Newest publications
Diacetoxyscirpenol, a Fusarium exometabolite, prevents efficiently the incidence of the parasitic weed Striga hermonthica
(2022) Anteyi, Williams Oyifioda; Klaiber, Iris; Rasche, Frank; Anteyi, Williams Oyifioda; Institute of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), University of Hohenheim, Stuttgart, Germany; Klaiber, Iris; Core Facility Hohenheim, University of Hohenheim, Stuttgart, Germany; Rasche, Frank; Institute of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), University of Hohenheim, Stuttgart, Germany
Background: Certain Fusarium exometabolites have been reported to inhibit seed germination of the cereal-parasitizing witchweed, Striga hermonthica , in vitro . However, it is unknown if these exometabolites will consistently prevent S. hermonthica incidence in planta . The study screened a selection of known, highly phytotoxic Fusarium exometabolites, in identifying the most potent/efficient candidate (i.e., having the greatest effect at minimal concentration) to completely hinder S. hermonthica seed germination in vitro and incidence in planta , without affecting the host crop development and yield.
Results: In vitro germination assays of the tested Fusarium exometabolites (i.e., 1,4-naphthoquinone, equisetin, fusaric acid, hymeglusin, neosolaniol (Neo), T-2 toxin (T-2) and diacetoxyscirpenol (DAS)) as pre- Striga seed conditioning treatments at 1, 5, 10, 20, 50 and 100 µM, revealed that only DAS, out of all tested exometabolites, completely inhibited S. hermonthica seed germination at each concentration. It was followed by T-2 and Neo, as from 10 to 20 µM respectively. The remaining exometabolites reduced S. hermonthica seed germination as from 20 µM ( P < 0. 0001). In planta assessment (in a S. hermonthica -sorghum parasitic system) of the exometabolites at 20 µM showed that, although, none of the tested exometabolites affected sorghum aboveground dry biomass ( P > 0.05), only DAS completely prevented S. hermonthica incidence. Following a 14-d incubation of DAS in the planting soil substrate, bacterial 16S ribosomal RNA (rRNA) and fungal 18S rRNA gene copy numbers of the soil microbial community were enhanced; which coincided with complete degradation of DAS in the substrate. Metabolic footprinting revealed that the S. hermonthica mycoherbicidal agent, Fusarium oxysporum f. sp. strigae (isolates Foxy-2, FK3), did not produce DAS; a discovery that corresponded with underexpression of key genes (Tri5, Tri4) necessary for Fusarium trichothecene biosynthesis ( P < 0.0001).
Conclusions: Among the tested Fusarium exometabolites, DAS exhibited the most promising herbicidal potential against S. hermonthica . Thus, it could serve as a new biocontrol agent for efficient S. hermonthica management. Further examination of DAS specific mode of action against the target weed S. hermonthica at low concentrations (≤ 20 µM), as opposed to non-target soil organisms, is required.
Conformational dynamics of proteins in bacterial pathogens and the innate immune response
(2024) Hau, Jann-Louis; Fritz, Günter
Global health is facing two major threads, the rapid rise of multi-drug resistant bacterial pathogens and the increase autoimmune diseases. Therefore, studying the components of host-pathogen interactions is crucially important for the development of novel drugs and diagnostic tools to fight these threats. Both, virulence factors of pathogenic bacteria and the components of the host’s innate immune response are build up by multimeric protein complexes. In order to understand how these systems respond to different conditions and environments and to uncover the underlying molecular mechanisms, the conformational dynamics of these proteins must be resolved.
This study focuses on the two important examples of a host-defence protein, S100A8/A9, and a bacterial virulence factor, the Na+-translocating NADH:ubiquinone oxidoreductase (NQR).
