Hansschlegelia zhihuaiae S113降解玉米根际土壤苄嘧磺隆残留机制的研究

Bensulfuron-methy has been widely used in China. The residues of this herbicide have contaminated agricultural soil, and have exhibited phytotoxicity on rotation sensitive crops. The degradation process of herbicides residues in the agricultural soil is closely related to the functional microorganisms. Understanding the role of bacteria in the degradation process is of a great significance for the bioremediation of herbicides contaminated soil. The degrading strain Hansschlegelia zhihuaiae S113, which was isolated by our lab, was used to study the degradation mechanism of bensulfuron-methy residues in the rhizosphere of maize. In this study, we will investigate the effects of microbe ecology，and identify the species involved in the bensulfuron-methy degradation in the rhizosphere of maize. After inoculation of strain S113, we will observe the colonization of strain S113 and the formation of biofilms in the rhizosphere of maize, and elucidate the strain’s different responses to the maize root exudates and bensulfuron-methy residues. Further, we will identify the role of cheA in the chemotaxis, the formation of biofilm and the degradation of bensulfuron-methy residues. This research will reveal the mechanism of degradation of herbicides residues in the rhizosphere of maize, and provide theoretical instructions for bioremediation of herbicides contaminated agricultural soil.

除草剂苄嘧磺隆的大量使用，污染了农田土壤，对后茬敏感作物易造成药害。苄嘧磺隆残留在土壤中的降解与微生物密切相关，了解微生物在这一过程中的作用对于污染农田土壤的修复具有重要意义。本项目以申请者分离的苄嘧磺隆降解菌株Hansschlegelia zhihuaiae S113为材料，研究其在玉米根际土壤中降解苄嘧磺隆残留的机制。拟解析接种降解菌株对玉米根际土壤苄嘧磺隆残留降解的微生态效应；参与降解苄嘧磺隆残留的土著微生物种类；降解菌株在玉米根际的定殖、存活与生物膜的形成；降解菌株对玉米根系分泌物和苄嘧磺隆残留的趋化响应及差异；趋化基因cheA在降解菌株生物膜形成和苄嘧磺隆残留降解过程中的作用等内容。研究结果可进一步阐明玉米根际土壤苄嘧磺隆残留的微生物降解机制，为除草剂苄嘧磺隆残留污染农田土壤的修复提供更多的理论依据。

除草剂苄嘧磺隆残留药害问题引起了广泛关注，投加菌株S113可降解玉米根际土壤苄嘧磺隆残留，但具体降解机制仍不清楚。本课题分析了玉米根系分泌物对降解菌株S113生长、定殖、趋化、生物膜形成的影响。发现降解菌株S113在玉米根系和根际土壤中最少定殖15d。玉米根系分泌物可促进菌株S113的生长和对苄嘧磺隆的降解。菌株S113对玉米根系分泌物中的L-苹果酸、草酸、酒石酸的趋化作用较强，L-苹果酸还可以显著诱导S113在玉米根系的定殖。成膜试验发现玉米根系分泌物和有机酸促进了菌株S113的生物膜的形成。研究了菌株S113的生物膜形成对降解根际土壤中苄嘧磺隆残留贡献度，菌株S113的降解功能在该过程中起着主要作用，生物膜的形成具有一定的促进作用。通过转录组测序研究了玉米根系分泌物在生物膜形成条件下对菌株S113基因表达的影响，发现受到调控的基因为营养代谢、跨膜运输、信号转导以及趋化运动等方面。分析了参与趋化作用的基因cheA在菌株S113定殖过程中的作用，发现cheA的敲除会导致菌株S113的趋化和定殖能力显著下降，但不影响菌株的生长和降解能力。发现丛枝菌根真菌的添加可以提高菌株S113降解根际土壤中苄嘧磺隆残留速率。通过高通量测序技术研究了微生物修复过程中玉米根际土壤细菌群落结构动态变化，发现投加菌株S113进行修复后Bacillus，Rhodococcus和Brevibacillus三个属的相对丰度逐渐升高而后逐渐降低，表明这些属中土著微生物可能参与了苄嘧磺隆代谢产物的进一步降解。投加降解菌株S113在一定程度上恢复了细菌群落结构丰富度和多样性。鉴定了苄嘧磺隆在根际土壤降解过程中的系列中间代谢产物，并分离了2株可降解代谢产物2-(氨基磺酰甲基)-苯甲酸甲酯的土著微生物纯培养，鉴定为Rhodococcus sp.。本研究结果为除草剂污染农田土壤的修复提供了更多的理论依据。