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

215SMP004Physiological constraints of microbial electron shuttling frombacteria via redox-active humic substances to poorly solubleFe(III) mineralsN. Rohrbach* 1 , M. Obst 2 , A. Kappler 11 University of Tuebingen, Geomicrobiology, Tuebingen, Germany2 University of Tuebingen, Env. Analytical Microscopy, Tuebingen,GermanyMicrobial redox processes in soils and sediments impact biogeochemicalcycling of elements and nutrients and are controlled by the availability ofdifferent electron acceptors. Reduction of Fe(III) poses a challenge tomicrobes, since Fe(III) is present at neutral pH in form of poorly solubleminerals. However, Fe(III)-reducing bacteria are known to overcome thissolubility problem and several mechanisms have been suggested forelectron transfer from the outer membrane to the surface of the ferric(oxyhydr)oxides: (i) direct electron transfer from outer membrane c-typecytochromes requiring direct cell-mineral contact, (ii) indirect reduction ofFe(III) via solubilization of the Fe(III) by organic chelators and uptake andreduction of the Fe(III) in the cell, or (iii) indirect reduction of the Fe(III)minerals via electron shuttles such as dissolved or solid-phase humicsubstances (HS) (Konhauser et al., 2011). HS are ubiquitous in theenvironment and can be used by a variety of microbes as electron acceptoras well as electron mediator to transfer electrons from the cell to otherelectron acceptors. However, it is currently unknown whether bothmineral-surface-associated and planktonic cells benefit from HS aselectron mediators and how microbes, minerals and HS are spatiallyarranged as a function of cell density.We studied the extent of microbial reduction of the Fe(III) mineralferrihydrite [Fe(OH) 3] by Shewanella oneidensis strain MR-1 at differentconcentrations of cells in the presence and absence of HS. As expected,HS stimulated Fe(III) reduction in high-cell-number systems in whichexcess planktonic cells transfer electrons via dissolved HS to the Fe(III)mineral surface that is otherwise inaccessible to them. Unexpectedly, wefound that the presence of HS also stimulated Fe(III) reduction in low-cellnumbersystems where all cells present had direct access to the mineralsurface. This suggests that even small spatial gaps between electronreleasingcell-surface proteins and the mineral surface can be bridged viaredox-active HS. Confocal laser scanning microscopy (CLSM) was used toimage cell-mineral-HS-aggregates and to visualize how the microbial cellswere distributed in the setups. These results emphasize the relevance of HSin biogeochemical redox processes in soils and sediments.Konhauser, K.O., Kappler, A., Roden, E.E. (2011) Iron in microbial metabolism. Elements, 7, 89-93.SMP005Studying colonization on stone surfaces by a model biofilm ina flow-through chamber approachF. Seiffert* 1 , A. Friedmann 2 , A. Heilmann 2 , A. Gorbushina 11 Federal Institute for Materials Research and Testing, 4.0: Model Biofilmsin Materials Research, Berlin, Russian Federation2 Fraunhofer Institute for Mechanics of Materials IWM, Department ofBiological and Macromolecular Materials, Halle, GermanySoil formation on weathering rock surfaces is intrinsically connected withprimary microbial colonization at the atmosphere-lithosphere interface.Rock-inhabiting life is ubiquitous on rock surfaces all around the world,but the laws of its establishment, and more important, quantification of itsgeological input are possible only in well-controlled and simplifiedlaboratory models. In a previous study [1] a model rock biofilm consistingof the heterotrophic black yeast Sarcinomyces petricola and thephototrophic and nitrogen-fixing cyanobacterium Nostoc punctiforme wasestablished.In the present work the growth of this model biofilm on diverse materialswith different physical and chemical properties was investigated underwell controlled laboratory conditions. To clarify the role of environmentalfactors, the parameters temperature, light intensity, CO 2 content andrelative humidity were varied in growth test series. For an acceleratedstone colonization and to increase the biomass yield different flow-throughchamber systems with semi-continuous cultures have been applied,simulating weathering conditions like flooding, desiccation and nutrientinput. The biofilm development was studied by (i) light and electronmicroscopy and (ii) qualitatively and quantitatively with respect to cellforms and biomass. Mixed and single cultures of the model biofilmprotagonists were compared to elucidate possible growth influencingeffects by the respective symbiotic partner.Under the mentioned environmental conditions two types of flow-throughchambers have been applied (i) with a neutral growth supportingmembrane and (ii) including mineral materials to explore possible rocksurface colonization. The first flow-through chamber type is directlyobservable under the light microscope and can be divided into twocompartments via a semi-permeable membrane allowing co-cultivation ofsingle cultures and a regular control of their cell morphology. With thissystem it is possible to determine if a metabolite exchange between themodel biofilm partners is sufficient for the symbiosis or if there is a needfor a direct cell-cell-contact. Possible biologically induced mineral surfacealterations were followed on various rock substrates exposed in the secondflow-through chamber system.