The mechanosensitive channel of small conductance (MscS) protects bacteria against hypoosmotic shock. It can sense the tension in the surrounding membrane and releases solutes if the pressure in the cell is getting too high. The membrane contacts MscS at sensor paddles, but lipids also leave the membrane and move along grooves between the paddles to reside as far as 15 Å away from the membrane in hydrophobic pockets. One sensing model suggests that a higher tension pulls lipids from the grooves back to the membrane, which triggers gating. However, it is still unclear to what degree this model accounts for sensing and what contribution the direct interaction of the membrane with the channel has. Here, we show that MscS opens when it is sufficiently delipidated by incubation with the detergent dodecyl-β-maltoside or the branched detergent lauryl maltose neopentyl glycol. After addition of detergent-solubilized lipids, it closes again. These results support the model that lipid extrusion causes gating: Lipids are slowly removed from the grooves and pockets by the incubation with detergent, which triggers opening. Addition of lipids in micelles allows lipids to migrate back into the pockets, which closes the channel even in the absence of a membrane. Based on the distribution of the aliphatic chains in the open and closed conformation, we propose that during gating, lipids leave the complex on the cytosolic leaflet at the height of highest lateral tension, while on the periplasmic side, lipids flow into gaps, which open between transmembrane helices.

Responses of the microbiota to diet are highly personalized but mechanistically not well understood because many metabolic capabilities and interactions of human gut microorganisms are unknown. Here we show that sulfoquinovose (SQ), a sulfonated monosaccharide omnipresent in green vegetables, is a selective yet relevant substrate for few but ubiquitous bacteria in the human gut. In human feces and in defined co-culture, Eubacterium rectale and Bilophila wadsworthia used recently identified pathways to cooperatively catabolize SQ with 2,3-dihydroxypropane-1-sulfonate as a transient intermediate to hydrogen sulfide (H2S), a key intestinal metabolite with disparate effects on host health. SQ-degradation capability is encoded in almost half of E. rectale genomes but otherwise sparsely distributed among microbial species in the human intestine. However, re-analysis of fecal metatranscriptome datasets of four human cohorts showed that SQ degradation (mostly from E. rectale and Faecalibacterium prausnitzii) and H2S production (mostly from B. wadsworthia) pathways were expressed abundantly across various health states, demonstrating that these microbial functions are core attributes of the human gut. The discovery of green-diet-derived SQ as an exclusive microbial nutrient and an additional source of H2S in the human gut highlights the role of individual dietary compounds and organosulfur metabolism on microbial activity and has implications for precision editing of the gut microbiota by dietary and prebiotic interventions.

The validation of novel target-specific radioligands requires animal experiments mostly using mice with xenografts. A pre-selection based on a simpler in vivo model would allow to reduce the number of animal experiments, in accordance with the 3Rs principles (reduction, replacement, refinement). In this respect, the chick embryo or hen’s egg test–chorioallantoic membrane (HET-CAM) model is of special interest, as it is not considered an animal until day 17. Thus, we evaluated the feasibility of quantitative analysis of target-specific radiotracer accumulation in xenografts using the HET-CAM model and combined positron emission tomography (PET) and magnetic resonance imaging (MRI). For proof-of-principle we used established prostate-specific membrane antigen (PSMA)-positive and PSMA-negative prostate cancer xenografts and the clinically widely used PSMA-specific PET-tracer [68Ga]Ga-PSMA-11. Tracer accumulation was quantified by PET and tumor volumes measured with MRI (n = 42). Moreover, gamma-counter analysis of radiotracer accumulation was done ex-vivo. A three- to five-fold higher ligand accumulation in the PSMA-positive tumors compared to the PSMA-negative tumors was demonstrated. This proof-of-principle study shows the general feasibility of the HET-CAM xenograft model for target-specific imaging with PET and MRI. The ultimate value for characterization of novel target-specific radioligands now has to be validated in comparison to mouse xenograft experiments.

Assessment of biodistribution and specific tumor accumulation is essential for the development of new radiopharmaceuticals and requires animal experiments. The HET-CAM (hens-egg test—chorioallantoic membrane) model can be used in combination with the non-invasive imaging modalities PET and MRI for pre-selection during radiopharmaceutical development to reduce the number of animal experiments required. Critical to the acceptance of this model is the demonstration of the quantifiability and reproducibility of these data compared to the standard animal model. Tumor accumulation and biodistribution of the PSMA-specific radiotracer [18F]F-siPSMA-14 was analyzed in the chick embryo and in an immunodeficient mouse model. Evaluation was based on MRI and PET data in both models. γ-counter measurements and histopathological analyses complemented these data. PSMA-specific accumulation of [18F]F-siPSMA-14 was successfully demonstrated in the HET-CAM model, similar to the results obtained by mouse model studies. The combination of MR and PET imaging allowed precise quantification of peptide accumulation, initial assessment of biodistribution, and accurate determination of tumor volume. Thus, the use of the HET-CAM model is suitable for the pre-selection of new radiopharmaceuticals and potentially reduces animal testing in line with the 3Rs principles of animal welfare.

Establishing the etiology of invasive fungal infections is important to guide therapeutic options and for epidemiologic purposes. Formalin-fixed, paraffin-embedded (FFPE) tissue specimens from patients with proven invasive fungal infections are valuable to determine the etiology of systemic fungal infections. We compared different polymerase chain reaction (PCR) amplification strategies from FFPE tissue blocks to identify agents of invasive fungal infections. We found that specific PCR assays show superior sensitivity in the identification of DNA of Mucorales and Aspergillus and mixed infections caused by both as compared to broad-range PCR assays. Shorter amplicon lengths and less detection of contaminating fungal DNA are potential factors involved. However, detection of fungal DNA by highly sensitive specific PCR assays in the absence of demonstration of fungal elements in tissue suggests that PCR results should be interpreted in the context of the histopathology and clinical findings.