Usmani, M. | bioRxiv Science

bioRxiv2024

Cryo-ET reveals the in situ architecture of the polar tube invasion apparatus from microsporidian parasites

Microsporidia are divergent fungal pathogens that employ a harpoon-like apparatus called the polar tube (PT) to invade host cells. The PT architecture and its association with neighboring organelles remain poorly understood. Here, we use cryo-electron tomography to investigate the structural cell biology of the PT in dormant spores from the human-infecting microsporidian species, Encephalitozoon intestinalis. Segmentation and subtomogram averaging of the PT reveal at least four layers: two protein-based layers surrounded by a membrane, and filled with a dense core. Regularly spaced protein filaments form the structural skeleton of the PT. Combining cryo-electron tomography with cellular modeling, we propose a model for the 3-dimensional organization of the polaroplast, an organelle that is continuous with the membrane layer that envelops the PT. Our results reveal the ultrastructure of the microsporidian invasion apparatus in situ, laying the foundation for understanding infection mechanisms.

microbiology↗

bioRxiv2023

Environmental Factors Associated with Incidence and Distribution of V. parahaemolyticus and V. vulnificus in Chesapeake Bay, Maryland, USA: A three-year case study

Members of the genus Vibrio are ecologically significant bacteria native to aquatic ecosystems globally, and a few can cause diseases in humans. Vibrio-related illnesses have increased in recent years, primarily attributed to changing environmental conditions. Therefore, understanding the role of environmental factors in the occurrence and growth of pathogenic strains is crucial for public health. Water, oyster, and sediment samples were collected between 2009 and 2012 from Chester River and Tangier Sound sites in Chesapeake Bay, Maryland, USA, to investigate the relationship between water temperature, salinity, and chlorophyll with the incidence and distribution of Vibrio parahaemolyticus (VP) and Vibrio vulnificus (VV). Odds ratio analysis was used to determine association between the likelihood of VP and VV presence and these environmental variables. Results suggested that water temperature threshold of 20{degrees}C or higher was associated with an increased risk, favoring the incidence of Vibrio spp. A significant difference in salinity was observed between the two sampling sites, with distinct ranges showing high odds ratio for Vibrio incidence, especially in water and sediment, emphasizing the impact of salinity on VP and VV incidence and distribution. Notably, salinity between 9-20 PPT consistently favored the Vibrio incidence across all samples. Relationship between chlorophyll concentrations and VP and VV incidence varied depending on sample type. However, chlorophyll range of 0-10 {micro}g/L was identified as critical in oyster samples for both vibrios. Analysis of odds ratios for water samples demonstrated consistent outcomes across all environmental parameters, indicating water samples offer a more reliable indicator of Vibrio spp. incidence. ImportanceUnderstanding the role of environmental parameters in the occurrence of Vibrio species posing significant public health risks and economic burdens such as Vibrio parahaemolyticus and Vibrio vulnificus are of paramount importance. These aquatic bacteria are responsible for various human diseases, including gastroenteritis and wound infections, which can be severe and sometimes fatal. Recent observations suggest that certain environmental conditions may favor the growth of Vibrio, leading to more severe disease outcomes. By investigating the environmental factors that influence the occurrence of Vibrio parahaemolyticus and Vibrio vulnificus, the need to gain insights into the favorable ranges of environmental variables is apparent. The significance of this research is in identifying the favorable ranges of environmental and ecological factors, which holds the potential to provide an aid in the intervention and mitigation strategies through the development of predictive models, ultimately enhancing our ability to manage and control diseases caused by these pathogens.

ecology↗

bioRxiv2020

3-Dimensional Organization and Dynamics of the Microsporidian Polar Tube Invasion Machinery

Microsporidia, a divergent group of single-celled eukaryotic parasites, harness a specialized harpoon-like invasion apparatus called the polar tube (PT) to gain entry into host cells. The PT is tightly coiled within the transmissible extracellular spore, and is about 20 times the length of the spore. Once triggered, the PT is rapidly ejected and is thought to penetrate the host cell, acting as a conduit for the transfer of infectious cargo into the host. The organization of this specialized infection apparatus in the spore, how it is deployed, and how the nucleus and other large cargo are transported through the narrow PT are not well understood. Here we use serial block-face scanning electron microscopy to reveal the 3-dimensional architecture of the PT and its relative spatial orientation to other organelles within the spore. Using high-speed optical microscopy, we also capture and quantify the entire PT germination process in vitro. Our results show that the emerging PT experiences very high accelerating forces to reach velocities exceeding 300 m.s-1, and that firing kinetics differ markedly between species. Live-cell imaging reveals that the nucleus, which is approximately 7 times larger than the diameter of the PT, undergoes extreme deformation to fit through the narrow tube, and moves at speeds comparable to PT extension. Our study sheds new light on the 3-dimensional organization, dynamics, and mechanism of PT extrusion, and shows how infectious cargo moves through the tube to initiate infection.

microbiology↗