Szczepaniak, C. | bioRxiv Science

bioRxiv2025

Pera virus mimics bacteria to infect Pedopumella sp. a freshwater heterotrophic Chrysophyceae

Heterotrophic Chrysophyceae play a key role in the functioning of many aquatic food webs as primary predators of prokaryotes, but their top-down regulatory factors are poorly understood. To date, no virus isolates from heterotrophic Chrysophyceae have been described in the literature. Here we describe Pera virus, a giant virus infecting the heterotrophic Chrysophyceae Pedospumella sp.. Pera virus have an icosahedral capsid-vesicle morphology, a feature unprecedented in viruses. We hypothesize that this vesicle mimics the shape of bacteria so that the virus is recognized as such by its bacteriophage protist host. This constitutes a morphological evolution of viruses that promotes infection of their heterotrophic host. The capside measures 414 nm in diameter. The vesicle has a variable diameter ranging from 231 to 587 nm. The virion as a whole can reach 1008 nm in length. We searched for this new type of virus under environmental conditions during time series studies in hyper-eutrophic freshwater lakes. Surprisingly, we report the existence of Pera virus-like particles (PVLs) of various shapes and size that can reach 5 {micro}m illustrating the hidden diversity of this undescribed virus types. The dynamics of PVLs, which can reach 2.4 x 105 PVL.mL-1, are closely associated with those of unicellular heterotrophic eukaryotes, acting as major regulatory agents of protozoan bacterivory in freshwater. This pair provides a new model for understanding the evolution of giant viruses and their ecological role.

ecology↗

bioRxiv2022

Spatial distribution and physicochemical properties of respirable volcanic ash from the 16-17 August 2006 Tungurahua eruption (Ecuador), and alveolar epithelium response in-vitro

BackgroundTungurahua volcano (Ecuador) intermittently emitted ash between 1999 and 2016, enduringly affecting the surrounding rural area and its population, but its health impact remains poorly documented. ObjectivesWe aim at assessing the respiratory health hazard posed by the 16-17 August 2006 most intense eruptive phase of Tungurahua. MethodsBased on detailed field surveys and grain size analyses, we mapped the spatial distribution of the health-relevant ash size fractions produced by the eruption in the area impacted by ash fallout. We used Scanning Electron Microscopy and Raman Spectroscopy to quantify the mineralogy, composition, surface texture and morphology of a respirable ash sample isolated by aerodynamic separation. The cytotoxicity and pro-inflammatory potential of this respirable ash towards lung tissues was assessed in-vitro using A549 alveolar epithelial cells, by Electron Microscopy and biochemical assays (LDH assay, RT-qPCR, multiplex immunoassays). ResultsThe eruption produced a high amount of inhalable and respirable ash (12.0-0.04 kg/m2 of sub-10 {micro}m and 5.3-0.02 kg/m2 of sub-4 {micro}m ash deposited). Their abundance and proportion vary greatly across the deposit within the first 20 km from the volcano. The respirable ash is characteristic of an andesitic magma and no crystalline silica is detected. Morphological features and surface textures are complex and highly variable, with few fibres observed. In-vitro experiments show that respirable volcanic ash are internalized by A549 cells and processed in the endosomal pathway, causing little cell damage, but some changes in cell morphology and membrane texture. The ash trigger a weak pro-inflammatory response. DiscussionThese data provide the first understanding of the respirable ash hazard near Tungurahua, and the extent to which it varies spatially in a fallout deposit. Given the long exposure duration of the surrounding population, the chronic effects of this inhalable, weakly bio-reactive ash on health could be further investigated.

ecology↗