title: Characterizing metabolic interactions in a clostridial co-culture for consolidated bioprocessing.
abstract: BACKGROUND
  Clostridial co-culture containing cellulolytic and solventogenic species is a potential consolidated bioprocessing (CBP) approach for producing biochemicals and biofuels from cellulosic biomass. It has been demonstrated that the rate of cellulose utilization in the co-culture of Clostridium acetobutylicum and Clostridium cellulolyticum is improved compared to the mono-culture of C. cellulolyticum (BL 5:119-124, 1983). However, the metabolic interactions in this co-culture are not well understood. To investigate the metabolic interactions in this co-culture we dynamically characterized the physiology and microbial composition using qPCR.
  
  
  RESULTS
  The qPCR data suggested a higher growth rate of C. cellulolyticum in the co-culture compared to its mono-culture. Our results also showed that in contrast to the mono-culture of C. cellulolyticum, which did not show any cellulolytic activity under conditions similar to those of co-culture, the co-culture did show cellulolytic activity even superior to the C. cellulolyticum mono-culture at its optimal pH of 7.2. Moreover, experiments indicated that the co-culture cellulolytic activity depends on the concentration of C. acetobutylicum in the co-culture, as no cellulolytic activity was observed at low concentration of C. acetobutylicum, and thus confirming the essential role of C. acetobutylicum in improving C. cellulolyticum growth in the co-culture. Furthermore, butanol concentration of 350 mg/L was detected in the co-culture batch experiments.
  
  
  CONCLUSIONS
  These results suggest the presence of synergism between these two species, while C. acetobutylicum metabolic activity significantly improves the cellulolytic activity in the co-culture, and allows C. cellulolyticum to survive under harsh co-culture conditions, which do not allow C. cellulolyticum to grow and metabolize cellulose independently. It is likely that C. acetobutylicum improves the cellulolytic activity of C. cellulolyticum in the co-culture through exchange of metabolites such as pyruvate, enabling it to grow and metabolize cellulose under harsh co-culture conditions.
authors.forename: Fahimeh
authors.initials: F
authors.lastname: Salimi
authors.affiliation: Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON M5S 2E6, Canada. krishna.mahadevan@utoronto.ca.
authors.forename: Radhakrishnan
authors.initials: R
authors.lastname: Mahadevan
mesh_terms: D056804:Biofuels; D018533:Biomass; D000440:Butanols / Q000378:metabolism; D002482:Cellulose / Q000378:metabolism; D046969:Clostridium acetobutylicum / Q000254:growth & development*; D046973:Ruminiclostridium cellulolyticum / Q000254:growth & development*; D018920:Coculture Techniques / Q000379:methods*; D003470:Culture Media / Q000737:chemistry; D005285:Fermentation; D006863:Hydrogen-Ion Concentration; D019289:Pyruvic Acid / Q000378:metabolism
chemical_list: D056804:Biofuels; D000440:Butanols; D003470:Culture Media; D019289:Pyruvic Acid; D002482:Cellulose