Effect of Organic Nitrogen Supplements on Syngas Fermentation Using Clostridium autoethanogenum

In this study, the effects of organic nitrogen supplements, such as tryptone and peptone, on microbial growth and ethanol and acetic acid production were investigated to improve ethanol productivity in a Clostridium autoethanogenum culture using syngas as the sole carbon source. The concentration of yeast extract, which is an organic nitrogen source in a basal medium, was optimized to 0.5 g/L before adding the supplements. In the C. autoethanogenum culture using tryptone and peptone as supplements, microbial growth and acetic acid formation were proportionate to the supplement concentration till up to 5.0 g/L of tryptone or peptone. However, ethanol concentration reached a maximum level of 4.57 g/L and 4.23 g/L in the cultures supplemented with 0.5 g/L of tryptone and 0.5 g/L of peptone, respectively. Ethanol production did not increase at a supplement concentration higher than 0.5 g/L. Thus, the addition of tryptone and peptone at a concentration of 0.5 g/L showed the best volumetric ethanol productivities (0.286 and 0.264 g/L·d, respectively), which were enhanced by 45.9% and 44.3% compared to the results of the control experiment.