The heterodimeric protein complex S100A8/A9 is secreted in very high amounts by immune cells at sites of infection and tissue damage. S100A8/A9 is a key element of the innate immune system. It strongly activates inflammatory response and exhibits antimicrobial properties by binding of essential transition metal nutrients. Therefore it is defined as a danger-associated molecular pattern (DAMP). Its role as a DAMP during inflammation and absence in healthy tissue defines S100A8/A9 is used as an excellent biomarker for a variety of inflammatory diseases in human and veterinary medicine. Only the human S100A8/A9 is thoroughly characterised so far. Imaging of S100A8/A9 by a tracer molecule would allow for sensitive and accurate imaging of pathogenic or sterile inflammation. Here, a new protocol for fast and and efficient isolation of human and porcine S100A8/A9 is established, which is also applicable to S100A8/A9 of other species. The characterisation of porcine S100A8/A9 revealed similar properties with respect to structure and metal binding to human S100A8/A9, while the antimicrobial properties of the porcine protein are less pronounced than in the human orthologue. The structures of human S100A9 in complex with different tracer molecules were determined by X-ray crystallography, revealing that the molecular benzimidazole core of the tracer binds into a dynamically adapting pocket of S100A9. Applying a newly established tryptophan fluorescence-based assay, it was shown that the affinity of the tracer is not affected by different imaging tags attached to the benzimidazole core. Since the bezimidazole core exhibits non-favourable pharmacokinetic properties, novel lead compounds for the targeting of S100A8/A9 in inflammation have to be established. New lead structures, which could serve as novel molecular cores, were identified by fragment-based crystallographic screening. As exemplified by the benzimidazole imaging tracers, S100A8/A9 ligands have to fulfil the requirements of the dynamic binding pocket. The identified molecules represent an excellent starting point for the development of a novel class of imaging probes for the sensitive detection of inflammation.
The NQR is part of the respiratory chain of the human pathogen Vibrio cholerae. It couples the oxidation of NADH and the reduction of ubiquinone to the translocation of Na+ from the cytoplasm to the periplasm. The resulting Na+ electrochemical gradient, the sodium motive force, is vital for V. cholerae and drives several processes critical for pathogenesis, like e.g. movement of the flagellum and efflux of antibiotics. NQR-activity is linked to the expression of pathogenic factors including the cholera toxin and is therefore classified as a virulence factor itself. Since the NQR has no homologs in humans and is widespread among Gram-negative pathogenic bacteria, it is a promising target for the development of novel classes of antibiotics. However, the mechanism of electron transfer and the coupled sodium translocation as well as the quinone binding site had been elusive. Based on first structural information on the NQR, which exhibited unusual large distances between redox cofactors, drastic conformational changes had been proposed (Steuber et al., 2014). In this study, the structure of the NQR with substrates or inhibitors bound was determined by single particle cryo electron microscopy. The structures reveal that the coupling of electron transfer to conformational changes in the NQR subunits NqrC and NqrF are governed by the redox state of the intramembrane [2Fe-2S] cluster between NqrD/E, defining the NQR as a conformationally coupled redox pump. Furthermore, the binding site of ubiquinone and the NQR inhibitor HQNO was located in NqrB. Sodium ions were identified bound in NqrB, which could represent exit sites of the sodium translocation path. These findings were confirmed for the NQR of Prevotella byrantii by homology modelling. Taken together, the molecular mechanism described for the V. cholerae NQR applies also to NQRs from other organisms and homologous complexes. The described NQR mechanism and substrate binding sites lay the foundation for the structure-based design of NQR-inhibitors which could serve as new antibacterial drugs.
In summary, the findings presented in this study promote the development of novel diagnostic tools and new antibiotics to combat the emerging threats of autoimmune diseases and multidrug resistant bacterial pathogens.
A research note: effect of pH on meat iridescence in precooked cured pork
(2022) Ruedt, Chiara; Gibis, Monika; Weiss, Jochen; Ruedt, Chiara; Department of Food Material Science, Institute of Food Science and Biotechnology, University of Hohenheim, Stuttgart, Germany; Gibis, Monika; Department of Food Material Science, Institute of Food Science and Biotechnology, University of Hohenheim, Stuttgart, Germany; Weiss, Jochen; Department of Food Material Science, Institute of Food Science and Biotechnology, University of Hohenheim, Stuttgart, Germany
Objective: The objective of this study was to investigate the effect of pH change of cooked cured pork M. longissimus thoracis et lumborum on iridescence intensity and extent (= percentage of iridescent area) since interaction with light may be related to pH-induced alterations in microstructure. Muscles were injected with brines of different pH values, cooked, sliced perpendicular to muscle fiber direction, and visually evaluated by a panel of 20 experienced panelists.
