VAAM-Jahrestagung 2011 Karlsruhe, 3.–6. April 2011

mobilized via leaching processes driven by AMD and microbial leachingwith Acidithiobacillus ferrooxidans. During the leaching process, theleachate percolated through the isolation layer and contaminated theunderground with mobilized heavy metals and salts.After removal of the heap material, the salt and heavy metal rich sedimentled to a pH in the range of 3 to 4,5, while the content of organic matter isvery limited. As a result, an obvious decrease in numbers of cfu per gramsoil of 100 to 1000fold was observed in comparison to an uncontaminatedsoil. The test field Gessenwiese was installed in 2001. Three large plots wereprepared with different treatments: 5cm topsoil, 5cm compost or noamendment as control are investigated.To understand the interdependencies between affecting conditions and toinvestigate the influence of heavy metals, the population dynamics andgrowth characteristics of single isolates were studied including bothcultivation-dependent and DNA-based fingerprinting methods. Plating,strain isolation, direct cell counts and respiration measurements were used toestablish surface and vertical profiles at the heavy metal contaminated fieldsite to follow microbial diversity over time. 16S rDNA libraries wereprepared at different time points to observe changes in communitycomposition.EMP090Spatiotemporal patterns of microbial communities in ahydrologically dynamic alpine porous aquifer(Mittenwald, Germany)Y. Zhou*, C. kellermann, C. GrieblerGroup of Microbial Ecology, Institue of Groundwater Ecology, HelmholtzCenter, Munich, GermanyFollowing the working hypothesis that microbial communities ingroundwater are driven by the prevailing hydrological dynamics, a porous‘pristine’ groundwater ecosystem in the alpine Isar River valley nearMittenwald (Germany) was investigated with respect to spatiotemporalpatterns of suspended and attached microbial communities. Characterized bya very high hydraulic conductivity and groundwater flow velocities ofseveral meters per day, the aquifer underlies strong seasonal hydrologicaldynamics mainly governed by precipitation events and snow melting. In atwo-year study, water collected from the Isar River and groundwater wassampled from 4 selected monitoring wells varying in its distance to theRiver. The bacterial abundance in groundwater ranged from 1.1 - 8.0 ×10 4cells mL -1 and only 0.1% to 5.6% of the total cell numbers were found asviable counts (CFUs) on R2A agar plates. Water from the Isar Rivergenerally revealed higher total cell counts. The proportion of activemicrobial biomass in river and groundwater, determined via ATP analysis,was highest in spring and autumn. Bacterial carbon production determinedby the incorporation of [ 3 H]-leucine into cell biomass was found extremelylow in the pristine groundwater, ≤ 0.3 μg C L -1 h -1 , revealed that bacterialactivity in groundwater becomes more pronounced in relation to river waterin summer. This carbon production is related to concentrations of AOC(assimilable organic carbon) of only 5 to 20 μg L -1 , accounting for 0.1 to1.3% of the DOC. The highest concentration of AOC went along with thehighest proportion of active biomass. Bacterial community fingerprinting viaT-RFLP analysis showed that community structure in terms of dominatingspecies/groups in groundwater significantly changed with season. Thebacterial diversity was highest in spring and lowest in summer. In contrary,bacterial communities on natural sediments from the Isar River exhibitedstable community patterns over the time period of several months whenexposed to groundwater in monitoring wells. This leads us to thepreliminary conclusion that groundwater bacterial communities in suchhighly dynamic aquifers are strongly determined by the origin of waterrecharged to the aquifer. The enormous amounts of water from snow meltingin spring, which passes the investigated aquifer in summer, result in a severedecline in ‘visible’ bacterial diversity. Bacterial communities are thendominated by only a few species/groups (T-RFs). In autumn the systemreturns to more microbiologically stable conditions.EMP091The epoxide antibiotic produced by Pantoea agglomeransand its function in the biocontrol