The impact of plant secondary metabolites on the soil microbiota (MICROSEC)

在本项目中，我们重点研究了三种植物代谢物，苯并恶唑烷酮(BOA)、谷胺和槲皮素对农业土壤中细菌群落结构的影响。在之前的资助期间，将三种代谢物直接添加到土壤中，并通过下一代聚合酶链式反应扩增片段的测序记录细菌组成的变化。结果表明，多个细菌属的丰度在BOA、葡萄糖胺或槲皮素的作用下发生改变。BOA处理只增加了少数属的丰度，主要是放线菌，而许多属的丰度降低。另一方面，谷氨酰胺和栎素处理导致了许多变形杆菌的增加。此外，经过植物代谢产物处理后，分离和培养了110多株细菌。目前正在对这些菌株进行个体测试，以确定它们对BOA、格拉明或栎素的耐受性。几种耐受BOA的细菌可以将BOA转化为硝化和亚硝化化合物，其中一些可以聚合产生彩色物质。一株耐葡萄糖胺的菌株，节杆菌GB1，能将葡萄胺降解成吲哚-3-甲醛等产物。我们将在菌株GB1中寻找和鉴定与谷胺降解有关的基因。此外，我们还分离到了三株对槲皮素具有耐受性的菌株。细菌质膜是细菌对抗有害植物代谢物的第一道屏障。脂质分析表明，在葡萄胺存在下，节杆菌GB1中二糖基脂的丰度显著增加。我们将分析GB1中二糖基脂的结构和数量，以了解潜在的脂适应过程的功能。此外，我们还将研究其他分离的耐受BOA、葡萄糖胺或槲皮素的细菌的血脂变化。我们目前正在分析植物代谢物的降解产物的结构，以及它们对拟南芥和大麦植物的影响。我们还将测试分离的菌株对拟南芥或大麦植株的促生长特性。

In the present project, we focus on the impacts of three plant metabolites, benzoxazolinone (BOA), gramine and quercetin, on the bacterial community structure in agricultural soil. During the previous funding period, the three metabolites were directly added to the soil, and changes in bacterial composition were recorded by next generation sequencing of PCR amplicons. The results show that the abundances of many bacterial genera were altered by BOA, gramine or quercetin. BOA treatment resulted in the increase of the abundance of only few genera, mostly Actinobacteria, while many genera were decreased. On the other hand, gramine and quercetin treatment caused the increase in many Proteobacteria. In addition, more than 110 bacterial strains were isolated and cultivated after treatment with the plant metabolites. The strains are currently tested on an individual basis for their tolerance to BOA, gramine or quercetin. Several BOA-tolerant bacteria can convert BOA into nitrated and nitrosylated compounds, some of which can be polymerized to give rise to colorful substances. One gramine-tolerant strain, Arthrobacter GB1, can degrade gramine into indole-3-carbaldehyde and other products. We will search for and characterize the genes involved in gramine degradation in strain GB1. Furthermore, we isolated three strains tolerant to quercetin. The bacterial plasma membrane represents the first barrier of the bacteria against harmful plant metabolites. Lipid analyses showed that the abundance of a diglycosyl lipid was strongly increased in the presence of gramine in Arthrobacter GB1. We will analyze the structure and the amount of the diglycosyl lipid in GB1 to understand the function of the underlying lipid adaptation process. Furthermore, we will study lipid changes in other isolated bacteria tolerant to BOA, gramine or quercetin. We are currently analyzing the structure of the degradation products of the plant metabolites, and their impacts on Arabidopsis and barley plants. We will also test the growth promoting properties of the isolated strains for Arabidopsis or barley plants.