title: The opposite roles of agdA and glaA on citric acid production in Aspergillus niger.
abstract: Citric acid is produced by an industrial-scale process of fermentation using Aspergillus niger as a microbial cell factory. However, citric acid production was hindered by the non-fermentable isomaltose and insufficient saccharification ability in A. niger when liquefied corn starch was used as a raw material. In this study, A. niger TNA 101ΔagdA was constructed by deletion of the α-glucosidase-encoding agdA gene in A. niger CGMCC 10142 genome using Agrobacterium tumefaciens-mediated transformation. The transformants A. niger OG 1, OG 17, and OG 31 then underwent overexpression of glucoamylase in A. niger TNA 101ΔagdA. The results showed that the α-glucosidase activity of TNA 101ΔagdA was decreased by 62.5 % compared with CGMCC 10142, and isomaltose was almost undetectable in the fermentation broth. The glucoamylase activity of the transformants OG 1 and OG 17 increased by 34.5 and 16.89 % compared with that of TNA 101ΔagdA, respectively. In addition, for the recombinants TNA 101ΔagdA, OG 1 and OG 17, there were no apparent defects in the growth development. Consequently, in comparison with CGMCC 10142, TNA 101ΔagdA and OG 1 decreased the residual reducing sugar by 52.95 and 88.24 %, respectively, and correspondingly increased citric acid production at the end of fermentation by 8.68 and 16.87 %. Citric acid production was further improved by decreasing the non-fermentable residual sugar and increasing utilization rate of corn starch material in A. niger. Besides, the successive saccharification and citric acid fermentation processes were successfully integrated into one step.
authors.affiliation: School of Biological Science and Engineering, South China University of Technology, Guangzhou, 510006, People's Republic of China.
authors.forename: Lu
authors.initials: L
authors.lastname: Wang
authors.affiliation: College of Biotechnology, Tianjin University of Science & Technology, Tianjin, 300457, People's Republic of China.|Key Laboratory of Industrial Fermentation Microbiology, Ministry of Education, Tianjin, 300457, People's Republic of China.
authors.forename: Zhanglei
authors.initials: Z
authors.lastname: Cao
authors.affiliation: College of Biotechnology, Tianjin University of Science & Technology, Tianjin, 300457, People's Republic of China.|Key Laboratory of Industrial Fermentation Microbiology, Ministry of Education, Tianjin, 300457, People's Republic of China.
authors.forename: Li
authors.initials: L
authors.lastname: Hou
authors.affiliation: College of Biotechnology, Tianjin University of Science & Technology, Tianjin, 300457, People's Republic of China.|Key Laboratory of Industrial Fermentation Microbiology, Ministry of Education, Tianjin, 300457, People's Republic of China.
authors.forename: Liuhua
authors.initials: L
authors.lastname: Yin
authors.affiliation: College of Biotechnology, Tianjin University of Science & Technology, Tianjin, 300457, People's Republic of China.|Key Laboratory of Industrial Fermentation Microbiology, Ministry of Education, Tianjin, 300457, People's Republic of China.
authors.forename: Dawei
authors.initials: D
authors.lastname: Wang
authors.affiliation: College of Biotechnology, Tianjin University of Science & Technology, Tianjin, 300457, People's Republic of China.|Key Laboratory of Industrial Fermentation Microbiology, Ministry of Education, Tianjin, 300457, People's Republic of China.|National and Local United Engineering Lab of Metabolic Control Fermentation Technology, Tianjin, 300457, People's Republic of China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Gao
authors.affiliation: School of Biological Science and Engineering, South China University of Technology, Guangzhou, 510006, People's Republic of China. btzhqwu@scut.edu.cn.
authors.forename: Zhenqiang
authors.initials: Z
authors.lastname: Wu
authors.affiliation: College of Biotechnology, Tianjin University of Science & Technology, Tianjin, 300457, People's Republic of China. 15620074987@163.com.|Key Laboratory of Industrial Fermentation Microbiology, Ministry of Education, Tianjin, 300457, People's Republic of China. 15620074987@163.com.|National and Local United Engineering Lab of Metabolic Control Fermentation Technology, Tianjin, 300457, People's Republic of China. 15620074987@163.com.
authors.forename: Depei
authors.initials: D
authors.lastname: Wang
mesh_terms: D001234:Aspergillus niger / Q000235:genetics* / Q000378:metabolism*; D019343:Citric Acid / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D005087:Glucan 1,4-alpha-Glucosidase / Q000235:genetics / Q000378:metabolism*; D060847:Metabolic Engineering; D000520:alpha-Glucosidases / Q000235:genetics / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; D019343:Citric Acid; D000520:alpha-Glucosidases; D005087:Glucan 1,4-alpha-Glucosidase
keywords: Aspergillus niger; Citric acid; Gene deletion; Multicopy overexpression; glaA gene; α-Glucosidase