Inhibition of biofilm formation by Cd2+ on Bacillus subtilis 1JN2 depressed its biocontrol efficiency against Ralstonia wilt on tomato
2018
Yang, Wei | Yan, Haixia | Zhang, Ji | Gao, Yuming | Xu, Wei | Shang, Jinshan | Luo, Yuming
Bacillus subtilis 1JN2 can serve as an effective biocontrol agent against Ralstonia wilt on tomato, but the efficiency of control depends on the levels of heavy metals in the rhizosphere soil. Here, we investigated how the heavy metal Cd²⁺ affects the biocontrol efficacy of B.subtilis 1JN2 on Ralstonia wilt. We found that low Cd²⁺ content of 2 mM or lower had no effects on the biofilm formation of 1JN2, while media containing 3 mM or higher Cd²⁺ levels inhibited biofilm formation. Interestingly, high concentration of Cd²⁺ (5 mM) showed inhibition of B.subtilis 1JN2 cell growth. We next tested the effects of Cd²⁺ on the colonization of 1JN2 by supplementing artificial Cd²⁺ in the tomato rhizosphere in a greenhouse setting. We found that 3 mM Cd²⁺ in the tomato rhizosphere inhibited the colonization of B.subtilis 1JN2, Only 10³ CFU/mL 1JN2 was detected one week post treated with 10⁷ CFU/mL but 10⁵ CFU/mL could be detected without Cd²⁺ in the soil. The presence of Cd²⁺ had no effect on the colonization of Ralstonia solanacearum on tomato, but the biocontrol efficacy against Ralstonia wilt by 1JN2 decreased 54.2% when the soil contained 3 mM Cd²⁺ compared to the control without Cd²⁺. Taken together, we found that the failure of biofilm formation of Bacillus subtilis 1JN2 that affected by Cd²⁺ lead to the decrease of its biocontrol efficacy against Ralstonia wilt on tomato.
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