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

Abstract

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.

Keywords: endophytes; essential oil; genome; plant microbiota; volatile organic compounds.

Figure 1

(A) Schematic representation of the average number of colony-forming units (CFU) of each target strain, normalized on the initial titer, in the absence (orange bar) or in the presence (blue bar) of the endophytic tester strain. (B) Ratio between the average CFU in the presence and absence of the endophytic tester strain. Black bars represent standard errors.

Figure 2

Effect of Arthrobacter sp. OVS8’s VOCs on growth of target strains.

Figure 3

Terpenoid backbone biosynthesis KEGG map. Enzymes retrieved by the DuctApe software suite are reported in blue.

Figure 4

Monoterpenoid biosynthesis KEGG map. Enzymes retrieved by the DuctApe software suite are reported in blue.

Figure 5

Schematic representation of the GEN III microplate of the Biolog system, divided into the C-source utilization (left) and sensitivity test (right) well subsets. Each well is colored based on the calculated AV, which is indicated by the reported number.