Affiliation:
1. Abteilung für Allgemeine Mikrobiologie, Institut für Mikrobiologie und Genetik, Grisebachstrasse 8, D-37077 Göttingen, Germany
2. Institute of Veterinary Bacteriology, University of Bern, Länggass-Strasse 122, CH-3001 Bern, Switzerland
Abstract
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 which 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 NADH
2
. 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.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
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