Isolation and molecular characterization of endophytic bacterial communities from medicinal plants: toward the identification of boactive molecules producing isolates

Background: Bacterial endophytes play important roles in plant biology by promoting the plant growth, and also producing bioactive molecules, with important medical and biotechnological applications. The therapeutic properties of medicinal plants are therefore likely related to their endophytic communities that can directly produce antimicrobial and other bioactive compounds and/or elicit plant metabolism and growth. Objectives: The isolation and the molecular characterization of bacterial communities from the medicinal plants Lavadula officinalis, Echinacea purpurea, and Echinacea angustifolia were performed with the aim to: i) study the variation of the endophytic communities from the soil to the internal tissues of the same species and among species, ii) individuate and build a collection of bacterial isolates showing antimicrobial activities against human pathogens. Methods: Cultivable bacteria were isolated from surface sterilized tissues (stems, leaves and roots) and from the rhizosphere of the three medicinal plants; 16S rDNA sequencing and RAPD fingerprinting of 1000 randomly selected isolated were carried out, followed by taxonomic identification matching against RPD database. Antimicrobial activity testing was performed with the cross-streak method. Conclusions: Results highlight that: i) there is strong variation in the communities between the different plant species (although grown in physical proximity) and in different organs/soil in the same species, suggesting a selection of the endophytic microflora by the plant species and tissue; ii) several isolates have a strong antimicrobial activity against human opportunistic pathogens such as Burkholderia spp.