Characterization and application of Bacillus velezensis D6 co-producing α-amylase and protease.

Background: Research on the co-production of multiple enzymes by Bacillus velezensis as a novel species is still a topic that needs to be studied. This study aimed to investigate the fermentation characteristics of B. velezensis D6 co-producing α-amylase and protease and to explore their enzymatic properties and applications in fermentation.

Results: The maximum co-production of α-amylase and protease reached 13.13 ± 0.72 and 2106.63 ± 64.42 U mL, respectively, under the optimal fermented conditions (nutrients: 20.0 g L urea, 20.0 g L glucose, 0.7 g L MnCl; incubation conditions: initial pH 7.0, temperature 41 °C, 8% inoculation size and 30% working volume). Moreover, the genetic co-expression of α-amylase and protease increased from 0 to 24 h and then decreased after 36 h at the transcriptional level, which coincided with the growth trend of B. velezensis D6. The optimal reaction temperature of α-amylase was 55-60 °C, while that of protease was 35-40 °C. The activities of α-amylase and protease were retained by over 80% after thermal treatment (90 °C, 1 h), which indicated that two enzymes co-produced by B. velezensis D6 demonstrated excellent thermal stability. Moreover, the two enzymes were stable over a wide pH range (pH 4.0-8.0 for α-amylase; pH 4.0-9.0 for protease). Finally, the degrees of hydrolysis of corn, rice, sorghum and soybeans by α-amylase from B. velezensis D6 reached 44.95 ± 2.95%, 57.16 ± 2.75%, 52.53 ± 4.01% and 20.53 ± 2.42%, respectively, suggesting an excellent hydrolysis effect on starchy raw materials. The hydrolysis degrees of mackerel heads and soybeans by protease were 43.93 ± 2.19% and 26.38 ± 1.72%, respectively, which suggested that the protease from B. velezensis D6 preferentially hydrolyzed animal-based protein.

Conclusion: This is a systematic study on the co-production of α-amylase and protease by B. velezensis D6, which is crucial in widening the understanding of this species co-producing multi-enzymes and in exploring its potential application. © 2024 Society of Chemical Industry.