title: Spaceflight-induced enhancement of 2-keto-L-gulonic acid production by a mixed culture of Ketogulonigenium vulgare and Bacillus thuringiensis.
abstract: Two bacterial strains used for industrial production of 2-keto-L-gulonic acid (2-KLG), Ketogulonigenium vulgare 2 and Bacillus thuringiensis 1514, were loaded onto the spacecraft Shenzhou VII and exposed to space conditions for 68 h in an attempt to increase their fermentation productivities of 2-KLG. An optimal combination of mutants B. thuringiensis 320 and K. vulgare 2194 (KB2194-320) was identified by systematically screening the pH and 2-KLG production of 16 000 colonies. Compared with the coculture of parent strains, the conversion rate of L-sorbose to 2-KLG by KB2194-320 in shake flask fermentation was increased significantly from 82·7% to 95·0%. Furthermore, a conversion rate of 94·5% and 2-KLG productivity of 1·88 g l(-1)  h(-1) were achieved with KB2194-320 in industrial-scale fermentation (260 m(3) fermentor). An observed increase in cell number of K2194 (increased by 47·8%) during the exponential phase and decrease in 2-KLG reductase activity (decreased by 46·0%) were assumed to explain the enhanced 2-KLG production. The results suggested that the mutants KB2194-320 could be ideal substitutes for the currently employed strains in the 2-KLG fermentation process and demonstrated the feasibility of using spaceflight to breed high-yielding 2-KLG-producing strains for vitamin C production.
  
  
  CONCLUSIONS
  KB2194-320, a combination of two bacterial strains bred by spaceflight mutation, exhibited significantly improved 2-KLG productivity and hence could potentially increase the efficiency and reduce the cost of vitamin C production by the two-step fermentation process. In addition, a new pH indicator method was applied for rational screening of K2, which dramatically improved the efficiency of screening.
authors.affiliation: Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, China.
authors.forename: W
authors.initials: W
authors.lastname: Yang
authors.forename: L
authors.initials: L
authors.lastname: Han
authors.forename: M
authors.initials: M
authors.lastname: Mandlaa
authors.forename: H
authors.initials: H
authors.lastname: Chen
authors.forename: M
authors.initials: M
authors.lastname: Jiang
authors.forename: Z
authors.initials: Z
authors.lastname: Zhang
authors.forename: H
authors.initials: H
authors.lastname: Xu
mesh_terms: D001413:Bacillus thuringiensis / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D019149:Bioreactors; D018920:Coculture Techniques; D005285:Fermentation; D007218:Industrial Microbiology; D007700:Kinetics; D050296:Microbial Viability; D009154:Mutation; D041902:Rhodobacteraceae / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D013013:Sorbose / Q000378:metabolism; D013026:Space Flight; D013400:Sugar Acids / Q000378:metabolism*
chemical_list: D013400:Sugar Acids; C011491:provitamin C; D013013:Sorbose