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Lactose-over-Glucose Preference in Bifidobacterium longum NCC2705: glcP, Encoding a Glucose Transporter, Is Subject to Lactose Repression

Stephan Parche,^1, Manfred Beleut,^2, Enea Rezzonico,¹ Doris Jacobs,¹ Fabrizio Arigoni,¹ Fritz Titgemeyer,² and Ivana Jankovic^1*

Nestlé Research Center, Vers-chez-les-Blanc, 1000 Lausanne 26, Switzerland,¹ Lehrstuhl für Mikrobiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany²

Received 25 August 2005/ Accepted 30 November 2005

Analysis of culture supernatants obtained from Bifidobacterium longum NCC2705 grown on glucose and lactose revealed that glucose utilization is impaired until depletion of lactose. Thus, unlike many other bacteria, B. longum preferentially uses lactose rather than glucose as the primary carbon source. Glucose uptake experiments with B. longum cells showed that glucose transport was repressed in the presence of lactose. A comparative analysis of global gene expression profiling using DNA arrays led to the identification of only one gene repressed by lactose, the putative glucose transporter gene glcP. The functionality of GlcP as glucose transporter was demonstrated by heterologous complementation of a glucose transport-deficient Escherichia coli strain. Additionally, GlcP exhibited the highest substrate specificity for glucose. Primer extension and real-time PCR analyses confirmed that expression of glcP was mediated by lactose. Hence, our data demonstrate that the presence of lactose in culture medium leads to the repression of glucose transport and transcriptional down-regulation of the glucose transporter gene glcP. This may reflect the highly adapted life-style of B. longum in the gastrointestinal tract of mammals.

Supplemental material for this article may be found at http://jb.asm.org/.

Both authors contributed equally to this work.

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