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

217substrates as carbon sources. Within the German BiodiversityExploratories project we focus on functional interrelations betweenAcidobacteria and land use. Six extensively managed sites from theExploratories Schwäbische Alb, Hainich-Dün, and Schorfheide-Chorin,one grassland and one woodland soil per exploratory, were selected for ahigh throughput cultivation approach. Microtiter plates were inoculatedwith 10 and 50 cells per well, respectively, using five media atin situpH.The media tested contained (i) highly diluted carbon sources (HD1:10), (ii)low amounts of sugars, fatty acids, and amino acids (C-Mix), (iii) solublehumic acids (e.g., sodium salicylate, furfural, phthalic acid), (iv) insolublehumic acids (e.g., quercetin, coumestrol, solanine), and (v) a mix ofpolymeric substrates (e.g., chitin, pectin, cellulose). Culturability of totalaerobes ranged from below 0.2% (Schorfheide-Chorin, grassland, solublehumic acids) to 9.2% (Schwäbische Alb, woodland, HD1:10).Acidobacteria-positve wells were identified via a specific PCR approach.The percentages of cultured Acidobacteria among all cultured Bacteriaranged from 0% (Schorfheide-Chorin, woodland, polymeric substrates) to19.5% (Schwäbische Alb, woodland, polymeric substrates). TheAcidobacteria recovered were affiliated with sd 1, 3, 4, and 6. Inpolymers-supplemented media, only representatives of sd 1 were detected.In contrast, most members of sd 6 Acidobacteria were cultivated in C-mixmedium. For both, total aerobes and Acidobacteria, cultivation successwas highest with media containing easily available carbon sources,indicating that low amounts of these substrates favor growth of soilbacteria, in particular Acidobacteria.Characterization of novelAcidobacteria as relevant members of the soil microbial community willimprove our knowledge about biogeochemical cycling in soils.SMP014Carbon Isotope Fractionation of Italian Rice Field Soil underH 2 /CO 2 and different temperature regimes.M. Blaser*, R. ConradMax-Planck-Institute for terrestrial microbiology, biogeochemistry,Marburg, GermanyIn anoxic environments organic matter is fermented to short chain fattyacids, alcohols as well as CO 2 and H 2. The two gaseous products can befurther converted to either methane by methanogenic archaea or to acetateby acetogenic bacteria. Methanogenesis is energetically more favourablethan acetogenesis. Nevertheless acetogens can outcompete methanogens atlow temperatures. To investigate the contribution of both processes weincubated anoxic rice slurry under H 2/CO 2 at 15°, 30° and 50° C andfollowed the isotopic signatures of the carbon compounds (CO 2, CH 4,acetate) by mass spectrometry. For better differentiation of the twoprocesses a second incubation was performed with bromoethanesulfonatean inhibitor of methanogenesis.SMP015Methanogens at the top of the worldK. Aschenbach* 1 , R. Angel 1 , K. Rehakova 2 , K. Janatkova 2 , R. Conrad 11 Max-Planck-Institute for terrestrial microbiology, biogeochemistry, Marburg,Germany2 Institute of Botany As CR, Trebon, Czech RepublicDeserts (semiarid, arid and hyperarid regions) cover around one third ofthe Earth´s surface. Desert soils are typically covered by a unique layertermed biological soil crust (BSC), a few millimetres thick and denselycolonized by microorganisms. During dry periods the BSC is mostlyinactive, but following wetting the microbial activity increases and oxygenbecomes limiting. It was previously shown that BSC from hot deserts canthen produce methane (1). We wanted to investigate whether thisphenomenon can also be observed in high-altitude cold deserts in theHimalayas (Ladakh, India). For this purpose, soil samples from threedifferent vegetation zones: semiarid, steppe, and subglacial, as well asfrom front and lateral moraines of a receding glacier were collected andtested for the production of methane.We incubated 5 g soil with 5 ml water at 25 °C under anoxic conditionsand followed up gas production (CH 4, CO 2 and H 2) and the isotopicsignature of the carbon in the CH 4 and CO 2. Almost each sample from thevegetation zones produced methane, and also some from the morainetransects. Methane production was faster in the BSC compared to thedeeper soil layers, demonstrating that most methanogens are likely to beconcentrated at the top layer. The isotopic analysis showed that methaneprobably developed from both acetate and CO 2 with no significantdifference between the layers. Our results demonstrate the existence of anactive methanogenic community even at such extreme oxic environment.1. Angel R, Matthies D, Conrad R (2011) Activation of Methanogenesis in Arid Biological SoilCrusts Despite the Presence of Oxygen. PLoS ONE 6(5): e20453SMP016Community