Microbial endophytes from the pepper bark tree

The plant apoplast represents an ecological niche for a broad diversity of microorganisms. As compared to other habitats such as the soil or the rhizosphere, the diversity and function of endophytic microbes have been rarely addressed. Mutualistic interactions between plants and its beneficial endophytic population are considered - the plant may offer a habitat that is less competitive than soil or rhizosphere and provides nutrients, whereas endophytes may support plant vitality. Endophytes encounter in planta a range of complex organic compounds that are not found in soils or other environments, some of them showing antibacterial and/or antifungal activities. Therefore, a wide metabolic versatility among endophytes is expected. However, it is still poorly understood how and to which extent microbes make use of plant metabolites or how endophytes can withstand the chemical defense mechanism of plants towards microbes. In the proposed project, we aim at answering the following questions: (1) Does the composition of secondary metabolites in a plant affect the endophytic community? (2) Which strategies have been developed by endophytes to deal with putatively antimicrobial substances produced by the host plant? In order to address these questions, we will perform a polyphasic approach to study the function and physiology of culturable and non-culturable endophytes colonizing Warburgia ugandensis, a tropical tree with high medical potential. Stem bark and roots will be collected from randomly selected trees grown on two distinct and well characterized sites in Kenya, and used for the isolation of plant metabolites, DNA and microbes. In each site, three replicate plants of three different developmental stages will be selected. Plant metabolites will be extracted with organic solvents from plant organs. Microorganisms will be isolated on several media in order to allow a functional characterization of the cultured proportion of the community. Cultivation-independent community analysis will provide information on the influence of the sesquiterpene composition within a plant on the endophytic community structure. High-quality, high-molecular weight DNA of candidate plants and tissues will be used for constructing a metagenomic library. Substrate induced gene expression experiments will be performed to screen for genes that are relevant for the metabolization of plant exudates, and the resistance towards antibacterial and antifungal compounds will be considered.

The plant apoplast represents an ecological niche for a broad diversity of microorganisms. As compared to other habitats such as the soil or the rhizosphere, the diversity and function of endophytic microbes have been rarely addressed. Mutualistic interactions between plants and its beneficial endophytic population are considered - the plant may offer a habitat that is less competitive than soil or rhizosphere and provides nutrients, whereas endophytes may support plant vitality. Endophytes encounter in planta a range of complex organic compounds that are not found in soils or other environments, some of them showing antibacterial and/or antifungal activities. Therefore, a wide metabolic versatility among endophytes is expected. However, it is still poorly understood how and to which extent microbes make use of plant metabolites or how endophytes can withstand the chemical defense mechanism of plants towards microbes. In the proposed project, we aim at answering the following questions: (1) Does the composition of secondary metabolites in a plant affect the endophytic community? (2) Which strategies have been developed by endophytes to deal with putatively antimicrobial substances produced by the host plant? In order to address these questions, we will perform a polyphasic approach to study the function and physiology of culturable and non-culturable endophytes colonizing Warburgia ugandensis, a tropical tree with high medical potential. Stem bark and roots will be collected from randomly selected trees grown on two distinct and well characterized sites in Kenya, and used for the isolation of plant metabolites, DNA and microbes. In each site, three replicate plants of three different developmental stages will be selected. Plant metabolites will be extracted with organic solvents from plant organs. Microorganisms will be isolated on several media in order to allow a functional characterization of the cultured proportion of the community. Cultivation-independent community analysis will provide information on the influence of the sesquiterpene composition within a plant on the endophytic community structure. High-quality, high-molecular weight DNA of candidate plants and tissues will be used for constructing a metagenomic library. Substrate induced gene expression experiments will be performed to screen for genes that are relevant for the metabolization of plant exudates, and the resistance towards antibacterial and antifungal compounds will be considered.