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Alternative Lactose Catabolic Pathway in Lactococcus lactis IL1403

Department of Microbial Biochemistry, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland,¹ Department of Genetics, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands,² Laboratoire de Génétique Microbienne, Institut National de Recherches Agronomiques, 78352 Jouy-en-Josas Cedex, France³

Received 20 April 2005/ Accepted 25 May 2005

In this study, we present a glimpse of the diversity of Lactococcus lactis subsp. lactis IL1403 ß-galactosidase phenotype-negative mutants isolated by negative selection on solid media containing cellobiose or lactose and X-Gal (5-bromo-4-chloro-3-indolyl-ß-D-galactopyranoside), and we identify several genes essential for lactose assimilation. Among these are ccpA (encoding catabolite control protein A), bglS (encoding phospho-ß-glucosidase), and several genes from the Leloir pathway gene cluster encoding proteins presumably essential for lactose metabolism. The functions of these genes were demonstrated by their disruption and testing of the growth of resultant mutants in lactose-containing media. By examining the ccpA and bglS mutants for phospho-ß-galactosidase activity, we showed that expression of bglS is not under strong control of CcpA. Moreover, this analysis revealed that although BglS is homologous to a putative phospho-ß-glucosidase, it also exhibits phospho-ß-galactosidase activity and is the major enzyme in L. lactis IL1403 involved in lactose hydrolysis.