Isolation and identification of endophytic bacteria from Satureja Khuzestanica and evaluation of its secondary metabolites for antimicrobial activity against plant pathogenic bacteria

In many parts of the world, medicinal plants have been used as an alternative medicine to promote human health and longevity since ancient times. Microbes residing within plant tissues are known as endophytes. The compounds produced by these microbes have the potential to be employed in modern medicine, agriculture, and other industries. Endophytic bacteria isolated from medicinal plants are valuable sources of novel bioactive compounds with diverse activities, including antimicrobial, anticancer, and antiviral properties. This study aimed to isolate, identify, and screen endophyte bacteria with antimicrobial activity against plant pathogenic bacteria. Aromatic plants such as Satureja khuzestanica are utilized in traditional medicine due to their secondary metabolites, but data regarding its naturally occurring bacterial endophytes is limited.

In the current study, 17 strains of bacterial endophytes were isolated in a Tryptic Soy Agar medium from the medicinal plant Satureja khuzestanica. Based on sequencing the 16S rRNA encoding gene, researchers isolated bacterial strains from the Bacillus, Streptomyces, and Pseudomonas genera with the highest activity against plant pathogenic bacteria. Under standard conditions, these endophytic bacteria’s bioactive secondary metabolites were extracted with ethyl acetate and analyzed using Gas Chromatography-Mass Spectrometry (GC-MS). The mass spectra of the compounds were compared to the National Institute of Standards and Technology (NIST) library’s database. Moreover, microbroth dilution techniques were used to determine the minimum inhibitory concentration (MIC) values for five different bacteria species.

The GC-MS analysis revealed the presence of a number of compounds, including dibutyl phthalate (DBP), eicosane, octadecanoic acid, hexadecanoic acid, and hexadecane 1,4- dicyclohexylbutane. Four of the selected bacterial endophytes exhibited antimicrobial activity against three plant pathogens: Ralstonia solanacearum, Pectobacterium carotovorum subsp., carotovorum, and Clavibacter insidiosus. Data analysis revealed significant differences in antimicrobial activity, with the minimum inhibitor concentration ranging from 0.312 mg/ml to 2. 5 mg/ml. Furthermore, we identified bioactive secondary metabolites with reported biological activities in antimicrobial, anti-inflammatory, and antioxidant properties with biotechnological applications in medicine, agriculture, and other industries based on an endophytic crude extract data analysis.

Our findings shed new light on the antimicrobial properties of naturally occurring bacterial endophytes in S. khuzestanica.