MICROBIAL DIVERSITY AS A CONTROLLING FACTOR OF AEROBIC METHANE CONSUMPTION

Abstract

Background. Aerobic methane oxidizing bacteria (MOB) play a vital role in the global climate by degrading the greenhouse gas CH4. The process of CH4 consumption is sensitive to disturbance leading to strong variability in CH4 emission from ecosystems. Mechanistic explanations for variability in CH4 emission from soil and sediment ecosystems may be found in the diversity and ecology of these microbes. The objective of the presented work is to link the community composition and ecology of these microbes to the environmental variability observed in CH4 consumption. Methods. Methane consumption was investigated in a river floodplain along the river Rhine. Methane oxidation kinetics were determined in vitro in slurry incubations as well as on intact cores. Methanotrophic community composition was assessed using pmoA-based micro array and QPCR on mRNA as well as DNA. Stable isotope probing (SIP) of lipids and mRNA was applied to detect the active methanotrophic species. Results. The flooding regime in the Rhine floodplain established a distinct CH4 consumption pattern with a maximum exactly in the part of the floodplain between permanently and irregularly flooded sites. This pattern was mirrored by the MOB community composition. Diversity index as assessed by micro array and activity components (initial consumption, Vmax, Vmax/Km) were positively correlated. These analyses as well as SIP showed that -proteobacterial MOB were responsible for the observed kinetics with a distinct optimum in the gradient whereas α-proteobacterial MOB increased with decreasing flooding intensity. Conclusion. In general it can be concluded that the environmental disturbances shaped the CH4-consuming microbial community leading to differential eco-distribution of MOB. The relative abundance of specific subgroups controlled CH4 consuming activity which makes it evident that knowledge on the microbial community composition is necessary to predict effects of environmental change on methane cycling