Download Bacterial Shapes and Size: Cocci, Bacillus, and Spirals and more Study notes Bacteriology in PDF only on Docsity! Shape of Bacteria Bacteria are prokaryotic single-celled, microscopic organisms (Exceptions have been discovered that can reach sizes just visible to the naked eye. They include Epulopiscium fishelsoni, a bacillus-shaped bacterium that is typically 80 micrometers (µm) in diameter and 200-600 µm long, and Thiomargarita namibiensis, a spherical bacterium between 100 and 750 µm in diameter.) generally much smaller than eukaryotic cells. very complex despite their small size. Even though bacteria are single-celled organisms, they are able to communicate with one another through a process called quorum sensing. In this way they can function as a multicellular population rather than as individual bacteria. Bacterial cell shape is determined primarily by a protein called MreB. MreB forms a spiral band – a simple cytoskeleton – around the interior of the cell just under the cytoplasmic membrane. It is thought to define shape by recruiting additional proteins that then direct the specific pattern of bacterial cell growth. For example, bacillus-shaped bacteria that have an inactivated MreB gene become coccoid shaped, and coccus-shaped bacteria naturally lack the MreB gene. Most bacteria come in one of three basic shapes: coccus, rod or bacillus, and spiral. 1. Coccus The cocci are spherical or oval bacteria having one of several distinct arrangements based on their planes of division. a. Division in one plane produces either a diplococcus or streptococcus arrangement. diplococcus: cocci arranged in pairs . Streptococcus pneumoniae, Neisseria a diplococcus streptococcus: cocci arranged in chains - Streptococcus pyogenes, a streptococcus - Enterococcus b. Division in two planes produces a tetrad arrangement. tetrad: cocci arranged in squares of 4 - Micrococcus luteus showing several tetrads c. Division in three planes produces a sarcina arrangement. sarcina: cocci in arranged cubes of 8 d. Division in random planes produces a staphylococcus arrangement. staphylococcus: cocci arranged in irregular, often grape-like clusters - Staphylococcus aureus An average coccus is about 0.5-1.0 micrometer (µm) in diameter. (A micrometer equals 1/1,000,000 of a meter.) Coccus
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Staphylococcus species
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Streptococcus species
Bacillus Clostridiumspp. Listeriaspp. Mycobacterium tuberculosis
Klebsiella pneomonae
Spirochetes
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Leptospira
Treponema pallidum
Spirochetes
