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Electronic Journal of Biotechnology
Universidad Católica de Valparaíso
ISSN: 0717-3458
Vol. 8, No. 2, 2005, pp. 146-161
Bioline Code: ej05017
Full paper language: English
Document type: Research Article
Document available free of charge

Electronic Journal of Biotechnology, Vol. 8, No. 2, 2005, pp. 146-161

 en Continuous citric acid secretion by a high specific pH dependent active transport system in yeast Candida oleophila check for this species in other resources ATCC 20177
Anastassiadis ,Savas & Rehm, Hans-Jürgen

Abstract

The pH influence on continuous citric acid secretion was investigated in Candida oleophila check for this species in other resources ATCC 20177 (var.) under NH4+ limiting state steady conditions, using glucose. Highest citric acid concentration of 57.8 g/l, citrate/isocitrate ratio of 15.6, space-time yield of 0.96 g/(l x hr) and biomass specific productivity of 0.041 g/(g x hr) were obtained at pH 5 and 60 hrs residence time. Only 22.8 g/l (39.4%) and a ratio of 9.9 were achieved at pH 6 pH and 12.4 g/l (21.5%) and a ratio of 3.7 at pH 3. Under non producing conditions, in excess of nitrogen, biomass concentration increased at raising pH. An iron concentration of 200 ppm was determined in biomass of C. oleophila at pH 5, compared with only 26 ppm found at pH 3 (factor 7.7). Intra- and extracellular concentrations of citrates and glucose confirmed the existence of a high specific, pH dependent active transport system for citrate secretion, while isocitrate isn't a high-affine substrate, displaying a strong correlation with ATP/ADP ratio. Differences between extra- and intracellular concentration of citrate higher than 1 and up to about 60 were determined. The active transport systemfor citrate excretion appears to be the main speed-determining factor in citrate overproduction by yeasts.

Keywords
active citrate export, citric acid fermentation, energy consuming citric acid secretion, specific active transport system.

 
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