title: Use of the two-liquid phase concept to exploit kinetically controlled multistep biocatalysis.
abstract: The two-liquid phase concept was used to develop a whole cell biocatalytic system for the efficient multistep oxidation of pseudocumene to 3,4-dimethylbenzaldehyde. Recombinant Escherichia coli cells were employed to express the Pseudomonas putida genes encoding xylene monooxygenase, which catalyzes the multistep oxygenation of one methyl group of toluene and xylenes to corresponding alcohols, aldehydes, and acids. A fed-batch based two-liquid phase bioconversion was established with bis(2-ethylhexyl)- phthalate as organic carrier solvent and a phase ratio of 0.5; the product formation pattern, the impact of the nutrient feeding strategy, and the partitioning behavior of the reactants were studied. On the basis of the favorable conditions provided by the two-liquid phase system, engineering of the initial pseudocumene concentration allowed exploiting the complex kinetics of the multistep reaction for the exclusive production of 3,4-dimethyl- benzaldehyde. Further oxidation of the product to 3,4-dimethylbenzoic acid could be inhibited by suitable concentrations of pseudocumene or 3,4-dimethylbenzyl alcohol. The optimized biotransformation setup includes a completely defined medium with high iron content and a nutrient feeding strategy that avoids severe glucose limitation as well as high inhibitory glucose levels. Using such a system on a 2-liter scale, we were able to produce, within 14.5 h, 30 g of 3,4-dimethylbenzaldehyde as predominant reactant in the organic phase and reached a maximal productivity of 1.6 g per liter liquid volume per hour. The present study implicates that the two-liquid phase concept is an efficient tool to exploit the kinetics of multistep biotransformations in general.
authors.affiliation: Institute of Biotechnology, Swiss Federal Institute of Technology Zurich, CH-8093 Zurich, Switzerland.
authors.forename: Bruno
authors.initials: B
authors.lastname: Bühler
authors.forename: Irene
authors.initials: I
authors.lastname: Bollhalder
authors.forename: Bernhard
authors.initials: B
authors.lastname: Hauer
authors.forename: Bernard
authors.initials: B
authors.lastname: Witholt
authors.forename: Andreas
authors.initials: A
authors.lastname: Schmid
mesh_terms: D001547:Benzaldehydes / Q000138:chemical synthesis* / Q000302:isolation & purification; D001555:Benzene Derivatives / Q000378:metabolism*; D019149:Bioreactors / Q000382:microbiology*; D002384:Catalysis; D002478:Cells, Cultured; D004051:Diethylhexyl Phthalate / Q000378:metabolism*; D004926:Escherichia coli / Q000145:classification / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D005240:Feasibility Studies; D005947:Glucose / Q000378:metabolism; D005990:Glycerol / Q000378:metabolism; D007218:Industrial Microbiology / Q000379:methods; D007700:Kinetics; D009097:Multienzyme Complexes / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism*; D011786:Quality Control; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012680:Sensitivity and Specificity; D012996:Solutions / Q000378:metabolism; D013045:Species Specificity; D013379:Substrate Specificity
chemical_list: D001547:Benzaldehydes; D001555:Benzene Derivatives; D009097:Multienzyme Complexes; D011994:Recombinant Proteins; D012996:Solutions; C476925:3,4-dimethylbenzaldehyde; C010313:pseudocumene; D004051:Diethylhexyl Phthalate; D010105:Oxygenases; C067624:xylene monooxygenase; D005947:Glucose; D005990:Glycerol; D010100:Oxygen