Microbial Diversity And Responses Of Arsenic Resistance Genes To The Environment Of High-arsenic Groundwater In Datong Basin, Northern China

It has become a worldwide problem facing the common humanity of arsenic poisoning due to long-term drinkable groundwater of high arsenic. In recent years, microbes associate with arsenic metabolism in nature and its important role in the formation of groundwater arsenic contamination have become the new research hotspot. Datong Basin is a typical drinking-water type endemic arsenic poisoning area, and we used Shanyin County which is serious endemic arseniasis as study area. The thesis first studied bacterial community composition and discussed ecosystem functions in the basin groundwater. The culturable method was then used to isolate high arsenite-resistant strains and analyzed the high arsenic groundwater culturable microbial community structure and dominant population. In addition, we analysised the quantitative distribution of the bacterial16S rDNA gene and arsenic reduction functional genes among the groundwater environmental samples and its response to the groundwater environmental conditions for groundwater arsenic resistant mechanism of the microbes in a hypothesis. This provided the scientific basis for groundwater arsenic pollution control, and ensure the safety of residents drinking water.By constructing and comparing16S rDNA clone libraries of high arsenic and low arsenic groundwater we found that β-Proteobacteria、α-Proteobacteria and y-Proteobacteria are the dominant population, this class is usually aerobic bacteria. Low arsenic groundwater were given priority to with Proteobacteria, Actinobacteria, Bacteroidete and Chloroflexi, high arsenic groundwater coverd Proteobacteria, Bacteroidetes, Planctomycetes, Nitrospira, etc., but the unknown strains also occupied large proportion in the community. This suggests that microbial flora is rich in Datong basin groundwater and has great value in research. Used Dotur and RDP on-line analysis software, we found that community structure of high arsenic and low arsenic groundwater are different, the latter’s diversity is higher. Through phylogenetic tree to find similar sequence analysis, we found bacterias in low arsenic groundwater ecological system are similar to the bacterias isolated from other environment and can resistant to low temperature, heavy metals or other polluting environment. The bacterial metabolism is varied include denitrification or transformation and degradation of compound. While in high arsenic groundwater ecological system may exist ammoxidation by Nitrosomonas, or sulfoxidation by Thiothrix.By dilution culture method adding the plus arsenic source we found that arsenic affected microbial growth in the groundwater environment of high-arsenic. Low concentration arsenic has promoting effect on microbial growth, high concentrations arsenic could inhibit the growth of microorganism. Overall arsenite can inhibit most microbial growth, but the inhibition is inconsistent in different environments, high TDS content of arsenic poisoning inhibition has a buffer role, microorganism quantity change much. Cultivate arsenic-resistant bacterias belonged to the genus Pseudomonas, Enterobacter, Aeromonas, Paenibacillus and Bacillus. y-Proteobacteria is widely distributed in high arsenic groundwater environment, Pseudomonas and Bacillus are the main microbes in high arsenic groundwater. Microbial activity may promote the formation of high-arsenic groundwater through change groundwater hydration conditions such as pH by analysising phylogenetic tree. We isolated strains belonged to the genus Enterobacterand and tolerant to150mg·L-1NaAsO2, it is easy to grow in the common medium of facultative anaerobic bacteria, and could be used to repair the arsenic contamination groundwater. Quantitative PCR analysis of genes showed that the copy number of bacterial16S rDNA gene, acr3gene, arsB, arrA gene respectively are2.30*109～1.39*1012,2.25*106～2.70*108,9.43*104～6.20*107,5.89*104～5.49*106, the four genes have significant positive correlation. HCO3-concentration with acr3gene copy number have significant positive correlation. Acr3gene, arsB gene and arrA gene in environmental samples can indicate the arsenic content in a certain extent, but this relationship is not absolute. Result also shows that respiratory As (V) bacterias are relatively rare.Research shows that arsenic and microorganism interact each other. Arsenic reduction genes are widely distributed in Datong Basin groundwater. This paper preliminary discusses the microbial diversity, arsenic reduction functional gene distribution and the relationship with the groundwater chemical conditions, enriched the functional genes information of arsenic pollution area in our country. For further understanding microbial evidence in the formation of high arsenic groundwater and arsenic-resistance mechanisms, future research can be focused on microbial community structure, physiological and biochemical properties of arsenic-resistant strains and its role in the process of migration and transformation of arsenic. Additional the evolutionary relationships of related functional genes also need thorough analysis.