Submitted to: FEMS Microbiology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2009
Publication Date: 2/1/2011
Citation: Lian, L., Duan, Y., Wu, Z., Xie, L. 2011. Antagonistic activity and mechanisms of Bacillus subtilis SB1 against Ralstonia solanacearum. FEMS Microbiology Letters. 41:219-224. Interpretive Summary: Bacterial wilt disease has a global impact on agriculture, causing devastating loss to many economically important crops. The need for alternative methods to control the disease without relying on chemicals still exists. Bacillus species are known as effective biological control agents and plant growth promoters. We have isolated a new strain of Bacillus subtilis, namely SB1. It was found that antimicrobial compounds produced by B. subtilis SB1 had a strong inhibitory effect on the pathogen causing bacterial wilt and suppressed the growth of several other plant pathogens. To explore the potentials of B. subtilis SB1 as an effective biological control agent, the molecular mechanism of the antimicrobial activity of the SB1 antimicrobial compound and the optimization of the SB1 compound production were also studied. The results indicate that B. subtilis SB1 may be an effective biological control agent of bacterial wilt disease.
Technical Abstract: A potential biocontrol agent of bacterial wilt, Bacillus subtilis SB1, showed a broad-spectrum of antimicrobial activity in vitro experiments. In addition to Ralstonia solanacearum, strain SB1 inhibited the growth of many other plant pathogens, including Fusarium oxysporum, Botrytis cinerea, Phytophthora capsici, Xanthomonas oryzae pv. oryzae and tomato mosaic virus. To enhance the production of antibacterial compounds, five media with different components were used, and it was found that glucose and mineral salts promote secretion of the active compounds. An active fraction was isolated from the supernatant of potato dextrose broth cultures and identified as two isoforms of surfactin by silica column and high performance liquid chromatography. In addition, the surfactin and iturin A synthetase genes were also detected by PCR. The SB1 srfA shares from 98% sequence identity to the partial regions of the known B. subtilis surfactin operon, and the SB1 ituB shares 97.2% sequence identity to the corresponding region of the reported iturin A operon. Another study was undertaken to investigate the possible mechanisms of the active compounds on R. solanacearum. The results indicated that cell morphology and DNA synthesis of R. solanacearum were greatly altered by the active compounds from B. subtilis SB1. The active compounds caused hyperchromic effects on bacterial DNA, inhibition on the expression of two extra-cellular and two intra-cellular proteins, condensation of cytoplasm and cells lysis of R. solanacearum.