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Gram-negative (LPS-diderm) cell wall structure Gram-positive and -negative bacteria are differentiated chiefly by their cell wall structure. Conventional gram-negative (LPS-diderm) bacteria display the following characteristics: [citation needed] An inner cell membrane is present (cytoplasmic)
Bacteria within the Deinococcota group may also exhibit Gram-positive staining behavior but contain some cell wall structures typical of Gram-negative organisms. Imbedded in the Gram-positive cell wall are polyalcohols called teichoic acids, some of which are lipid-linked to form lipoteichoic acids.
There are two main types of bacterial cell walls, those of Gram-positive bacteria and those of Gram-negative bacteria, which are differentiated by their Gram staining characteristics. For both these types of bacteria, particles of approximately 2 nm can pass through the peptidoglycan. [ 3 ]
Gram staining differentiates bacteria by the chemical and physical properties of their cell walls. Gram-positive cells have a thick layer of peptidoglycan in the cell wall that retains the primary stain, crystal violet. Gram-negative cells have a thinner peptidoglycan layer that allows the crystal violet to wash out on addition of ethanol.
According to some definitions, the term is used to describe Gram-negative bacteria. [3] [4] According to other definitions, the term also encompasses yeasts. [5] [6] The name spheroplast stems from the fact that after the microbe's cell wall is digested, membrane tension causes the cell to acquire a characteristic spherical shape. [4]
E. coli is a gram-negative, facultative anaerobe, nonsporulating coliform bacterium. [18] Cells are typically rod-shaped, and are about 2.0 μm long and 0.25–1.0 μm in diameter, with a cell volume of 0.6–0.7 μm 3. [19] [20] [21] E. coli stains gram-negative because its cell wall is composed of a thin peptidoglycan layer and an outer membrane.
In 1962, R.G.E. Murray proposed to divide the "kingdom" (now domain [8]) Bacteria into three divisions (= phyla) on the basis of the cell wall types: Gram-negative Gracilicutes, with a thin cell wall and little peptidoglycan; Gram-positive Firmicutes, with a thicker cell wall and more peptidoglycan (the name was later changed in "Firmicutes"), and
Gracilicutes (Latin: gracilis, slender, and cutis, skin, referring to the cell wall) is a clade in bacterial phylogeny. [2]Traditionally gram staining results were most commonly used as a classification tool, consequently until the advent of molecular phylogeny, the Kingdom Monera (as the domains Bacteria and Archaea were known then) was divided into four phyla, [1] [3]