title: Ultrasound-enhanced attenuated total reflection mid-infrared spectroscopy in-line probe: acquisition of cell spectra in a bioreactor.
abstract: This article presents a novel method for selective acquisition of Fourier transform infrared (FT-IR) spectra of microorganisms in-line during fermentation, using Saccharomyces cerevisiae as an example. The position of the cells relative to the sensitive region of the attenuated total reflection (ATR) FT-IR probe was controlled by combing a commercially available ATR in-line probe with contact-free, gentle particle manipulation by ultrasonic standing waves. A prototype probe was successfully constructed, assembled, and tested in-line during fed-batch fermentations of S. cerevisiae. Control over the position of the cells was achieved by tuning the ultrasound frequency: 2.41 MHz was used for acquisition of spectra of the cells (pushing frequency f(p)) and 1.87 MHz, for retracting the cells from the ATR element, therefore allowing spectra of the medium to be acquired. Accumulation of storage carbohydrates (trehalose and glycogen) inside the cells was induced by a lack of a nitrogen source in the feed medium. These changes in biochemical composition were visible in the spectra of the cells recorded in-line during the application of f(p) and could be verified by reference spectra of dried cell samples recorded off-line with a FT-IR microscope. Comparison of the cell spectra with spectra of trehalose, glycogen, glucose, and mannan, i.e., the major carbohydrates present in S. cerevisiae, and principal components analysis revealed that the changes observed in the cell spectra correlated well with the bands specific for trehalose and glycogen. This proves the applicability and capability of ultrasound-enhanced in-line ATR mid-IR spectroscopy as a real-time PAT method for the in situ monitoring of cellular biochemistry during fermentation.
authors.affiliation: Institute of Chemical Technologies and Analytics, Vienna University of Technology , Getreidemarkt 9/164-UPA, 1060 Vienna, Austria.
authors.forename: Cosima
authors.initials: C
authors.lastname: Koch
authors.forename: Markus
authors.initials: M
authors.lastname: Brandstetter
authors.forename: Patrick
authors.initials: P
authors.lastname: Wechselberger
authors.forename: Bettina
authors.initials: B
authors.lastname: Lorantfy
authors.forename: Maria Reyes
authors.initials: MR
authors.lastname: Plata
authors.forename: Stefan
authors.initials: S
authors.lastname: Radel
authors.forename: Christoph
authors.initials: C
authors.lastname: Herwig
authors.forename: Bernhard
authors.initials: B
authors.lastname: Lendl
mesh_terms: D019149:Bioreactors; D005285:Fermentation; D015335:Molecular Probes / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D014465:Ultrasonics
chemical_list: D015335:Molecular Probes