title: Developing a mesophilic co-culture for direct conversion of cellulose to butanol in consolidated bioprocess.
abstract: BACKGROUND
  Consolidated bioprocessing (CBP) of butanol production from cellulosic biomass is a promising strategy for cost saving compared to other processes featuring dedicated cellulase production. CBP requires microbial strains capable of hydrolyzing biomass with enzymes produced on its own with high rate and high conversion and simultaneously produce a desired product at high yield. However, current reported butanol-producing candidates are unable to utilize cellulose as a sole carbon source and energy source. Consequently, developing a co-culture system using different microorganisms by taking advantage of their specific metabolic capacities to produce butanol directly from cellulose in consolidated bioprocess is of great interest.
  
  
  RESULTS
  This study was mainly undertaken to find complementary organisms to the butanol producer that allow simultaneous saccharification and fermentation of cellulose to butanol in their co-culture under mesophilic condition. Accordingly, a highly efficient and stable consortium N3 on cellulose degradation was first developed by multiple subcultures. Subsequently, the functional microorganisms with 16S rRNA sequences identical to the denaturing gradient gel electrophoresis (DGGE) profile were isolated from consortium N3. The isolate Clostridium celevecrescens N3-2 exhibited higher cellulose-degrading capability was thus chosen as the partner strain for butanol production with Clostridium acetobutylicum ATCC824. Meanwhile, the established stable consortium N3 was also investigated to produce butanol by co-culturing with C. acetobutylicum ATCC824. Butanol was produced from cellulose when C. acetobutylicum ATCC824 was co-cultured with either consortium N3 or C. celevecrescens N3-2. Co-culturing C. acetobutylicum ATCC824 with the stable consortium N3 resulted in a relatively higher butanol concentration, 3.73 g/L, and higher production yield, 0.145 g/g of glucose equivalent.
  
  
  CONCLUSIONS
  The newly isolated microbial consortium N3 and strain C. celevecrescens N3-2 displayed effective degradation of cellulose and produced considerable amounts of butanol when they were co-cultured with C. acetobutylicum ATCC824. This is the first report of application of co-culture to produce butanol directly from cellulose under mesophilic condition. Our results indicated that co-culture of mesophilic cellulolytic microbe and butanol-producing clostridia provides a technically feasible and more simplified way for producing butanol directly from cellulose.
authors.affiliation: School of Life Science and Technology, Harbin Institute of Technology, Harbin, 150001 China.
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Wang
authors.affiliation: School of Life Science and Technology, Harbin Institute of Technology, Harbin, 150001 China.|State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090 China.
authors.forename: Guangli
authors.initials: G
authors.lastname: Cao
authors.affiliation: School of Life Science and Technology, Harbin Institute of Technology, Harbin, 150001 China.
authors.forename: Ju
authors.initials: J
authors.lastname: Zheng
authors.affiliation: School of Life Science and Technology, Harbin Institute of Technology, Harbin, 150001 China.
authors.forename: Defeng
authors.initials: D
authors.lastname: Fu
authors.affiliation: School of Life Science and Technology, Harbin Institute of Technology, Harbin, 150001 China.
authors.forename: Jinzhu
authors.initials: J
authors.lastname: Song
authors.affiliation: School of Food Science and Engineering, Harbin Institute of Technology, Harbin, 150090 China.
authors.forename: Junzheng
authors.initials: J
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090 China.
authors.forename: Lei
authors.initials: L
authors.lastname: Zhao
authors.affiliation: School of Life Science and Technology, Harbin Institute of Technology, Harbin, 150001 China.|State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090 China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Yang
keywords: Biobutanol; Cellulose; Co-culture; Consolidated bioprocessing; Conversion