Cellular & Molecular Imaging

Environmental predation is a major driver of bacterial evolution and may indirectly shape virulence through coincidental selection. However, how sustained versus fluctuating predator pressure influences long-term adaptive trajectories remains poorly understood. Here, we used experimental evolution to investigate the genetic and phenotypic responses of Pseudomonas aeruginosa to continuous, absent, or fluctuating exposure to the protozoan predator Tetrahymena thermophila over 180 days. Whole-population and isolate-level shotgun metagenomic sequencing revealed increasing mutation frequencies over time, extensive site-specific parallel evolution, and signatures of positive and purifying selection, with evidence of balancing selection under fluctuating conditions. High-frequency mutations targeted diverse functional pathways, indicating both shared and condition-specific adaptive responses. Phenotypic assays revealed widespread changes in motility, biofilm formation, siderophore production, protease activity, hemolysis, and cell size, while overall virulence in an invertebrate host model remained unchanged. Correlation analyses uncovered coordinated phenotypic shifts and genotype–phenotype associations, highlighting trade-offs among virulence-associated traits. Together, our results demonstrate that temporal variation in predator-mediated selection shapes both the pace and targets of bacterial adaptation, constraining the retention of virulence-related traits and emphasizing the ecological context underlying opportunistic pathogenicity.

Abstract During cell adhesion, integrin clusters support the transmission of mechanical forces to the substrate (mechanotransduction) and regulate biochemical signaling in response to substrate stiffness. Our current understanding of cell adhesion and mechanotransduction is based primarily on studies performed on rigid substrates. On fluid substrates such as supported lipid bilayers (SLBs), integrin ligands are mobile and, conventionally, adhesive complexes cannot serve as anchoring points to promote cell spreading. Here, we demonstrate that cells spread on SLBs coated with Invasin, a high-affinity integrin ligand. We show that, in contrast to SLBs functionalized with RGD peptides, integrin clusters grow in size and complexity on Invasin-SLBs to a similar extent as on glass. While actomyosin contraction dominates adhesion maturation on stiff substrates, we find that integrin mechanotransduction and cell spreading on fluid SLBs rely on dynein pulling forces along microtubules perpendicular to the supporting membranes and microtubules pushing on adhesive complexes, respectively. These forces, which may also occur on non-deformable surfaces, are hereby revealed in fluid substrate systems. Our findings, supported by a theoretical model, demonstrate a new mechanical role for microtubules in integrin clustering.

Here, we reconstituted bronchial epithelia from adult and child donors and show that SARS-CoV-2 infections spread fast, resulting in the formation and synchronized release of large clusters of infected cells and syncytia into the apical lumen, contributing to virus dissemination. Some epithelia, for the most part from children, revealed an intrinsic resistance to infection and virus spread. This infection control correlates with faster type III interferon secretion and can be transferred to permissive epithelia through exogenous interferon application. Child epithelia also showed a muted inflammatory response compared with adult, suggesting a specific and age-adapted epithelial response to SARS-CoV-2 infection that may explain why children are less susceptible to severe COVID-19.

Tara Expeditions are global scientific voyages that probe morphological and molecular diversity, evolution and ecology of marine plankton to explore how they are impacted by changes in the Earth's climate. The first expeditions collected samples of marine plankton containing viruses, bacteria, archaea, protists and planktonic metazoans living in the photic layer of the world's oceans. These expeditions, the first taking place between 2009 and 2013, include Tara Oceans: a global view, and Tara Oceans Polar Circle, both of which followed the same sampling protocol. This dataset includes 1074 pictures of 284 planktonic taxa (mainly microalgae and other Ciliate and Radiolarian protists) collected from the vicinity of the Marquesas Islands in the Southern Pacific Ocean during the Tara Oceans expedition. Multiple samples particularly of the size fractions 5-20 and 20 180 um from four sites and two depths were processed with different methods and studied in detail using scanning electron microscopy.

Light microscopy and scanning electron microscopy images of snow algae field samples containing Rosetta gen. nov., including type material.

Bacteria occupy heterogeneous environments, attaching and growing within pores in materials, living hosts, and matrices like soil. Systems that permit high-resolution visualization of dynamic bacterial processes within the physical confines of a realistic and tractable porous media environment are rare. Here we use microfluidics to replicate the grain shape and packing density of natural sands in a 2D platform to study the flow-induced spatial evolution of bacterial biofilms underground. We introduce a wildtype strain (Pantoea sp. YR343, n=3) or an EPS-defective strain (Pantoea sp. YR343 ΔUDP, n=3) to the porous media platform and then simulate a rainfall event using gravity-driven flow of bacterial growth media.

Aberrant biomolecular condensates are implicated in multiple incurable neurological disorders, including Amyotrophic Lateral Sclerosis, Frontotemporal Dementia, and DYT1 dystonia. However, the role of condensates in driving disease etiology remains incompletely understood. Here, we establish myeloid leukemia factor 2 (MLF2) as a disease-associated phase transition biomarker and develop a scalable high-content platform that identifies condensate modulators across broad chemical and genetic space. We uncover FDA-approved drugs that remodel aberrant condensate composition, validating the approach for drug discovery. A genome-wide CRISPR/Cas9 screen identifies genes linked to microcephaly and related neurodevelopmental disorders whose loss drives nuclear condensate accumulation. Machine learning resolves two phenotypic clusters: RNF26 deletion induces nuclear envelope condensates reminiscent of nuclear pore defects, whereas loss of microcephaly-associated ZNF335 drives accumulation of distinct nucleoplasmic condensates. Our study provides a scalable resource for identifying corrective modulators of aberrant condensates and establishes a link between dysregulated phase transitions and neurodevelopmental disorders.

Objectives: Reactive oxygen species (ROS) are short-lived and act in a site-specific manner, underscoring the importance of identifying the subcellular localization of their sources. ROS-generating NADPH oxidases (NOX) regulate pancreatic beta cell (dys)function. However, their subcellular localization and cytokine-mediated regulation in these cells remain largely unknown. We characterized the expression, subcellular localization and time-dependent cytokine-induced regulation of NOX isoforms in beta cells. Methods: Isoforms were studied via RT-qPCR, immunoblotting and immunofluorescence in rat islets and beta cell lines. Results: Beta cells express DUOX1 and DUOX2 proteins and Duoxa2 transcripts; lacking Duoxa1 expression. In INS-1E cells, NOX1 and DUOX1 localize in the endoplasmic reticulum (ER); DUOX2 in insulin vesicles; and NOX2 and NOX4 in vesicles, ER and plasma membrane. In INS-1E, cytokines increased expression of Nox1 and Duox1 at 4-8 h (returning to baseline at 16 h) and Nox2 and p47phox at 8 h (persisting until 24 h). Duox(a)2, p67phox and p40phox were downregulated and DUOX1 upregulated at 16-24 h. Conclusion: The absence of Duoxa1 in beta cells might lead to DUOX1 mismatching, impairing its trafficking and activity. NOXs in beta cells are diverse in subcellular localization and cytokine-induced regulation, suggesting their isoform-specific involvement in beta cell function, stress and apoptosis.

The Darwin Tree of Life project has the goal to sequence the genomes of 70,000 species of eukaryotic organisms in Britain and Ireland. This is a collection of photographs of the samples included in the study, provided by the National History Museum (NHM).

The Darwin Tree of Life project has the goal to sequence the genomes of 70,000 species of eukaryotic organisms in Britain and Ireland. This is a collection of photographs of the samples included in the study, provided by the National History Museum (NHM).