铜污染对土壤细菌群落结构及重金属抗性基因的影响

重金属Cu在土壤中长期积累会对微生物产生毒害作用，为了探究Cu污染对土壤细菌群落及重金属抗性基因的影响，本研究建立了不同Cu浓度（50、100、200、300、500、750和1000 mg·kg^-1）的土壤微宇宙，基于高通量测序和荧光定量PCR技术分析比较不同Cu浓度下培养14 d后土壤细菌群落及重金属抗性基因的变化.结果表明，当Cu浓度≤ 100 mg·kg^-1时，随着铜浓度增加细菌群落丰度和多样性增加；而Cu浓度≥ 500 mg·kg^-1时，Cu浓度的增加会导致细菌群落丰度和多样性显著降低（p<0.05）.随着Cu浓度的升高，变形菌门的相对丰度增加，酸杆菌门和芽单胞菌门的相对丰度降低（p<0.05）；在属水平，溶杆菌属、黄杆菌属和Brevundimonas等13个属的相对丰度升高，而芽孢杆菌属、假单胞菌属和Subgroup_6等17个属的相对丰度降低.抗性基因检测结果显示，当Cu浓度≥ 500mg·kg^-1时，重金属抗性基因的丰度显著高于其它样品中的丰度（p<0.05），其中，copB、copA和czcA的丰度较高，copB和czcA与Cu浓度之间呈显著正相关（p<0.001），而copA与Cu浓度则呈显著负相关（p<0.001）.网络分析表明，抗性基因丰度的升高或降低可能是由于Cu污染对其潜在宿主影响所造成.本研究结果表明，不同Cu污染水平下土壤细菌群落重金属抗性的选择影响着群落多样性的变化，也为重金属Cu污染修复提供了理论依据.

Effects of copper pollution on soil bacterial community structure and heavy-metal resistance genes

The accumulation of copper in soil impose toxic effects on microorganisms. However, there were still poor understandings of the structure and heavy metal resistance genes of soil bacterial communities under different soil Cu contents. In this study, soil microcosms were established under different Cu concentrations (50, 100, 200, 300, 500, 750, and 1000 mg·kg^-1).The high-throughput sequencing and fluorescence quantitative PCR were employed to detect the changes of soil bacterial community and resistance genes with the increase of Cu concentration after 14-d cultivation. Our results showed that soils bacterial abundance and diversity were increased when Cu concentration was lower than 100 mg·kg^-1 (p<0.05). However, the abundance and diversity of soil bacteria were decreased with Cu concentration higher than 500 mg·kg^-1 (p<0.05). The relative abundance of Proteobacteria increased with the increase of Cu concentration, whereas the relative abundance of Acidobacteria and Bacillus decreased. Thirteen genera, such as Lysobacterium, Flavobacterium and Brevundimonas, were enriched at the genus level. The relative abundance of 17 genera including Bacillus, Pseudomonas and Subgroup_6 was reduced. The abundance of heavy metal resistance genes significantly increased with Cu concentration higher than 500 mg·kg^-1 (p<0.05). CopB, copA and czcA was most abundant among the heavy metal resistance genes in such soil copper conditions. There were significant positive correlations between copB, czcA and Cu concentration (p<0.001), while copA showed a significant negative correlation with Cu concentration (p<0.001). Further, co-occurrence network analysis indicated that the changes in the abundance of resistance genes might be due to the effect of Cu contamination on its potential hosts. The results suggested that the selection of soil bacterial heavy metal resistance would affect the diversity of soil bacterial community under different Cu pollution levels, and provided a theoretical basis for the remediation of Cu contaminate.