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

225SMP048Interactions between bacteria antagonistic towards Rhizoctoniasolani, lettuce and indigenous rhizosphere communities in threesoil typesS. Schreiter*, E. Scholz, U. Zimmerling, P. Zocher, R. Grosch, K. SmallaJulius Kühn Institute, Institute for Epidemiology and PathogenDiagnostics, Braunschweig, GermanyRhizoctonia solani is a soil-borne plant pathogen which causes bottom rotdisease and leads to a massive loss of lettuce and potato every year. Thelack of effective fungicides makes it difficult to control this and other plantpathogens. So it is necessary to find alternative strategies. A promisingapproach is the use of natural antagonists of the plant pathogen. Underlaboratory and greenhouse conditions, two isolates, Pseudomonas jesseniiRU47 and Serratia plymuthica 3Re4-18, showed the ability to reducedisease symptoms. But the efficiency of biocontrol agents was reported asvery variable and the reason for this variability is largely unknown.Therefore, a better understanding of the interaction of the microbialcommunity, the plant rhizosphere and the bulk soil is required for asuccessful exploitation of this antagonistic potential. Within the frame of aDFG-Project a field experiment has been set up with a uniqueexperimental plot system in Großbeeren comparing three different soiltypes. This made it possible to analyze the influence of the soil typeindependently from other factors such as climate and cropping history.First results showed a different survival of the two antagonistic strains inthe tree soil types. Also the damages caused by the pathogen are differentin the soil types. We assume that these observations are related withdifferences in the microbial communities of the three soils. Indeed highlysignificant differences between the soil types were revealed by denaturinggradient gel electrophoresis analysis of bacterial and fungal communities.Looking at the rhizosphere, it could be confirmed that after three weeks,when lettuce is especially susceptible to the pathogen, the antagonisticstrains are dominant populations. The antagonists compensated the damagecaused by the pathogen similarly in all soils as revealed by dry weight andrating of the lettuce. Also the antagonistic strains did not affect theindigenous microbial community. Therefore a negative ecological effect is notexpected. The antagonistic strains had a positive influence on lettuceindependent from the indigenous microbial community and the pathogen so thebiological mechanism remains unknown. In conclusion the strains arepromising biocontrol agents to compensate the lack of effective fungicides.SMP049Effects of resource quality and quantity on fungalcommunities in an agricultural soilJ. Moll* 1 , K. Goldmann 1 , D. Krüger 1 , F. Buscot 1,21 UFZ-Helmholtz Centre for Environmental Research GmbH, Soil Ecology,Halle, Germany2 University of Leipzig, Institute of Biology I, Leipzig, GermanyDue to their high diversity and a wide decomposition potential, fungi arewell adapted to the heterogeneous soil environment and are a majorcomponent of soil microbial communities.In the frame of the DFG-funded (German Research Foundation) researchunit FOR 918 „Carbon flow in belowground food webs assessed byisotope tracers“ we investigate the role of saprobiotic fungi in the transferof organic carbon from plant origin to belowground food webs of anagricultural soil. To tackle how carbon quality and availability influencethe fungal communities, a field experiment has been installed where twocrops, maize (Zea mays L.) und wheat (Triticum aestivum L.), arecultivated in a design cross manipulating addition of maize litter. Soil fromthree depths was sampled in July, September and December in 2009 and2010 to analyze seasonal shifts in the fungal community composition.ARISA (automated ribosomal intergenic spacer analysis) which was usedas DNA-fingerprint method resulted in 198 OTUs (operational taxonomicunits). Univariate statistical analysis revealed that fungal species richnessvaries according to the crop and the manipulated carbon input in terms ofadded litter. Furthermore fungal species richness was highest in Septemberin both years. Despite a reduced carbon availability in the B-horizon nodecline in species richness with increasing depth was found.Multivariate statistical analysis demonstrated that the soil fungalcommunity is mostly affected by soil depth, followed by the impact of theplants and related root exudates. These results indicate strong reactions ofthe fungi to different nutrient supplies.In follow up microcosm experiments with variable nutrient availabilityfungal key players actively assimilating carbon will be identified usingrRNA-SIP (stable isotope probing).SMP050Minimal nutrient requirements of Myxococcus xanthusDK1622R. Pietsch*, L. Blaß, E. HeinzleSaarland University, Biochemical Engineering, Saarbrücken, GermanyThe