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

218broad distribution in nature, occurring commonly in soil and in associationwith plants, fungi and animals, where mutualistic as well as parasiticinteractions can be found. The importance of Burkholderia species asopportunistic pathogens (e.g. in cystic fibrosis patients) is increasinglyrecognized and the molecular mechanisms underlying virulence have beenextensively studied. However, little is known so far about the abundance,the diversity and the biogeography of the genus Burkholderia in naturalenvironments such as soils. Reports from the literature indicate thatBurkholderia species are often isolated from acidic environments, whichsuggests that pH could be an important factor in shaping the biogeographyof Burkholderia. To assess this question, 46 soil DNA samples collectedacross North and South America were used (Fierer and Jackson, 2006). Aspecific real time PCR protocol targeting Burkholderia 16S rRNA genewas developed to analyse the relative abundance of Burkholderia sp. inthese soil samples. Results suggest that pH has a significant effect onBurkholderia relative abundance in soils: the highest relative abundancewas observed in soils ranging between pH 5 and pH 6 where up to 6.7 %of total bacterial 16S rRNA genes were represented by Burkholderiaspecies. Lower pH soils also showed high relative abundance ofBurkholderia (up to 2.8%). However, Burkholderia 16S rRNA copynumbers were not detected in alkaline soils. We are currently investigatingthe diversity of Burkholderia in a subset of 15 selected sites varying in pH,C:N ratio, location of sampling and relative abundance of Burkholderia.This will allow us to better understand which populations are particularlyaffected by pH and which other factors are shaping the abundance, thediversity and the biogeography of soil Burkholderia species.1. N. Fierer and R.B. Jackson, The diversity and biogeography of soil bacterial communities,PNAS,103(2006), p. 626-631.SMP019Characterization of microbial dehalogenation using compoundspecific stable isotope analysisJ. Renpenning*, J. Kaesler, I. NijenhuisHelmholtz Centre for Environmental Research - UFZ, Department ofIsotope Biogeochemistry, Leipzig, GermanyChlorinated ethenes are the most common soil and groundwatercontaminants worldwide. Technical application of tetra- andtrichloroethenes (PCE, TCE) in the dry cleaning industry and metaldegreasing resulted in big scale production and release in the environment.Chloroethenes are an issue of serious risk for human health and suspectedto be carcinogenic. During the last decade several bacterial strains wereisolated from contaminated soil and groundwater capable of reductivedehalogenation of chlorinated ethenes. However, the actual reactionmechanism and the involved genes responsible for specific dehalogenationare still a point of interest.We aim to investigate and characterize the reductive dehalogenationreaction in several strains, using stable isotope techniques. Compoundspecific stable isotope analysis can be used to analyze the reactionmechanism and degradation pathway. Previously, we observed that thecarbon stable isotope fraction was highly variable when comparingdifferent strains capable of the reductive dehalogenation of the chlorinatedethenes [1]. These differences may either be due to differences in enzymemechanism or to e.g. rate limiting effects and substrate uptake processes asobserved for Sulfurospirillum multivorans and Desulfitobacteriumsp. strainPCE-S [2]. Our preliminary experiment have shown that rate limitationdoes not appear to play a role in Dehalobacter restrictus and that highlysimilar enzymes, although present in different organisms i.e. D. restrictusand Desulfitobacterium sp. PCE-S, produced similar isotope effects,contrary to previous publications. Further studies should allow analysis ofthe causes for different isotope fractionation of the chlorinated ethenes byother bacteria such as Geobacter or Desulfuromonas.Acknowledgement: This work is supported by the DFG (research unit FOR1530)1. Cichocka, D., et al.,Variability in microbial carbon isotope fractionation of tetra-and trichloroethene uponreductive dechlorination.Chemosphere, 2008.71(4): p. 639-648.2. Nijenhuis, I., et al.,Stable isotope fractionation of tetrachloroethene during reductive dechlorination bySulfurospirillum multivorans and Desulfitobacterium sp. strain PCE-S and abiotic reactions withcyanocobalamin.Applied and Environmental Microbiology, 2005.71(7): p. 3413.SMP020Abundance, distribution, and activity of Fe(II)-oxidizing andFe(III)-reducing microorganisms in hypersaline sediments ofLake Kasin, Southern RussiaM. Emmerich*, A. Bhansali, T. Lösekann-Behrens, C. Schröder, A. Kappler,S. BehrensCenter for Applied Geosciences, Geosciences, Tübingen, GermanyThe extreme osmotic conditions prevailing in hypersaline environmentsresult in decreasing metabolic diversity with increasing salinity. Variousmicrobial metabolisms have been shown to occur even at high salinity,including photosynthesis, sulfate and nitrate reduction. However,information about anaerobic microbial iron metabolism in hypersalineenvironments is scarce. We studied the phylogenetic diversity, distribution,and metabolic activity of iron(II)-oxidizing and iron(III)-reducing bacteriaand archaea in iron-rich salt lake sediments (Lake Kasin, Southern Russia;salinity 348.6 g L -1 ) using a combination of culture-dependent and-independent techniques. 