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Variable inhibition of different Legionella species by antagonistic bacteria
Item type: Journal Article
Cavallaro, Alessio; Probst, Silke; Duft, Tobias; et al. (2025)
The genus Legionella includes opportunistic pathogens inhabiting engineered aquatic ecosystems, where managing their presence and abundance is crucial for public health. In these environments, Legionella interact positively or negatively with multiple members of the microbial communities. Here, we identified bacteria and compounds with Legionella-antagonistic properties. We isolated 212 bacterial colonies from various water sources in Switzerland and screened them for their ability to inhibit one reference strain of Legionella pneumophila. Ten selected antagonistic isolates were subsequently tested with spot-on-lawn assays for inhibition toward seven environmental and two clinical isolates of Legionella, representing different species and strains. The antagonists produced highly variable inhibition patterns, highlighting distinct differences in susceptibility among Legionella species and even strains. Only three isolates, all identified as Pseudomonas lurida, inhibited all Legionella species. We analyzed the genomes of the antagonistic bacteria and identified genes for several probable inhibitory compounds. We specifically found the gene cluster for the biosurfactant viscosin to be uniquely encoded by all three P. lurida isolates. This compound was subsequently detected in the supernatant of co-cultures inoculated with P. lurida and selected Legionella strains. However, additional experiments with a viscosin-deficient mutant of Pseudomonas fluorescens did not definitively demonstrate the importance of this compound for Legionella inhibition. This study provides new insights on the ability of aquatic microorganisms to compete with Legionella in controlled laboratory settings. It specifically highlights the diversity across and within Legionella species in their resistance to external antagonistic stress and further supports the potential anti-Legionella activity of some biosurfactants. These results can contribute to the understanding of how different Legionella species inhabit separate niches in the environment and expand the discussion around alternative Legionella mitigation strategies.IMPORTANCEUnderstanding the nature of bacterial interactions allows us to have a broader overview of their lifestyle and their differences, while also paving the way toward new research and potential applications. This paper provides insights into the response of multiple pathogenic species of Legionella to aquatic antagonistic bacteria, highlighting interesting intra-genus differences that are then discussed in light of potential ecological implications. Moreover, we identified new antagonistic bacteria toward Legionella spp. and identified the biosurfactant viscosin as one of the likely compounds active against at least some Legionella species. Together, these results suggest different properties and possibly different environmental behaviors within the genus Legionella, while adding to previous studies with newly identified inhibitory organisms and compounds. We furthermore discuss the possibility that the latter could be explored in future research in order to develop a biological-based mitigation strategy against Legionella in engineered aquatic ecosystems, based on strains and bioactive compounds identified in this and other studies.
From clinics to sewers: leveraging environmental surveillance and whole genome sequencing to inform transmission of ESBL-Escherichia coli in Switzerland
Item type: Journal Article
Conforti, Sheena; Du Plessis, Louis; Bagutti, Claudia; et al. (2026)
Extended-spectrum beta-lactamase-producing Escherichia coli (ESBL-E. coli) is a major antimicrobial resistance concern spreading across human, animal, and environmental domains. To assess between-source transitions, we analyzed 762 ESBL-E. coli genomes collected from wastewater (used as a community shedding indicator), clinical settings, cattle, and wildlife across Switzerland (2021-2023). ST131 was the most prevalent sequence type (ST), and 76% of isolates carried resistance to at least two antibiotic classes in addition to beta-lactams. Phylogenetic analysis showed isolates were interspersed across sources, yet genetically similar strains were more common within compartments. Clonal isolates (0 SNPs) were rarely shared (n = 2) between wastewater and corresponding clinics. Ancestral state reconstruction revealed compartmentalization of isolates between wastewater and clinics across the whole phylogeny. However, this pattern disappears within human-associated ST131, ST69, and ST1193, highlighting exchange between clinics and communities. These findings show that wastewater surveillance captures community circulation of ESBL-E. coli, which overlaps with circulating clinically relevant strains.
