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Journal of Bacteriology, December 2005, p. 8039-8046, Vol. 187, No. 23
0021-9193/05/$08.00+0     doi:10.1128/JB.187.23.8039-8046.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Minimal Functions and Physiological Conditions Required for Growth of Salmonella enterica on Ethanolamine in the Absence of the Metabolosome

Shaun R. Brinsmade, Tenzin Paldon, and Jorge C. Escalante-Semerena*

Department of Bacteriology, University of Wisconsin—Madison, Madison, Wisconsin

Received 11 May 2005/ Accepted 12 September 2005

During growth on ethanolamine, Salmonella enterica synthesizes a multimolecular structure that mimics the carboxysome used by some photosynthetic bacteria to fix CO2. In S. enterica, this carboxysome-like structure (hereafter referred to as the ethanolamine metabolosome) is thought to contain the enzymatic machinery needed to metabolize ethanolamine into acetyl coenzyme A (acetyl-CoA). Analysis of the growth behavior of mutant strains of S. enterica lacking specific functions encoded by the 17-gene ethanolamine utilization (eut) operon established the minimal biochemical functions needed by this bacterium to use ethanolamine as a source of carbon and energy. The data obtained support the conclusion that the ethanolamine ammnonia-lyase (EAL) enzyme (encoded by the eutBC genes) and coenzyme B12 are necessary and sufficient to grow on ethanolamine. We propose that the EutD phosphotransacetylase and EutG alcohol dehydrogenase are important to maintain metabolic balance. Glutathione (GSH) had a strong positive effect that compensated for the lack of the EAL reactivase EutA protein under aerobic growth on ethanolamine. Neither GSH nor EutA was needed during growth on ethanolamine under reduced-oxygen conditions. GSH also stimulated growth of a strain lacking the acetaldehyde dehydrogenase (EutE) enzyme. The role of GSH in ethanolamine catabolism is complex and requires further investigation. Our data show that the ethanolamine metabolosome is not involved in the biochemistry of ethanolamine catabolism. We propose the metabolosome is needed to concentrate low levels of ethanolamine catabolic enzymes, to keep the level of toxic acetaldehyde low, to generate enough acetyl-CoA to support cell growth, and to maintain a pool of free CoA.


* Corresponding author. Mailing address: Department of Bacteriology, University of Wisconsin—Madison, 144A Enzyme Institute, 1710 University Avenue, Madison, WI 53726-4087. Phone: (608) 262-7379. Fax: (608) 265-7909. E-mail: escalante{at}bact.wisc.edu.


Journal of Bacteriology, December 2005, p. 8039-8046, Vol. 187, No. 23
0021-9193/05/$08.00+0     doi:10.1128/JB.187.23.8039-8046.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.




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