A snapshot of bacterial endophytes isolated from the roots of Vetiver grass (Chrysopogon zizanioides) grown at Bien Hoa airbase, Dong Nai province

Vetiver grass (Chrysopogon zizanioides) with a strong root system has been widely used for environmental pollution treatment. Recently, this grass has been cultivated at Bien Hoa airbase to mitigate dioxin concentration in the contaminated soil. Bacterial endophytes have been recognized to play key roles in plant growth promotion and responses of plant hosts to environmental factors. However, a beneficial association between endophytic bacteria and Vetiver grass root system grown in dioxin-contaminated soil has not been elucidated. In the present study, we isolated sixteen endophytic bacterial strains from the roots of Vetiver grass. The results of DNA sequencing of the 16S rRNA gene revealed that these culturable bacterial endophytes belong to 9 species of different genera. Four strains, including Klebsiella variicola B1, Enterobacter cloacae B4, Enterobacter kobei B6, and Enterobacter cloacae B11, produce high amounts of indol acetic acid (IAA). Strains K. variicola B1 and E. cloacae B4 also produce phytase and phosphatase to dissolve phytate and phosphate, respectively. These strains were selected to evaluate their abilities in promoting the growth of tomato plants as a model. After 28 days of inoculation with the tested strains through the roots, tomato plants grew 19% to 22% faster than the control plants. Conclusively, this study shows for the first time the successful isolation of endophytic bacteria from the roots of Vetiver grass cultivated in dioxin-contaminated soil, and some culturable bacterial strains exhibit as promising candidates for plant growth promotion.