analyses of fermentative hydrogen producers inenvironmental samplesO. Schmidt*, M.A. Horn, H.L. DrakeUniversity of Bayreuth, Department of Ecological Microbiology, Bayreuth,United StatesFermenters produce Hydrogen (H 2) to excrete excess reductant.Fermentative H 2 production is catalyzed by either [FeFe]-hydrogenases(e.g., during butyrate fermentation of Clostridium butyricum) or Group 4[NiFe]-hydrogenases (e.g., during mixed acid fermentation of Escherichiacoli). Similarity correlations between in silico translated amino acidsequences from publicly available hydrogenase genes and corresponding16S rRNA genes showed that closely related hydrogenases (i.e., 80%amino acid sequence similarity) belonged to host organisms within thesame family. However, due to gene duplication and subsequentdiversification, distantly related hydrogenases did not necessarily belong tohosts of different families. Degenerate primers targeting [FeFe]- andGroup 4 [NiFe]-hydrogenase genes were developed to identify potentiallyactive hydrogen producers in environmental samples. [FeFe]-hydrogenasegene sequences obtained from a methane emitting fen were affiliated to theClostridia, Alpha- and Deltaproteobacteria, Chloroflexi, Bacteroidetes,Verrucomicrobia and Negativicutes. Group 4 [NiFe]-hydrogenase genesequences obtained from H 2-emmiting earthworm gut content wereaffiliated to the Gammaproteobacteria, Clostridia and Verrucomicrobia.These results demonstrated that the new hydrogenase primers are usefulfor the detection of a wide range of [FeFe]- and Group 4 [NiFe]-hydrogenases in environmental samples and that 80% amino acid sequencesimilarity is a reasonable cut-off to group hydrogenases from fermentativehydrogen producers on the family level.SMP017Electrochemical Quantification of Microbial Humic SubstanceReductionA. Piepenbrock* 1 , M. Sander 2 , A. Kappler 11 University of Tuebingen, Geomicrobiology, Tübingen, Germany2 ETH Zurich, Institute of Biogeochemistry and Pollutant Dynamics,Zurich, SwitzerlandHumic substances (HS) are ubiquitous in soils, sediments and waters andhave been shown to shuttle electrons between microorganisms and poorlysoluble electron acceptors such as Fe(III) minerals. Since HS can bereduced by a variety of microorganisms including Fe(III)-reducing,sulfate-reducing and dechlorinating bacteria, but also chemically forexample by sulfide, electron transfer via HS has the potential to contributesignificantly to the electron fluxes in the environment. While microbial HSreduction has been studied for a variety of different HS andmicroorganisms, these results were semi-quantitative due to indirectquantification of HS redox states.We quantitatively followed the microbial reduction of HS of differentorigin (soil, peat, and aquatic) by the dissimilatory Fe(III)-reducingbacterium Shewanella oneidensis MR-1 using mediated electrochemicalreduction and oxidation. Microbial HS reduction resulted in a decrease inthe number of electrons that could be transferred to the HSelectrochemically (electron accepting capacity, EAC) and in a concomitantincrease in the number of electrons donated from the same HS to theworking electrode (electron donating capacity, EDC). Thus, microbial HSreduction could be shown and the amount of electrons transferred from themicrobes to the HS could be quantified over time. Aeration of the cultureswith air resulted in an increase in the EAC and a decrease in the EDC,indicating the re-oxidation of the previously reduced moieties in the HS.Subsequently, the HS were re-reduced by the bacteria as could be seen in adecrease in the EAC and increase in the EDC. These findings demonstratethe reversibility of the microbial HS reduction. Throughout the entireexperiment, the sum of EAC and EDC remained constant, demonstrating thatmicrobial reduction did not alter the total number of redox active moieties in theHS. Overall, our results provide important new quantitative insights into theextent of microbial HS reduction and give new indications about thesignificance of this process in environmental systems: HS redox reactions cancontribute significantly to the (trans)formation of iron minerals and the(im)mobilization and reductive degradation of organic and inorganic pollutantsand to the redox buffer capacity of systems such as peats.SMP018Biogeography of soil Burkholderia populationsN. Stopnisek* 1 , N. Fierer 2 , L. Eberl 1 , L. Weisskopf 11 University of Zurich, Institute of Plant Biology, Department ofMicrobiology, Zurich, Switzerland2 University of Colorado, Department of Ecology and EvolutionaryBiology, Boulder, CO, USA, United StatesThe genus Burkholderia is an important component of soil microbialcommunities and comprises over 60 species. Burkholderia species have aBIOspektrum | Tagungsband 2012