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J. Bacteriol. doi:10.1128/JB.00576-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Copper-Induction of Lactate Oxidase (LctO) of Lactococcus lactis: A Novel Metal Stress-Response

Department of Clinical Pharmacology, University of Berne, Murtenstrasse 35, 3010 Berne, Switzerland

^* To whom correspondence should be addressed. Email: marc.solioz{at}ikp.unibe.ch.

	Abstract

Lactococcus lactis IL1403, a lactic acid bacterium widely used for food fermentation, is often exposed to stress conditions. One such condition is exposure to copper, such as in cheese making in copper vats. Copper is an essential micronutrient in prokaryotes and eukaryotes, but can be toxic if in excess. Thus, copper homeostatic mechanisms, chiefly consisting of copper transporters and their regulators, have evolved in all organisms to control cytoplasmic copper levels. Using proteomics to identify novel proteins involved in the response of L. lactis IL1403 to copper, cells were exposed to 200 µM copper sulphate for 45 min, followed by resolution of the cytoplasmic fraction by two-dimensional gel electrophoresis. One protein strongly induced by copper was LctO, which was shown to encode a NAD-independent lactate oxidase. It catalyzed the conversion of lactate to pyruvate in vivo and in vitro. Copper, cadmium and silver induced LctO, as shown by real time quantitative PCR. A copper regulatory element was identified in the 5'-region of the lctO gene and shown to interact with the CopR regulator, encoded by the unlinked copRZA operon. Induction of LctO by copper represents a novel copper stress response and we suggest that it serves in the scavenging of molecular oxygen.

This article has been cited by other articles:

• Magnani, D., Barre, O., Gerber, S. D., Solioz, M. (2008). Characterization of the CopR Regulon of Lactococcus lactis IL1403. J. Bacteriol. 190: 536-545 [Abstract] [Full Text]