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Applied and Environmental Microbiology, February 2007, p. 740-749, Vol. 73, No. 3
0099-2240/07/$08.00+0     doi:10.1128/AEM.01885-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Coupling of Methanothermobacter thermautotrophicus Methane Formation and Growth in Fed-Batch and Continuous Cultures under Different H2 Gassing Regimens{triangledown} ,{dagger}

Linda M. I. de Poorter, Wim J. Geerts, and Jan T. Keltjens*

Department of Microbiology, Faculty of Science, Radboud University of Nijmegen, Nijmegen, The Netherlands

Received 8 August 2006/ Accepted 16 November 2006

In nature, H2- and CO2-utilizing methanogenic archaea have to couple the processes of methanogenesis and autotrophic growth under highly variable conditions with respect to the supply and concentration of their energy source, hydrogen. To study the hydrogen-dependent coupling between methanogenesis and growth, Methanothermobacter thermautotrophicus was cultured in a fed-batch fermentor and in a chemostat under different 80% H2-20% CO2 gassing regimens while we continuously monitored the dissolved hydrogen partial pressures (pH2). In the fed-batch system, in which the conditions continuously changed the uptake rates by the growing biomass, the organism displayed a complex and yet defined growth behavior, comprising the consecutive lag, exponential, and linear growth phases. It was found that the in situ hydrogen concentration affected the coupling between methanogenesis and growth in at least two respects. (i) The microorganism could adopt two distinct theoretical maximal growth yields (YCH4 max), notably approximately 3 and 7 g (dry weight) of methane formed mol–1, for growth under low (pH2 < 12 kPa)- and high-hydrogen conditions, respectively. The distinct values can be understood from a theoretical analysis of the process of methanogenesis presented in the supplemental material associated with this study. (ii) The in situ hydrogen concentration affected the "specific maintenance" requirements or, more likely, the degree of proton leakage and proton slippage processes. At low pH2 values, the "specific maintenance" diminished and the specific growth yields approached YCH4 max, indicating that growth and methanogenesis became fully coupled.

* Corresponding author. Mailing address: Department of Microbiology, Faculty of Science, Radboud University of Nijmegen, Toernooiveld 1, NL-6525 ED Nijmegen, The Netherlands. Phone: 31-24-3653437. Fax: 31-24-3652830. E-mail: J.Keltjens{at}science.ru.nl.

{triangledown} Published ahead of print on 1 December 2006.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, February 2007, p. 740-749, Vol. 73, No. 3
0099-2240/07/$08.00+0     doi:10.1128/AEM.01885-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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