产多胺细菌Bacillus megaterium N3对镉的钝化及阻控小麦富集镉机制研究

Heavy metal pollution in farmland soils has increased concurrently with mining and smelting activities, and the overuse of pesticides and chemical fertilizers. For soil remediation in farmlands with mild and moderate heavy metal pollution, Bacillus megaterium N3, a polyamine-producing and plant growth-promoting bacteria, was used as the test strain to determine whether it can inhibit cadmium accumulation in wheat. The goal of this study was to ensure the safety of agricultural products and improve the ecological environment of farmlands. Experiments were carried out using sand culture, liquid adsorption, and soil culture of functional bacterial strain to determine the outcomes and mechanisms of cadmium fixation using electron microscopy, infrared spectroscopy, X-ray, plasma emission spectroscopy, and other techniques. In addition, we investigated the utility of Bacillus megaterium N3 in reducing cadmium accumulation, as well as the involved mechanisms, in wheat using pot and field experiments through metagenomics, fluorescence-based quantitative PCR, and modern environmental science techniques. The effects of the functional bacterial strain on the yield, quality, and cadmium content of wheat were analyzed to elucidate the role of the functional bacterial strain in regulating wheat quality. The changes in the pH, enzyme activity, organic matter content, aggregates, polyamines content, cadmium content, population structure of indigenous functional bacteria (polyamine-producing bacteria, urease-producing bacteria, and siderophore-producing bacteria), and abundance of functional genes (aguA and ureC) in the rhizosphere and bulk soil were assessed to elucidate the mechanisms through which the bacterial strain decreased cadmium accumulation in wheat and improved soil quality. Our results provide theoretical and practical data for the remediation of heavy metal contaminated soil in farmlands using functional bacterial strains and for improving the safety of agricultural products.

针对中轻度重金属污染农田修复现状，在保证农产品安全生产和改善农田生态环境的前提下，本项目以前期筛选得到的产多胺细菌Bacillus megaterium N3为研究对象，通过小麦苗期砂培、溶液吸附和土壤静置培养等实验，借助电镜-能谱、X衍射、红外光谱和等离子体发射光谱等技术研究供试菌株对Cd的固定效应与机制。通过盆栽和田间实验，借助宏基因组学、荧光定量PCR和现代环境化学等技术研究供试菌株对小麦产量、品质和Cd含量的影响，评价供试菌株调控小麦质量的作用；通过测定小麦根际与非根际土壤pH、酶活、团聚体、多胺含量、Cd赋存形态、土著功能细菌（产多胺细菌、产脲酶细菌和产铁载体细菌）种群结构和功能基因（aguA和ureC）丰度的变化，阐明供试菌株阻控小麦富集Cd的机制和改善土壤质量的生态效应。预期研究结果为阐明功能菌株钝化农田重金属和保障农产品安全生产提供理论依据和实践基础。

微生物钝化技术兼具绿色、廉价和无二次污染等特点，适用于中轻度Cd超标麦田修复。本项目通过溶液吸附和盆栽试验，借助电镜表征和组学测序技术系统研究了产多胺细菌Bacillus sp. N3钝化Cd和阻控小麦吸收Cd的效应和机制。溶液吸附试验表明菌株N3通过细胞壁吸附、胞内富集和提高溶液pH等作用吸附钝化Cd。此外，菌株N3分泌的多胺也能螯合Cd。水培试验表明菌株N3通过上调根内与DNA复制、植物激素和铁锌转运蛋白等蛋白的表达来阻控Cd进入小麦根内。进一步的土壤盆栽试验表明菌株N3能够提高土壤中多胺的含量、提高土壤pH值、提高土壤小团聚体的比例和诱导铁氧化物矿相转变降低土壤中DTPA-Cd的含量。此外菌株N3还能提高小麦根际土壤细菌共生细菌间的复杂性，增强了有益微生物种群的竞争优势，如具有重金属固定能力、植物促生能力和异化铁还原能力的菌属在小麦根际土壤中大量的定殖，从而固定土壤中的Cd，降低了小麦对Cd的吸收。研究结果为利用重金属固定细菌修复重金属污染农田提供理论依据和技术支撑。