Isolation, characterization and antimicrobial activity characterization of endophitic bacterial communities from Echinacea species: identification of bioactive molecules producing isolates from medicinal plants

Endophytes are fundamental in plant life promoting their growth and producing bioactive molecules with important medical and biotechnological applications. The therapeutic properties of medicinal plants are therefore likely related also to their endophytic communities that can directly produce bioactive compounds and/or elicit plant metabolism and growth. We carried out the isolation and the molecular characterization of bacterial communities from the medicinal plants Echinacea purpurea, and Echinacea angustifolia 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) functionally characterize the strains testing their resistance to antibiotics, heavy metals, hydrogen peroxide and gasoil, iii) identify bacterial isolates showing antimicrobial activities against human pathogens to establish a biobank specific for of such type of strains. Bacteria were isolated from leaves and roots and from the rhizosphere of the two medicinal plants; 16S rDNA sequencing and RAPD fingerprinting of 600 randomly selected isolated were carried out, followed by taxonomic identification. The functional characterization was performed testing bacterial growth on solid media supplemented with various substrates at different concentration. Finally the cross-streak method was used to test their antimicrobial activity versus ten strains of Burkholdera cepacia complex (Bcc), an opportunistic human pathogen causing infections in Cystic Fibrosis patients. Results highlighted a strong variation in the communities between the different plant species (although grown in physical proximity) and in different organs/soil in the same species, moreover a variability was observed in response to different growth conditions, suggesting a selection of the endophytic microflora by the plant species and tissue; finally, several isolates showed an antimicrobial activity against different Bcc strains.