16S rRNA gene clone libraries for Bacteria andArchaea revealed a microbial community composition typical forhypersaline sediments. Most probable number experiments and enrichmentcultures confirmed the presence of microbial iron(II) oxidation andiron(III) reduction in the salt lake sediments. Microbial iron(III) reductionwas detected in the presence of 5 M NaCl, thereby extending the naturalhabitat boundaries for this important microbial respiratory process.Quantitative real-time PCR showed that 16S rRNA gene copy numbers oftotal Bacteria, total Archaea, and species dominating the iron(III)-reducingenrichment cultures (relatives of Halobaculum gomorrense, Desulfosporosinuslacus, and members of the Bacilli) were highest in an iron oxide-rich sedimentlayer. Combined with the presented geochemical and mineralogical data, ourfindings suggest the presence of an active microbial iron cycle at saltconcentrations close to the solubility limit of NaCl.SMP021Microbial, geochemical, and mineralogical contributions toarsenic removal from drinking water in house hold sand filtersin VietnamA. Bhansali*, K. Nitzsche*, A. Kappler, S. BehrensCenter for Applied Geosciences, Geosciences, Tübingen, GermanyWorldwide more than 100 million people ingest detrimental concentrationsof arsenic by consuming groundwater contaminated from natural geogenicsources. Many Asian countries, in particular Vietnam, Bangladesh, India,and Cambodia are known to be affected by high groundwater arsenicconcentrations as a result of chemically reducing aquifer conditions.Household sand filters are simple to operate and remove on average 80%of arsenic from groundwater containing 1 mg/L of ferrous iron or aniron/arsenic ratio of about 50. The installation and operation costs ofhousehold sand filters are low and the construction materials are locallyavailable. The filters can treat a reasonable amount of groundwater withina short time and they can easily be installed by the affected communities.Oxidation of dissolved iron present in the groundwater leads to theformation of sparsely soluble iron(hydr)oxide particles in the sand filters,which bind negatively charged arsenic species and reduce arsenicconcentrations in the water. Although household sand filters have beenproven to be an effective technical solution for mitigating arsenicexposure, not much is known about microbial iron, manganese, arsenicredox-processes occurring in the filters and their effect on filter efficiency.Therefore, one of the goals of this study was to isolate, identify, andquantify Fe, Mn, and As-oxidizing and -reducing microorganisms from aarsenic removal sand filter and to study their specific Fe, Mn, and Asredox activities. Water samples and filter solids were collected from alocal sand filter close to the city of Hanoi, Vietnam. The samples weregeochemically and mineralogically characterized. Total iron, arsenic,manganese, and phosphate concentrations, pH, TOC, TIC measurements,as well as total cell counts were performed on samples from various depth ofthe sand filter. Most probable number counts confirmed the presence andactivity of various iron, manganese, arsenic redox-processes and theirdistribution within the water filter. The goals of this research project are tobetter understand the microbial redox transformation processes that drivearsenic/manganese/iron mineral interactions in household sand filters and togive recommendations for improved filter use and filter material disposal.SMP022Impact of Biochar Amendment on Microbial Nitrogen-Cyclingin Agricultural SoilS. Schüttler*, N. Hagemann*, J. Harter, H.-M. Krause, A. Kappler, S. BehrensCenter for Applied Geosciences, Geosciences, Tübingen, GermanyN 2O is a major greenhouse gas (GHG) contributing 8% to global GHGemissions with agricultural sources representing 84% of anthropogenicN 2O emissions. N 2O is a product of microbial denitrification and itsformation is correlated to fertilizer use. Soil biochar amendment has beenobserved to decrease soil N 2O emissions. Biochar is a stable, carbon richproduct that is manufactured by thermal decomposition of organic materialunder limited oxygen supply. Although the effect of biochar on nitrousoxide emissions from soil has been studied previously the mechanismsbehind the reduced N 2O emission from biochar amended soil are not yetunderstood. We investigated whether the decrease in N 2O emissionscaused by biochar amendment is due to changes in the functionalcomposition of the nitrogen-cycling microbial community. For this reasonagricultural soil was incubated in microcosms with different amounts ofbiochar under oxic (60% WFPS - water filled pore space) and anoxic(100% WFPS) conditions over a period of 3 month. Copy numbers ofdifferent functional genes involved in the microbial nitrogen cycle werequantified by real-time PCR. Gene abundance and expression werecorrelated to N 2O, CO 2, CH 4 emissions as well as soil NH + -4 , NO 2 and-NO 3 concentrations. Differences in microbial respiration rates in thepresence of various nitrogen compounds in the treatments with andwithout biochar were quantified in BIOLOG assays. Our experimentsBIOspektrum | Tagungsband 2012