VAAM-Jahrestagung 2012 18.–21. März in Tübingen

211potential, and (ii) a highly diverse, nitrate limted denitrifier communityassociated with potential N 2O fluxes in a pH-neutral fen soil.SMV004Emission of Denitrification-derived Nitrogenous Gases byBrazilian EarthwormsP.S. Depkat-Jakob* 1 , G.G. Brown 2 , S.M. Tsai 3 , M.A. Horn 1 , H.L. Drake 11 University of Bayreuth, Ecological Microbiology, Bayreuth, Germany2 Embrapa Florestas, Colombo, Brazil3 University of São Paulo, Center of Nuclear Energy in Agriculture,Piracicaba, BrazilEarthworms are an abundant soil macrofauna. Small to medium sizedearthworms belonging to the family Lumbricidae emit the greenhouse gasnitrous oxide (N 2O) and dinitrogen (N 2) produced by ingested denitrifiyingsoil bacteria. The large earthworm Octochaetus multiporus(Megascolecidae) from New Zealand does not emit nitrogenous gases butits gut displays a high denitrification potential. To extend the knowledgeabout the emission of nitrogenous gases (i.e., N 2O and N 2) by earthworms,nine small, medium and large earthworm species belonging to the familiesGlossoscolecidae (Rhinodrilus alatus, Glossoscolex paulistus,Glossoscolex sp., Pontoscolex corethrurus), Megascolecidae (Amynthasgracilis, Perionyx excavatus), Acanthodrilidae (Dichogaster annae,Dichogaster sp.), and Eudrilidae (Eudrilus eugeniae) from Brazil wereanalyzed. All earthworm species except for G. paulistus and G. sp. emittedN 2O. Except for D. sp., acetylene greatly increased the emission of N 2Oindicating denitrification as the main source of N 2O. On a per worm basis,the up to 63 cm long R. alatus emitted the highest amounts of nitrogenousgases, primarily N 2 indicative of complete denitrification. Nitrite greatlystimulated the emission of N 2O and N 2 by A. gracilis and resulted in aminor emission of N 2O and N 2 by G. paulistus. Gut nitrate reducers anddenitrifiers of gut content and soil of G. paulistus (large) and A. gracilis(small) were analyzed via barcoded amplicon pyrosequencing with thestructural gene markers narG, nirK, and nosZ, encoding for a subunit ofthe nitrate reductase, nitrite reductase, and N 2O reductase, respectively.Gene sequences of narG, nirK, and nosZ in the gut and soil of G. paulistuswere highly similar. Sequences in gut and soil of A. gracilis weresignificantly different from each other and from gut and soil of G.paulistus. However, gene analysis indicated a soil derived nitrate reducinggut microbiota for both earthworms, mainly consisting of members of theRhizobiales. The collective results suggest that the emission of N 2O and N 2is a common feature of earthworms. It remains unresolved whether gutsize, feeding guild, or other factors contribute to the apparent inability ofG. paulistus to emit nitrogenous gases.SMV005Anaerobic methane oxidizers prevent methane emissions froma minerotrophic peatlandB. Zhu 1 , G. van Dijk 2 , C. Fritz 2 , M.S.M. Jetten 1 , K.F. Ettwig* 11 RU, IWWR, Dept. of Microbiology, Nijmegen, Netherlands2 RU, IWWR, Dept of Aquatic Ecology, Nijmegen, NetherlandsFreshwater sediments which receive nitrate fluxes from agricultural runoffand methane from methanogenesis theoretically provide ideal conditionsfor the recently discovered process of anaerobic methane oxidationcoupled to denitrification. Methylomirabilis oxyfera, the responsiblebacterium, employs a novel pathway, whereby N 2 and O 2 are formed fromnitrite without N 2O as an intermediate; the oxygen is then used in thecanonical aerobic methane oxidation pathway [1]. To further ourunderstanding of the role of M. oxyfera in the environment, we determinedmethane and nitrate depth profiles in a minerotrophic peatbog duringseveral seasons. Methane was depleted before reaching the oxic zone, andthe depth where nitrate and methane coexisted displayed anaerobicmethane oxidation activity. As measured by quantitiative PCR, alsobacteria related to M. oxyfera were most abundant in this depth. It wassubsequently used as an inoculum for an anaerobic, methanotrophicenrichment culture, using in situ water with nitrite and nitrate as electronacceptors and a pH of 6.2. During incubation, methane oxidation andnitrite conversion were regularly monitored. Stable-isotope experimentsshowed that nitrite was preferred over nitrate, and methane oxidationceased without either electron acceptor. FISH microscopy and PCRamplification of the 16S rRNA (95% similarity) and particulate methanemonooxygenase (pmoA) gene (90% similarity) revealed that newMethylomirabilis-like bacteria had been enriched. Taken together, theseresults suggest that novel M. oxyfera-like bacteria are responsible formethane depletion in the anaerobic zone of the investigated peatland.