Enhancement of Acid Protease Activity of Aspergillus oryzae Using Atmospheric and Room Temperature Plasma

Liang Shu,Jinglan Sun,Wenyan Ma,Depei Wang,Jian Zhang,Xiaoguang Si,Xinda Yang,Qiang Gao,Xianli Xue

doi:10.3389/fmicb.2020.01418

Abstract

Atmospheric and room temperature plasma (ARTP) system is a novel and efficient mutagenesis protocol for microbial breeding. In this study, ARTP was employed to treat spores of Aspergillus oryzae strain 3.042 for selection of high acid protease producers. With an irradiation time of 150 s at the lethal rate of 90%, 19 mutants with higher acid protease activity were initially selected based on different mutant colony morphology and ratio of the clarification halo of protease activity to the colony diameter. Measurements of the acid protease activity revealed that mutant strain B-2 is characterized by a steady hereditary stability with increased acid protease, neutral protease and total protease activities of 54.7, 17.3, and 8.5%, respectively, and decreased alkaline protease activity of 8.1%. In summary, the identified mutant strain B-2 exhibits great potential for the enhancement of the insufficient acid protease activity during the middle and later stages of soy sauce fermentation.

Highlights

Soy sauce, a traditional condiment in China, Japan, South Korea, and Southeast Asia, is fermented from soybean and wheat flour and is used in many countries worldwide
Several mutation attempts demonstrate the feasibility of breeding strains with high acid protease activity for the soy sauce fermentation industry
The current study demonstrated that the mutant strain B2 exhibited an overall 8.5% increase in total acid, neutral and alkaline protease activity compared with A. oryzae strain 3.042

Summary

Introduction

A traditional condiment in China, Japan, South Korea, and Southeast Asia, is fermented from soybean and wheat flour and is used in many countries worldwide. Compared with yeasts and lactic acid bacteria, Aspergillus oryzae plays a decisive role in the production of soy sauce koji, which determines the utilization of raw proteins and the quality of soy sauce (Luh, 1995; Xu et al, 2013; Zhao et al, 2015a, 2018; Harada et al, 2017). This organism is widely used for the manufacturing of various traditionally fermented foods (Zhao et al, 2013; Kitamato, 2015). Genetic engineering technology has made great achievements in strain breeding using advanced molecular genetic techniques, the safety of the generated strains is still questioned due to the introduction of foreign genes (Szyjka et al, 2017)

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Results

Discussion

Conclusion