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

136OTV024Induction of systemic resistance in soybean by the antagonisticepiphyte Pseudomonas syringae 22d/93H. WeingartJacobs University Bremen, School of Engineering and Science, Bremen,GermanyThe use of naturally occurring antagonists to suppress plant diseases offersan alternative to classical methods of plant protection. The epiphytePseudomonas syringae 22d/93, isolated from a healthy soybean leaf,shows great potential for controlling P. syringae pv. glycinea, the causalagent of bacterial blight of soybean. Its activity against P. syringae pv.glycinea is highly reproducible even in field trials, and the antagonisticmechanisms involved are of our special interest. It has been proposed thatseveral attributes contribute to biocontrol, including antibiosis, competitionfor nutrients, niche exclusion, interference with cell signalling systems,and induction of systemic plant resistance.We used Affymetrix soybean genome arrays to examine transcriptionalchanges that occur in soybean leaves inoculated with the antagonist P.syringae 22d/93. If the antagonist is able to trigger plant defencemechanisms prior to infection by the pathogen, disease can be reduced.The resulting elevated state of resistance in plant parts distant from the siteof primary triggering is variably referred to as systemic acquired resistance(SAR) or induced systemic resistance (ISR). SAR is characterized by anearly increase in salicylic acid, which appears to be an essential signallingmolecule in the SAR pathway and by the accumulation of pathogenesisrelated(PR)-proteins. ISR is induced by non-pathogenic organisms, e.g.plant growth-promoting rhizobacteria and depends on the plant signallingmolecule jasmonic acid. Infiltration of soybean leaves with P. syringae22d/93 led to the up- or down-regulation of more than 2.800 genes,respectively, more than twofold as compared with control plants.Noteworthy, several genes encoding PR-proteins and genes involved inphytoalexin production were up-regulated, indicating that P. syringae22d/93 can induce SAR in soybean.OTV025Anaerobic denitrifying methane oxidation in a deep oligotrophicfreshwater lakeJ. Deutzmann*, B. SchinkUniversität Konstanz, Biology/Microbial Ecology, Konstanz, GermanyDenitrifying methane oxidation has first been described in 2006 for anenrichment culture originating from an eutrophic freshwater habitat.Bacteria of subgroup a of the NC10 phylum are proposed to carry out thisnovel process. However, nothing but scarce sequence information and onereport on denitrifying methane oxidation in a wastewater treatment plant isavailable on the distribution of this process and the respective bacteria inthe environment.To assess the importance of denitrifying methane oxidation in naturalhabitats, we investigated the occurrence of this process and the distributionof the respective NC10 bacteria in sediments of Lake Constance.Radiotracer experiments were performed to track the process in littoral andprofundal sediments and the diversity of NC10 bacteria was analyzedusing molecular methods.Denitrifying methane oxidation was reliably detected only in profundalsediments, but rates were about 20 times lower than aerobic methaneoxidation rates in these experiments. After those indications for a spatialdistribution pattern of this process, the community composition anddistribution of NC10 bacteria were investigated in greater detail and athigher spatial resolution. NC10 bacteria of group a, the denitrifyingmethanotrophs, were not detectable in Lake Constance sediments atshallow water sites (80 m), indicating that littoral sediments do notprovide a suitable habitat for these bacteria.More studies on different habitats are needed to estimate the role ofdenitrifying methane oxidation in the global carbon and nitrogen cycle, buthere we present first evidence for the occurrence this process in deepoligotrophic lakes and revealed a clear spatial distribution pattern of theresponsible microorganisms.OTV026Life inside the nucleus - an unusual symbiont of amoebaerelated to rickettsiaeF. Schulz*, M. Kuroll, K. Aistleitner, M. HornUniversity of Vienna, Department of Microbial Ecology, Vienna, Austriasequencing as Hartmannella sp. These amoebae were stably infected withbacteria that unexpectedly were located inside the host nucleus, asdemonstrated by fluorescence in situ hybridization and electronmicroscopy. All known amoeba symbionts live in the host cytoplasm; anendonuclear symbiont has not been described, and such a life style is alsorare in other eukaryotic hosts. Phylogenetic analysis of these bacteria,named FS-5, revealed an only low degree of 16S rRNA sequencesimilarity (89 %) to their closest relative, the paramecium symbiontCaedibacter caryophilus. Endonuclear symbiosis requires a complexinfection