Bacteria - Morphology


Further information: Bacterial cellular morphologies

Bacteria display a wide diversity of shapes and sizes, called morphologies. Bacterial cells are about one tenth the size of eukaryotic cells and are typically 0.5–5.0 micrometres in length. However, a few species — for example, Thiomargarita namibiensis and Epulopiscium fishelsoni — are up to half a millimetre long and are visible to the unaided eye; E. fishelsoni reaches 0.7 mm. Among the smallest bacteria are members of the genus Mycoplasma, which measure only 0.3 micrometres, as small as the largest viruses. Some bacteria may be even smaller, but these ultramicrobacteria are not well-studied.

Most bacterial species are either spherical, called cocci (sing. coccus, from Greek κόκκος-kókkos, grain, seed), or rod-shaped, called bacilli (sing. bacillus, from Latin baculus, stick). Elongation is associated with swimming. Some rod-shaped bacteria, called vibrio, are slightly curved or comma-shaped; others, can be spiral-shaped, called spirilla, or tightly coiled, called spirochaetes. A small number of species even have tetrahedral or cuboidal shapes. More recently, bacteria were discovered deep under the Earth's crust that grow as long rods with a star-shaped cross-section. The large surface area to volume ratio of this morphology may give these bacteria an advantage in nutrient-poor environments. 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.

Many bacterial species exist simply as single cells, others associate in characteristic patterns: Neisseria form diploids (pairs), Streptococcus form chains, and Staphylococcus group together in "bunch of grapes" clusters. Bacteria can also be elongated to form filaments, for example the Actinobacteria. Filamentous bacteria are often surrounded by a sheath that contains many individual cells. Certain types, such as species of the genus Nocardia, even form complex, branched filaments, similar in appearance to fungal mycelia.

Bacteria often attach to surfaces and form dense aggregations called biofilms or bacterial mats. These films can range from a few micrometers in thickness to up to half a meter in depth, and may contain multiple species of bacteria, protists and archaea. Bacteria living in biofilms display a complex arrangement of cells and extracellular components, forming secondary structures such as microcolonies, through which there are networks of channels to enable better diffusion of nutrients. In natural environments, such as soil or the surfaces of plants, the majority of bacteria are bound to surfaces in biofilms. Biofilms are also important in medicine, as these structures are often present during chronic bacterial infections or in infections of implanted medical devices, and bacteria protected within biofilms are much harder to kill than individual isolated bacteria.

Even more complex morphological changes are sometimes possible. For example, when starved of amino acids, Myxobacteria detect surrounding cells in a process known as quorum sensing, migrate towards each other, and aggregate to form fruiting bodies up to 500 micrometres long and containing approximately 100,000 bacterial cells. In these fruiting bodies, the bacteria perform separate tasks; this type of cooperation is a simple type of multicellular organisation. For example, about one in 10 cells migrate to the top of these fruiting bodies and differentiate into a specialised dormant state called myxospores, which are more resistant to drying and other adverse environmental conditions than are ordinary cells.

Read more about this topic:  Bacteria

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Morphology may mean:

  • Morphology (linguistics), the study of the structure and content of word forms
  • Morphology (biology), the study of the form or shape of an organism or part thereof
  • Morphology (molecular), study of how the shape and form of molecules affect their chemical properties, dynamic reconfiguration and interactions
  • Morphology (astronomy), the shape of astronomical objects such as nebulae, galaxies, or other extended objects
  • Morphology (folkloristics), the structure of narratives such as folk tales
  • Geomorphology, the study of landforms
  • Mathematical morphology, a theoretical model based on lattice theory, used for digital image processing
  • Morphology (Architecture and Engineering), a research, which is based on theories of two dimensional and three dimensional symmetries, and then uses these geometries for planning buildings and structures.
  • River morphology, the field of science dealing with changes of river platform
  • Urban morphology, the study of growth and development of functions in cities
  • Morphological analysis (disambiguation)
  • Morphology (materials science), the study of shape, size, texture and phase distribution of physical objects.
  • Morphology (ideology), the study of the conceptual structure of ideologies, and the rules defining the admissibility of meanings into concepts.
  • Morphology (journal), ISSN 1871-5621

Famous quotes containing the word morphology:

    I ascribe a basic importance to the phenomenon of language.... To speak means to be in a position to use a certain syntax, to grasp the morphology of this or that language, but it means above all to assume a culture, to support the weight of a civilization.
    Frantz Fanon (1925–1961)