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A coccus (plural cocci, from the Latin coccinus (scarlet) and derived from the Greek kokkos (berry)), is any microorganism (usually bacteria) [1] whose overall shape is spherical or nearly spherical. [2] [3] [4] Coccus refers to the shape of the bacteria and can contain multiple genera, such as staphylococci or streptococci. Cocci can grow in ...
Cell shape is generally characteristic of a given bacterial species, but can vary depending on growth conditions. Some bacteria have complex life cycles involving the production of stalks and appendages (e.g. Caulobacter) and some produce elaborate structures bearing reproductive spores (e.g. Myxococcus, Streptomyces).
Bacterial morphological plasticity refers to changes in the shape and size that bacterial cells undergo when they encounter stressful environments. Although bacteria have evolved complex molecular strategies to maintain their shape, many are able to alter their shape as a survival strategy in response to protist predators, antibiotics, the immune response, and other threats.
A small number of other unusual shapes have been described, such as star-shaped bacteria. [42] This wide variety of shapes is determined by the bacterial cell wall and cytoskeleton and is important because it can influence the ability of bacteria to acquire nutrients, attach to surfaces, swim through liquids and escape predators. [43] [44]
Along with cell shape, Gram staining is a rapid diagnostic tool and once was used to group species at the subdivision of Bacteria. Historically , the kingdom Monera was divided into four divisions based on Gram staining: Firmicutes (+), Gracillicutes (−), Mollicutes (0) and Mendocutes (var.). [ 4 ]
It is described using terms like brittle, creamy, sticky and dry. Staphylococci are considered to have a creamy consistency, [1]: 173 while some Neisseria species are sticky, and colonies of diphtheroid bacteria and beta-hemolytic streptococci are typically dry. [1]: 167–8 Bacteria that produce capsules often have a slimy (mucoid) consistency.
However, this is not true pleomorphism, as individual virions are not changing shape, but being succeeded by virions with different shapes. One example is the bacterial viruses of the Plasmaviridae family. [13] A group of haloarchaeal viruses has been shown to exhibit pleomorphism as well. [14]
Cyanobacterial morphology refers to the form or shape of cyanobacteria. Cyanobacteria are a large and diverse phylum of bacteria defined by their unique combination of pigments and their ability to perform oxygenic photosynthesis. [2] [3] Cyanobacteria often live in colonial aggregates that can take a multitude of forms. [3]