钼还原促生菌的筛选及对紫花苜蓿钼吸收的调控作用

Screening of molybdate-reducing bacteria capable of promoting the growth and regulating the molybdate uptake of Medicago sativa

摘要:

目的 根际微生物协同植物修复重金属污染土壤具有较高的应用潜力。本研究旨在强化土壤钼污染修复的理论与技术，分析添加外源钼还原促生菌对紫花苜蓿生长和钼富集活性的影响，为植物-微生物联合修复钼污染土壤提供理论参考。方法 采集钼尾矿区内优势植物，分离与筛选钼还原内生细菌；结合形态学特征和分子生物学手段对菌株进行鉴定；测定钼还原菌株的促生特性。通过外源添加钼还原促生菌，研究其对紫花苜蓿生物量、生理活性及钼富集量的影响。结果 获得2株钼还原活性强的菌株M9和M13，结合形态特征、16S rRNA基因序列及gyrB基因序列分析结果，2株细菌(M9和M13)均被鉴定为普利茅斯沙雷氏菌(Serratia plymuthica)。促生特性分析表明，2株细菌均具有固氮、溶磷、解钾、产吲哚-3-乙酸(indole-3-acetic acid, IAA)、铁载体及1-氨基环丙烷-1-羧酸(1-amino cyclopropane-1-carboxylic acid, ACC)脱氨酶的能力。在钼胁迫条件下，外源添加M9、M13及M9+M13复配菌株后对紫花苜蓿的促生作用显著。与未接菌对照组相比，其株高、根长和鲜重均显著增加，同时紫花苜蓿中叶绿素含量显著提高，过氧化物酶(peroxidase, POD)活性增加，丙二醛(malondialdehyde, MDA)含量降低。此外，钼还原菌株M9和M13显著影响紫花苜蓿的钼富集量，接菌处理组紫花苜蓿地上部和地下部钼含量均显著低于未接菌处理组，其富集因子显著降低，表明接种钼还原菌株后减少了紫花苜蓿对土壤中钼的吸收和转运。结论 钼还原菌株M9和M13具有显著的植物促生特性，能够促进紫花苜蓿在钼污染土壤中的生长，并降低其钼含量。本研究为揭示微生物强化植物钼修复的机制以及促进植物-微生物联合修复钼污染土壤的相关研究提供了参考。

Abstract:

Objective The rhizosphere microorganism-plant combined approach has high application potential for the remediation of heavy metal-contaminated soil. This study observed the effects of adding exogenous plant growth-promoting bacteria (PGPB) on the growth and molybdenum (Mo) accumulation of alfalfa (Medicago sativa), aiming to provide theoretical references for plant-microbial remediation of Mo-contaminated soil.Methods The endophytic bacteria were isolated from dominant plants of Mo tailing and they were identified based on morphological characteristics and molecular evidence. The plant growth-promoting (PGP) properties of molybdate-reducing strains were determined. By adding exogenous PGPB into the soil, we investigated the effects of adding exogenous PGPB on the biomass, physiological activity, and Mo accumulation of alfalfa.Results Two molybdate-reducing strains M9 and M13 were obtained and identified as Serratia plymuthica based on morphological characteristics, 16S rRNA gene sequence, and gyrB sequence. M9 and M13 had the abilities to fix nitrogen, solubilize phosphorus, solubilize potassium, and secrete indole-3-acetic acid (IAA), siderophores, and 1-amino cyclopropane-1-carboxylic acid (ACC) deaminase. Under Mo stress, the inoculation of M9, M13, and M9+M13 significantly promoted the growth of alfalfa, increasing the plant height, root length, and fresh weight of alfalfa compared with the non-inoculation control group. At the same time, the inoculation increased the chlorophyll content and peroxidase (POD) activity while decreasing the malondialdehyde (MDA) content in alfalfa. M9 and M13 significantly affected the Mo accumulation of alfalfa. The Mo content in the above-ground and under-ground parts of alfalfa inoculated with M9, M13, and M9+M13 significantly decreased compared with that in the non-inoculation control group. The decreased enrichment factor of Mo in alfalfa indicated that inoculation with molybdate-reducing strains reduced the uptake and transport of Mo in alfalfa.Conclusion The molybdate-reducing strains M9 and M13 can promote the growth and reduce the Mo content of alfalfa in Mo-contaminated soil. This finding can provide theoretical reference for revealing the mechanism of microbial-enhanced Mo remediation by plants as well as the joint remediation of Mo-contaminated soil by plants and microorganisms.