Results: Muscles with lowest pH (5.38) showed the lowest iridescence score of 4.63 (p < 0.05). Iridescence was greatest in muscles with normal (5.78) and high pH (6.03, respectively 6.59), but did not differ significantly (p > 0.05). Iridescence was positively correlated (p < 0.01) with pH and water content, and negatively correlated (p < 0.01) with cooking loss. Hence, hydration state and light scattering from microstructure may be important factors that determine the degree of iridescence in cooked meat products.
Carbon cycling in a future agroecosystem
(2024) Leyrer, Vinzent; Kandeler, Ellen
Climate change is putting increasing pressure on the soil microbiome, driver of vital ecosystem functions. Predicting its future state is of great interest as it provides insight into how rising temperatures and increasing water scarcity will affect a fundamental process in terrestrial ecosystems: carbon (C) cycling between soil, vegetation and the atmosphere. However, climate is changing in both moderate and extreme ways. Mean conditions are changing with increases in temperature and shifts in precipitation patterns. In addition, an increased frequency of extreme droughts raises the question of how ecosystem functions will be affected in the future.
In this thesis, we investigated soil microbial abundance and functions and the associated soil C dynamics under long-term predicted warmer and drier mean climatic conditions. By then exposing the soils of this system to drought, we aimed to highlight the difference in how drought affects C cycling between soil and the atmosphere under future compared to current mean climatic conditions. This allowed us to make a realistic prediction of how future drought will affect soil C dynamics if the mean climatic conditions are also warmer and drier overall. Our study is conducted in an ecosystem that is still strongly underrepresented in related studies, namely agricultural ecosystem soils. In addition to their importance in terms of total area, annual cropping in agricultural ecosystems defines their unique characteristics in terms of how C enters, transforms and exits the system. This is fundamentally different from comparable natural ecosystem soils such as forests or grasslands.
The first study built the foundation of the thesis. A future mean climatic scenario was simulated at field scale for one decade, to assess broad patterns of future microbial abundance and activity. The key elements of soil C dynamics were monitored: its dynamic part — substrate availability, soil microbial biomass and respiration — in relation to the background, the total soil organic carbon (SOC) content. We then exposed this field to extreme drought and studied the response of the microbiome, which we assumed was adapted to warmer and drier conditions. Would this response be different from how the soil microbiome responds today, and can we derive a future prediction from this? If so, what are the driving forces behind the different response? First, we again used integrative parameters such as soil respiration to identify differences in the big picture. We expanded on this by using an in situ 13C pulse labelling experiment, tracing C from plants to soil and back to the atmosphere during extreme drought.
From the first year, the change in mean climatic conditions led to a shift in the C dynamics of the arable soil. Whereas reducing the summer precipitation had no effect at all, warming was a strong accelerator of soil respiration and there was no sign of acclimation to the warmer regime. The microbial biomass C pool turned out to be unresponsive to the changing conditions and, therefore, the consistent increase in respiration indicated a shift in the microbial physiology in a warmer environment. Yet the simultaneously higher labile C input weighed up for the higher respiration and consequently, the total SOC content remained unchanged. This suggested that in a warmer world, arable soils of the temperate zone may exhibit relatively high stability regarding their C budget.
