From MicrobeWiki, the student-edited microbiology resource
A Microbial Biorealm page on the genus Clostridium botulinum
Higher order taxa
Description and significance
The bacterium Clostridium botulinum is a rod-shaped organism of the genus Clostridium. Most commonly found in soil, Clostridium botulinum are found to grow most efficiently in low-oxygen conditions. Clostridium botulinum was first discovered and isolated by Emile van Ermengem in 1896, and was later determined to survive by forming spores, remaining in a dormant state until environmental conditions arise that allow them to grow. The importance of sequencing the genome of Clostridium Botulinum lies in its ability to produce a toxin known as botulin, one of the most powerful known toxins that leads to the paralytic illness known as botulism.
The genome size of C. botulinum is estimated to be around 4,039 kbp, determined from the summation of restriction fragments of MluI, RsrII, and SmaI restriction endonuclease digestions. The size of the chromosome of C. botulinum is relatively larger than many other gram-positive bacteria studied, possibly indicating that extra genomic requirements are needed for sporulation or the formation of disease-inducing toxins. Genomic analysis by pulse-field gel electrophoresis revealed genes encoding neurotoxin, hemagglutinin A, and genese for a temperate phage, and various transposon Tn916 sites.
Cell structure and metabolism
Clostridium botulinum is a gram-positive bacteria that is typically rod-shaped and arranged as singles, pairs, or chains. C. botulinum lies dormant in the form of spores until the right environmental conditions are met. These spores are very resistant to adverse environmental effects, making them amenable to most environments and very hard to kill. The spores will grow under favorable conditions (anaerobiosis and substrate-rich environments) and will begin to produce their toxins as they rapidly propagate.
To prevent the occurrence of this bacterium in processed foods, many companies can their food with a pressurized boil to kill the bacterium with high temperatures. Other techniques include high levels of oxygen, high acidity, high ratio of dissolved sugar, or very low levels of moisture.
The endospores that are produced from C. botulinum can survive in a vast array of environments until it meets the correct conditions to proliferate. In order for proliferation to occur, the spores need to be present in non-halophilic salinity and anaerobic conditions. C. botulinum can have multiple habitats, mainly in the soil and possibly food products. This bacterium is also mesophilic, with an optimal temperature of around 37 degrees celsius.
Clostridium botulinum consists of seven different subtypes, labeled with the letters A-G. Each of these subtypes produce a different botulin toxin, all of which, with the exception of C and D, are human pathogens. Types A and B, which are commonly found in soil, are primarily the cause of botulism outbreaks in the United States, while Type E, which is found in fish, also contributes to cases of botulism in the country.
The botulinum toxins most active forms are as dichain molecules, where heavy chains are linked to light chains via disulphide bonding. Toxicity has appeared to be associated with the L chain, which blocks primarily on peripheral cholinergic synapses to prevent the calcium mediated release of acetylcholine, most likely interfering with the mechanism of exocytosis where vesicles containing neurotransmitters fuse with the cell membrane. The toxin prevents the propagation of action potentials to the muscle fibers, inducing paralysis by inhibiting muscle contraction. A main cause of death from this disease involve death by asphyxiation, which is caused by the inability of the chest muscles to contract to facilitate breathing. Other effects of botulism, which affects both man and animals, include impaired vision and widespread muscular weakness.
Currently there is no known cure for the toxic paralysis of botulism. Although antitoxins do exist for this disease, by the time the symptoms of botulism show the toxin is irreversibly bound. At most the antitoxins may serve to neutralize the unbound toxin, but it is unable to reverse the binding of any toxins that are already exacting their effect.
Application to Biotechnology
One conventional use of the toxins form C. botulinum include its effectiveness in treating a variety of conditions involving involuntary muscle spasm. A neurotoxin-haemagglutinin complex from Subtype A of Clostridium botulinum is used as a therapeutic toxin as an alternative to surgery in the treatment of strabismus and some focal dystonias.
Clostridium botulinum A A (Hall strain A (ATCC 3502)) (Project ID: 193) at Sanger Institute [In progress]
Mitchell WJ, Tewatia P, Meaden PG. Genomic analysis of the phosphotransferase system in Clostridium botulinum. J Mol Microbiol Biotechnol. 2007;12(1-2):33-42. PMID: 17183209 [PubMed - in process]
Devriese, PP (1999) "On the discovery of Clostridium botulinum" J Hist Neurosci 8: 43-50
Lin, WJ, Johnson, EA Genome analysis of Clostridium botulinum type A by pulsed-field gel electrophoresis Appl. Environ. Microbiol. 1995 61: 4441-4447
Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill. ISBN 0838585299.
Madigan M; Martinko J (editors). (2005). Brock Biology of Microorganisms, 11th ed., Prentice Hall. ISBN
Wells CL, Wilkins TD (1996). Botulism and Clostridium botulinum in: Baron's Medical Microbiology (Baron S et al, eds.), 4th ed., Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1
Edited by Brannon Peralta student of Rachel Larsen and Kit Pogliano