[1] A.A. Gorbushina and W.J. Broughton (2009). Annu. Rev. Microbiol.63: 431-450.SMP006Composition of methanogenic archaea of the El’gygytgynCrater Lake NE-SiberiaJ. Görsch*, J. Griess, D. WagnerAWI, Potsdam, Potsdam, GermanyArctic lakes are an important source of methane, which has a 26 timesstronger greenhouse gas effect than CO 2. An increase of abundance andsurface of North Siberian lakes has lead to a rise of methane emission upto 58% from 1974 to 2000 [1]. Nevertheless, the knowledge about methanedynamics in arctic lakes and methanogenic archaea in deeper sedimentdeposits is still limited.To deepen the understanding of methane dynamics in arctic lakes, amolecular biological characterization of methanogenic archaea was carriedout in 10.000 to 400.000 years old sediment deposits of the El’gygytgynCrater Lake drilled in scope of the ICDP-project ‘Scientific Drilling inEl’gygytgyn Crater Lake’ [2]. Archaeal DNA was successfully amplifiedthroughout deposits of Middle and Late Pleistocene as well as Holocene.Furthermore, on the base of 16S rRNA, denaturing gradient gelelectrophoresis and clone libraries of selected samples showed a diversityof methanogens affiliated with Methanosarcinales, Methanocellales andMethanomicrobiales. The methanogenic diversity strongly variedthroughout the sediment depths with two areas of high diversity in 250.000and 320.000 years old sediments. Additionally, a positive correlationbetween the diversity and the amount of organic carbon was discovered.Application of propidium monoazide helped to distinguish between viablecells and free DNA and showed that a great proportion of amplified DNAcame from intact cells. The oldest living archaea was isolated out of390.000 years old sediment deposits. Moreover, a higher methaneproduction rate was detected in areas of high diversity. Conclusively,methanogenic archaea are able to survive in a metabolic active stage overhundreds of thousand years under lake conditions. As the temperature ofdeeper lake sediments is rising in the context of climate change, it is to beexpected that their activity and consequently the methane emission willincrease. Summarising the results give valuable insights in the methanedynamic in deeper sediment deposits and confirm the influence of oldcarbon source to positive feedback loop of climate change.[1] K.M. Walter et al., Nature 443 (2006), p. 71-75.[2] M. Melles et al., Scientific Drilling 11 (2011), p. 29-40.SMP007Population analysis and Fluorescence in situ Hybridisation ofaerobic chloroethene degrading bacteriaT. Teutenberg* 1 , S. Kanukollu 1 , S. Mungenast 2 , A. Tiehm 2 , T. Schwartz 11 KIT Campus North, IFG, Microbiology of Natural and TechnicalInterfaces Department, Eggenstein-Leopoldshafen, Germany2 DVGW - Water Technology Center (TZW), Department of EnvironmentalBiotechnology, Karlsruhe, GermanyChloroethenes are a major source of groundwater and soil contamination.Several mixed cultures and pure bacterial strains, which grow underanaerobic conditions using chloroethenes as electron acceptor in additionto auxiliary substrates, have been published and examined in regard toapplication as bioremediation agent. However, aerobic microorganismsthat use the target pollutant like vinyl chloride (VC) as growth substratewould be favourable for bioremediation processes.This study has the aim to identify microorganisms involved in aerobicdegradation of chloroethenes to use them for bioremediation ofcontaminated sites.Different species were identified via 16S-rRNA PCR-DGGE experimentsusing eubacterial primers and subsequent sequence analysis using BLASTof the NCBI database. Based on these results species specific primers forPCR and specific gene probes for fluorescence in-situ hybridisation (FISH)were designed.According to the sequence analysis results, five different species, whichbelong to the ß-proteobacteria sub-family, were identified in metabolicchloroethene degrading batch cultures inoculated with ground watersamples of contaminated sites. Focussing on these species, conventionalPCR approaches with specific primers were performed.FISH analysis can determine the presence of the specific bacteria insamples from the contaminated site using the previously designed geneprobes. For that, a preceding treatment regarding the cell wall permeabilitywas established and the hybridization conditions were optimized for eachFISH probe. To verify the quality and specificity of the gene probesdifferent reference bacteria were used as positive and negative control.Quantitative PCR experiments targeting possible candidate genes forchloroethene biotransformation will be performed for molecularcharacterization of aerobic decontamination processes.BIOspektrum | Tagungsband 2012