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Journal of Bacteriology, April 2008, p. 2966-2971, Vol. 190, No. 8
0021-9193/08/$08.00+0     doi:10.1128/JB.01925-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Microcompartments for B₁₂-Dependent 1,2-Propanediol Degradation Provide Protection from DNA and Cellular Damage by a Reactive Metabolic Intermediate

Edith M. Sampson¹ and Thomas A. Bobik^2*

Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa 50011,¹ Department of Otolaryngology, University of Florida, Gainesville, Florida 32610²

Received 11 December 2007/ Accepted 11 February 2008

Salmonella enterica grows on 1,2-propanediol (1,2-PD) in a coenzyme B₁₂-dependent fashion. Prior studies showed that a bacterial microcompartment (MCP) is involved in this process and that an MCP-minus mutant undergoes a 20-h period of growth arrest during 1,2-PD degradation. It was previously proposed that growth arrest resulted from propionaldehyde toxicity, but no direct evidence was presented. Here, high-pressure liquid chromatography analyses of culture medium were used to show that the major products of aerobic 1,2-PD degradation are propionaldehyde, propionate, and 1-propanol. A MCP-minus mutant accumulated a level of propionaldehyde 10-fold higher than that of the wild type (1.6 mM compared to 15.7 mM), associating this compound with growth arrest. The addition of propionaldehyde to cultures of S. enterica caused growth arrest from 8 to 20 mM, but not at 4 mM, providing direct evidence for propionaldehyde toxicity. Studies also indicated that propionaldehyde was toxic due to the inhibition of respiratory processes, and the growth arrest ended when propionaldehyde was depleted primarily by conversion to propionate and 1-propanol and secondarily due to volatility. The Ames test was used to show that propionaldehyde is a mutagen and that mutation frequencies are increased in MCP-minus mutants during 1,2-PD degradation. We propose that a primary function of the MCPs involved in 1,2-PD degradation is the mitigation of toxicity and DNA damage by propionaldehyde.

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* Corresponding author: Mailing address: Iowa State University, Department of Biochemistry, Biophysics and Molecular Biology, Ames, IA 50011. Phone: (515) 294-4165. Fax: (515) 294-0453. E-mail: bobik{at}iastate.edu

Published ahead of print on 22 February 2008.

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Journal of Bacteriology, April 2008, p. 2966-2971, Vol. 190, No. 8
0021-9193/08/$08.00+0     doi:10.1128/JB.01925-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

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