Origanum vulgare L. Associated Microbiota conclusion, this study regarded the characterization of O. vulgare L. chemotype and of the bacterial communities associated to this medicinal plant, also allowing the evaluation of antibiotic resistance and antagonistic interactions. This study provided the bases for further analyses on the possible involvement of endophytic bacteria in the production of antimicrobial molecules that could have an important role in clinical and therapeutic applications.
Medicinal aromatic plants’ essential oils (EOs) are mixtures of volatile compounds showing antimicrobial activity, which could be exploited to face the emerging problem of multi-drug resistance. Their chemical composition can depend on the interactions between the plant and its endophytic microbiota, which is known to synthesize volatile organic compounds (VOCs). However, it is still not clear whether those volatile metabolites can contribute to the composition of the aroma profile of plants’ EOs. The aims of this study were to characterize medicinal plant O. vulgare ssp. vulgare bacterial endophyte VOCs, evaluating their ability to antagonize the growth of opportunistic human pathogens belonging to the Burkholderia cepacia complex (Bcc) and compare them with O. vulgare EO composition. Many of the tested endophytic strains showed (i) a bactericidal and/or bacteriostatic activity against most of Bcc strains and (ii) the production of VOCs with widely recognized antimicrobial properties, such as dimethyl disulfide, dimethyl trisulfide, and monoterpenes. Moreover, these monoterpenes were also detected in the EOs extracted from the same O. vulgare plants from which endophytes were isolated. Obtained results suggest that endophytes could also play a role in the antibacterial properties of O. vulgare ssp. vulgare and, potentially, in determining its aromatic composition.
Multidrug-resistant pathogens represent a serious threat to human health. The inefficacy of traditional antibiotic drugs could be surmounted through the exploitation of natural bioactive compounds of which medicinal plants are a great reservoir. The finding that bacteria living inside plant tissues, (i.e., the endophytic bacterial microbiome) can influence the synthesis of the aforementioned compounds leads to the necessity of unraveling the mechanisms involved in the determination of this symbiotic relationship. Here, we report the genome sequence of four endophytic bacterial strains isolated from the medicinal plant Origanum vulgare L. and able to antagonize the growth of opportunistic pathogens of cystic fibrosis patients. The in silico analysis revealed the presence of gene clusters involved in the production of antimicrobial compounds, such as paeninodin, paenilarvins, polymyxin, and paenicidin A. Endophytes' adaptation to the plant microenvironment was evaluated through the analysis of the presence of antibiotic resistance genes in the four genomes. The diesel fuel degrading potential was also tested. Strains grew in minimum media supplemented with diesel fuel, but no n-alkanes degradation genes were found in their genomes, suggesting that diesel fuel degradation might occur through other steps involving enzymes catalyzing the oxidation of aromatic compounds.
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