Identification of Long-Chain Specific Aldehyde Reductase and Its Application in Long Chain Fatty Alcohol and Alkane Production

Biosynthesis of long chain alcohols and alkanes in microbial foundries offers a sustainable and drop-in supplement to traditional fossil fuels and chemicals. There is no direct natural reservoir for long chain fatty alcohol production but it can be produced by using intermediate gene of alkane biosynthesis pathway which converts fatty acyl-ACP to a fatty aldehyde. Escherichia coli has been the major microbial platform for this effort, however, the terminal endogenous enzyme responsible for converting fatty aldehydes of chain length C14-C18 to corresponding fatty alcohols is still been elusive and not studied. Through our in silico analysis, we selected 35 endogenous enzymes of E. coli having the potential of converting long-chain fatty aldehydes to fatty alcohols and studied their role under in vivo condition. We found that deletion of the ybbO gene, which encodes NADPH-dependent aldehyde reductase, led to 90% reduction in long chain fatty alcohol production. This feature was found to be strain-transcending and reinstalling ybbO gene via plasmid retained the ability of the mutant to produce long chain fatty alcohols. Along with the endogenous production of fatty aldehyde via optimized heterologous expression of cyanobacterial acyl-ACP reductase (AAR), YbbO overexpression resulted in 169 mg/L of long chain fatty alcohols. Further engineering involving modulation of central carbon metabolic pathway and phospholipid pathway has improved fatty alcohol production to over 2 g/L under Fed-batch fermentation. Since fatty aldehyde is the common intermediate precursor for both alkane and alcohol and we found that with the deletion of ybbO, alkane production has been increased. Our study shows for the first time a predominant role and advantage of a single aldehyde reductase in the production of long chain fatty alcohols and alkane.