Production of 1,3-Propanediol by Clostridium butyricum VPI 3266 in continuous cultures with high yield and productivity

The effects of dilution rate and substrate feed concentration on continuous glycerol fermentation by Clostridium butyricum VPI 3266, a natural 1,3-propanediol producer, were evaluated in this work. A high and constant 1,3-propanediol yield (around 0.65 mol/mol), close to the theoretical value, was obtained irrespective of substrate feed concentration or dilution rate. Improvement of 1,3-propanediol volumetric productivity was achieved by increasing the dilution rate, at a fixed feed substrate concentration of 30, 60 or 70 g l^-1. Higher 1,3-propanediol final concentrations and volumetric productivities were also obtained when glycerol feed concentration was increased from 30 to 60 g l^-1, at D=0.05-0.3 h^-1, and from 60-70 g l^-1, at D=0.05 and 0.1 h^-1·30 g l ^-1 of 1,3-propanediol and the highest reported value of productivity, 10.3 g l^-1 h^-1, was achieved at D=0.30 h^-1 and 60 g l^-1 of feed glycerol. A switch to an acetate/butyrate ratio higher than one was observed for 60 g l^-1 of feed glycerol and a dilution rate higher than 0.10 h^-1; moreover, at D=0.30 h ^-1 3-hydroxypropionaldehyde accumulation was observed for the first time in the fermentation broth of C. butyricum.