bacteria. The similar effects on the biochemical activities were observed that the higher the concentration ofcadmium applied, the more significant the inhibition to these activities was, The results also indicated that the order of anaerobic biochemical activities inhibited by cadmium was the methane emission activity, the sulfate reduction activity and the denitrification activity. For the effect of cadmium on the soil enzyme activity, the order of four soil enzyme activities being sensitive to cadmium indicated as: urease > hydrogen peroxidase > phosphatases > fructosidase. There were significant negative relationship, however, between the cadmium concentrations and the population of actinomycetes, hydrogen-producing acetogenic bacteria, anaerobic nitrogen-fixing bacteria, methanogeneic bacteria, microbial respiration, the sulfate rereduction activity, the methanogeneic activity, urease activity, and hydrogen peroxidase activity. Therefore, these populations and these activities can be used as indexes to indicate the contamination degree of paddy soil by Cd +. According to these microbial index, about l~5mg cadmium /kg dried soil was suggested as the critical level of cadmium in submerged paddy soil.2. Based on the studies of traditional microbial pollution ecology, the efficient total soil community DNA extraction methods were etablished. Total soil community DNA used for PCR was extracted and the total 16S rDNA and their V3 variable region was amplified. Variations of microbial gene diversity in submerged paddy soil stressed by heavy metal cadmium were studied using the denaturing gradient gel electrophoresis (DGGE) technique. The result showed that there are some significant differences between bacterial communities in paddy soils treated with different concentrations of cadmium. Cadmium had obvious toxicity on bacterial community during the earlier days after Cd treatment, making gene diversity decrease. There was, however, little difference among variations of microbial genes come from soil treated with different concentrations of cadmium during the late stage after Cd treatment, but it could affect the abundances of various kinds of bacteria. Obviously, it is possible to provide a new way and foundation to research microbial gene diversity of microorganisms in contaminated env...