Physiology and Sporulation in Clostridium
- Author: Peter Dürre1
- Editors: Patrick Eichenberger2, Adam Driks3
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VIEW AFFILIATIONS HIDE AFFILIATIONSAffiliations: 1: Institut für Mikrobiologie und Biotechnologie, Universität Ulm, 89069 Ulm, Germany; 2: New York University, New York, NY; 3: Loyola University Medical Center, Maywood, IL
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Received 12 October 2012 Accepted 31 March 2014 Published 08 August 2014
- Correspondence: P. Dürre, [email protected]

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Abstract:
Clostridia are Gram-positive, anaerobic, endospore-forming bacteria, incapable of dissimilatory sulfate reduction. Comprising approximately 180 species, the genus Clostridium is one of the largest bacterial genera. Physiology is mostly devoted to acid production. Numerous pathways are known, such as the homoacetate fermentation by acetogens, the propionate fermentation by Clostridium propionicum, and the butyrate/butanol fermentation by C. acetobutylicum, a well-known solvent producer. Clostridia degrade sugars, alcohols, amino acids, purines, pyrimidines, and polymers such as starch and cellulose. Energy conservation can be performed by substrate-level phosphorylation as well as by the generation of ion gradients. Endospore formation resembles the mechanism elucidated in Bacillus. Morphology, contents, and properties of spores are very similar to bacilli endospores. Sporulating clostridia usually form swollen mother cells and accumulate the storage substance granulose. However, clostridial sporulation differs by not employing the so-called phosphorelay. Initiation starts by direct phosphorylation of the master regulator Spo0A. The cascade of sporulation-specific sigma factors is again identical to what is known from Bacillus. The onset of sporulation is coupled in some species to either solvent (acetone, butanol) or toxin (e.g., C. perfringens enterotoxin) formation. The germination of spores is often induced by various amino acids, often in combination with phosphate and sodium ions. In medical applications, C. butyricum spores are used as a C. difficile prophylaxis and as treatment against diarrhea. Recombinant spores are currently under investigation and testing as antitumor agents, because they germinate only in hypoxic tissues (i.e., tumor tissue), allowing precise targeting and direct killing of tumor cells.
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Citation: Dürre P. 2014. Physiology and Sporulation in Clostridium. Microbiol Spectrum 2(4):TBS-0010-2012. doi:10.1128/microbiolspec.TBS-0010-2012.




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Abstract:
Clostridia are Gram-positive, anaerobic, endospore-forming bacteria, incapable of dissimilatory sulfate reduction. Comprising approximately 180 species, the genus Clostridium is one of the largest bacterial genera. Physiology is mostly devoted to acid production. Numerous pathways are known, such as the homoacetate fermentation by acetogens, the propionate fermentation by Clostridium propionicum, and the butyrate/butanol fermentation by C. acetobutylicum, a well-known solvent producer. Clostridia degrade sugars, alcohols, amino acids, purines, pyrimidines, and polymers such as starch and cellulose. Energy conservation can be performed by substrate-level phosphorylation as well as by the generation of ion gradients. Endospore formation resembles the mechanism elucidated in Bacillus. Morphology, contents, and properties of spores are very similar to bacilli endospores. Sporulating clostridia usually form swollen mother cells and accumulate the storage substance granulose. However, clostridial sporulation differs by not employing the so-called phosphorelay. Initiation starts by direct phosphorylation of the master regulator Spo0A. The cascade of sporulation-specific sigma factors is again identical to what is known from Bacillus. The onset of sporulation is coupled in some species to either solvent (acetone, butanol) or toxin (e.g., C. perfringens enterotoxin) formation. The germination of spores is often induced by various amino acids, often in combination with phosphate and sodium ions. In medical applications, C. butyricum spores are used as a C. difficile prophylaxis and as treatment against diarrhea. Recombinant spores are currently under investigation and testing as antitumor agents, because they germinate only in hypoxic tissues (i.e., tumor tissue), allowing precise targeting and direct killing of tumor cells.

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Figures

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FIGURE 1
Vegetative growth and sporulation/germination cycle in clostridia. During normal growth, Clostridium cells (shown is C. acetobutylicum) divide and multiply (left). During this period, acids, carbon dioxide, and hydrogen are formed. Upon signals not yet determined, cells start to differentiate into "clostridial forms" with granulose as a storage material (solventogenic species produce at this time acetone, butanol, or isopropanol), then form endospores, which finally will germinate into vegetative cells again.

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FIGURE 2
Signal transduction in C. acetobutylicum and B. subtilis leading to the onset of sporulation. (A) In C. acetobutylicum, three sensor kinases autophosphorylate at a histidine residue and transfer the phosphoryl group to an aspartate residue of the response regulator Spo0A. Cac0323 acts alone, while Cac0903 and Cac3319 act in concert. Cac0437 is a protein masquerading as a kinase, but acting as a phosphatase. (B) In B. subtilis, five different kinases channel the phosphoryl group to Spo0A via a phosphorelay consisting of Spo0F and Spo0B.
Tables

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TABLE 1
Major metabolic features of Clostridium
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