Expression of C. thermocellum cellulases in C. acetobutylicum. (a) Recombinant C. acetobutylicum strains expressing the Cel8A, Cel9B and Cel9K cellulases were grown until late stationary phase (OD600 > 3) and their supernatants TCA precipitated, concentrated 100-fold and analysed by SDS-PAGE. (b) The recombinant strain expressing the Cel48S was grown in buffered 2xYTG until early exponential phase (OD600 of 0.4 and 0.8), concentrated 100-fold and separated by SDS-PAGE. All four cellulases were detected using ANTI-FLAG M2 monoclonal antibody-horseradish peroxidise conjugate (Sigma). Expected molecular masses are indicated by arrows. M, ColorPlus Prestained Protein Ladder (10–230 kDa; New England Biolabs), Flag, N-Flag-Bap control protein (50 kDa, 50 ng/lane; Sigma).