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Journal of Bacteriology, March 2008, p. 1928-1936, Vol. 190, No. 6
0021-9193/08/$08.00+0     doi:10.1128/JB.01424-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Mutagenesis of the C1 Oxidation Pathway in Methanosarcina barkeri: New Insights into the Mtr/Mer Bypass Pathway{triangledown}

Paula V. Welander and William W. Metcalf*

Department of Microbiology, University of Illinois at Urbana-Champaign, B103 Chemical and Life Science Laboratory, 601 South Goodwin Avenue, Urbana, Illinois 61801

Received 3 September 2007/ Accepted 23 December 2007

A series of Methanosarcina barkeri mutants lacking the genes encoding the enzymes involved in the C1 oxidation/reduction pathway were constructed. Mutants lacking the methyl-tetrahydromethanopterin (H4MPT):coenzyme M (CoM) methyltransferase-encoding operon ({Delta}mtr), the methylene-H4MPT reductase-encoding gene ({Delta}mer), the methylene-H4MPT dehydrogenase-encoding gene ({Delta}mtd), and the formyl-methanofuran:H4MPT formyl-transferase-encoding gene ({Delta}ftr) all failed to grow using either methanol or H2/CO2 as a growth substrate, indicating that there is an absolute requirement for the C1 oxidation/reduction pathway for hydrogenotrophic and methylotrophic methanogenesis. The mutants also failed to grow on acetate, and we suggest that this was due to an inability to generate the reducing equivalents needed for biosynthetic reactions. Despite their lack of growth on methanol, the {Delta}mtr and {Delta}mer mutants were capable of producing methane from this substrate, whereas the {Delta}mtd and {Delta}ftr mutants were not. Thus, there is an Mtr/Mer bypass pathway that allows oxidation of methanol to the level of methylene-H4MPT in M. barkeri. The data further suggested that formaldehyde may be an intermediate in this bypass; however, no methanol dehydrogenase activity was found in {Delta}mtr cell extracts, nor was there an obligate role for the formaldehyde-activating enzyme (Fae), which has been shown to catalyze the condensation of formaldehyde and H4MPT in vitro. Both the {Delta}mer and {Delta}mtr mutants were able to grow on a combination of methanol plus acetate, but they did so by metabolic pathways that are clearly distinct from each other and from previously characterized methanogenic pathways.

* Corresponding author. Mailing address: Department of Microbiology, University of Illinois at Urbana-Champaign, 601 S. Goodwin Avenue, Urbana, IL 61801. Phone: (217) 244-1943. Fax: (217) 244-6697. E-mail: metcalf{at}uiuc.edu

{triangledown} Published ahead of print on 4 January 2008.

Journal of Bacteriology, March 2008, p. 1928-1936, Vol. 190, No. 6
0021-9193/08/$08.00+0     doi:10.1128/JB.01424-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Kulkarni, G., Kridelbaugh, D. M., Guss, A. M., Metcalf, W. W. (2009). Hydrogen is a preferred intermediate in the energy-conserving electron transport chain of Methanosarcina barkeri. Proc. Natl. Acad. Sci. USA 106: 15915-15920 [Abstract] [Full Text]  


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