soil bacterium Myxococcus xanthus DK1622 naturally feeds on lysedmicroorganisms by secretion of proteases [1, 2]. Since the growth is pooron defined media like A1 or M1 [3, 4, 5], but good on casein and caseinhydrolysates, we studied the degradation and uptake of related peptides. Itslack of a hexose uptake system [1] does not allow utilizing mono- orpolysaccharides. Isoleucine, leucine and valine are essential because theycannot be synthesized [3], but their uptake is enabled by the branchedchain amino acid transport system [6].Like in the degradation of -casein by Lactococcus lactis [7], uptake ofpeptides should be possible with a maximal length of 18 amino acids viathe oligopeptide permease [8]. The biological fate of peptides in theculture supernatant of M. xanthus was followed via Matrix-assisted laserdesorption/ionisation mass spectrometry (Maldi-MS) with bradykinin 1-7as internal standard (any occurrence of m/z=757 in supernatant). Thesequences of single peptides were confirmed by tandem measurements(MS/MS) with collision induced decay and a novel software tool(PeptideChopper 2.0) which aligns the found masses of peptides andfragment ions to all four casein subtype sequences.Main degradation detectable by Maldi-MS takes place at -casein 59-92and 144-162. We identified main and alternative degradation pathways byboth C- and N-terminal exopeptidases. A kinetic model was developed todescribe the degradation of peptides.To observe whether uptake of peptides with a length of nine amino acids ispossible without further degradation, synthesized -casein peptides 74-82and 145-153 which contain all amino acids essential for growth wereincubated with concentrated proteases from the culture supernatant to findthe putative degradation products. In a second experiment, they were usedas the only carbon and nitrogen sources.This way, we elucidated degradation pathways of -casein by M. xanthusDK1622. Offering a high amount of synthetic peptides containing all essentialamino acids is not sufficient for efficient growth of M. xanthus DK1622 even ifthey are parts of the major degradation pathways of casitone.1. L. J. Shimkets, M. Dworkin and H. Reichenbach in “The Procaryotes”, ed. M. Dworkin (Springer, NewYork) (2006), p. 60.2. A. Konovalova, T. Petters and L. Søgaard-Andersen, FEMS Microbiol Rev 34 (2010), p. 99.3. A. P. Bretscher and D. J. Kaiser, J Bacteriol 133 (1978), p. 763.4. S. S. Witkin and E. Rosenberg, J Bacteriol 103 (1970), p. 641-649.5. M. Dworkin, J Bacteriol 84 (1962), p. 250-257.6. H. B. Bode, M. W. Ring, G. Schwär, M. O. Altmeyer, C. Kegler, I. R. Jose, M. Singer and R. Müller,Chem Bio Chem 10 (2009), p. 128-140.7. E. R. S. Kunji, G. Fang, C. M. Jeronimus-Stratingh, A. P. Bruins, B. Poolman and W. N. Konings MolMicrobiol 27 (1998), p. 1107-11188. K. Savijoki, H. Ingmer and P. Varmanen Appl Microbiol Biotechnol 71 (2006), p. 398SMP051Insights in anaerobic hydrocarbon biodegradation undermethanogenic conditionsF. Gründger* 1 , F. von Netzer 2 , N. Jimenez-Garcia 3 , T. Lüders 2 , H.-H. Richnow 3 , M. Krüger 11 Bundesanstalt für Geowissenschaften und Rohstoffe, Geomikrobiologie,Hannover, Germany2 Helmholtz Zentrum München, Institut für Grundwasserökologie, Neuherberg,Germany3 Helmholtz Zentrum für Umweltforschung, Isotopenbiogeochemie, Leipzig,GermanyEnrichment, isolation and characterisation of hydrocarbon degradingmicroorganisms are of great importance to understand the biochemicalmechanisms responsible for oil biodegradation in contaminatedenvironments and in petroleum reservoirs. With respect to decreasingconventional energy resources this understanding also helps in the searchfor methods of enhanced hydrocarbon recovery, like the microbialconversion of oil or coal to recoverable methane.The main focus of this work therefore is the biodiversity of hydrocarbondegraders and their metabolic processes of methanogenesis. We started toinvestigate the physiological characteristics and activities of microbialconsortia enriched from freshwater and marine sediments as well as fromoil and coal reservoirs.Stable isotope measurements showed the conversion of 13 C-labelledhydrocarbons into methane. With the use of T-RFLP and Q-PCR a largebacterial diversity was detected while the archaeal was limited to three orfour dominant species. Both domains were highly abundant in allenrichment cultures. Genes indicative of metal reduction, sulphatereduction, and methanogenesis were also detected in high numbers in theseincubations. The sequencing analysis revealed a low phylogenetic diversityof Archaea comprised of Euryarchaeota and Crenarchaeota. Members ofMethanosarcinales and Methanomicrobiales dominated the archaeal partof the community in the enrichment cultures. The main bacterialrepresentatives were Syntrophus spp., Desulfovibrio spp. andSyntrophomonas spp.. Using stable isotope probing with different 13 C-BIOspektrum | Tagungsband 2012