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Journal of Bacteriology, April 2001, p. 2172-2177, Vol. 183, No. 7
Department of Chemistry and Biochemistry,
Utah State University, Logan, Utah 84322-0300
Received 3 July 2000/Accepted 9 January 2001
The bacterial metabolism of propylene proceeds by epoxidation to
epoxypropane followed by a sequence of three reactions resulting in
epoxide ring opening and carboxylation to form acetoacetate. Coenzyme M
(2-mercaptoethanesulfonic acid) (CoM) plays a central role in epoxide
carboxylation by serving as the nucleophile for epoxide ring opening
and the carrier of the C3 unit that is ultimately carboxylated to acetoacetate, releasing CoM. In the present work, a
320-kb linear megaplasmid has been identified in the gram-negative bacterium Xanthobacter strain Py2, which contains the genes
encoding the key enzymes of propylene oxidation and epoxide
carboxylation. Repeated subculturing of Xanthobacter strain
Py2 under nonselective conditions, i.e., with glucose or acetate as the
carbon source in the absence of propylene, resulted in the loss of the
propylene-positive phenotype. The propylene-negative phenotype
correlated with the loss of the 320-kb linear megaplasmid, loss of
induction and expression of alkene monooxgenase and epoxide
carboxylation enzyme activities, and the loss of CoM biosynthetic
capability. Sequence analysis of a hypothetical protein (XecG), encoded
by a gene located downstream of the genes for the four enzymes of
epoxide carboxylation, revealed a high degree of sequence identity with
proteins of as-yet unassigned functions in the methanogenic archaea
Methanobacterium thermoautotrophicum and
Methanococcus jannaschii and in Bacillus
subtilis. The M. jannaschii homolog of XecG, MJ0255,
is located next to a gene, MJ0256, that has been shown to encode a key
enzyme of CoM biosynthesis (M. Graupner, H. Xu, and R. H. White,
J. Bacteriol. 182: 4862-4867, 2000). We propose that the
propylene-positive phenotype of Xanthobacter strain Py2 is
dependent on the selective maintenance of a linear megaplasmid
containing the genes for the key enzymes of alkene oxidation, epoxide
carboxylation, and CoM biosynthesis.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.7.2172-2177.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Evidence that a Linear Megaplasmid Encodes Enzymes
of Aliphatic Alkene and Epoxide Metabolism and Coenzyme M
(2-Mercaptoethanesulfonate) Biosynthesis in Xanthobacter
Strain Py2
*
Corresponding author. Mailing address: Department of
Chemistry and Biochemistry, Utah State University, Logan, UT
84322-0300. Phone: (435) 797-3969. Fax: (435) 797-3390. E-mail:
ensigns{at}cc.usu.edu.
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