Coxiella burnetii: Difference between revisions
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Being that Coxiella burnetti is a Gram-negative bacterium, this distinction marks important properties about the cell structure. Gram-negative bacteria have two membranes, an inner and outer membrane. The outer membrane lacks an energy source, but compensates by having porins fused into the membrane. The organism does not have a thick cell wall composed of peptidoglycan like Gram-positive bacteria. In between the two membranes lies the periplasmic space. Lipopolysaccharides are anchored to the membrane. During its life cycle, phagocytosis brings the bacteria into the cell, where it remains in phagocytic vacuoles and replicates in the phagolysozyme. | Being that Coxiella burnetti is a Gram-negative bacterium, this distinction marks important properties about the cell structure. Gram-negative bacteria have two membranes, an inner and outer membrane. The outer membrane lacks an energy source, but compensates by having porins fused into the membrane. The organism does not have a thick cell wall composed of peptidoglycan like Gram-positive bacteria. In between the two membranes lies the periplasmic space. Lipopolysaccharides are anchored to the membrane. During its life cycle, phagocytosis brings the bacteria into the cell, where it remains in phagocytic vacuoles and replicates in the phagolysozyme. | ||
Compared to free-living bacteria, Coxiella burnetti does not have a broader range of transport capacities. In spite of this limitation, this bacterium possesses more transport capacities than other obligate parasites like Rickettsia organisms. For active transport mechanisms by ion-coupled transport, Na+/H+ exchangers are thought to be significant in maintaining pH in the acidic environment Coxiella burnetti thrive in. Although group transfer mechanisms via the phosphotransferase system are not evident in Coxiella, enzymes involved in the system, such as HPr and enzyme 1, are present and play a regulatory role. (3) | Compared to free-living bacteria, Coxiella burnetti does not have a broader range of transport capacities. In spite of this limitation, this bacterium possesses more transport capacities than other obligate parasites like Rickettsia organisms. For active transport mechanisms by ion-coupled transport, Na+/H+ exchangers are thought to be significant in maintaining pH in the acidic environment Coxiella burnetti thrive in. Although group transfer mechanisms via the phosphotransferase system are not evident in Coxiella, enzymes involved in the system, such as HPr and enzyme 1, are present and play a regulatory role. (3) | ||
Unlike the other obligate parasites, the greater metabolic capacities of Coxiella burnetti permit the bacteria to undergo glycolysis, gluconeogenesis, pentose phosphate pathway, and TCA cycle. The absence of ATP/ADP exchangers in their transport system highlights that they do not have a way to utilize ATP as an energy source. The bacterium utilizes few sugars, including xylose and glucose, and their uptake is aided by a membrane gradient. Amino acids are taken into the cell by an outstanding number of 15 transporters and peptides have three. Due to the copious number of transporters required for the uptake of these organic nutrients, amino acids and peptides may be the major carbon sources for this bacterium. (3) | Unlike the other obligate parasites, the greater metabolic capacities of Coxiella burnetti permit the bacteria to undergo glycolysis, gluconeogenesis, pentose phosphate pathway, and TCA cycle. The absence of ATP/ADP exchangers in their transport system highlights that they do not have a way to utilize ATP as an energy source. The bacterium utilizes few sugars, including xylose and glucose, and their uptake is aided by a membrane gradient. Amino acids are taken into the cell by an outstanding number of 15 transporters and peptides have three. Due to the copious number of transporters required for the uptake of these organic nutrients, amino acids and peptides may be the major carbon sources for this bacterium. (3) | ||
Revision as of 01:23, 6 June 2007
A Microbial Biorealm page on the genus Coxiella burnetii
Classification
Higher order taxa
Bacteria; Proteobacteria; Gammaproteobacteria; Legionellales; Coxiellaceae; Coxiella (1)Bacteria; Proteobacteria; Gammaproteobacteria; Legionellales; Coxiellaceae; Coxiella (1)
Species
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NCBI: Taxonomy |
Coxiella burnetti
Description and significance
Coxiella burnetti is an obligate intracellular Gram-negative coccobacillus bacterium that is known to be the main pathogen that causes Q fever in mammals and humans. (3) Harold Cox and MacFarlane Burnet initially identified Q fever as “query fever” in 1935 when a number of infections were found to be from an Australian slaughterhouse. Once the perplexity of this disease was elucidated to be a human infection, the name was properly changed to Q fever. (4) Its global pathogenic effect demonstrates the need for preventive measures to control the rate of infection worldwide and its potential use for bioterrorism. The significance of a completed sequenced genome is the benefit of being able to further understand the mechanisms of pathogenesis and use this knowledge to fight against this infectious disease. Sheep, cattle, and goats are major sources of Coxiella burnetti that can potentially help spread the disease to other organisms. The most common mode of transmission to humans is primarily through external waste excretions from infected animals. The aerosol route to infection is frequent by inhalation of contaminated air that contains many of these organisms or through an insect vector. (5) Coxiella burnetti live in a wildlife livestock environment and can withstand heat, dryness, and antibacterial compounds, allowing this bacterium to persist outside the host for an extensively long period of time. It is an acidophile, meaning it tends to surround itself in an environment with low pH. Uniquely enough, it can be endocytosed by a macrophage and complete replication inside the phagolysozyme during its life cycle. (3)
