Abstract
Summary
We live in a microbial world. Microorganisms were the first life forms on our planet, shaping the Earth as we know it today. During Earth's history, a set of metabolic processes evolved exclusively in microorganisms that thrived in the absence of oxygen. One of these processes is the last step in the anaerobic degradation of organic matter: methanogenesis. This process is performed by methanogenic archaea belonging to the phylum Euryarchaeota. Although several studies indicated the potential for methanogenesis outside of this phylum, so far, no experimental evidence exists. The methane (CH4), which is the terminal product of the methanogenic pathway, contains a lot of energy and is therefore an ideal substrate for a wide range of methanotrophic organisms which constitute the biological CH4 sink. Methanotrophs occur in both the archaeal and bacterial domain, and several terminal electron acceptors can be used in the process. Anaerobic methanotrophic archaea (or ANME archaea) use the reverse methanogenesis pathway for CH4 activation and subsequent oxidation to carbon dioxide (CO2). Aerobic methanotrophic bacteria including the intra-aerobic “Candidatus Methylomirabilis sp.” species use oxygen and methane monooxygenases (MMOs) to activate CH4.
The aim of this thesis was to investigate the interplay between CH4 producing and consuming organisms of the microbial CH4 cycle in a warming world. It is important to investigate climate impacts, since the balance between methanogens and methanotrophs determines the CH4 fluxes into the atmosphere. In turn, this largely determines the greenhouse gas (GHG) potential of an ecosystem, mainly due to the significantly higher climate impact of CH4, which has a 34-fold higher warming potential than CO2. To assess environmental impacts such as warming and increased nutrient availability, their effects on the microbial CH4 cycle, their interactions, and net GHG fluxes within a variety of manmade and natural methanogenic ecosystems were studied.
