Streptococcus mitis: Difference between revisions
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==Cell structure and metabolism== | ==Cell structure and metabolism== | ||
4.1 Cell Structure | |||
As demonstrated by electron microscopy, ''S. mitis'' strains usually carry sparsely distributed, long fibrils, and their cell surfaces are often regarded as being soft. The electrophoretic softness and fixed negative charge density of -1.2 to -4.3×106 Cm-3 in the polyelectrolyte layer of ''S. mitis'' strains, were determined by the soft particle analysis using measured electrophoretic mobilities (5). | |||
There is a very high frequency of occurrence of extracellular surface structures on ''S. mitis'' strains and a variety of appendages with different lengths up to several microns have been found (5). Between different strains, the density of appendages on cell surfaces can vary significantly (5). | |||
''S. mitis'' is characterized by its C-polysaccharide cell wall and a teichoic acid-like polysaccharide. The teichoic acid-like polysaccharide contains a heptasaccharide phosphate repeating unit that neither consists of ribitol nor glycerol phosphate as normally seen in teichoic acids (6). The C-polysaccharide of S. mitis contains, in each repeating unit, two residues of phosphocholine and both galactosamine residues (6). | |||
4.2 Metabolism | |||
''S. mitis'' is a facilitated anaerobe which makes its metabolism very versatile. The utilization and synthesis of intracellular glycogen and its catabolism to lactate has been detected in ''S. mitis''. The glycogen-like polysaccharide functions as the only source of utilizable energy in ''S. mitis'' (7). | |||
When an exogenous energy source is absent, the break down of polysaccharide provides ''S. mitis'' with energy in a utilizable form, for cells that have polysaccharide increased in β-galactosidase activity when induced with thiomethyl galactoside (8). When induced in a similar manner, cells that lack polysaccharide, and a polysaccharide-negative variant of ''S. mitis'' did not increase in β-galactosidase activity. The only substrate for the endogenous metabolism of ''S. mitis'' is intracellular polysaccharide (8). | |||
==Ecology== | ==Ecology== | ||
Revision as of 19:42, 29 August 2007
A Microbial Biorealm page on the genus Streptococcus mitis
Classification
Higher order taxa
Bacteria; Firmicutes; Bacilli; Lactobacillales; Streptococcaceae;
Species
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NCBI: Taxonomy |
Streptococcus mitis
Description and significance
Streptococcus mitis are commensal bacteria that colonize hard surfaces in the oral cavity such as dental hard tissues as well as mucous membranes and are part of the oral flora. They are usually arranged in short chains in the shape of cocci (10). These Gram-positive bacteria are not usually pathogenic but commonly cause bacterial endocarditis, which is the inflammation of an inner layer of the heart. S. mitis are alpha hemolytic, meaning it can break down red blood cells. S. mitis are not motile, do not form spores and lack group-specific antigens (2). S. mitis live optimally at temperatures between 30 and 35 degrees Celsius, making them mesophiles. They are facultative anaerobes, which is a bacterium that makes ATP by aerobic respiration if oxygen is present but is also capable of switching to fermentation in the absence of oxygen (7).
Genome structure
The genome of S. mitis has been sequenced and consists of a circular chromosome with about two million bp that varies with different strains. Its GC and AT content are respectively 40.4% and 59.1%. There are a total of 2222 genes of which 2149 are protein coding genes (3).
The genes encoding the lipoproteins Pb1A and Pb1B in S. mitis are clustered close to the genes that are very similar to the streptococcal phages r1t, 01205 and Dp-1. This implies that Pb1A and Pb1B might be located within a prophage (4). To test this possibility, mitomycin C and UV light were used because both can induce the lytic cycle of many phages. Cultures of S. mitis were exposed to this and a significant increase expression of Pb1A and Pb1B were detected by Western blot analysis. Phage particles were visible in the cultures of S. mitis, which was named SM1. This phage had a DNA genome of about 35 kb. All these experiments concluded that Pb1A and Pb1B are encoded by a lysogenic bacteriophage (4).
Cell structure and metabolism
4.1 Cell Structure
As demonstrated by electron microscopy, S. mitis strains usually carry sparsely distributed, long fibrils, and their cell surfaces are often regarded as being soft. The electrophoretic softness and fixed negative charge density of -1.2 to -4.3×106 Cm-3 in the polyelectrolyte layer of S. mitis strains, were determined by the soft particle analysis using measured electrophoretic mobilities (5).
There is a very high frequency of occurrence of extracellular surface structures on S. mitis strains and a variety of appendages with different lengths up to several microns have been found (5). Between different strains, the density of appendages on cell surfaces can vary significantly (5).
S. mitis is characterized by its C-polysaccharide cell wall and a teichoic acid-like polysaccharide. The teichoic acid-like polysaccharide contains a heptasaccharide phosphate repeating unit that neither consists of ribitol nor glycerol phosphate as normally seen in teichoic acids (6). The C-polysaccharide of S. mitis contains, in each repeating unit, two residues of phosphocholine and both galactosamine residues (6).
4.2 Metabolism
S. mitis is a facilitated anaerobe which makes its metabolism very versatile. The utilization and synthesis of intracellular glycogen and its catabolism to lactate has been detected in S. mitis. The glycogen-like polysaccharide functions as the only source of utilizable energy in S. mitis (7).
When an exogenous energy source is absent, the break down of polysaccharide provides S. mitis with energy in a utilizable form, for cells that have polysaccharide increased in β-galactosidase activity when induced with thiomethyl galactoside (8). When induced in a similar manner, cells that lack polysaccharide, and a polysaccharide-negative variant of S. mitis did not increase in β-galactosidase activity. The only substrate for the endogenous metabolism of S. mitis is intracellular polysaccharide (8).
Ecology
Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.
Pathology
How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
Application to Biotechnology
Does this organism produce any useful compounds or enzymes? What are they and how are they used?
Current Research
Enter summaries of the most recent research here--at least three required
References
Edited by student of Rachel Larsen
