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产物苯并恶唑啉酮（BOA）、芦竹碱和槲皮素对农业土壤细菌群落结构的影响。在上一个资助期间，这三种代谢物被直接添加到土壤中，通过下一代PCR扩增子测序记录细菌组成的变化。结果表明，BOA、芦竹碱和槲皮素对多种细菌属的丰度均有不同程度的影响。BOA处理导致只有少数属的丰度增加，主要是放线菌，而许多属的丰度下降。另一方面，芦竹碱和槲皮素处理引起了许多变形菌的增加。此外，在用植物代谢物处理后，分离和培养了110多个细菌菌株。目前正在对菌株进行个体测试，以确定其对BOA、芦竹碱或槲皮素的耐受性。几种BOA耐受细菌可以将BOA转化为硝化和亚硝基化合物，其中一些可以聚合产生彩色物质。其中一株节杆菌GB 1能将禾本科植物的碱降解为吲哚-3-甲醛等产物。我们将寻找和表征菌株GB 1中参与禾本科降解的基因。此外，我们还分离到了三株槲皮素耐受菌株。细菌质膜是细菌抵抗有害植物代谢物的第一道屏障。脂质分析表明，在节杆菌GB 1中存在禾本科碱的情况下，二糖基脂质的丰度强烈增加。我们将分析GB 1中二糖基脂质的结构和数量，以了解潜在的脂质适应过程的功能。此外，我们还将研究其他对BOA、芦竹碱或槲皮素耐受的分离细菌的脂质变化。我们目前正在分析植物代谢产物的结构，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物的生长促进特性。

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.