The role of microbial diversity in the dynamics and stability of global methane consumption: microbial methane oxidation as a model-system for microbial ecology (METHECO) (EuroDIVERSITY 018)
Final Report Abstract
Earth’s biodiversity is declining forcing mankind to consider how ecosystems’ stability and services will change in future. The biodiversity-stability discussion combines two multi-facetted concepts comprising species number and evenness, and resistance and resilience, respectively. Prokaryotic microbes can catalyze all biogeochemical cycles and have done so before the advent of eukaryotes. They have been assumed to be functionally redundant and virtually inextinguishable. However, recent work indicates that microbes may well be sensitive to environmental disturbance. Overall, soil microbial diversity is indeed very high. Therefore, functional guilds with a well-defined substrate usage are prime candidates not only to study potentially endangered microbial functions, but also to contribute to the general discussion about biodiversity and ecosystem functioning. These prime candidates include methanotrophs, the methane oxidizing bacteria. Methanotrophs are able to use methane both for catabolism and anabolism. They have a large yet tractable biodiversity. Methane is an important greenhouse gas contributing substantially to global warming. Methanotrophs serve as a biological filter significantly mitigating methane emissions from wetlands, rice fields and landfills, and are the only biological sink to atmospheric methane. The key enzyme of all methanotrophs is the methane monooxygenase (MMO) existing either as a particulate membrane bound form (pMMO) in virtually all methanotrophs. The pmoA gene encodes a subunit of pMMO, being highly conserved and an excellent marker gene for cultivation independent studies. Microbial ecology is largely depending on molecular methods. To make results comparable between ecosystems and laboratories involved, we contributed to the first ring analysis in environmental microbiology, assessing both inter- as intra-laboratory reproducibility of community composition analyses. We conclude that consistent results can be reached at least on the same target soil, if sticking meticulously to the same protocol, and preferably using the same equipment. Methanotrophs can be found virtually everywhere, but they are not universally distributed, showing correlations to ecosystems: upland soils harbor other communities than any other environment, and even aquatic methanotrophs show different preferences e.g. for freshwater sediments, natural wetlands, and rice fields. One group is exclusively found in rice paddies. Combining community analysis with process measurements made it possible to answer questions pertaining to both the role of microbial biodiversity in stabilizing and maintaining methane oxidation, and how this globally important function and its resilience is affected by environmental perturbations. In high methane environments, methanotrophic communities are quite resilient, probably due to a large seed bank of viable yet inactive cells. Even a simulated die-off of 97.5% could be compensated, however resulting in a reduced evenness. It is not yet shown, but probable that such effects accumulate upon repeated disturbances potentially affecting stability on the long term. Low methane environments like upland soils are vulnerable needing decades to recover from disturbances. Defining and validating the boundary layer between resilient and vulnerable ecosystems in terms of biodiversity, function and controls remains a major challenge for future work.
Publications
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(2007). A methane-driven microbial food web in a wetland rice soil. Environ. Microbiol. 9: 3025-3034
Murase J and Frenzel P
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(2008). Selective grazing of methanotrophs by protozoa in a rice field soil. FEMS Microbiol. Ecol. 65: 408-414
Murase J and Frenzel P
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(2008). Selective stimulation of type I methanotrophs in a rice paddy soil by urea fertilization revealed by RNA-based stable isotope probing. FEMS Microbiol. Ecol. 65: 125-132
Noll M, Frenzel P, and Conrad R
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(2009). EuroDIVERSITY Mid-term Report
Frenzel P
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(2009). Scientific report on networking activity: METHECO project meeting, Abisko, Sweden, October 25-28, 2009
Svenning MM and Frenzel P
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(2009). Spatial heterogeneity of methanotrophs: a geostatistical analysis of pmoA-based T-RFLP patterns in a paddy soil. Environ. Microbiol. Rep. 1: 393-397
Krause S, Lüke C, and Frenzel P
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Biogeography of wetland rice methanotrophs. Environ Microbiol (2010); e-pub ahead of print, 27 December 2009
Lüke C, Krause S, Cavigioli S, Greppi D, Lupotto E, and Frenzel P
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(2010). Final Report of the Collaborative Research Project “METHECO”
Frenzel P
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(2010). Molecular ecology and biogeography of methanotrophic bacteria in wetland rice fields. Ph.D. Thesis, Universität Marburg
Lüke C
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(2010). Ökologie methanotropher Bakterien: Räumliche Verteilung und Funktion methanotropher Bakterien in Feuchtgebieten. Ph.D. Thesis, Universität Marburg
Krause S
