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J. Bacteriol. doi:10.1128/JB.01393-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Identification of two gene clusters and a transcriptional regulator required for Pseudomonas aeruginosa glycine betaine catabolism

Department of Microbiology and Immunology and Department of Medicine, Dartmouth Medical School, Hanover, NH 03755

^* To whom correspondence should be addressed. Email: dhogan{at}dartmouth.edu.

	Abstract

Glycine betaine (GB), which is found freely in the environment and is an intermediate in the catabolism of choline and carnitine, can serve as a sole source of carbon or nitrogen in Pseudomonas aeruginosa. Twelve mutants defective in growth on GB as a sole carbon source were identified through a genetic screen of a non-redundant PA14 transposon mutant library. Further growth experiments determined that strains with mutations in two genes, gbcA (PA5410) and gbcB (PA5411), were capable of growth on dimethylglycine (DMG), a catabolic product of GB, but not GB itself. Subsequent NMR experiments with 1,2-¹³C-labeled choline indicated these genes were necessary for GB conversion to DMG. Similar experiments showed that strains with mutations in dgcA-B (PA5398-PA5399), with homology to genes that encode other enzymes with demethylase activity, are required for the conversion of DMG to sarcosine. Mutant analyses and ¹³C-NMR studies also confirmed that the soxBDAG genes, predicted to encode a sarcosine oxidase, are required for sarcosine catabolism. Our screen also identified a predicted AraC-family transcriptional regulator, encoded by gbdR (PA5380), that is required for growth on GB and DMG and the induction of gbcA, gbcB, and dgcAB in response to GB or DMG. Mutants defective in the previously described gbt gene (PA3082) grew on GB with kinetics similar to the wild type in both PAO1 and PA14 strain backgrounds. These studies provide important insight into both the mechanism and regulation of the catabolism GB in P. aeruginosa.