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Applied and Environmental Microbiology, May 2009, p. 2605-2612, Vol. 75, No. 9
0099-2240/09/$08.00+0     doi:10.1128/AEM.02680-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Effect of Substrate Concentration on Carbon Isotope Fractionation during Acetoclastic Methanogenesis by Methanosarcina barkeri and M. acetivorans and in Rice Field Soil{triangledown}

Dennis Goevert and Ralf Conrad*

Max Planck Institute for Terrestrial Microbiology, Karl von Frisch Strasse, 35043 Marburg, Germany

Received 24 November 2008/ Accepted 20 February 2009

Methanosarcina is the only acetate-consuming genus of methanogenic archaea other than Methanosaeta and thus is important in methanogenic environments for the formation of the greenhouse gases methane and carbon dioxide. However, little is known about isotopic discrimination during acetoclastic CH4 production. Therefore, we studied two species of the Methanosarcinaceae family, Methanosarcina barkeri and Methanosarcina acetivorans, and a methanogenic rice field soil amended with acetate. The values of the isotope enrichment factor ({varepsilon}) associated with consumption of total acetate ({varepsilon}ac), consumption of acetate-methyl ({varepsilon}ac-methyl) and production of CH4 ({varepsilon}CH4) were an {varepsilon}ac of –30.5{per thousand}, an {varepsilon}ac-methyl of –25.6{per thousand}, and an {varepsilon}CH4 of –27.4{per thousand} for M. barkeri and an {varepsilon}ac of –35.3{per thousand}, an {varepsilon}ac-methyl of –24.8{per thousand}, and an {varepsilon}CH4 of –23.8{per thousand} for M. acetivorans. Terminal restriction fragment length polymorphism of archaeal 16S rRNA genes indicated that acetoclastic methanogenic populations in rice field soil were dominated by Methanosarcina spp. Isotope fractionation determined during acetoclastic methanogenesis in rice field soil resulted in an {varepsilon}ac of –18.7{per thousand}, an {varepsilon}ac-methyl of –16.9{per thousand}, and an {varepsilon}CH4 of –20.8{per thousand}. However, in rice field soil as well as in the pure cultures, values of {varepsilon}ac and {varepsilon}ac-methyl decreased as acetate concentrations decreased, eventually approaching zero. Thus, isotope fractionation of acetate carbon was apparently affected by substrate concentration. The {varepsilon} values determined in pure cultures were consistent with those in rice field soil if the concentration of acetate was taken into account.

* Corresponding author. Mailing address: Max Planck Institute for Terrestrial Microbiology, Karl von Frisch Str., 35043 Marburg, Germany. Phone: 49 6421 178 801. Fax: 49 6421 178 809. E-mail: conrad{at}mpi-marburg.mpg.de

{triangledown} Published ahead of print on 27 February 2009.

Applied and Environmental Microbiology, May 2009, p. 2605-2612, Vol. 75, No. 9
0099-2240/09/$08.00+0     doi:10.1128/AEM.02680-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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