title: Metabolic engineering of acid resistance elements to improve acid resistance and propionic acid production of Propionibacterium jensenii.
abstract: Propionic acid (PA) and its salts are widely used in the food, pharmaceutical, and chemical industries. Microbial production of PA by propionibacteria is a typical product-inhibited process, and acid resistance is crucial in the improvement of PA titers and productivity. We previously identified two key acid resistance elements-the arginine deaminase and glutamate decarboxylase systems-that protect propionibacteria against PA stress by maintaining intracellular pH homeostasis. In this study, we attempted to improve the acid resistance and PA production of Propionibacterium jensenii ATCC 4868 by engineering these elements. Specifically, five genes (arcA, arcC, gadB, gdh, and ybaS) encoding components of the arginine deaminase and glutamate decarboxylase systems were overexpressed in P. jensenii. The activities of the five enzymes in the engineered strains were 26.7-489.0% higher than those in wild-type P. jensenii. The growth rates of the engineered strains decreased, whereas specific PA production increased significantly compared with those of the wild-type strain. Among the overexpressed genes, gadB (encoding glutamate decarboxylase) increased PA resistance and yield most effectively; the PA resistance of P. jensenii-gadB was more than 10-fold higher than that of the wild-type strain, and the production titer, yield, and conversion ratio of PA reached 10.81 g/L, 5.92 g/g cells, and 0.56 g/g glycerol, representing increases of 22.0%, 23.8%, and 21.7%, respectively. We also investigated the effects of introducing these acid resistance elements on the transcript levels of related enzymes. The results showed that the expression of genes in the engineered pathways affected the expression of the other genes. Additionally, the intracellular pools of amino acids were altered as different genes were overexpressed, which may further contribute to the enhanced PA production. This study provides an effective strategy for improving PA production in propionibacteria; this strategy may be useful for the production of other organic acids. Biotechnol. Bioeng. 2016;113: 1294-1304. © 2015 Wiley Periodicals, Inc.
authors.affiliation: Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, China.
authors.forename: Ningzi
authors.initials: N
authors.lastname: Guan
authors.affiliation: Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, China.|Key Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, China.
authors.forename: Jianghua
authors.initials: J
authors.lastname: Li
authors.affiliation: School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta.
authors.forename: Hyun-Dong
authors.initials: HD
authors.lastname: Shin
authors.affiliation: Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, China.|Key Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, China.
authors.forename: Guocheng
authors.initials: G
authors.lastname: Du
authors.affiliation: Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, China.|Key Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Chen
authors.affiliation: Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, Jiangnan University, Wuxi, China. longliu@jiangnan.edu.cn.|Key Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University, Wuxi, 214122, China. longliu@jiangnan.edu.cn.
authors.forename: Long
authors.initials: L
authors.lastname: Liu
mesh_terms: D049109:Cell Proliferation / Q000502:physiology; D024861:Genetic Enhancement / Q000379:methods; D005968:Glutamate Decarboxylase / Q000235:genetics*; D006863:Hydrogen-Ion Concentration; D006867:Hydrolases / Q000235:genetics*; D060847:Metabolic Engineering / Q000379:methods*; D011422:Propionates / Q000302:isolation & purification / Q000378:metabolism*; D011424:Propionibacterium / Q000737:chemistry* / Q000502:physiology*
chemical_list: D011422:Propionates; D006867:Hydrolases; C019723:arginine deiminase; D005968:Glutamate Decarboxylase; C029658:propionic acid
keywords: Propionibacterium jensenii; acid resistance element; arginine deaminase system; glutamate decarboxylase system; propionic acid