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Applied and Environmental Microbiology, January 2006, p. 319-326, Vol. 72, No. 1
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.1.319-326.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Cometabolism of Citrate and Glucose by Enterococcus faecium FAIR-E 198 in the Absence of Cellular Growth

Research Group of Industrial Microbiology, Fermentation Technology and Downstream Processing, Department of Applied Biological Sciences and Engineering, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium,¹ Laboratory of Dairy Research, Department of Food Science and Technology, Agricultural University of Athens, Iera Odos 75, 118 55 Athens, Greece²

Received 17 June 2005/ Accepted 9 October 2005

Citrate metabolism by Enterococcus faecium FAIR-E 198, an isolate from Greek Feta cheese, was studied in modified MRS (mMRS) medium under different pH conditions and glucose and citrate concentrations. In the absence of glucose, this strain was able to metabolize citrate in a pH range from constant pH 5.0 to 7.0. At a constant pH 8.0, no citrate was metabolized, although growth took place. The main end products of citrate metabolism were acetate, formate, acetoin, and carbon dioxide, whereas ethanol and diacetyl were present in smaller amounts. In the presence of glucose, citrate was cometabolized, but it did not contribute to growth. Also, more acetate and less acetoin were formed compared to growth in mMRS medium and in the absence of glucose. Most of the citrate was consumed during the stationary phase, indicating that energy generated by citrate metabolism was used for maintenance. Experiments with cell-free fermented mMRS medium indicated that E. faecium FAIR-E 198 was able to metabolize another energy source present in the medium.