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Journal of Bacteriology, April 2001, p. 2463-2475, Vol. 183, No. 8
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.8.2463-2475.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

The Alternative Electron Acceptor Tetrathionate Supports B12-Dependent Anaerobic Growth of Salmonella enterica Serovar Typhimurium on Ethanolamine or 1,2-Propanediol

Marian Price-Carter,1 Justin Tingey,1,dagger Thomas A. Bobik,2 and John R. Roth1,*

Department of Biology, University of Utah, Salt Lake City, Utah 84112,1 and Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida 326112

Received 12 June 2000/Accepted 19 January 2001

Synthesis of cobalamin de novo by Salmonella enterica serovar Typhimurium strain LT2 and the absence of this ability in Escherichia coli present several problems. This large synthetic pathway is shared by virtually all salmonellae and must be maintained by selection, yet no conditions are known under which growth depends on endogenous B12. The cofactor is required for degradation of 1,2-propanediol and ethanolamine. However, cofactor synthesis occurs only anaerobically, and neither of these carbon sources supports anaerobic growth with any of the alternative electron acceptors tested thus far. This paradox is resolved by the electron acceptor tetrathionate, which allows Salmonella to grow anaerobically on ethanolamine or 1,2-propanediol by using endogenously synthesized B12. Tetrathionate provides the only known conditions under which simple cob mutants (unable to make B12) show a growth defect. Genes involved in this metabolism include the ttr operon, which encodes tetrathionate reductase. This operon is globally regulated by OxrA (Fnr) and induced anaerobically by a two-component system in response to tetrathionate. Salmonella reduces tetrathionate to thiosulfate, which it can further reduce to H2S, by using enzymes encoded by the genes phs and asr. The genes for 1,2-propanediol degradation (pdu) and B12 synthesis (cob), along with the genes for sulfur reduction (ttr, phs, and asr), constitute more than 1% of the Salmonella genome and are all absent from E. coli. In diverging from E. coli, Salmonella acquired some of these genes unilaterally and maintained others that are ancestral but have been lost from the E. coli lineage.

* Corresponding author. Mailing address: Department of Biology, University of Utah, Salt Lake City, UT 84112. Phone: (801) 581-3412. Fax: (801) 585-6207. E-mail: Roth{at}Bioscience.utah.edu.

dagger Present address: Armed Services Medical School, Washington, D.C.

Journal of Bacteriology, April 2001, p. 2463-2475, Vol. 183, No. 8
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.8.2463-2475.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.