This study demonstrates that both genetic engineering and culture adaptation in the FBB can be used to develop mutant strains of C. tyrobutyricum and improve die process economics for butyrate fermentation. The adapted culture from the FBB is physiologically different from the original culture used to seed the bioreactor. This important finding has never been reported in conventional fermentation systems. The high productivity and high product concentration obtained in the FBB are either comparable or better than those reported in the literature. The manipulation of acid-forming pathways by gene inactivation and overexpression proved to be feasible for obtaining metabolically advantageous mutants for butyrate production from sugars. The fermentation kinetic studies of these mutants also provided valuable information about gene function in cellular metabolism, which can guide future effort to engineer novel super-producing strains of C. tyrobutyricum for industrial applications. The increased productivity and selectivity by mutant strains of C. tyrobutyricum immobilized in the FBB should lower the cost of bio-based butyrate and allow it to compete favorably in the market.

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