The deletion of aldehyde:ferredoxin oxidoreductase-encoding genes inClostridium ljungdahliiresults in changes in the product spectrum with various carbon sources

Abstract

AbstractBiofuels, such as ethanol, can be produced by the microbial fermentation of waste gases that contain carbon dioxide (CO2) and carbon monoxide (CO). The acetogenic model microbeClostridium ljungdahliiconverts those substrates into acetyl-CoA with the Wood-Ljungdahl pathway. During autotrophic conditions, acetyl-CoA can be reduced further to ethanolviaacetic acid by the enzymes aldehyde:ferredoxin oxidoreductase (AOR) and alcohol dehydrogenase. Here, the genes encoding both tungsten-dependent AORs (aor1, CLJU_c20110 andaor2, CLJU_c20210) were deleted from the genome ofC. ljungdahlii. Ethanol formation was enhanced forC. ljungdahliiΔaor1with different carbon sources, that is, fructose, a mixture of hydrogen (H2) and CO2, and CO. The highest and lowest ethanol:acetic acid ratio was detected during growth with H2/CO2and CO, respectively. Oscillating patterns were observed during growth with CO, underpinning the importance of a balanced redox metabolism.