Biocontrol and molecular characterization of Bacillus velezensis D against tobacco bacterial wilt

Natural rhizosphere bacteria has the potential to act as an alternative of chemical pesticides for sustainable agriculture. In the current study, tobacco rhizosphere Bacillus velezensis D exhibited great antibacterial effect against Ralstonia solanacearum, and significantly enhanced the tobacco resistance against bacterial wilt in pot experiments. Then Bacillus velezensis D was labeled with gfp marker and found to stably colonize in tobacco root, the colonization density of strain D in root still remained 5.33 × 104 CFU/gat 30 days post-inoculation. Subsequently, field trials for two years (2021–2022) showed the control effects of the strain D on the tobacco bacterial wilt were 12.26% and 36.37%, respectively, indicating the application of B. velezensis D could improve plant resistance to R.solanacearum. In order to further study the antibacterial activities of strain D, effects of the crude extracts on the swimming ability, cell viability and the morphology of R. solanacearum were analyzed. The results showed that the crude extracts reduced the motility of R. solanacearum, and caused cell wall rupture and cell death. Furthermore, MALDI-TOF-MS and HPLC-QTOF-MS analysis indicated that lipopeptides (fengycin and iturin) and polyketides (bacillaene) were detected in the crude extracts of strain D. Based on these findings, we speculated that Bacillus velezensis D firstly colonized in tobacco root, then produced antibacterial substances at ecological sites to exert antagonistic effects, inhibiting motility traits of R. solanacearum and damaging the cell well. Hence, Bacillus velezensis D could be used as a potential biological control agents against tobacco bacterial wilt.