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

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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.