Ultrasound: Enhance the detachment of exosporium and decrease the hydrophobicity of Bacillus cereus spores

Because of the hydrophobicity and formation of biofilm, Bacillus cereus spores are highly resistant and widespread in food industry. The outermost layer: exosporium of Bacillus cereus spore plays an important role in its surface property. Previous work indicated that ultrasound detached the exosporium of spores, thus the surface properties were further investigated in this study. The detachment of exosporium was observed without damage to inner layers through TEM micrographs. Besides, the size of spores dropped rapidly from 2017.67 to 960.53 nm after 1 min ultrasound treatment. At the same time, the absolute zeta potential value also decreased rapidly. The ratio of hydrophobic spores (RHS) was defined as hydrophobicity, and it dropped-off with the detachment of exosporium. The SDS-PAGE results showed that the intensity of protein bands dropped especially that with higher molecular weight after ultrasound treatment. What's more, a lot of bands disappeared because of the separation of exosporium. In a word, these results indicated that ultrasound could detach exosporium and decrease the hydrophobicity of spores, which had lower adhesion to hydrophobic surface and easier to be cleaned.