Rickettsia prowazekii

A Microbial Biorealm page on the genus Rickettsia prowazekii

Classification

Higher order taxa

Bacteria; Proteobacteria; Alphaproteobacteria; Rickettsiales; Rickettsiaceae

Species

Rickettsia prowazekii

Description and significance

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.

Rickettsia prowazekii is an intracellular, bacilli bacteria that is the cause of epidemic typhus in humans. In the early 20th century, Howard Ricketts linked typhus to Spotted Fever while Stanislaus von Prowazek discovered typhus was transmitted to humans by the feces of lice, not the bite. Both Ricketts and Prowazek were killed by typhus while working with the disease, so the bacteria was named for them. The genome was fully sequenced by the end of the century. Since World War II the only other major breakout was during the Burundo civil war in the late 1990's. Now, the main point of research regarding R. prowazekii is its linkage to the origin of mitochondria. R. prowazekii has a small genome and is the first alpha-proteobacterial, gram negative genome to be sequenced.

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?

The R. prowazekii genome is composed of a singular circular chromosome, containing 1,111,523 base pairs and 834 protein coding genes. Also, 24% of R. prowazekii DNA is non-coding- the largest amount in any microbial genome. No genes code for anaerobic glycolosis, however, complete coding sequences for the tricarboxylicacid (TCA) cycle and respiratory-chain complex are found.

Cell structure and metabolism

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

R. prowazekii is a Gram-, intracellular bacteria with a bacilli (rod like) structure. Genomic codes for LPS and Peptidoglycan formation are both complete in R. prowazekii'.

As mentioned above, R. prowazekii cannot produce pyruvate from any glycolytic pathway. However, enzymes required for pyruvate metabolism are coded for by Rickettsia "indicating that the microbe must acquire it somehow." One such mechanism for this acquisition is acquiring Phosphoenol Pyruvate (PEP) directly from it's host. Rickettsia also lack coding sequences for Nitrogen metabolism which allows the synthesis of glutamine, indicating that, like PEP, glutamine must be acquired directly from the host cells.

Rickettsia also gain energy from oxidative phosphorylation and ATP translocases. First, Rickettsia code for 5 copies of ATP translocases indicating the importance they have in obtaining energy for the microbe. The translocases allow the cell to take up ATP produced by the host. This is the major ATP capturing method for Rickettsia since the cell will use translocases after entering a host cell to capture the host ATP before initiating its own pathways. Once it has used up all the host ATP, it will initiate the electron transport chain, which culminates with ATP Synthase and the production of ATP.

Another key molecule produced is polyhydroxyalkanoate (PHA), the concentration of which increases in low nutrient environments. PHA's are great carbon storing molecules and in the case of cellular starvation, PHA will serve as a carbon and energy source to maintain survival.

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?

As mentioned above in the Metabolism section, R. prowazekii produce PHA's which are excellent for storing carbon. Current reasearch on PHA's includes looking into their usefulness as a biodegradable plastic. PHA's exhibit material properties that can range from rubber-like to the stiff and brittle class of PHA's known as PHB (poly-beta-hydroxybutyrate) making them a very viable substitute for synthetic plastics. [5]