Actinobacillus actinomycetemcomitans: Difference between revisions
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===Higher order taxa=== | ===Higher order taxa=== | ||
Bacteria; Proteobacteria; Gammaproteobacteria; Pasteurellales; Pasteurellaceae | Bacteria; Proteobacteria; Gammaproteobacteria; Pasteurellales; Pasteurellaceae | ||
===Species=== | ===Species=== | ||
Revision as of 22:06, 28 August 2007
A Microbial Biorealm page on the genus Actinobacillus actinomycetemcomitans
Classification
Higher order taxa
Bacteria; Proteobacteria; Gammaproteobacteria; Pasteurellales; Pasteurellaceae
Species
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NCBI: Taxonomy |
Actinobacillus actinomycetemcomitans
Description and significance
Actinobacillus actinomycetemcomitans is one of the most completely studied periodontal bacteria. It stays in the periodontal pocket of the oral cavity and damages tooth supporting tissues. See Pathology section for more details (4).
Actinobacillus actinomycetemcomitans is a gram negative bacterium which is spherical or rod-shaped (2). It’s a facultative anaerobe which can grow under either aerobic or anaerobic conditions (1). Actinobacillus actinomycetemcomitans is a typical cause of periodontitis but it may also be related to systemic infections and arterial plaques. Isolated Actinobacillus actinomycetemcomitans from periodontitis patients releases leukotoxin which kills T cells by some pathways (3). This will be discussed later in Pathology section.
A complete genomic sequence of Actinobacillus actinomycetemcomitans is available in publication by David Dyer, Bruce Roe and colleagues at the University of Oklahoma.
Genome structure
The entire DNA genome of the Actinobacillus actinomycetemcomitans bacteriophage AaΦ23 was sequenced by using the shotgun sequencing (6). Linear DNA contained in the phage particles is circularly mixed and abundant in the end. Therefore, the entire DNA genome structure is circular. Its size is 43,033 bp with an overall molar G+C content of 42.5 mol%. Sixty-six potential open reading frames (ORFs) were found. This includes an ORF resulting from a translational frameshift, meaning if a ribosome changes frame when translating the genetic code (5). 23 of ORFs have a putative function. Twenty-three other ORFs are homologous with other bacteria. 20 ORFs came out to be specific to the phage AaΦ23. The organization of the phage genome and several genetic functions share extensive similarities with lambdoid phages (a large group of phages). However, AaΦ23 encodes a DNA adenine methylase, and the DNA packaging strategy is more closely related to the P22 system. The attachment sites of AaΦ23 (attP) and several A. actinomycetemcomitans hosts (attB) are 49 bp long (6).
Cell structure and metabolism
Actinobacillus actinomycetemcomitans was separated from periodontitis patients and grown in a specific condition to characterize energy metabolism of A. actinomycetemcomitans. It was grown in fructose-limited chemostat cultures under anaerobic [redox potential (Eh)<-400 mV] and microaerobic (Eh=-200 mV) conditions. In a controlled medium containing 5.2 mM K+ and 24 mM Na+, the growth rate of fructose is higher under the microaerobic condition. However, when we count the ATP yield from fermentation, the overall value of microaerobic condition is lower than the anaerobic condition. We also need to count ATP production from the respiration (7). Therefore, the total ATP production of both conditions is relatively similar which enables A. actinomycetemcomitans to grow under either aerobic or anaerobic conditions. Additionally, there is a comparison of cell growth among different concentration of media. As a result, the higher concentrations of extracellular K+ are required for rapid growth of A. actinomycetemcomitans (7).
Actinobacillus actinomycetemcomitans is a gram negative bacterium. There are some significant aspects of gram negative characteristic. A. actinomycetemomitans contains the polysaccharide region of lipopolysaccharide (LPS). From the LPS region, the structure of the O antigen is identified by analyzing the aqueous phase LPS from a phenol-water extract of A. actinomycetemcomitans (8). Interestingly, even though A. actinomycetecomitans is gram negative, peptidoglycans can be separated by boiling in 4% sodium dodecyl sulfate and by digestion with pronase, trypsin and alpha-amylase. This indicates that peptidoglycans eventually be responsible for destruction of periodontal tissues (10) (see Pathology).
Ecology
Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.
Pathology
Periodontitis Periodontitis is a bacterial infection of tooth-supporting tissues which may lead to loss of teeth. It is most common bacterial infection among middle aged people and elderly people. Also, periodontitis is considered as indicator of systemic diseases (14).
Actinobacillus actinomycetemcomitans is the major cause of periodontitis. Kaplan and his collegues found that Actinobacillus actinomycetemcomitans strains comprised three major phylogenetic lineages suggesting it carries virulence potential (9).
Cardiovascular diseases Chronic dental infections, such as periodontitis, increase the risk for cardiovascular disease. The mechanism between periodontitis and cardiovascular diseases are only partly understood but here are some clues. Lipopolysaccharide of Actinobacillus actinomycetemcomitans modifies low-density lipoprotein which eventually helps accumulation of cholesterol with a support of macrophagederived foam cells (11, 13). The macrophagederived foam cells are from local inflammatory response of periodontitis. Also, high-density lipoprotein, preventing oxidation of low-density lipoprotein, reversing cholesterol transport and neutralizing LPS in the circulation, is low in concentration among periodontitis patients. Therefore, low level of high-density lipoprotein causes accumulation of cholesterol (12, 13).
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
