Rank: Species
Lineage: Bacteria;Firmicutes;Clostridia;Clostridiales;Clostridiaceae;Clostridium;Clostridium tetani
Description: Clostridium. This genus comprises about 150 metabolically diverse species of anaerobes that are ubiquitous in virtually all anoxic habitats where organic compounds are present, including soils, aquatic sediments and the intestinal tracts of animals and humans. Characteristic of clostridia is the shape of their cells that resembles a drumstick or spindle ("kloster" is Greek for "spindle"). This shape is attributed to the presence of endospores that develop under conditions unfavorable for vegetative growth and distend single cells terminally or sub-terminally. The endospores of many species are extremely sturdy and survive extended boiling in water and exposure to air. Spores germinate under conditions favorable for vegetative growth, such as anaerobiosis and presence of organic substrates. From the evolutionary perspective, clostridia are considered to be the most ancient bacteria. It is believed that present day Mollicutes (Eubacteria) have evolved regressively (i.e., by genome reduction) from gram-positive clostridia-like ancestors with a low GC content in DNA. Several species of clostridia (e.g., C. perfringens, C. botulinum, C. tetani) are known opportunistic toxin-producing pathogens in animals and humans. Some species are capable of producing organic solvents (acetone, ethanol, etc,), molecular hydrogen and other useful compounds. There are also species that can fix molecular nitrogen and thus are important participants in biological turnaround of nitrogen compounds in nature.Clostridium tetani. This organism causes tetanus (lockjaw) in humans. C. tetani spores can be acquired from any type of skin trauma involving an infected device. If an anaerobic environment is present, the spores will germinate and eventually form active C. tetani cells. At the tissue level, the bacterium then releases an exotoxin called tetanospasmin that causes certain nervous system irregularities by means of retrograde tramsmission through neurons to the brain. One of the toxin's effects includes constant skeletal muscle contraction due to a blockage of inhibitory interneurons that regulate muscle contraction. Prolonged infection eventually leads to respiratory failure, among other things. If not treated early, the mortality rates of this disease are high.Tetanospasmin initially binds to peripheral nerve terminals. It is transported within the axon and across synaptic junctions until it reaches the central nervous system. There it becomes rapidly fixed to gangliosides at the presynaptic inhibitory motor nerve endings, and is taken up into the axon by endocytosis. The effect of the toxin is to block the release of inhibitory neurotransmitters (glycine and gamma-amino butyric acid) across the synaptic cleft, which is required to check the nervous impulse. If nervous impulses cannot be checked by normal inhibitory mechanisms, it produces the generalized muscular spasms characteristic of tetanus. Tetanospasmin appears to act by selective cleavage of a protein component of synaptic vesicles, synaptobrevin II, and this prevents the release of neurotransmitters by the cells.
Reference Material:
https://www.ncbi.nlm.nih.gov/genome/?term=Clostridium%20tetani
