Endophytic Bacteria From the Roots of the Medicinal Plant Tausch (): Exploration of Plant Growth Promoting Properties and Potential Role in the Production of Plant Secondary Metabolites.

Alkannin and shikonin (A/S) are enantiomeric naphthoquinones produced in the roots of certain plants from the Boraginaceae family such as spp. and spp. They possess antimicrobial, anti-tumoral and wound healing properties. The production of secondary metabolites by might be influenced by its endomicrobiome. To study the interaction between this medicinal plant and its bacterial endophytes, we isolated bacteria from the roots of wild growing collected near to Athens and Thessaloniki in Greece. Representative strains selected by MALDI-TOF mass spectrometry were identified by partial 16S rRNA gene sequence analysis. In total, 197 distinct phylotypes of endophytic bacteria were detected. The most abundant genera recovered were , , , , , , and . Several bacteria were then tested for their plant growth promoting activity and the production of cell-wall degrading enzymes. Strains of , , and showed positive plant growth properties whereas those of Bacteroidetes and showed pectinase and cellulase activity . In addition, bacterial responses to alkannin and shikonin were investigated through resistance assays. Gram negative bacteria were found to be resistant to the antimicrobial properties of A/S, whereas the Gram positives were sensitive. A selection of bacteria was then tested for the ability to induce A/S production in hairy roots culture of . Four strains belonging to sp., sp., sp., and sp., resulted in significantly more A/S in the hairy roots than the uninoculated control. As these bacteria can produce cell-wall degrading enzymes, we hypothesize that the A/S induction may be related with the plant-bacteria interaction during colonization.