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Applied and Environmental Microbiology, June 2003, p. 3238-3243, Vol. 69, No. 6
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.6.3238-3243.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Unusual Organization for Lactose and Galactose Gene Clusters in Lactobacillus helveticus

Maria Grazia Fortina,^* Giovanni Ricci, Diego Mora, Simone Guglielmetti, and Pier Luigi Manachini

Industrial Microbiology Section, Department of Food Science and Microbiology, University of Milan, 20133 Milan, Italy

Received 2 December 2002/ Accepted 20 March 2003

The nucleotide sequences of the Lactobacillus helveticus lactose utilization genes were determined, and these genes were located and oriented relative to one another. The lacLM genes (encoding the ß-galactosidase protein) were in a divergent orientation compared to lacR (regulatory gene) and lacS (lactose transporter). Downstream from lacM was an open reading frame (galE) encoding a UDP-galactose 4 epimerase, and the open reading frame had the same orientation as lacM. The lacR gene was separated from the downstream lacS gene by 2.0 kb of DNA containing several open reading frames that were derived from fragmentation of another permease gene (lacS'). Northern blot analysis revealed that lacL, lacM, and galE made up an operon that was transcribed in the presence of lactose from an upstream lacL promoter. The inducible genes lacL and lacM were regulated at the transcriptional level by the LacR repressor. In the presence of glucose and galactose galE was transcribed from its promoter, suggesting that the corresponding enzyme can be expressed constitutively. Lactose transport was inducible by addition of lactose to the growth medium.

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* Corresponding author. Mailing address: Dipartimento di Scienze e Tecnologie Alimentari e Microbiologiche, Sezione di Microbiologia Industriale, Università degli Studi di Milano, Via Celoria 2, 20133 Milan, Italy. Phone: 39 02 50316692. Fax: 39 02 50316694. E-mail: grazia.fortina{at}unimi.it.

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Applied and Environmental Microbiology, June 2003, p. 3238-3243, Vol. 69, No. 6
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.6.3238-3243.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

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