Bacterial endophytes from Lavandula officinalis: a possible source of medically relevant bioactive compounds producing isolates

Endophytes play important roles in plant biology by promoting plant growth; they are also relevant in biotechnology as they produce bioactive molecules, such as novel antimicrobial compounds. Besides, it is likely that the therapeutic properties of medicinal plants are also influenced by their endophytic communities as bacterial strains can directly produce bioactive compounds and/or elicit plant metabolism to produce them. This study aimed at the isolation and molecular characterization of bacterial communities from the widely used aromatic and medicinal plants Lavadula officinalis and to check the inhibitory capacity of endophytic isolates toward human pathogens and build a collection of bacterial isolates showing antimicrobial activity. To this purpose bulks of 5 plants were built and cultivable bacteria were isolated from both surface sterilized tissues (roots stems, and leaves) and from the rhizosphere; sequencing of the 16S rRNA genes from 400 randomly selected isolated (100 isolates for each sample) was carried out, followed by taxonomic identification matching against RPD database. Antimicrobial activity testing was performed with the cross-streak method against Cystic Fibrosis opportunistic pathogens belonging to the Burkholderia cepacia complex (Bcc). Data obtained revealed that: i) a strong variation in the composition of the communities between the different plant tissue, ad example Rhizobiales constitutes the 45% of the endophytic community of the root, but are absent in the stem and leaves; the lowest diversity of species was registered in the stem whose communities is dominated by members of the Pseudomondales; ii) a low overall diversity in the composition was found; iii) many known PGPR species were identified; iv) several isolates exhibited a strong antimicrobial activity against Bcc bacteria. In conclusion our results suggested that medicinal plants appear to be an important source of interesting isolates with biotechnological applications potential.