Affiliation:
1. Department of Microbiology and Molecular Genetics, University of Vermont College of Medicine, Burlington, Vermont, USA
2. The Vermont Lung Center, University of Vermont College of Medicine, Burlington, Vermont, USA
Abstract
ABSTRACT
Sarcosine (
N
-methylglycine) is present in many environments inhabited by pseudomonads and is likely most often encountered as an intermediate in the metabolism of choline, carnitine, creatine, and glyphosate. While the enzymology of sarcosine metabolism has been relatively well studied in bacteria, the regulatory mechanisms governing catabolism have remained largely unknown. We previously determined that the sarcosine-catabolic (
sox
) operon of
Pseudomonas aeruginosa
is induced by the AraC family regulator GbdR in response to glycine betaine and dimethylglycine. However, induction of these genes was still observed in response to sarcosine in a
gbdR
deletion mutant, indicating that an independent sarcosine-responsive transcription factor also acted at this locus. Our goal in this study was to identify and characterize this regulator. Using a transposon-based genetic screen, we identified PA4184, or SouR (
s
arcosine
o
xidation and
u
tilization
r
egulator), as the sarcosine-responsive regulator of the
sox
operon, with tight induction specificity for sarcosine. The
souR
gene is required for appreciable growth on sarcosine as a carbon and nitrogen source. We also characterized the transcriptome response to sarcosine governed by SouR using microarray analyses and performed electrophoretic mobility shift assays to identify promoters directly regulated by the transcription factor. Finally, we characterized PA3630, or GfnR (
g
lutathione-dependent
f
ormaldehyde
n
eutralization
r
egulator), as the regulator of the glutathione-dependent formaldehyde detoxification system in
P. aeruginosa
that is expressed in response to formaldehyde released during the catabolism of sarcosine. This study expands our understanding of sarcosine metabolic regulation in bacteria through the identification and characterization of the first known sarcosine-responsive transcriptional regulator.
IMPORTANCE
The
Pseudomonas aeruginosa
genome encodes many diverse metabolic pathways, yet the specific transcription regulators controlling their expression remain mostly unknown. Here, we used a genetic screen to identify the sarcosine-specific regulator of the sarcosine oxidase operon, which we have named SouR. SouR is the first bacterial regulator shown to respond to sarcosine, and it is required for growth on sarcosine. Sarcosine is found in its free form and is also an intermediate in the catabolic pathways of glycine betaine, carnitine, creatine, and glyphosate. The similarity of SouR to the regulators of carnitine and glycine betaine catabolism suggests evolutionary diversification within this regulatory family to allow response to structurally similar but physiologically distinct ligands.
Funder
HHS | NIH | National Institute of Allergy and Infectious Diseases
HHS | NIH | National Institute of General Medical Sciences
National Aeronautics and Space Administration
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
31 articles.
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