An overall warmer world in the future will in addition increasingly be challenged by extreme drought. First of all, exposing the arable soil to drought showed expected patterns of a general decline in microbial activity. However, it also revealed unexpected findings of stable or even increasing microbial biomass C pools. As bacterial levels decreased and fungal levels remained unaffected, part of this net increase in microbial biomass C was to be attributed to intracellular C accumulation, a microbial measure to avert death under extreme drought. Another unexpected observation was that warming stimulated respiration even under drought. This is counterintuitive because the stimulus of warming acts via increasing reaction rates between enzymes and C compounds, which requires a liquid phase to allow their contact. Still, this observation was consistent in both drought studies and showed that the effect of drought on microbial related parameters depends on the overall temperature conditions in which the drought occurs. Apart from that, both drought experiments revealed that it is not only the direct effect of warming that modifies the microbial response to drought. We also found indications that exposing the soil microbiome to a decade of reduced summer precipitation left a legacy on how microorganisms use and acquire C during drought. In specific, in soils with a history of drier summer months we found the stimulatory effect of warming on respiration to be limited. This was a remarkable finding, which we explained by the highest fungal biomass in these soils, as fungi are known to have a high C-use efficiency. However, this remained largely elusive as no other parameter — neither substrate availability nor enzyme dynamics — could contribute to an explanation. Interestingly, the legacy effect of reduced summer precipitation also appeared elsewhere in the second study, where microbes pre-exposed to drier summer months shifted their C acquisition by using SOC rather than rhizodeposits to meet their C demand when conditions became extremely dry. Both observations, the first on respiration and the second on C acquisition, showed that not only repeated extreme droughts can create a legacy effect that drives microbial abundance and activity during drought. Even relatively moderate shifts in precipitation patterns can.
Taking a step back, our study suggests that future C cycling between temperate arable soils and the atmosphere will be driven mainly by temperature increases, rather than by shifts in moderate precipitation patterns. However, it is both factors taken together that can alter the response of the system to drought. In the future, the impact of drought on microbially mediated C cycling will be different from what we observe today based on (1) expected warmer temperatures that will co-occur with drought and (2) legacy effects from historical precipitation patterns. Importantly, we show that both factors interact to modify the impact of drought on microbial abundance and activity. This suggests that the anticipation of realistic future scenarios requires an equal consideration of past legacies.
Integrative description of Temnothorax siculus sp. n.: a new ant species from Sicily, Italy (Hymenoptera, Formicidae)
(2025) Schifani, Enrico; Alicata, Antonio; Prebus, Matthew M.; Csősz, Sándor; Schifani, Enrico; Department of Chemistry, Environmental Sustainability, and Life Sciences, University of Parma, Parco Area delle Scienze 11/A, 43124 Parma, Italy; Alicata, Antonio; Department of Biological, Geological and Environmental Sciences, University of Catania, Via Androne 81, 95124 Catania, Italy;; Prebus, Matthew M.; Social Insect Research Group, School of Life Sciences, Arizona State University, 550 E Orange St., Tempe, AZ 85281, USA;; Csősz, Sándor; HUN-REN-ELTE-MTM Integrative Ecology Research Group, Pázmány Péter ave 1/C, 1117 Budapest, Hungary; Fernández, Fernando; Guerrero, Roberto José
The mostly Holarctic genus Temnothorax (Hymenoptera, Formicidae) is the most diverse ant genus in temperate regions. The Mediterranean, a biodiversity hotspot of rare ant species, hosts over 150 Temnothorax taxa, including several short-range endemics. Over the last few years, phylogenomic reconstructions and integrative taxonomy have significantly improved the understanding of global Temnothorax diversity, but much taxonomic work is still needed in the Mediterranean region. Here, we present the integrative description of a new species of the genus, discovered in the central Mediterranean island of Sicily: Temnothorax siculus sp. n. is defined and compared to congeneric species integrating morphometrics and phylogenomics. It is a ground-nesting, lowland species, of which workers were regularly observed foraging on bushes and small trees. In the global phylogeny, covering all the main lineages of the region, it belongs to the Palearctic clade and is related to the tuberum and unifasciatus complexes. Morphological separation from other Sicilian Temnothorax species can generally be achieved on qualitative characters, but we also provide morphometric discriminant functions to separate it from T. apenninicus and especially T. unifasciatus . Temnothorax siculus has been rarely collected but appears to be widespread in Sicily, and may occur in neighboring regions.