Genome structure
Random shotgun method was used to sequence the genome of Coxiella burnetti. (3) The genome of this organism is attributed by the presence of a single 1,995,281 base-pair circular chromosome and a single 37,393 base-pair QpH1 circular plasmid. (1) In the chromosome, there are 1,022 protein-coding genes found for known proteins, 179 genes for proteins of unknown function, 3 stable rRNAs, and 42 stable tRNAs. Percent of G+C content is approximately 42.6% and percent coding is approximately 89.1% in the chromosome. As for QpH1, there are 11 genes found for known proteins, 5 for proteins of unknown function, and no stable RNAs. 39.3% represents the percent of G+C content and 78.8% is the percent coding in the plasmid. (6) Examining 20 highly conserved proteins in 16S rRNA gene sequence analysis proved the fundamental phylogenetic difference with the α-proteobacterial Rickettsia organisms and confirmed that Coxiella are truly γ-proteobacterial. In genomic comparison with other similar obligate parasites such as those from Rickettsia, the genome of Coxiella was found to contain mobile elements, metabolic and transport capabilities not typically found for the kind of bacteria they are. In addition, 29 insertion sequences were located in the genome; this is noteworthy information because other obligate parasites have very little or none of these elements. However, the presence of pathogenecity islands along with the unique transposons found in the genome does not suggest recent exchange of mobile genetic elements with other organisms. A notion that Coxiella burnetti are enduring a genome reduction, in which certain genes that encode important genetic information ultimately lose its functionality and degrade, has been proposed due to the fact that 83 pseudogenes have been identified. Proteins synthesized by this bacterium has a particularly high pI, which may give rise to the acidic environment Coxiella burnetti reside in. (3)
Cell structure and metabolism
Being that Coxiella burnetti is a Gram-negative bacterium, this distinction marks important properties about the cell structure. Gram-negative bacteria have two membranes, an inner and outer membrane. The outer membrane lacks an energy source, but compensates by having porins fused into the membrane. The organism does not have a thick cell wall composed of peptidoglycan like Gram-positive bacteria. In between the two membranes lies the periplasmic space. Lipopolysaccharides are anchored to the membrane. During its life cycle, phagocytosis brings the bacteria into the cell, where it remains in phagocytic vacuoles and replicates in the phagolysozyme.
Compared to free-living bacteria, Coxiella burnetti does not have a broader range of transport capacities. In spite of this limitation, this bacterium possesses more transport capacities than other obligate parasites like Rickettsia organisms. For active transport mechanisms by ion-coupled transport, Na+/H+ exchangers are thought to be significant in maintaining pH in the acidic environment Coxiella burnetti thrive in. Although group transfer mechanisms via the phosphotransferase system are not evident in Coxiella, enzymes involved in the system, such as HPr and enzyme 1, are present and play a regulatory role. (3)
Unlike the other obligate parasites, the greater metabolic capacities of Coxiella burnetti permit the bacteria to undergo glycolysis, gluconeogenesis, pentose phosphate pathway, and TCA cycle. The absence of ATP/ADP exchangers in their transport system highlights that they do not have a way to utilize ATP as an energy source. The bacterium utilizes few sugars, including xylose and glucose, and their uptake is aided by a membrane gradient. Amino acids are taken into the cell by an outstanding number of 15 transporters and peptides have three. Due to the copious number of transporters required for the uptake of these organic nutrients, amino acids and peptides may be the major carbon sources for this bacterium. (3)
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
Coxiella burnetii infection (Q fever). American Veterinary Medical Association. 02 May 2007 <http://www.avma.org/reference/zoonosis/zncoxiel2.asp>.
ExPASy. Swiss Institute of Bioinformatics. 02 May 2007 <http://expasy.org/sprot/hamap/COXBU.html>.
Genome Project. <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=Add%20to%20Clipboard&DB=genomeprj>.
Q fever. Centers for Disease Control and Prevention. 02 May 2007 <http://0-www.cdc.gov.mill1.sjlibrary.org/ncidod/dvrd/qfever/>.
NIAID Biodefense Image Library. National Institute of Allergy and Infectious Diseases. 02 May 2007 <http://www3.niaid.nih.gov/biodefense/Public/Images.htm>.
Seshadri R, Paulsen IT, Eisen JA, et al. Complete genome sequence of the Q-fever pathogen coxiellaburnetii. PNAS. 2003;100:5455-5460.
Edited by Lisa Leung, student of Rachel Larsen and Kit Pogliano
