Employing Genome Mining to Unveil a Potential Contribution of Endophytic Bacteria to Antimicrobial Compounds in the Origanum vulgare L. Essential Oil.

Essential oils (EOs) from medicinal plants have long been used in traditional medicine for their widely known antimicrobial properties and represent a promising reservoir of bioactive compounds against multidrug-resistant pathogens. Endophytes may contribute to the yield and composition of EOs, representing a useful tool for biotechnological applications. In this work, we investigated the genomic basis of this potential contribution. The annotated genomes of four endophytic strains isolated from Origanum vulgare L. were used to obtain KEGG ortholog codes, which were used for the annotation of different pathways in KEGG, and to evaluate whether endophytes might harbor the (complete) gene sets for terpene and/or plant hormone biosynthesis. All strains possessed ortholog genes for the mevalonate-independent pathway (MEP/DOXP), allowing for the production of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) precursors. Ortholog genes for the next steps in terpenoid biosynthesis were scarce. All the strains possess potential plant growth promotion (PGP) ability, as shown by the presence of orthologous genes involved in the biosynthesis of indoleacetic acid. The main contribution of endophytes to the yield and composition of O. vulgare EO very likely resides in their PGP activities and in the biosynthesis of precursors of bioactive compounds.

Genomic, Molecular, and Phenotypic Characterization of Arthrobacter sp. OVS8, an Endophytic Bacterium Isolated from and Contributing to the Bioactive Compound Content of the Essential Oil of the Medicinal Plant Origanum vulgare L.

Medicinal plants play an important role in the discovery of new bioactive compounds with antimicrobial activity, thanks to their pharmacological properties. However, members of their microbiota can also synthesize bioactive molecules. Among these, strains belonging to the genera Arthrobacter are commonly found associated with the plant's microenvironments, showing plant growth-promoting (PGP) activity and bioremediation properties. However, their role as antimicrobial secondary metabolite producers has not been fully explored. The aim of this work was to characterize the Arthrobacter sp. OVS8 endophytic strain, isolated from the medicinal plant Origanum vulgare L., from molecular and phenotypic viewpoints to evaluate its adaptation and influence on the plant internal microenvironments and its potential as a producer of antibacterial volatile molecules (VOCs). Results obtained from the phenotypic and genomic characterization highlight its ability to produce volatile antimicrobials effective against multidrug-resistant (MDR) human pathogens and its putative PGP role as a producer of siderophores and degrader of organic and inorganic pollutants. The outcomes presented in this work identify Arthrobacter sp. OVS8 as an excellent starting point toward the exploitation of bacterial endophytes as antibiotics sources.