耐镉促生菌株的分离鉴定及对大豆的促生效应

Isolation and identification of cadmium-resistant growth-promoting strains and their growth-promoting effects on soybean

摘要:

【背景】华南地区镉(Cd)污染严重，与有益微生物共生能够使作物通过直接或间接的机制解除镉毒，提高抗逆性，进而促进生长。耐镉促生菌剂具有广泛的应用前景。【目的】从华南地区受镉污染植株的根内和根际筛选出耐镉且能促进大豆生长的促生菌，以丰富促进田间大豆生产的优异菌种资源。【方法】采用平板划线法从植株的根内或根际分离菌株，通过生理生化特性和16S rRNA基因序列分析对分离菌株进行初步研究，利用盆栽试验探究镉胁迫下菌株对大豆生长的影响，通过测定丙二醛含量和总抗氧化能力探究菌株的耐镉机制。【结果】分离获得4株菌D1、D2、D3和D4，促生特性试验证明4株菌均具有溶磷、产吲哚乙酸和铁载体的能力。经16S rRNA基因序列分析鉴定，D1、D2、D3和D4菌株分别属于不动杆菌属、微小杆菌属、类芽孢杆菌属和普罗威登斯菌属。用这4株菌进行不同镉处理的大豆(巴西10号)盆栽试验，结果表明，4株菌均具有耐镉和促进大豆生长的作用。不添加镉的条件下，大豆接种D4菌株的地上部干重、根部干重和株高分别增加了28%、35%和31%；在添加20 mg/kg-CdCl₂·5/2H₂O的条件下，接种D1、D2、D3和D4菌株的大豆地上部干重分别增加了35%、55%、53%和43%，接种D2和D4菌株的大豆叶片其丙二醛含量分别降低了23%和29%，接种D1和D4菌株的大豆叶片总抗氧化能力分别增加了11%和13%。【结论】筛选获得的菌株有望研制成微生物菌肥用于镉污染的农田，促进作物生长、提高产量。同时，本研究为植物促生菌的耐镉机制研究提供了理论依据。

Abstract:

[Background] South China suffers from serious cadmium (Cd) pollution. Symbiosis with beneficial microorganisms can relieve Cd toxicity and improve crop resistance to Cd through direct or indirect mechanisms, and thereby promote crop growth. Cd-resistant growth-promoting bacterial inoculants have broad application prospects. [Objective] Growth-promoting bacteria that can resist Cd and promote soybean growth are screened from the roots or rhizosphere of Cd-contaminated plants in South China, which is expected to enrich beneficial microbial resources in soybean production. [Methods] Strains were isolated from the roots or rhizosphere of the plants with the streak plate method, and preliminarily identified through the analysis of physiological and biochemical characteristics and 16S rRNA gene sequence. Meanwhile, pot experiment was used to explore the effects of these strains on soybean growth under Cd stress. Malondialdehyde (MDA) content and total antioxidant capacity (T-AOC) were determined to explore Cd-resistant mechanism of these strains. [Results] Four strains D1, D2, D3, and D4 were isolated, which all can solubilize phosphate and produce indole-3-acetic acid (IAA) and siderophore. They belong to Acinetobacter, Microbacterium, Paenibacillus, and Providencia, respectively. The pot experiment on soybean Baxi 10 showed that these four strains had Cd-resistant capacity and could promote soybean growth. Shoot dry weight, root dry weight, and plant height of soybean inoculated with D4 were increased by 28%, 35% and 31%, respectively, in the absence of Cd. In the presence of 20 mg/kg-CdCl₂·5/2H₂O, shoot dry weight of soybean plants inoculated with D1, D2, D3, and D4 was raised by 35%, 55%, 53%, and 43%, respectively. The MDA content in the shoots of soybean plants inoculated with D2 and D4 was decreased by 23% and 29%, respectively. The T-AOC in the shoots of soybean plants inoculated with D1 and D4 was elevated by 11% and 13%, respectively. [Conclusion] The screened strains are expected to be developed into microbial fertilizers and applied into Cd-contaminated farmland for improvement of crop growth and yield. Meanwhile, it lays a theoretical basis for the study of Cd-resistant mechanisms of plant growth-promoting bacteria.