Chapter 16 : Clostridium perfringens Sporulation and Sporulation-Associated Toxin Production

Ultrastructure of C. perfringens spores. Transmission electron micrograph of a spore from C. perfringens strain H-6, a food poisoning strain. Components of spore shown include proteinaceous spore coat layers, the cortex region, and the core with ribosomes giving a granular appearance. The bar represents 1.0 µM. Reproduced with permission from reference 9 .

Sporulation-associated sigma factors are required for C. perfringens sporulation. Shown are photomicrographs of sporulating cultures of SM101, a transformable derivative of a food poisoning strain, after growth for 8 h in Duncan-Strong sporulation medium. Also shown is the absence of sporulating cells in similar Duncan-Strong cultures of a sigF or sigG null mutant of SM101 (SM101::sigF or SM101::sigG). This loss of sporulation was specifically due to inactivation of the sigF or sigG genes in those mutants since the effect was reversible by complementation, i.e., by adding back a wild-type sigF or sigG gene, respectively, to those mutants (SM101::sigFComp or SM101::sigGComp). Reproduced with permission from reference 28 . Similar loss of sporulation was observed with sigE or sigK mutants of SM101 ( 29 ).

Sporulation in C. perfringens. Working through unidentified intermediates, the Agr QS system and CcpA affect Spo0A expression or, possibly, phosphorylation to initiate sporulation. This triggers a cascade of sigma factors where SigF controls production of the three other sporulation-associated sigma factors. Two of these sigma factors (SigE and SigK) then regulate CPE production during sporulation. Compiled from references 28 , 29 , 31 , and 44 . Not shown in this drawing, SigE (and possibly SigK) can also regulate production of TpeL toxin ( 97 ).

DNA binding properties of recombinant His6-tagged SASP4. (A) Electromobility shift assays (EMSAs) showing binding to biotin-labeled C. perfringens DNA by purified rSASP4 from F4969 (a CPE-positive non-foodborne human GI disease strain that forms sensitive spores and produces an SASP4 variant with a Gly at residue 36), SM101 or 01E809 (two CPE-positive food poisoning isolates that form resistant spores and produce an SASP4 variant with Asp at residue 36). (B) EMSAs showing binding by purified SM101 rSASP4 or rSASP2 to (left) C. perfringens AT-rich biotin-labeled DNA or (right) biotin-labeled C. perfringens GC-rich DNA. Reproduced with permission from references 42 and 78 .

Current model for the mechanism of action of CPE. CPE binds to claudin receptors to form small complexes. Those small complexes then oligomerize on the host cell surface to form an ∼450-kDa prepore known as CH-1. The prepore inserts into the membrane to form an active pore that alters host plasma membrane permeability for small molecules. As a result, calcium enters the cytoplasm and triggers either apoptosis (caused by low CPE doses, where there is a modest calcium influx) or oncosis (caused by high CPE doses, where there is a strong calcium influx). Reproduced with permission from reference 1 .