[1] Ettwig et al. (2010) Nitrite-driven anaerobic methane oxidation by oxygenic bacteria. Nature 464, 543-548.SMV006Microorganisms affecting the stabilisation of soil organiccarbon in cryoturbated soils of the Siberian ArcticA. Gittel* 1 , J. Barta 2 , I. Lacmanova 2 , V. Torsvik 1 , A. Richter 3 , S. Owens 4 ,J. Gilbert 4 , C. Schleper 3,1 , T. Urich 31 University of Bergen, Bergen, Austria2 University of South Bohemia, Ceske Budejovice, Czech Republic3 University of Vienna, Vienna, Austria4 Argonne National Laboratory, Argonne, Illinois, United StatesPermafrost underlies ~26% of terrestrial ecosystems and is estimated tocontain around 50% of the world’s soil organic carbon (SOC). Asignificant proportion of this SOC is stored in the subducted organic matterof cryosols. SOC decomposition in cryosols is strongly retarded suggestingthat cryoturbation (= mixing of soil layers due to freezing and thawing)may be one of the most important mechanisms of Arctic carbon storageand long term stabilization. To eventually identify potential microbial keyfactors in the stabilization of SOC within cryoturbated soils, approximatelya hundred soil samples were collected from three different landscapes inthe East Siberian tundra (Cherskii, Northern Siberia; 69°N, 162°E).Samples covered organic topsoils, cryoturbated soils and its adjacentmineral horizons, and the underlying permafrost. Cryoturbated horizonsshowed similar soil characteristics as the topsoil horizons and were clearlydistinguishable from the subsoils. Bacterial and archaeal abundances incryoturbated horizons were found to be several orders of magnitude higherthan in the surrounding mineral soils. However, the relative reduction offungi in cryoturbations resulted in lower fungal:bacterial ratios comparedto the top- and subsoil. This might be a key factor for elevated SOCstabilisation and its retarded decomposition in cryoturbated layers.Community profiling on the Illumina GAIIx genome analyzer identifiedmembers of the Actinobacteria, Proteobacteria, Firmicutes and theVerrucomicrobia as the most abundant phyla. Additionally, phylogeneticanalyses revealed a community shift of potential indicator taxa andfunctional groups (e.g., Firmicutes, Desulfuromonadales) from the topsoilto the subsoil reflecting a change in redox conditions and a shift fromaerobic/microaerophilic to anaerobic microorganisms. The communitycomposition of cryoturbated soils was highly variable being rather similarto the subsoil or represent an intermediate stage from the top- to thesubsoil. This variability presumably reflected differences in the parent soil,age and history of the cryoturbation and the degrees of SOC stabilisation.SMV007Could bacterial residues be an important source of SOM? - acase study from a glacier forefieldC. Schurig* 1 , R. Smittenberg 2 , J. Berger 3 , F. Kraft 1 , S.K. Woche 4 , M.-O. Göbel 4 , H.J. Heipieper 1 , A. Miltner 1 , M. Kästner 11 Helmholtz Institute for Environmental Research - UFZ, EnvironmentalBiotechnology, Leipzig, Germany2 Stockholm University, Geological Sciences, Stockholm, Sweden3 Max Planck Insitute for Developmental Biology, Electron MicroscopyUnit, Tübingen, Germany4 Leibniz Universität Hannover, Insitute of Soil Science, Hannover,GermanyRecently, stocks of soil organic matter (SOM) have been shown to decrease inEuropean soils and also worldwide, which compromises soil fertility andenhances emissions of carbon dioxide and other, even worse green-house gases,to the atmosphere. However, the general structure of SOM, and thereby themechanisms behind its genesis and loss, remain unclear.In this framework, microbial biomass is generally regarded to be of lowimportance for SOM formation. In particular on freshly exposed surfaces,however, bacteria colonize barren mineral surfaces faster than fungi orhigher plants. Moreover, recent results indicate that bacterial cell wallfragments frequently occur on soil mineral surfaces and also accompanythe microbial colonization of previously clean and sterile activated carbonsurfaces after incubation in groundwater. Hence, we hypothesized that, atleast, in the initial stages of soil formation bacteria and their fragmentsmay play an important role in particulate SOM formation bearing in mindthat most dead organic matter entering the soil is processed by bacteria.This hypothesis was proven by tracing the development of SOM in achronosequence with samples from the forefield of a receding glacier(Damma-glacier, Canton Uri,Switzerland) by scanning electronmicroscopy and other methods. The initially barren mineral surfaces havebeen shown to be rapidly covered with microbial residues as soil ageincreases. Moreover, this data compares well to growing C/N-ratios, watercontact angles and fatty acid contents in earlier deglaciated samples.BIOspektrum | Tagungsband 2012