Isolation and identification of a Bacillus velezensis strain against plant pathogenic Xanthomonas spp.

Abstract:

[Objective] To obtain biocontrol bacteria to control bacterial leaf streak (BLS) of rice caused by Xanthomonas oryzae pv. oryzicola (Xoc). [Methods] A bacterial strain 504 with antibacterial activity was screened from water spinach rhizosphere soil by agar disk dilution and inhibition zone method using an Xoc model strain RS105 as target. Strain 504 was identified through morphological, physiological and biochemical characteristics in combination with 16S rDNA and gyrA sequence analysis. Antagonistic activity of 504 against some plant pathogenic Xanthomonas spp. was measured and stability of its sterile fermentation broth against Xoc was analyzed by Oxford Cup method. We predicted the genes encoding the synthesis of multiple lipopeptide and polyketide compounds by PCR amplification. Antibacterial activities of 504 against Xoc in the leaves of rice seedlings were evaluated by injection inoculation method. [Results] Strain 504 was identified as Bacillus velezensis, named B. velezensis 504. B. velezensis 504 showed specific inhibitory effects on some plant pathogenic Xanthomonas, especially on X. oryzae pv. oryzae. The secondary metabolites prediction showed that B. velezensis 504 contains genes such as fenA, dhbA, sfrA, bmyA, beaS, dfnA and bacA encoding the biosynthesis of various peptidoglycans and polyketose antibacterial compounds. The cell-free supernatant showed stable inhibitory effects against Xoc under high temperature and by protease treatment, however, there is no inhibitory activities when the pH value of supernatant is beyond 5.5 to 8.9. B. velezensis 504 exhibits significantly inhibitory effect on water-soaked lesions caused by Xoc in the leaves of the high susceptible rice cultivar Yuanfengzao. [Conclusion] B. velezensis 504 exhibits the broad-spectrum antagonistic activity against Xanthomonas spp., and has the potential as an effective biocontrol agent on diseases caused by plant pathogenic Xanthomonas spp..

Key words:Xanthomonas oryzae pv. oryzicola;Bacillus velezensis;biological control;antagonistic activity