Abstract
Clostridium sordellii is an often-lethal bacterium causing human and animal disease. Crucial to the infectious cycle of C.sordellii is its ability to produce spores, which can germinate into toxin-producing vegetative bacteria under favorable conditions. However, structural details of the C.sordellii spore are lacking. Here, we used a range of electron microscopy techniques together with superresolution optical microscopy to characterize the C.sordellii spore morphology with an emphasis on the exosporium. The C.sordellii spore is made up of multiple layers with the exosporium presenting as a smooth balloon-like structure that is open at the spore poles. Focusing on the outer spore layers, we compared the morphologies of C.sordellii spores derived from different strains and determined that there is some variation between the spores, most notably with spores of some strains having tubular appendages. Since Clostridium difficile is a close relative of C.sordellii, their spores were compared by electron microscopy and their exosporia were found to be distinctly different from each other. This study therefore provides new structural details of the C.sordellii spore and offers insights into the physical structure of the exosporium across clostridial species. IMPORTANCEClostridium sordellii is a significant pathogen with mortality rates approaching 100%. It is the bacterial spore that is critical in initiating infection and disease. An understanding of spore structures as well as spore morphology across a range of strains may lead to a better understanding of C.sordellii infection and disease. However, the structural characteristics of the C.sordellii spores are limited. In this work, we have addressed this lack of detail and characterized the C.sordellii spore morphology. The use of traditional and advanced microscopy techniques has provided detailed new observations of C.sordellii spore structural features, which serve as a reference point for structural studies of spores from other bacterial species.
Highlights
Clostridium sordellii is an often-lethal bacterium causing human and animal disease
The spore morphology of C. sordellii strains that represent clinical and animal isolates derived from different geographical locations and which represent a range of clades was characterized by TEM imaging of the whole spore (Fig. 1)
Within each C. sordellii strain, there was a wide distribution in spore measurements, with spores showing the greatest variation in their exosporial lengths (Fig. 2C) and the least variation in their inner spore width (Fig. 2B)
Summary
Clostridium sordellii is an often-lethal bacterium causing human and animal disease. Crucial to the infectious cycle of C. sordellii is its ability to produce spores, which can germinate into toxin-producing vegetative bacteria under favorable conditions. Structural details of the C. sordellii spore are lacking. This study provides new structural details of the C. sordellii spore and offers insights into the physical structure of the exosporium across clostridial species. An understanding of spore structures as well as spore morphology across a range of strains may lead to a better understanding of C. sordellii infection and disease. TcsL and TcsH are orthologs of the Clostridium difficile ( known as Clostridioides difficile [1]) TcdB and TcdA toxins, respectively, and are believed to be important for C. sordellii-mediated disease pathogenesis [11]. The exosporium is believed to be functionally important as it is the point of contact between the spore and the environment
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