Effects of various reducing agents on syngas fermentation by "Clostridium ragsdalei".

The bacterium "Clostridium ragsdalei" previously was identified as ca- pable of producing ethanol from CO, CO2 and H2. In order to enhance the production of ethanol from these gases, three reducing agents (methyl viologen, benzyl viologen, and neutral red) were added to fermentation medium at a concentration of 0.1 mM. The medium was inoculated with "C. ragsdalei," and the headspace gas was ex- changed daily with a gas mix of 20% CO, 15% CO2, 5% H2, and 60% N2. Reducing agents were added to the culture after 91 h of cell growth. Benzyl viologen caused cell death, and no ethanol production was detected. Methyl viologen promoted ethanol production as compared to the control containing no reducing agent, while neutral red neither promoted nor detracted from ethanol production when compared to the control. Addition of 0.2 or 0.3 mM methyl viologen delayed the production of ethanol as compared with 0.1 mM methyl viologen.

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