Low-intensity ultrasound-assisted adaptive laboratory evolution of Bacillus velezensis for enhanced production of peptides

This work aimed to explore low-intensity ultrasound-assisted adaptive laboratory evolution (US-ALE) of Bacillus velezensis and fermentation performance of mutant strains were investigated by nitrogen transformation metabolism. Results showed ultrasound accelerated the process of adaptive evolution and enhanced cell dry weight, amylase and protease activity of mutant strains, accompanied with the improved transformation abilities of NO-3N to NH4+-N. Compared with original strain, the total peptide-N, peptide-N (<3 kDa) and autolytic peptide-N of mutant strains increased by the maximum 23.17%, 66.07% and 30.30%, respectively, based on ideal fermentation medium. According to the actual liquid-state fermentation of soybean meal and corn gluten meal with mutant strains, the highest peptide yields of 50.63% and 23.67% were noticed in mutant strain US-ALE-BV3, accompanied with the improved amino acid composition by bacterial autolysis technology. Thus, this study showed that low-intensity ultrasound could accelerate the process of adaptive evolution and US-ALE will provide more possibilities for modifying fermentation strains.