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

ISV11No abstract submitted!ISV12Monitoring of human pathogens and source identifiers indischarges across the United States: QMRA from sourceto bathing siteS. Wuertz* 1 , G. McBride 2 , W. Miller 3 , D. Wang 1 , A. Kundu 1 , D. Bambic 41 Department of Civil and Environmental Engineering, University ofCalifornia, Davis, Davis, USA2 National Institute of Water and Atmospheric Research (NIWA), Auckland,New Zealand3 Department of Pathology, Microbiology & Immunology, School ofVeterinary Medicine, University of California, Davis, USA4 AMEC Earth & Environmental, Nashville, USAThis study has increased knowledge about relationships between pathogenindicators, source identifiers and pathogens to support QuantitativeMicrobial Risk Assessment (QMRA) efforts and the implementation ofrevised recreational water quality criteria. Data gaps for waterbornepathogens and indicators in fecally-impacted discharges to recreationalwaters were identified and filled by targeted monitoring campaigns.Simultaneous detection of pathogens in water samples used genetic-,culture-, and microscopy-based methodologies for Salmonella,Campylobacter jejuni, Vibrio cholerae, Cryptosporidium, Giardia,Toxoplasma gondii, adenoviruses, enteroviruses, noroviruses, rotaviruses,Bacteroidales, Enterococcus, and Escherichia coli.The potential health risks associated with discharges-were estimated usingQMRA and three scenarios: primary contact by adults, secondary contact byadults and/or inhalation by persons of any age, and primary contact bychildren. The differences in these three scenarios were driven by differentwater ingestion rates (adults ingest more water during primary thansecondary contact; children ingest more water than adults; water inhalationrate is less than water ingestion rate for any age class). Norovirus posed themost dominant health risk followed by rotavirus. Norovirus andEnterococcus both had significant correlations with pathogens in discharges.Using the same DNA extracts from discharge samples, microbial sourcetracking qPCR data on the fecal source identifier Bacteroidales was obtainedand used in a new model to predict the true amount of human fecalcontamination in a water sample by relating a human-associated geneticmarker to a universal assay for fecal sources. The model output can be usedto implement and evaluate management options intended to restoremicrobial water quality.ISV13No abstract submitted!ISV14No abstract submitted!ISV15Xanthomonas TALEs - from plant pathogen weapon tobiotech hypeJ. Boch*, U. BonasInstitute of Biology, Department of Genetics, Martin-Luther-UniversityHalle-Wittenberg, Halle (Saale), GermanyXanthomonas spp. are Gram-negative plant pathogenic bacteria withpowerful molecular weapons to attack their plant hosts. Key forpathogenicity of Xanthomonas is a type III secretion system that injects acocktail of effector proteins into plant cells to function as potent virulencefactors. TALEs (transcription activator-like effectors) constitute a majorfamily of Xanthomonas effectors that function as transcriptional activatorsof plant genes. The first TALE, AvrBs3, was identified 20 years ago. Today,more than 100 TALEs are known and all exhibit the same structuralfeatures: eukaryotic nuclear localisation sequences mediate import into theplant cell nucleus and a C-terminal activation domain is essential for targetgene activation. A fascinating characteristic of TALEs is their centralprotein domain of tandem, near-identical 34 amino-acid repeats. DifferentTALEs differ in the number and order of repeats which can be classified viatwo adjacent hypervariable amino acids. Importantly, the repeats wereshown to confer DNA-binding and only recently [1], the remarkably simpleDNA-target specificity code was cracked. Each TALE repeat recognizes asingle base pair in a contiguous DNA sequence and the variable diresiduesspecify the base that is bound. This uniquely modular DNA-binding codeallows to straightforwardly read the specificity of any TALE from its repeatsequence. In addition, the modular architecture allows a simplereprogramming of DNA-binding specificity. First powerful tools forbiotechnology have emerged.[1] Boch, J. et al (2009): Breaking the code of DNA binding specificity of TAL-type III effectors.Science 326, 1509-1512.ISV16Toxin producing endofungal bacteriaC. HertweckLeibniz Institute for Natural Product Research and Infection Biology, HansKnoll Institute (HKI) and Friedrich-Schiller-University, Jena, GermanyPathogenic fungi generally exert their destructive effects through virulencefactors. An important example is the macrocyclic polyketide rhizoxin, thecausative agent of rice seedling blight, from the fungus Rhizopusmicrosporus. The phytotoxin efficiently binds to rice ß-tubulin, whichresults in inhibition of mitosis and cell cycle arrest.By a series of experiments we could unequivocally demonstrate thatrhizoxin is not biosynthesized by the fungus itself, but by endosymbioticbacteria of the genus Burkholderia. Our unexpected findings unveil aremarkably complex symbiotic-pathogenic alliance that extends the fungus–plant interaction to a third, bacterial key player. In addition, we were able toculture the symbionts to produce antitumoral rhizoxin derivatives, and toelucidate the biosynthesis of the toxin. A second example for the formationof a ‘mycotoxin’ by endofungal bacteria is the cyclopeptide rhizonin.Surprisingly, in the absence of bacterial endosymbionts the fungal host isnot capable of vegetative reproduction. Formation of sporangia and spores isonly restored upon re-introduction of endobacteria. The fungus has becometotally dependent on endofungal bacteria, which in return provide a highlypotent toxin for defending the habitat and accessing nutrients from decayingplants.This talk highlights the significance of toxin-producing endofungal bacteriain the areas of ecology, medicine, and nutrition. Furthermore, progress instudying the molecular basis for the development and persistence of this raremicrobial interaction is presented.ISV17Plants and arbuscular mycorrhizal fungi: born to befriendsP. BonfanteDepartment of Plant Biology, University of Torino, ItalyArbuscular mycorrhizas (AMs) are symbiotic associations, which arecommonly described as the result of co-evolution events betweenGlomeromycota fungi and plants where both partners benefit from thereciprocal nutrient exchange. Data from fossil records, recentcharacterizations of AM fungi in basal plant taxa, and live cell imaging ofangiosperm colonization processes, indicate the ancient origin of AMinteractions. Among the conserved cellular mechanisms, the presence of asymbiotic interface compartment which allows fungal development insidethe cell lumen and maintains host cell integrity, is considered a landmark forAMs establishment.The presentation will focus on mechanisms which are associated with theperception of the AM fungus and its accommodation inside the lumen of thehost plant cell, leading to the assembly of the perifungal membrane andsymbiotic interface. Our findings, based on an in vivo confocal microscopyapproach, demonstrate that root cells perceive AM fungal signals and triggercalcium-mediated signaling in their nucleoplasm, both before and upondirect contact with the fungus. Nuclear calcium spiking seems to be a prerequisiteto the cellular reorganization that initiates after the adhesion of thefungal hyphopodium to the root and leads to the assembly of the so-calledprepenetration apparatus (PPA) inside one or a few contacted epidermalcells. Lastly, and at least in in vitro conditions, PPA is instrumental for theassembly of the interface construction.These features have been identified in legumes and in not-legume plants, butso far not in naturally collected plants or in lower taxa. Answers to thesespektrum | Tagungsband 2011