Bacillus anthracis

From MicrobeWiki, the student-edited microbiology resource

A Microbial Biorealm page on the genus Bacillus anthracis

Classification

Higher order taxa

cellular organisms; Bacteria (domain); Firmicutes (phylum); Bacilli (class); Bacillales (order); Bacillaceae (family); Bacillus (genus); Bacillus cereus group

Genus

Bacillus anthracis


NCBI: Taxonomy

Description and significance

Bacillus anthracis is a gram-positive, rod-shaped, aerobic bacterium. When vegetative cells are deprived of certain nutrients, endospores are formed. Initially, the septum forms asymmetrically in the nutrient deprived cells that produce large (mother cell)and small (forespore) genome containing compartments. The forespore is engulfed by the mother cell and surrounded with three layers (cortex, coat, and exosporium), which are simultaneously formed. The thickest and innermost layer is the cortex. It is made up of peptidoglcan. The coat, consisting of a large number of different proteins, tightly covers the cortex. The exosporium is a loose-fitting, balloon-like structure that encloses the spore. It is composed of at least a dozen different proteins and glycoproteins. The mother cell lyses and the spore is released when spore formation is finished. Spores can live in the soil environment for many years because, once spores have matured, they are resistant to physical and chemical damage. Spores germinate and grow as vegetative cells when they find an aqueous environment with the proper nutrients. Small-molecule germinants, including inosine and l-alanine, are recognized by spore receptors and activate germination. The receptors are found within the membrane of the spore that is under the cortex. Spores that enter a host germinate and grow, producing a fatal toxin.

Bacillus anthracis is an important molecule to study and genome sequence because its use as a biological weapon created concern. The interactions between the host's immune system cells and the spores are an important area of research.

Other names for this organisms are Bacteridium anthracis and Bacillus cereus var. anthracis. Common names include "anthrax" and "anthrax bacterium."


Describe the appearance, habitat, etc. of the organism, and why it is important enough to have its genome sequenced. Describe how and where it was isolated. Include a picture or two (with sources) if you can find them.

Genome structure

Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence? Does it have any plasmids? Are they important to the organism's lifestyle?

Cell structure and metabolism

Describe any interesting features and/or cell structures; how it gains energy; what important molecules it produces.

Ecology

Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.

Pathology

Bacillus anthracis causes the anthrax diesease, which represents a complex interaction between the host and parasite. The particles of anthrax that are infectious are the Bacillus anthracis endospores. The organism penetrates into the blood stream and harms the host by producing toxins within the body. The toxin is a complex of three plasmid-encoded proteins. Two of the proteins are directly toxic, including LF (lethal factor) and EF (edema factor). LF destroys white blood cells while EF increases cyclic AMP levels. Energy and water balance is impaired by the increase in cyclic AMP. The other plasmid-encoded protein, named PA (protective antigen), ushers the two toxic proteins in cells. PA forms a multimeric ring, which inserts into the cell membranes of the host. PA is not toxic alone, but if it is inactivated, the two toxic proteins would not cause harm. This is because PA allows the toxic components to pass through the membrane via a special toxin delivery system. The slimy capsule layer that surrounds Bacillus anthracis allows it to resist phagocytosis by white cells.

There common disease forms are cutaneous, pulmonary, and gastrointestinal. The cutaneous form is caused by handling contaminated materials, and the pulmonary form is caused by inhalation. Skin abrasions allow spores to enter and cause local lesions by germinating there. Patients with a cutaneous anthrax diesease mostly recover within 10 days, although a few progress to a life-threatening disease. The pulmonary form of the disease results in a higher mortlity rate because the organism spreads through circulation. Macrophages in the lung's alveoli take up the spores and permit entry into the body.

Until the 20th century, anthrax was a prevalent diesease in humans and cattle. It is still an important pathogen in some countries today. Some scholars believe that the Egyptian plagues in the Bible may have been caused by Anthrax. However, most people had not heard of anthrax until the recent 2001 scare in the United States. Robert Koch and Louis Pasteur developed a vaccine against anthrax, which was the first infectious disease they studied. The vaccines today are not fully effective. However, if the disease is diagnosed soon enough after infection, treatment is effective. Methods to detect the organism quickly and new vaccines are under development. Because Bacillus anthracis lives in many soils, outbreaks are still reported. In fact, in the upper Midwest of the United States, many farms are under quarantine due to anthrax.

During the 20th century anthrax was used as a weapon in many countries. it has also been directed toward farm animals for warfare. The significance of anthrax as a terror weapon was realized in 2001. Although small outbreaks can result in a strong response, some people argue that anthrax is not an ideal biological weapon because the organism is not particularly pathogenic. To infect people, a large number of spores are needed. Also, anthrax is almost never transmitted between people. The most effective form of anthrax is a very fine powder. Therefore, to make anthrax a weapon, the preparation needs to be grinded into a fine powder. Anticaking agents are necessary as well to prevent clumping of the spores. Bacillus anthracis can be grown easily, but it is important to have special containment facilities and to be careful when working with them. They can be engineered to be resistant to antibiotics even though they are usually sensitive to antibiotics including penicillin and ciprofloxacin.

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

example:

http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=1392&lvl=3&lin=f&keep=1&srchmode=1&unlock Wheeler DL, Chappey C, Lash AE, Leipe DD, Madden TL, Schuler GD, Tatusova TA, Rapp BA (2000). Database resources of the National Center for Biotechnology Information. Nucleic Acids Res 2000 Jan 1;28(1):10-4 [PubMed]


http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1636282#r22 Jeremy A. Boydston, Ling Yue, John F. Kearney, and Charles L. Turnbough, Jr. "The ExsY Protein Is Required for Complete Formation of the Exosporium of Bacillus anthracis." J Bacteriol. 2006 November; 188(21): 7440–7448.


http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=303457 Hongbin Liu, Nicholas H. Bergman, Brendan Thomason, Shamira Shallom, Alyson Hazen, Joseph Crossno, David A. Rasko, Jacques Ravel, Timothy D. Read, Scott N. Peterson, John Yates III, and Philip C. Hanna. Formation and Composition of the Bacillus anthracis Endospore. J Bacteriol. 2004 January; 186(1): 164–178. doi: 10.1128/JB.186.1.164-178.2004.


Glockner, F. O., M. Kube, M. Bauer, H. Teeling, T. Lombardot, W. Ludwig, D. Gade, A. Beck, K Borzym, K Heitmann, R. Rabus, H. Schlesner, R. Amann, and R. Reinhardt. 2003. "Complete genome sequence of the marine planctomycete Pirellula sp. strain 1." Proceedings of the National Acedemy of Sciences, vol. 100, no. 14. (8298-8303)


Edited by Grace Ucar, student of Rachel Larsen and Kit Pogliano