title: A food-grade expression system for d-psicose 3-epimerase production inBacillus subtilisusing an alanine racemase-encoding selection marker.
abstract: BACKGROUND
  Food-grade expression systems require that the resultant strains should only contain materials from food-safe microorganisms, and no antibiotic resistance marker can be utilized. To develop a food-grade expression system for d-psicose 3-epimerase production, we use an alanine racemase-encoding gene as selection marker inBacillus subtilis.
  
  
  RESULTS
  In this study, the d-alanine racemase-encoding genedalwas deleted from the chromosome ofB. subtilis1A751 using Cre/loxsystem to generate the food-grade host. Subsequently, the plasmid-coded selection markerdalwas complemented in the food-grade host, and RDPE was thus successfully expressed indaldeletion strain without addition of d-alanine. The selection appeared highly stringent, and the plasmid was stably maintained during culturing. The highest RDPE activity in medium reached 46 U/ml at 72 h which was comparable to RDPE production in kanamycin-based system. Finally, the capacity of the food-gradeB. subtilis1A751D2R was evaluated in a 7.5 l fermentor with a fed-batch fermentation.
  
  
  CONCLUSIONS
  The alanine racemase-encoding gene can be used as a selection marker, and the food-grade expression system was suitable for heterologous proteins production inB. subtilis.
authors.affiliation: Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308 People's Republic of China.|Key Laboratory of Systems Microbial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308 People's Republic of China.
authors.forename: Jingqi
authors.initials: J
authors.lastname: Chen
authors.affiliation: School of Biological Engineering, Dalian Polytechnic University, Dalian, 116034 People's Republic of China.
authors.forename: Zhaoxia
authors.initials: Z
authors.lastname: Jin
authors.affiliation: Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308 People's Republic of China.
authors.forename: Yuanming
authors.initials: Y
authors.lastname: Gai
authors.affiliation: Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308 People's Republic of China.|Key Laboratory of Systems Microbial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308 People's Republic of China.
authors.forename: Jibin
authors.initials: J
authors.lastname: Sun
authors.affiliation: Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308 People's Republic of China.|Key Laboratory of Systems Microbial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308 People's Republic of China.
authors.forename: Dawei
authors.initials: D
authors.lastname: Zhang
keywords: Bacillus subtilis; Cre/lox system; Fed-batch fermentation; Food-grade system; d-Psicose 3-epimerase