Production improvement of an antioxidant in cariogenic Streptococcus mutans UA140

Abstract

Aims This study aimed to improve the production of mutantioxidin, an antioxidant encoded by a biosynthetic gene cluster (mao) in Streptococcus mutans UA140, through a series of optimization methods. Method and results Through construction of mao knockout strain S. mutans UA140∆mao, we identified mutantioxidin as the antioxidant encoded by mao and verified its antioxidant activity through a ROS tolerance assay. By optimizing the culture medium and fermentation time, 72 h of fermentation in CDM medium was determined as the optimal fermentation conditions. Based on two promoters commonly used in Streptococcus (ldhp and xylS1p), eight promoter refactoring strains were constructed, nevertheless all showed impaired antioxidant production. In-frame deletion and complementation experiments demonstrated the positive regulatory role of mao1 and mao2, on mao. Afterwards, the mao1 and mao2, overexpression strain S. mutans UA140/pDL278:: mao1mao2, was constructed, in which the production of mutantioxidin was improved significantly. Conclusions In this study, through a combination of varied strategies such as optimization of fermentation conditions and overexpression of regulatory genes, production of mutantioxidin was increased by 10.5 times ultimately.