title: Radiation induces acid tolerance of Clostridium tyrobutyricum and enhances bioproduction of butyric acid through a metabolic switch.
abstract: BACKGROUND
  Butyric acid as a renewable resource has become an increasingly attractive alternative to petroleum-based fuels. Clostridium tyrobutyricum ATCC 25755T is well documented as a fermentation strain for the production of acids. However, it has been reported that butyrate inhibits its growth, and the accumulation of acetate also inhibits biomass synthesis, making production of butyric acid from conventional fermentation processes economically challenging. The present study aimed to identify whether irradiation of C. tyrobutyricum cells makes them more tolerant to butyric acid inhibition and increases the production of butyrate compared with wild type.
  
  
  RESULTS
  In this work, the fermentation kinetics of C. tyrobutyricum cultures after being classically adapted for growth at 3.6, 7.2 and 10.8 g·L-1 equivalents were studied. The results showed that, regardless of the irradiation used, there was a gradual inhibition of cell growth at butyric acid concentrations above 10.8 g·L-1, with no growth observed at butyric acid concentrations above 3.6 g·L-1 for the wild-type strain during the first 54 h of fermentation. The sodium dodecyl sulfate polyacrylamide gel electrophoresis also showed significantly different expression levels of proteins with molecular mass around the wild-type and irradiated strains. The results showed that the proportion of proteins with molecular weights of 85 and 106 kDa was much higher for the irradiated strains. The specific growth rate decreased by 50% (from 0.42 to 0.21 h-1) and the final concentration of butyrate increased by 68% (from 22.7 to 33.4 g·L-1) for the strain irradiated at 114 AMeV and 40 Gy compared with the wild-type strains.
  
  
  CONCLUSIONS
  This study demonstrates that butyric acid production from glucose can be significantly improved and enhanced by using 12C6+ heavy ion-irradiated C. tyrobutyricum. The approach is economical, making it competitive compared with similar fermentation processes. It may prove useful as a first step in a combined method employing long-term continuous fermentation of acid-production processes.
authors.affiliation: Institute of Modern Physics, Chinese Academy of Sciences, 509 Nanchang Road, Lanzhou, Gansu 730000, PR China.
authors.forename: Xiang
authors.initials: X
authors.lastname: Zhou
authors.affiliation: Institute of Modern Physics, Chinese Academy of Sciences, 509 Nanchang Road, Lanzhou, Gansu 730000, PR China.
authors.forename: Xi-Hong
authors.initials: XH
authors.lastname: Lu
authors.affiliation: Institute of Modern Physics, Chinese Academy of Sciences, 509 Nanchang Road, Lanzhou, Gansu 730000, PR China.
authors.forename: Xue-Hu
authors.initials: XH
authors.lastname: Li
authors.affiliation: Institute of Modern Physics, Chinese Academy of Sciences, 509 Nanchang Road, Lanzhou, Gansu 730000, PR China.
authors.forename: Zhi-Jun
authors.initials: ZJ
authors.lastname: Xin
authors.affiliation: China Pharmaceutical University, #24 Tongjiaxiang, Nanjing 210009, PR China.
authors.forename: Jia-Rong
authors.initials: JR
authors.lastname: Xie
authors.affiliation: Institute of Modern Physics, Chinese Academy of Sciences, 509 Nanchang Road, Lanzhou, Gansu 730000, PR China.
authors.forename: Mei-Rong
authors.initials: MR
authors.lastname: Zhao
authors.affiliation: Institute of Modern Physics, Chinese Academy of Sciences, 509 Nanchang Road, Lanzhou, Gansu 730000, PR China.
authors.forename: Liang
authors.initials: L
authors.lastname: Wang
authors.affiliation: Institute of Modern Physics, Chinese Academy of Sciences, 509 Nanchang Road, Lanzhou, Gansu 730000, PR China.
authors.forename: Wen-Yue
authors.initials: WY
authors.lastname: Du
authors.affiliation: Institute of Modern Physics, Chinese Academy of Sciences, 509 Nanchang Road, Lanzhou, Gansu 730000, PR China.
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Liang