process. We showed that FS-5 is not limited to Hartmannellahosts but can also infect Acanthamoeba castellanii. We studied theinfection process and the developmental cycle in both hosts byfluorescence in situ hybridisation combined with DNA staining andassessed host fitness by propidium iodide staining and determination ofamoeba cell numbers. Hardly any bacteria could be detected in thecytoplasm at early time points, suggesting that the bacteria with a highdegree of specificity traffic to the host nucleus. High infection levels werereached after 120 h, at which time point the nucleus is pronouncedlyenlarged and completely filled with bacteria. Interestingly, there is noobvious deleterious effect on the amoeba hosts during the first 120 h postinfection, but host cell lysis was observed at later time points. Presently,further experiments regarding the host range of FS-5 and its distribution inthe environment, as well as genome sequence analysis is underway. Thiswill help elucidate the molecular mechanisms underlying the endonuclearlifestyle of this unique symbiont.OTV027Functional community analysis of a microbial mat involved inthe oxydation of iron by metatranscriptomicsA. Quaiser* 1 , X. Bodi 1 , A. Dufresne 1 , A. Dheilly 2 , S. Coudouel 2 ,D. Naquin 2 , A. Francez 1 , P. Vandenkoornhuyse 11 Université de Rennes 1, EcoBio, Rennes, France2 Université de Rennes 1, OSUR, Environmental Genomic plateforme,Rennes, FranceThrough the capacity to use Fe(II) as an electron source and theconservation of energy by this process neutrophilic iron oxidizingmicroorganisms (FOMs) play an important role in iron redox cycling.While the role of the biotic and abiotic process was seen controversiallyfor a long time, new data confirming the importance of microbialimplication in this process are accumulating. The typical characteristic ofdescribed FOMs living at circumneutral pH is their lithotrophicmetabolism using iron as their sole energy source. To compete with abioticiron oxidation this oxygen-dependent reaction must take place at the oxicanoxicinterface, conditions often only found in difficult accessiblemicroenvironments masked by complex ecosystems as soils andsediments. The recent detection of neutrophilic FOMs in a large variety ofenvironments, as sediments, iron seeps, wetland soils and rhizosphere, beartestimony to their wide distribution and their importance in global ironredox cycling. While most oxic-anoxic interfaces are difficult to accessand to analyze, FOMs are flourishing at the particular redox boundarycharacterized by steady fluxes of Fe(II) originating from an anoxic sourceand the oxygen is supplied from an oxygenated water body. Theseconditions are given and most obvious visible for example in iron-richmicrobial mats, spanning often several tenths of meters with variousdepths. This model implies several ecological questions in particular aboutthe multi- partnership mutualism and syntrophy, the coupling of thediversity with the function of the microbial actors and the long-termmaintenance of the mat. The major objective of our project is tounderstand the role of the interactions among microorganisms in thebiogeochemical functioning of an ecosystem involved in iron redoxcycling. The activities of the microbial community were analyzed bycomparative metatranscriptomics and correlated to biogeochemical factors.The analysis of the microbial diversity revealed the activities of a relativelimited number of species. The most abundant active microorganisms wereaffiliated only to three different groups: the Alveolata (eucaryote), themethanotrophs (gammaproteobacteria) and the betaproteobacteriapotentially involved in iron oxidation. While the presence of iron oxidizerwere expected, the activity of methanotrophs was surprising. The statisticalanalysis showed a vertical spatial structuring of the microbial communityin dependence of the depth with higher activities of methanotrophs nearthe sediment. These results indicate that the stability and the structuring ofthe mat is based on functional interactions among methanotrophs and ironoxidizing bacteria. Our study shows that in-depth metatranscriptomicapproaches allow the linkage of the microbial diversity to function as wellas the linkage of the microbial activity to environmental factors.Free-living amoebae are abundant in various habitats worldwide and areamong the most important predators of microorganisms. Some bacteria,however, are able to evade phagocytosis by amoebae and may establish astable and symbiotic relationship with these protozoa. Protozoa have thusbeen suggested to play an important role for the evolution of intracellularbacteria including human pathogens. From a nitrifying bioreactor werecently isolated a free-living amoeba strain identified by 18S rRNA geneBIOspektrum | Tagungsband 2012