of bacterial plantpathogensU. Sammer* 1 , D. Spiteller 2 , B. Völksch 11 Institute of Microbiology, Department of Microbial Phytopathology,Friedrich-Schiller-University, Jena, Germany2 Max Planck Institute for Chemical Ecology, Jena, GermanyThe strain Pantoea agglomerans 48b/90 (Pa48b) attracted our attentionbecause of its ability to inhibit the growth of important bacterial plantpathogens (i.e. Erwinia amylovora, Pseudomonas syringae pathovars,Agrobacterium tumefaciens) and the human pathogen Candida albicans invitro. Bioassay-guided fractionation using anion exchange chromatographyand HPLC under HILIC conditions yielded the bioactive, highly polarantibiotic. This compound was identified as 2-amino-3-(oxirane-2,3-dicarboxamido)-propanoyl-valine (APV) and was first described for thisspecies (1). Similar structures were described for two actinomycete isolates,Streptomyces collinus (A19009) and Micromonospora sp. (Sch 37137), andfor Serratia plymuthica CB25-I. Structurally related molecules interact withthe fungal (and bacterial) glucosamine-6-phosphate synthase (GlmS) andblock the formation of N-acetylglucosamine, a key compound of thebacterial peptidoglycan and fungal chitin (2). Supplementation of ourminimal medium with N-acetylglucosamine indeed resulted in APVbecoming inactive against E. amylovora and Candida albicans suggestingthat APV acts as GlmS inhibitor. Interestingly, the formation of APV invitro is growth associated and strongly temperature dependent: its optimalproduction rate is between 8 °C and 12 °C. Therefore, we conducted plantexperiments at moderate and low temperatures. In addition, thecoinoculation of an APV-negative mutant with the bacterial plant pathogensshould highlight the role of APV within the biocontrol of the bacterial blightpathogen Pseudomonas syringae pv. glycinea and the fireblight pathogenErwinia amylovora. Surprisingly, independent from the temperatureconditions the difference in suppression of disease symptoms betweenwildtyp Pa48b and mutant was minimal.[1] Sammer et al (2009): Appl. Environ. Microbiol. 75, 7710-7717.[2] Milewski (2002): Biochimica et Biophysica Acta 1597, 173- 192.EMP092Towards an improved understanding of trophicconnectivities in belowground microbial food websD. Dibbern*, T.Institute of Groundwater Ecology, Helmholtz Center Munich, Neuherberg,GermanyThe flow of carbon and energy through natural systems is largely controlledby organisms engaged in complex trophic interactions. Although such foodwebs have been intensively studied for higher organisms, involved microbesare mostly treated as a black box. In the frame of the DFG FOR-918(„Carbon flow in belowground food webs assessed by isotope tracers”), weaim to open this black box and uncover the interactions between bacteria andother trophic levels of a soil food web depending on plant carbon inputs andchannelling carbon into deeper unsaturated and saturated zones. To trace thisorganismic food web from its origins, a model community of microbial plantexudate consumers was enriched from an agricultural soil at our fieldsampling site (a maize field in Göttingen) with an artificial mixture of 13 C-labelled root exudates as substrate. Subsequently, labelled indigenousbacterial biomass was added to mesocosms with the same soil and secondarymicrobial consumers were traced by rRNA-SIP.Already after one day of the inoculation, T-RFLP fingerprints of ‘heavy’rRNA revealed secondary microbial consumers of the added biomass to beactive. Over time,13 C-labelled microbial subpopulations varied andindicated a complex and dynamic food web to be active within the bacteria.For identification of labelled OTUs, selected rRNA fractions are analyzedby massively paralleled 454-pyrotag sequencing. We use bidirectionalsequencing of bacterial rRNA amplicons, which allows for assembly, T-RFprediction and phylogenetic placement of dominating amplicon contigs.Furthermore, pyrotag data from the SIP experiment are compared torespective field community data to link the identified trophic connectivitiesto C-turnover in the field. As next step (in progress), links to other membersof the belowground food web (Fungi, Protozoa) will be elaborated togetherwith our partners within FOR-918.spektrum | Tagungsband 2011