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Large bell-shaped calcite formations called “Hells Bells” were discovered underwater in the stratified cenote El Zapote on the Yucatán Peninsula, Mexico. Together with these extraordinary speleothems, divers found a white, cloudy turbid layer into which some Hells Bells partially extend. Here, we address the central question if the formation of the turbid layer could be based on microbial activity, more specifically, on microbially induced calcite precipitation. Metagenomic and metatranscriptomic profiling of the microbial community in the turbid layer, which overlaps with the pelagic redoxcline in the cenote, revealed chemolithoautotrophic Hydrogenophilales and unclassified ß-Proteobacteria as the metabolic key players. Bioinformatic and hydrogeochemical data suggest chemolithoautotrophic oxidation of sulfide to zero-valent sulfur catalyzed by denitrifying organisms due to oxygen deficiency. Incomplete sulfide oxidation via nitrate reduction and chemolithoautotrophy are both proton-consuming processes, which increase the pH in the redoxcline favoring authigenic calcite precipitation and may contribute to Hells Bells growth. The observed mechanism of microbially induced calcite precipitation is potentially applicable to many other stagnant sulfate-rich water bodies.

BACKGROUND: Formerly, a substantial number of the 120 multiple-choice questions of the Swiss Society of General Internal Medicine (SSGIM) board examination were derived from publicly available MKSAP questions (Medical Knowledge Self-Assessment Program®). The possibility to memorise publicly available questions may unduly influence the candidates’ examination performance. Therefore, the examination board raised concerns that the examination did not meet the objective of evaluating the application of knowledge. The society decided to develop new, “Helvetic” questions to improve the examination. The aim of the present study was to quantitatively assess the degree of difficulty of the Helvetic questions (HQ) compared with publicly available and unavailable MKSAP questions and to investigate whether the degree of difficulty of MKSAP questions changed over time as their status changed from publicly available to unavailable. METHODS: The November 2019 examination consisted of 40 Helvetic questions, 40 publicly available questions from MKSAP edition 17 (MKSAP-17) and 40 questions from MKSAP-15/16, which were no longer publicly available at the time of the examination. An one factorial univariate analysis of variance (ANOVA) examined question difficulty (lower values mean higher difficulty) between these three question sets. A repeated ANOVA compared the difficulty of MKSAP-15/16 questions in the November 2019 examination with the difficulty of the exact same questions from former examinations, when these questions belonged to the publicly available MKSAP edition. The publicly available MKSAP-17 and the publicly unavailable Helvetic questions served as control. RESULTS: The analysis of the November 2019 exam showed a significant difference in average item difficulty between Helvetic and MKSAP-17 questions (71% vs 86%, p <0.001) and between MKSAP-15/16 and MKSAP-17 questions (70% vs 86%, p <0.001). There was no significant difference in item difficulty between Helvetic and MK

Unique bell-shaped underwater speleothems were recently reported from the deep (∼ 55 m) meromictic El Zapote sinkhole (cenote) on the Yucatán Peninsula, Mexico. The local diving community has termed these speleothems as Hells Bells because of their shape and appearance in a dark environment in ∼ 28-38 m water depth above a sulfidic halocline. It was also suggested that Hells Bells form under water, yet the mystery of their formation remained unresolved. Therefore, we conducted detailed hydrogeochemical and geochemical analyses of the water column and Hells Bells speleothems including stable carbon isotopes. Based on the comprehensive results presented in this study we deduce that both biogeochemical processes in the pelagic redoxcline and a dynamic halocline elevation of El Zapote cenote are essential for Hells Bells formation. Hells Bells most likely form in the redoxcline, a narrow 1-2 m thick water layer immediately above the halocline where a pelagic chemolithoautotrophic microbial community thrives from the upward diffusion of reduced carbon, nitrogen and sulfur species released from organic matter degradation in organic-rich debris. We hypothesize that chemolithoautotrophy, in particular proton-consuming nitrate-driven anaerobic sulfide oxidation, favors calcite precipitation in the redoxcline and hence Hells Bells formation. A dynamic elevation of the halocline as a hydraulic response to droughts, annual tidal variability and recharge events is further discussed, which might explain the shape of Hells Bells as well as their occurrence over a range of 10 m water depth. Finally, we infer that highly stagnant conditions, i.e., a thick halocline, a low-light environment and sufficient input of organic material into a deep meromictic cenote are apparent prerequisites for Hells Bells formation. This might explain their exclusivity to only a few cenotes in a restricted area of the northeastern Yucatán Peninsula.

Die getrennte Fütterung von hoch- und niederleistenden Milchkühen bietet Möglichkeiten die Tiergesundheit, die Leistung und das Wohlbefinden der Tiere zu steigern. Darüber hinaus ist auch die Umweltwirkung positiv zu bewerten. In kleinen und mittleren Herden ist eine Gruppentrennung jedoch mit einer höheren Arbeitsbelastung verbunden. Ziel der Untersuchung war daher die Möglichkeit einer elektronischen Gruppentrennung zu untersuchen. Es konnte gezeigt werden, dass der Arbeitszeitaufwand im Vergleich zur mechanischen Gruppentrennung deutlich reduziert kann, dass die Tore zuverlässig arbeiten und das sich die Tiere schnell an sie gewöhnen. Es wurde jedoch auch deutlich, dass die höheren Investitionskosten und der erhöhte Platzbedarf in die Bewertung einbezogen werden müssen.