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Applied and Environmental Microbiology, November 2008, p. 6941-6948, Vol. 74, No. 22
0099-2240/08/$08.00+0 doi:10.1128/AEM.01280-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

A. T. Phillips,2 and
R. F. Roberts1*
Department of Food Science, 421 Food Science Building, The Pennsylvania State University, University Park, Pennsylvania 16802,1 Department of Biochemistry and Molecular Biology, 208 South Frear, The Pennsylvania State University, University Park, Pennsylvania 168022
Received 9 June 2008/ Accepted 29 August 2008
Two strains of Bifidobacterium animalis subsp. lactis were indistinguishable by several nucleic acid-based techniques; however, the type strain DSMZ 10140 was glucose utilization positive, while RB 4825, an industrially employed strain, was unable to grow rapidly on glucose as the principal carbon source. This difference was attributed to the presence of a low-affinity facilitated-diffusion glucose transporter identified in DSMZ 10140 but lacking in RB 4825. Uptake of D-[U-14C]glucose in DSMZ 10140 was stimulated by monovalent cations (ammonium, sodium, potassium, and lithium) and inhibited by divalent cations (calcium and magnesium). When competitor carbohydrates were included in the uptake assays, stereospecific inhibition was exhibited, with greater competition by methyl-β-glucoside than methyl-
-glucoside. Significant inhibition (>30%) was observed with phloretin, an inhibitor of facilitated diffusion of glucose, whereas there was no inhibition by sodium fluoride, iodoacetate, sodium arsenate, sodium azide, 2,4-dinitrophenol, monensin, or valinomycin, which typically reduce energy-driven transport. Based on kinetic analyses, the mean values for Kt and Vmax were 14.8 ± 3.4 mM D-glucose and 0.13 ± 0.03 µmol glucose/min/mg cell protein, respectively. Glucose uptake by several glucose-utilizing commercial strains of B. animalis subsp. lactis was also inhibited by phloretin, indicating the presence of facilitated diffusion glucose transporters in those strains. Since DSMZ 10140 has been previously reported to lack a functional glucose phosphoenolpyruvate phosphotransferase system, the glucose transporter identified here is responsible for much of the organism's glucose uptake.
Published ahead of print on 12 September 2008.
Present address: Department of Food Science, 123A Babcock Hall, The University of Wisconsin—Madison, Madison, WI 53706.
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