Effect of selenium and tungsten on cell growth and metabolite production in syngas fermentation using “Clostridium autoethanogenum”

The effect of tungsten and selenium on cell growth and production of metabolites such as acetic acid and ethanol when fermenting syngas using “Clostridium autoethanogenum” was investigated to improve the process efficiency. General concentrations of selenium and tungsten in the medium are 0.01 µM during acetogenic syngas fermentation. We conducted culture experiments at concentrations of 0, 0.001, 0.01 and 0.1 µM for each heavy metal. The effect of selenium on cell growth and total metabolite production was greater than that of tungsten as the effect of selenium on formate dehydrogenase, an important enzyme of the Wood-Ljungdahl pathway, is greater than that of tungsten. Although an increase in tungsten had a marginal effect on total metabolite production, the ethanol/acetic acid production ratio increased significantly due to a decrease in acetic acid and an increase in ethanol production. Thus, tungsten plays a key role in activating aldehyde:ferredoxin oxidoreductase, a key enzyme in the reduction of acetate to ethanol. A specific ethanol productivity of 0.462 g ethanol/g DCW∙d was obtained in a culture using 0.01 µM selenium and 0.1 µM tungsten, which was 2.18 times higher than when using 0.01 µM of both selenium and tungsten.