Expansion of the ω-oxidation system AlkBGTL of Pseudomonas putida GPo1 with AlkJ and AlkH results in exclusive mono-esterified dicarboxylic acid production in E. coli

The AlkBGTL proteins coded on the alk operon from Pseudomonas putida GPo1 can selectively ω-oxidize ethyl esters of C6 to C10 fatty acids in whole-cell conversions with Escherichia coli. The major product in these conversions is the ω-alcohol. However, AlkB also has the capacity to overoxidize the substrate to the ω-aldehyde and ω-acid. In this study, we show that alcohol dehydrogenase AlkJ and aldehyde dehydrogenase AlkH are able to oxidize ω-alcohols and ω-aldehydes of esterified fatty acids respectively. Resting E. coli expressing AlkBGTHJL enabled exclusive mono-ethyl azelate production from ethyl nonanoate, with an initial specific activity of 61 U gcdw -1. Within 2 h, this strain produced 3.53 mM mono-ethyl azelate, with a yield of 0.68 mol mol-1. This strain also produced mono-ethyl dicarboxylic acids from ethyl esters of C6 to C10 fatty acids and mono-methyl azelate from methyl nonanoate. Adding ethyl nonanoate dissolved in carrier solvent bis-(2-ethylhexyl) phthalate enabled an increase in product titres to 15.55 mM in two-liquid phase conversions. These findings indicate that E. coli expressing AlkBGTHJL is an effective producer of mono-esterified dicarboxylic acids from fatty acid esters.