The Inhibitory Activity of Some Endophytic Bacteria from Satureja Khuzestanica Leaves against Phythopathogenic Bacteria

Microbes that reside inside the plant tissues are known as endophytes. These microbes produce an array of compounds that have the potential to be used in modern medicine and agriculture. The aim of this study was to isolate, screen, and identify endophytic bacteria that have antimicrobial activity toward phytopathogenic bacteria. Aromatic plants such as Satureja khuzestanica are used in traditional medicine due to their secondary metabolites but information regarding their naturally occurring bacterial endophytes is limited.

In the present study, 27 strains of endophytes were isolated from S. khuzestanica. Based on the sequencing of the 16S rRNA gene, isolated bacterial strains with the highest activity against phytopathogenic bacteria belong to Bacillus, Streptomyces, and Pseudomonas genera. The bioactive secondary metabolites of these endophyte bacteria were extracted using ethyl acetate, followed by Gas Chromatography-Mass Spectrometry (GC-MS) analysis under standard conditions. The minimum inhibitory concentration (MIC) values were determined for five species of bacteria via the microbroth dilution technique. The crude extracts of the five selected bacterial endophytes indicated an antimicrobial activity against five phytopathogenic species.

Data analysis showed significant differences in antimicrobial activity that ranged from 0.312 mg/ml to 2. 5 mg/ml. The minimum bactericidal concentrations ranged from 0.625 mg/ml to 10 mg/ml.

The major compounds in GC-MS analysis of endophyte bacteria in this study were 2,4-di-tert-butylphenol, beta-d-glucopyranose, hexadecane, tetradecane,  eicosane, and dibutyl phthalate. This study reports for the first-time bacterial endophytes of S. khuzestanica, with antimicrobial activity against bacterial phypathogens. Our findings provide new insights into the antimicrobial activities of natural bacteria endophytes from S. khuzestanica.