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Subject: Micro-Biology
Topic Name:- Phylum Spirochaetes: Bacteria with a Corkscrew Morphology
by - Vidyanand Jha
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INTRO
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The phylum Spirochaetes (Greek spira, a coil, and chaete, hair) contains Gram-negative, chemoorganotrophic bacteria distinguished by their structure and mechanism of motility. Carbohydrates, amino acids, long-chain fatty acids, and long-chain fatty alcohols may serve as carbon and energy sources summarizes some of the more distinctive properties of selected genera. Spirochetes are morphologically unique. They are slender, long bacteria (0.1 to 3.0 mm by 5 to 250 mm) with a flexible, helical shape.The central protoplasmic cylinder, which contains cytoplasm and the nucleoid, is bounded by a plasma membrane and a Gram-negative cell wall (figure 21.19). Two to more than a hundred flagella, called axial fibrils or periplasmic flagella, extend from both ends of the cylinder and often overlap one another in the center third of the cell (also see figure 3.47). The whole complex of periplasmic flagella lies inside a flexible outer. membrane sheath. This outer sheath is made of lipid, protein, and carbohydrate, and varies in structure between different genera. Its precise function is unknown, but the sheath is essential because spirochetes die if it is damaged or removed. The outer membrane sheath of Treponema pallidum, the causative agent of syphilis, has few proteins exposed on its surface. This helps the spirochete avoid attack by host antibodies.
Spirochetes are exceptionally diverse ecologically and grow in habitats ranging from mud to the human mouth. Members of the genus Spirochaeta are free-living and often grow in anoxic and sulfide-rich freshwater and marine environments. Some species of the genus Leptospira grow in oxic water and moist soil. Some spirochetes form symbiotic associations with other organisms and are found in a variety of locations: the hindguts of termites and wood-eating roaches, the digestive tracts of mollusks (Cristispira) and mammals, and the oral cavities of animals (Treponema denticola, T. oralis). Spirochetes from termite hindguts and freshwater sediments can fix nitrogen. Spirochetes coat the surfaces of many protists that live in the guts of termites and wood-eating roaches. For example, the flagellate Mixotricha paradoxa, a termite symbiont, is covered with slender spirochetes (0.15 by 10 mm in length) that are firmly attached and help move the protist
====== Tags ======
#phylum_spirochaetes
#corkscrew_morphology
#zilms
#Spirochaetes_Bacteria
#Spirochaetes_motility
#microbiology
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