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J. Bacteriol. doi:10.1128/JB.01103-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Glycerol metabolism is important for cytotoxicity of Mycoplasma pneumoniae

Abteilung für Allgemeine Mikrobiologie, Institut für Mikrobiologie und Genetik, Grisebachstraße 8, D-37077 Göttingen, Germany; Institute of Veterinary Bacteriology, University of Bern, Länggass-Strasse 122, CH-3001 Bern, Switzerland

^* To whom correspondence should be addressed. Email: jstuelk{at}gwdg.de.

	Abstract

Glycerol is one of the few carbon sources that can be utilized by Mycoplasma pneumoniae. Glycerol metabolism involves uptake by facilitated diffusion, phosphorylation and the oxidation of glycerol 3-phosphate to dihydroxyacetone phosphate, a glycolytic intermediate. We have analyzed the expression of the genes involved in glycerol metabolism and observed constitutive expression irrespective of the presence of glycerol or preferred carbon sources. Similarly, the enzymatic activity of glycerol kinase is not modulated by HPr-dependent phosphorylation. This lack of regulation is unique among the bacteria for that glycerol metabolism has been studied so far. Two types of enzymes catalyze the oxidation of glycerol 3-phosphate: oxidases and dehydrogenases. Here, we demonstrate that the enzyme encoded by the M. pneumoniae glpD gene is a glycerol 3-phosphate oxidase that forms hydrogen peroxide rather than NADH₂. The formation of hydrogen peroxide by GlpD is crucial for cytotoxic effects of M. pneumoniae. A glpD mutant exhibited a significantly reduced formation of hydrogen peroxide and a severely reduced cytotoxicity. Attempts to isolate mutants affected in the genes of glycerol metabolism revealed that only the glpD gene encoding the glycerol 3-phosphate oxidase is dispensable. In contrast, the glpF and glpK genes encoding the glycerol facilitator and the glycerol kinase, respectively, are essential in M. pneumoniae. Thus, the enzymes of glycerol metabolism are crucial for the pathogenicity of M. pneumoniae but also for other, essential, yet to be identified functions in the M. pneumoniae cell.