title: Monitoring and control of Gluconacetobacter xylinus fed-batch cultures using in situ mid-IR spectroscopy.
abstract: A partial least-squares calibration model, relating mid-infrared spectral features with fructose, ethanol, acetate, gluconacetan, phosphate and ammonium concentrations has been designed to monitor and control cultivations of Gluconacetobacter xylinus and production of gluconacetan, a food grade exopolysaccharide (EPS). Only synthetic solutions containing a mixture of the major components of culture media have been used to calibrate the spectrometer. A factorial design has been applied to determine the composition and concentration in the calibration matrix. This approach guarantees a complete and intelligent scan of the calibration space using only 55 standards. This calibration model allowed standard errors of validation (SEV) for fructose, ethanol, acetate, gluconacetan, ammonium and phosphate concentrations of 1.16 g/l, 0.36 g/l, 0.22 g/l, 1.54 g/l, 0.24 g/l and 0.18 g/l, respectively. With G. xylinus, ethanol is directly oxidized to acetate, which is subsequently metabolized to form biomass. However, residual ethanol in the culture medium prevents bacterial growth. On-line spectroscopic data were implemented in a closed-loop control strategy for fed-batch fermentation. Acetate concentration was controlled at a constant value by feeding ethanol into the bioreactor. The designed fed-batch process allowed biomass production on ethanol. This was not possible in a batch process due to ethanol inhibition of bacterial growth. In this way, the productivity of gluconacetan was increased from 1.8 x 10(-3) [C-mol/C-mol substrate/h] in the batch process to 2.9 x 10(-3) [C-mol/C-mol substrate/h] in the fed-batch process described in this study.
authors.affiliation: Serono Biotech Center, route de Fenil, ZI B, CH-1809 Fenil-sur-Corsier, Switzerland.
authors.forename: Henri
authors.initials: H
authors.lastname: Kornmann
authors.forename: Sergio
authors.initials: S
authors.lastname: Valentinotti
authors.forename: Philippe
authors.initials: P
authors.lastname: Duboc
authors.forename: Ian
authors.initials: I
authors.lastname: Marison
authors.forename: Urs
authors.initials: U
authors.lastname: von Stockar
mesh_terms: D000465:Algorithms; D019149:Bioreactors; D001709:Biotechnology / Q000295:instrumentation / Q000379:methods*; D002138:Calibration; D003470:Culture Media; D000431:Ethanol / Q000378:metabolism; D041822:Gluconacetobacter xylinus / Q000254:growth & development* / Q000378:metabolism*; D007218:Industrial Microbiology / Q000295:instrumentation / Q000379:methods*; D013055:Spectrophotometry, Infrared / Q000379:methods*
chemical_list: D003470:Culture Media; D000431:Ethanol