title: Integration of whole-cell reaction and product isolation: Highly hydrophobic solvents promote in situ substrate supply and simplify extractive product isolation.
abstract: Product isolation from aqueous-organic reaction mixtures that contain high concentrations of whole cells constitutes a challenging task in bioprocessing. Stirring of the biphasic reaction media leads to the formation of solvent droplets coated by cells and other surface active components and an emulsion forms. We used an early focus on phase separation to simplify a whole-cell bioreduction. Octanol, heptanol, hexanol, hexane and dipropylether were tested as co-solvents in the E. coli catalyzed reduction of o-chloroacetophenone. All solvents showed very similar performance in bioreductions and highest yields were obtained with low organic-to-aqueous phase ratios. Reaction mixtures were directly investigated for organic-phase recovery. Phase separation was optimized in small-scale settling experiments and confirmed by the isolation of 20.4g (S)-1-(2-chlorophenyl)ethanol from a 0.5L batch reduction containing 40gCDW/L whole-cell catalyst. Solvent consumption during product isolation could be halved by the simple addition of sodium hydroxide prior to product extraction. Basification to pH 13.5 and three extraction steps with a total of 1.2v/v hexane led to an isolated yield of 87% (97% reduction yield). A general emulsion destabilizing effect under harsh conditions, as extreme pH values and presence of toxic reactants, was observed.
authors.affiliation: Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Member of NAWI Graz, Austria.
authors.forename: Dorothea
authors.initials: D
authors.lastname: Leis
authors.affiliation: Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Member of NAWI Graz, Austria.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Lauß
authors.affiliation: Institute of Chemical Engineering and Environmental Technology, Graz University of Technology, Member of NAWI Graz, Austria.
authors.forename: Robert
authors.initials: R
authors.lastname: Macher-Ambrosch
authors.affiliation: Institute of Chemical Engineering and Environmental Technology, Graz University of Technology, Member of NAWI Graz, Austria; Department of Chemical Engineering, University of Liège, Liège, Belgium.
authors.forename: Andreas
authors.initials: A
authors.lastname: Pfennig
authors.affiliation: Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Member of NAWI Graz, Austria. Electronic address: bernd.nidetzky@tugraz.at.
authors.forename: Bernd
authors.initials: B
authors.lastname: Nidetzky
authors.affiliation: Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Member of NAWI Graz, Austria. Electronic address: regina.kratzer@tugraz.at.
authors.forename: Regina
authors.initials: R
authors.lastname: Kratzer
mesh_terms: D055162:Biocatalysis; D019149:Bioreactors / Q000382:microbiology; D001709:Biotechnology / Q000379:methods*; D001711:Biotransformation; D002498:Centrifugation; D004655:Emulsions / Q000737:chemistry; D004926:Escherichia coli / Q000737:chemistry; D005374:Filtration; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D009930:Organic Chemicals / Q000737:chemistry; D012997:Solvents / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D002721:omega-Chloroacetophenone / Q000737:chemistry
chemical_list: D004655:Emulsions; D009930:Organic Chemicals; D012997:Solvents; D014867:Water; D002721:omega-Chloroacetophenone
keywords: E. coli stabilized emulsion; Emulsion separation; Whole-cell bioreduction