Treponema pallidum) have been shown to contain a slime layer covering the cell. These include the outer and inner membrane, the peptidoglycan layer as well as the cytoplasmic membrane. Like a number of other bacteria, the cell body of spirochetes is enclosed within several layers. * The cell-wall-cell membrane complex is referred to as parietocytoplasmic membrane. Like other bacteria, the internal environment of the cell has a simple arrangement consisting of a nucleoid, mesosomes, vacuoles, and ribosome. This is the cell body and consists of a cell wall, cytoplasmic membrane as well as cell contents (cytoplasmic contents) enclosed within. The protoplasmic cylinder is located beneath the outer sheath. * The axial filaments/fibrils are also commonly referred to as the endocellular flagella in spirochetes. Apart from giving the organism its shape, the axial fibrils (axial filaments) have been shown to contribute to the movement of spirochetes through a twisting motion. When the sheath is removed, the internal core is estimated to range between 10 and 16nm in diameter. While it has similarities to the shaft found in bacterial flagella, it's located between the inner and outer membranes (within the periplasmic space) along the length of the organism.Īs already mentioned, the shaft (filament) of the axil fibril is covered by a sheath (covering that encloses the shaft). It also consists of an insertion apparatus that differentiate into a terminal knob.ĭepending on the species, the shaft has been shown to either have a filamentous or globular substructure. The axial fibril, which has a similar structure to flagellum found in bacteria, consists of a shaft and a covering sheath. Today, it's well understood that this morphology is a result of the flexible peptidoglycan cell wall wound by several axial fibrils.Īlong with the cell wall, these fibrils are in turn covered by an outer membrane similar to the membrane found in Gram-negative bacteria. From early records, it's believed that spirochetes were first observed under the microscope by Van Leeuwenhoek, who noted that in their motion, they "bent their body into curves in going forwards" (Holt, 1978, p. Some of the other habitats in which spirochetes can be found include:Īs the name suggests, spirochetes have a spiral morphology that has been used to classify them based on morphology. They are mostly found in different environments where they survive on a variety of organic matter (disaccharides, pentoses, and hexoses, etc). Anaerobic and facultative anaerobic spirochetes exist as free-living forms and include members of the genus Spirochaeta. Members of the genus Leptospira are classified as obligatory aerobic spirochetes. Obligatory aerobic spirochetes (need oxygen for metabolism) can be found in water and soil as free-living organisms with some species living as pathogens in their hosts. Lyme disease, dysentery, etc).īecause of the diversity between species and where they are found in nature, spirochetes have also been classified based on their distribution. While some of the species are beneficial, some are pathogenic and tend to cause diseases (e.g. Many of the species have been shown to exist as free-living organisms and can be found in various habitats in water (surface water/freshwater), lakes, salt marsh sediments, mud, sediments, and deep-sea vents among others.Īpart from the species found in these habitats, others form an association with various hosts (termites, protozoa, mammals, etc) and are therefore found living within these hosts (in the intestine). This order is further divided into three major phylogenetic families including Spirochaetaceae, Brachyspiraceae, and Leptospiraceae.Īs a group of bacteria, spirochetes are widely distributed in nature and can be found in different environments across the world. In nature, they may exist as facultative anaerobes, obligate anaerobes, or obligate aerobes. They display significant variation in their physiology and distribution. Order: Spirochaetales - Helically-shaped bacteria capable of locomotion. They are generally thin with a spiral-shaped appearance and possess flagella commonly known as axial filaments. Phylum: Spirochaetes - Bacterial cells characterized by a unique diderm (double-membrane) that gives them their Gram-negative characteristic. They may exist as parasites, free-living organisms or as symbionts with some of the species being very beneficial to man. Domain: Bacteria - A large group of single-celled prokaryotes (lacking membrane-bound organelles) found in just about any environment across the world (soil, water, air, hot streams etc).
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