KINETICS OF CELL GROWTH AND CITRIC ACID PRODUCTION BY YARROWIA LIPOLYTICA SUC+ TRANSFORMANTS IN SUCROSE MEDIA
 
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Pol. J. Food Nutr. Sci. 1997;47(4):49–54
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ABSTRACT
The purpose of the investigation was to assess the dynamics of biomass and citric acid production in sucrose media by two invertase-positive (Suc+) Yarrowia lipolytica transformants (W 29 ura3-302 and JM23/pINA169), originating from Laboratoire de Genetique Moleculaire et Cellulaire, INRA-CNRS. The industrial strain Y. lipolytica ATCC 20 460 (W29) with Suc- phenotype was used as a control. The growth of the two strains on sucrose was as good as on glucose under the conditions favourable for the expression of invertase activity in the transformants examined, i. e. in the presence of peptone and phosphate buffer at pH 6.8. The specific growth rates, µmax, were 0.5 - 0.536 h-1 and 0.492 - 0.565 h-1, respectively.The biomass yield on sucrose was 6 to 19% higher than that on glucose. Satisfactory cell growth of the two transformants was also observed in production media (based on pure sucrose or sugar beet molasses) at N deficiency and low pH 5.5. However, only W29 ura 3 - 302, the strain derived from the industrial strain W29, was able to produce high levels of citric acid. Maximum accumulation of the citric acid in 20% molasses broth fermented by this strain reached 50.2 g/L, which can be considered promising. However, further studies are required to improve productivity of this bioprocess. Moreover, the results obtained in the present study show that the expression of foreign SUC2 gene in Y.lipolytica, under the control of the XPR2 promoter and using the alkaline extracellular protease signal sequence (encoded by the XPR2 gene), allowed the production of citric acid on carbohydrate materials.
ISSN:1230-0322