Surfactin production by Bacillus subtilis B12 under Cd stress and its effect on biofilm formation and Cd removal

Abstract:

[Background] Bacillus subtilis can form biofilm by clustering, and biofilm plays an important role in the removal of heavy metals. [Objective] The purpose of this study was to examine the interactions of Bacillus subtilis B12 biofilm and lipopeptide compounds and cadmium removal, investigating the mechanism of B. subtilis B12 in alleviating Cd (CdSO4) stress. [Methods] Firstly, the effect of Cd stress on the formation of strain B12 biofilm was investigated. The lipopeptide compounds secreted by B12 strain under Cd stress were extracted, purified and identified by acid precipitation, reversed-phase high performance liquid chromatography (RP-HPLC) and liquid mass spectrometry (LC-MS). The effects of this major component on the biofilm formation and Cd adsorption of B. subtilis B12, Sinorhizobium meliloti Mr40 and B. amyloliquefaciens P29 were investigated. [Results] When 0?1.0 mg/L CdSO4 was applied in Msgg media, the dry weight of B. subtilis B12 biofilms increased significantly. Cd stress promoted the secretion of lipid peptide compounds by strain B12, and the content of surfactin was increased. In the Msgg media with 0.5 mg/L Cd concentration, biofilms dry weight of strains B12, Mr40, P29 were increased by 84.1% to 126.9% significantly when the strains were exposed to surfactin compared to control medium, whereas the planktonic cells counts were reduced significantly from 46.9% to 55.3%. Meanwhile, Cd removal rate of three strains were significantly increased by 23.0%–36.1%, biosorption capacities of Cd onto the strains biofilms significantly increased by 46.8% to 68.1%. [Conclusion] These findings suggest that B. subtilis B12 under exposure to Cd could trigger the effect of stronger surfactin and biofilm formation, and subsequent increased Cd absorption of the biofilms, thereby protecting them from Cd stress.