Optimization of fermentation conditions for production of soluble recombinant ADH and FDH in Escherichia coli

The use of purified recombinant enzymes produced in E. coli for the bioconversion of small aromatic compounds is a well-established approach in this branch of the biotech industry. In contrast to chemical conversion, use of these enzymes ensures correct chirality and improves overall quality of the final product. In this work, we have optimized culturing conditions in a small-scale bioreactor allowing production of relatively high yields of soluble and active recombinant alcohol dehydrogenase (ADH) and formate dehydrogenase (FDH) in E. coli. These enzymes are essential for the proposed two-enzyme bioconversion system used for biotransformation of trans-2-hexenal to more stable trans-2-hexanol, an aromatic compound often used in food and cosmetic industry. Although ADH is a tetrameric complex protein, which predominantly aggregates into insoluble inclusion bodies in E. coli cytoplasm, by careful optimization of cultivation conditions a high degree of solubility can be achieved.  We were able to produce ADH in the scale of 30 – 50 kU per liter of culture and 500 – 800 U of FDH per liter of culture, respectively. Both enzymes were purified using affinity chromatography utilizing engineered histidine-tag and their activity has been determined by standard procedures.