العربية
中国
Français
Deutsch
Ελληνική
हिन्दी
Italiano
日本語
Português
Русский
EspañolGRAM-POSITIVE
(Redirected from Gram positive)
'Gram-positive' bacteria are those that retain a crystal violet dye during the Gram stain process. Sherris Medical Microbiology, Ryan KJ; Ray CG (editors), , , McGraw Hill, 2004, ISBN 0838585299 Gram-positive bacteria appear blue or violet under a microscope, while Gram-negative bacteria appear red or pink. The Gram classification system is empirical, and largely based on differences in cell wall structure. Medical Microbiology, , Samuel, Baron, The University of Texas Medical Branch at Galveston, 1996, ISBN 0-9631172-1-1 The purpose of Gram staining is to visually differentiate groups of bacteria, primarily for identification.
The following characteristics are generally present in a Gram-positive bacterium: Brock Biology of Microorganisms, Madigan M; Martinko J (editors)., , , Prentice Hall, 2005, ISBN 0131443291
#A very thick cell wall (peptidoglycan).
#If a flagellum is present, it contains two rings for support as opposed to four in Gram-negative bacteria because Gram-positive bacteria have only one membrane layer.
#Teichoic acids and lipoteichoic acids are present, which serve to act as chelating agents, and also for certain types of adherence.
In the original bacterial phyla, the Gram-positive forms made up the phylum Firmicutes, a name now used for the largest group. It includes many well-known genera such as ''Bacillus'', ''Listeria'', ''Staphylococcus'', ''Streptococcus'', ''Enterococcus'', and ''Clostridium''. It has also been expanded to include the Mollicutes, bacteria like ''Mycoplasma'' that lack cell walls and so cannot be stained by Gram, but are derived from such forms.
The actinobacteria are another major group of Gram-positive bacteria; they and the Firmicutes are referred to as the high and low G+C groups based on the guanosine and cytosine content of their DNA. If the second membrane is a derived condition, the two may have been basal among the bacteria; otherwise they are probably a relatively recent monophyletic group. They have been considered as possible ancestors for the archaeans and eukaryotes, both because they are unusual in lacking the second membrane and because of various biochemical similarities such as the presence of sterols.
The Deinococcus-Thermus bacteria also have Gram-positive stains, although they are structurally similar to Gram-negative bacteria.
Both Gram-positive and Gram-negative bacteria may have a membrane called an S-layer. In Gram-negative bacteria, the S-layer is directly attached to the outer membrane. In Gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Unique to Gram-positive bacteria is the presence of teichoic acids in the cell wall. Some particular teichoic acids, lipoteichoic acids, have a lipid component and can assist in anchoring peptidoglycan, as the lipid component is embedded in the membrane.
★ Gram-negative
★
★ 3D structures of proteins associated with plasma membrane of Gram-positive bacteria
★ 3D structures of proteins associated with cell wall of Gram-positive bacteria
Gram-positive Bacillus anthracis bacteria (purple rods) in cerebrospinal fluid sample. The other cells are white blood cells
'Gram-positive' bacteria are those that retain a crystal violet dye during the Gram stain process. Sherris Medical Microbiology, Ryan KJ; Ray CG (editors), , , McGraw Hill, 2004, ISBN 0838585299 Gram-positive bacteria appear blue or violet under a microscope, while Gram-negative bacteria appear red or pink. The Gram classification system is empirical, and largely based on differences in cell wall structure. Medical Microbiology, , Samuel, Baron, The University of Texas Medical Branch at Galveston, 1996, ISBN 0-9631172-1-1 The purpose of Gram staining is to visually differentiate groups of bacteria, primarily for identification.
| Contents |
| Characteristics |
| History of Gram positive |
| See also |
| References |
| External links |
Characteristics
The following characteristics are generally present in a Gram-positive bacterium: Brock Biology of Microorganisms, Madigan M; Martinko J (editors)., , , Prentice Hall, 2005, ISBN 0131443291
#A very thick cell wall (peptidoglycan).
#If a flagellum is present, it contains two rings for support as opposed to four in Gram-negative bacteria because Gram-positive bacteria have only one membrane layer.
#Teichoic acids and lipoteichoic acids are present, which serve to act as chelating agents, and also for certain types of adherence.
History of Gram positive
In the original bacterial phyla, the Gram-positive forms made up the phylum Firmicutes, a name now used for the largest group. It includes many well-known genera such as ''Bacillus'', ''Listeria'', ''Staphylococcus'', ''Streptococcus'', ''Enterococcus'', and ''Clostridium''. It has also been expanded to include the Mollicutes, bacteria like ''Mycoplasma'' that lack cell walls and so cannot be stained by Gram, but are derived from such forms.
The actinobacteria are another major group of Gram-positive bacteria; they and the Firmicutes are referred to as the high and low G+C groups based on the guanosine and cytosine content of their DNA. If the second membrane is a derived condition, the two may have been basal among the bacteria; otherwise they are probably a relatively recent monophyletic group. They have been considered as possible ancestors for the archaeans and eukaryotes, both because they are unusual in lacking the second membrane and because of various biochemical similarities such as the presence of sterols.
The Deinococcus-Thermus bacteria also have Gram-positive stains, although they are structurally similar to Gram-negative bacteria.
Both Gram-positive and Gram-negative bacteria may have a membrane called an S-layer. In Gram-negative bacteria, the S-layer is directly attached to the outer membrane. In Gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Unique to Gram-positive bacteria is the presence of teichoic acids in the cell wall. Some particular teichoic acids, lipoteichoic acids, have a lipid component and can assist in anchoring peptidoglycan, as the lipid component is embedded in the membrane.
See also
★ Gram-negative
References
External links
★
★ 3D structures of proteins associated with plasma membrane of Gram-positive bacteria
★ 3D structures of proteins associated with cell wall of Gram-positive bacteria
This article provided by Wikipedia. To edit the contents of this article, click here for original source.
psst.. try this: add to faves
