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Electronic Journal of Biotechnology ISSN: 0717-3458 Vol. 9 No. 4, Issue of July 15, 2006
© 2006 by Pontificia Universidad Católica de Valparaíso -- Chile Received July 4, 2005 / Accepted November 19, 2005
DOI: 10.2225/vol9-issue4-fulltext-3  

Oxygen and temperature effect on continuous citric acid secretion in Candida oleophila

Savas Anastassiadis*
Pythia Institute of Biotechnology
Environmental Engineering Department
Democritus University of Thrace
Vat. #: 108851559
Avgi/Sohos, 57002 Thessaloniki, Greece
Tel: 302395051324
Tel/Fax: 302395051470

Hans-Jürgen Rehm
Institute of Molecular Microbiology and Biotechnology
University of Münster
Corrensstr. 3, 48149 Münster, Germany
(retired Professor)


*Corresponding author

Financial support: Part of the work that has been carried out at the Institute of Biotechnology 1 of Research Centre Jülich (Germany) was financed by Haarmann and Reimer, a daughter company of the company Bayer, Leverkusen, Germany.

Keywords: Candida oleophila , citric acid, citric acid secretion.


RT: Residence time, hrs
mp:Specific productivity of the generic product, g product/(g biomass x h)
Rj: Volumetric productivity of the generic product, g product/(l x h)
Rs: Volumetric glucose consumption rate, g/(l x h)

Full Text

The influence of air saturation and temperature on continuous citric acid secretion was studied in chemostat cultures of Candida oleophila ATCC 20177 (var.). Simultaneous measurements of intra- and extracellular concentration of glucose, citric and isocitric acid confirmed the involvement of a specific active transport system in citrate secretion, favouring citric acid over isocitrate. An optimum air oxygen saturation of 20% and temperature of 30-31ºC were determined for the continuous citric acid secretion. The highest values of citric acid concentration (98 g/L), citrate to isocitrate ratio (33.3:1), volumetric citric productivity (1.8 g/(L x h)), and specific citric acid productivity (0.1 g/(g x h)), were reached at 20% air saturation at a residence time of 54 hrs by the experiment's lowest biomass of 18 g/L. The highest isocitic acid volumetric productivity (55.6 mg/(L x h)) and specific productivity (0.99 mg/(g x h)) were identified at 50%, instead. The fastest citrate excretion rate of the generic product of 0.046 g/(g*h) was found at 30-31ºC. A concentration ratio between extra- and intracellular concentration of citrate of up to 9 was identified. The highest extra-/intracellular ratio of citrate and lowest intracellular concentrations of glucose, citric and isocitric acid were determined at optimum air saturation as a consequence of active citrate export. Abstract

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