Abstract: A total of 40 strains of Bacillus were isolated from 10 naturally fermented soybean pastes from 8 regions in northeastern China, including Qiqihar, Daqing and Shenyang. Strains QQHE-2 and DQ1-3, with good inhibitory effects (83.42% and 46.83%, respectively) on Penicillium, were obtained by plate confrontation method and agar column method. The two strains were identified as Bacillus subtilis by 16S rRNA gene analysis. It was found by scanning electron microscopy (SEM) that the fermentation supernatant of QQHE-2 changed the morphology of Penicillium hyphae, making the spores become dry and winkled and reducing the number of spores. Upon pH and temperature adjustment and treatment of the fermentation supernatant with protease, it was found that the acid and heat resistance of the antimicrobial substance were poor, and the inhibition rate against Penicillium was significantly reduced by protease treatment. It can be confirmed that the antimicrobial activity was attributed to the presence of a protein or peptide. The molecular mass of the antimicrobial substance produced by QQHE-2 strain was about 35 kDa as revealed by sodium dodecyl sulfate-polyacrymyl gel electrophoresis (SDS-PAGE).

Key words: Bacillus, Penicillium, antimicrobial activity