The deletion of aldehyde:ferredoxin oxidoreductase-encoding genes in Clostridium ljungdahlii results in changes in the product spectrum with various carbon sources
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Biofuels, such as ethanol, can be produced by the microbial fermentation of waste gases that contain carbon dioxide (CO 2 ) and carbon monoxide (CO). The acetogenic model microbe Clostridium ljungdahlii converts those substrates into acetyl-CoA with the Wood-Ljungdahl pathway. During autotrophic conditions, acetyl-CoA can be reduced further to ethanol via acetic acid by the enzymes aldehyde:ferredoxin oxidoreductase (AOR) and alcohol dehydrogenase. Here, the genes encoding both tungsten-dependent AORs ( aor1 , CLJU_c20110 and aor2 , CLJU_c20210) were deleted from the genome of C. ljungdahlii . Ethanol formation was enhanced for C. ljungdahlii Δ aor1 with different carbon sources, that is, fructose, a mixture of hydrogen (H 2 ) and CO 2 , and CO. The highest and lowest ethanol:acetic acid ratio was detected during growth with H 2 /CO 2 and CO, respectively. Oscillating patterns were observed during growth with CO, underpinning the importance of a balanced redox metabolism.