Arctic and Boreal Wildfires Impact Climate by Releasing Ancient Carbon and Light-Absorbing Particles
Item type: Journal Article
Ruppel, Meri. M.; Somero, Markus; Sippula, Olli; et al. (2026)
Climate warming induced wildfires are rapidly increasing at high latitudes, yet their climate impacts remain poorly understood. These deeply smoldering fires may release long-stored carbon and thus perturbate the global carbon cycle and further emit light-absorbing carbonaceous particles enhancing snow and ice melt after deposition. We newly investigate the carbon isotopic and light-absorbing characteristics of carbonaceous particles produced in laboratory combustion experiments on Arctic-boreal peats and compare these with biomass from boreal forest and savanna environments. We provide the first observational evidence that boreal and especially Arctic peat smoldering may release millennial-aged carbon into the atmosphere, which upsets radiocarbon-based source attribution, separating fossil-fuel-derived sources from modern biomass. Moreover, above- and below-ground material combust differently, and hence the fraction of modern carbon (F14C), i.e., the average age, of the original biomass and the produced carbonaceous particles may differ. Furthermore, we show that peat smoldering produces significant amounts of Brown Carbon, which absorbs light at a similar magnitude to Black Carbon in these samples. Our results indicate that the increasing number of Arctic-boreal peat fires may exacerbate Arctic warming more than previously estimated.
Chatbot and Voicebot Platform for Experimental Research
Item type: Other Research Data
Tillmanns, Sebastian (2026)
This software package implements a multi-instance chatbot and voicebot platform for experimental research on AI modality effects in customer service interactions. The system supports up to 10 concurrent chatbot instances (AI agnostic, deployed via FastAPI/Uvicorn) and 10 voicebot instances (OpenAI Realtime API), integrated with Qualtrics for experimental data collection. Key components include a PostgreSQL-backed conversation logging system, automatic schema management per bot instance, JWT-based session handling for voicebots, and a JavaScript frontend for seamless Qualtrics embedding. The platform was developed at the Center for AI Value, ETH Zürich, to support SNF project 100018_227553.
Diffusion-Controlled Solute and Isotope Transport in the Milk River Aquifer System, Alberta, Canada: Implications for Dating Old Groundwater
Item type: Journal Article
Musy, Stephanie L.; Purtschert, Roland; Sturchio, Neil C.; et al. (2026)
Krypton-81 (⁸¹Kr) and chlorine-36 (³⁶Cl) are among the few isotopic tracers capable of constraining groundwater residence times on 10⁵-10⁶ year timescales. In sedimentary aquifer systems bounded by low-permeability units, however, diffusive solute exchange can strongly modify tracer distributions and bias apparent ages derived from concentration ratios. In the transboundary Milk River Aquifer (MRA), progressive chloride enrichment caused by diffusion across shale aquitards complicates the interpretation of ³⁶Cl/Cl as a chronometer. Here, we combine new measurements of ⁸¹Kr, ³⁶Cl, stable chlorine isotopes (³⁷Cl/³⁵Cl), and ¹⁴C with advection-diffusion transport modeling to quantify the importance of matrix diffusion on tracer systematics and inferred groundwater ages. The simulations reproduce the observed decrease in ³⁶Cl/Cl and concomitant increase in delta ³⁷Cl along regional flow paths, demonstrating that diffusive influx of Cl-rich aquitard water dominates the evolution of the chlorine isotope system. In contrast, modeled and observed ⁸¹Kr activities show substantially lower sensitivity to diffusive exchange over the timescales considered. A comparison of simulated and measured tracer relationships indicates that, in the MRA, apparent ages derived from ³⁶Cl primarily reflect chloride addition rather than radioactive decay, whereas ⁸¹Kr provides a more robust and conservative chronometer for fossil groundwater. These results highlight the value of integrating stable and radioactive chlorine isotopes with noble gas dating and explicit transport modeling to disentangle decay from transport effects. The approach developed here provides a quantitative framework for interpreting multitracer data sets in regional aquifers affected by long-term diffusive exchange and has broader implications for assessing fossil groundwater resources in similar hydrogeological settings.