A Microbial Biorealm page on the genus Francisella tularensis
Higher order taxa
Class: Gamma Proteo Bacteria
Genus species: Francisella tularensis
Description and significance
Francisella tularensis is a gram-negative bacteria, with pili on the surface. In laboratory settings, Francisella tularensis appear as small (0.2 by 0.2 µm), and is grown best at 35-37 degrees Celcius.
Francisella tularensis is a highly contagious bacteria that causes tularemia, or "rabbit fever" that is contagious to humans. There are two strands of Francisella tularensis that are most studied: the more virulent Type A strain (found in North America), and the less virulent Type B strain (found in Europe). The bacteria was used in development of biological weapons in the World War II and post WWII years, and is considered as a very dangerous bioloterror threat today.
Francisella tularensis has a circular chromosome, and its entire genome is sequenced. It has 52 RNA genes at the length of 1,898,476 nt long. It has a G+C content of 32%, 79% of the genes are functional. Francisella tularensis contains no pseudogenes,
Cell structure and metabolism
Describe any interesting features and/or cell structures; how it gains energy; what important molecules it produces.
Contains AcpA, which is a repiratory, burst-inhibiting acid phosphatase
Has sideropore (which grows under iron-limiting conditions)-Reference http://jb.asm.org/cgi/content/full/188/11/3785
Most of the Francisella bacteria are homogeneous in shape and size. They are covered by a capsule-like coat with well-defined borders. The virulent strains, like Francisella tularensis, have thick capsules while avirulent strains have thinner capsules. Some Francisella tularensis bacteria are able to produce protrustions on the outer membrane. reference: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9289274&dopt=Abstract
Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.
Francisella tularensis infects small mammals such as rabbit and rodents with the disease tularemia. Francisella tularensis can also infect human through contact with infected animals or vectors such as fleas and mosquitos. It can also be spread to humans by being in their water or food supply (It can survive for along time in animal carcasses).
The F. tularensis is a highly contagious bacteria that can be spread from animals to humans, through vectors such as mosquitos and fleas, or from being breathed in from the air. It primarily infects macrophages of the host organism after it is ingested by phagocytosis. F. tularensis multiply inside the macrophage and later break out the macrophage and invades other cells. No proven vaccine has been created for tularemia, and the general treatment for the disease is antibiotics.
Some symptoms of tularemia are fever, ulcers, dyspnea, and others (depending on what part of the body is affected).
Application to Biotechnology
Francisella tularensis was researched and used as a biological weapon during World War II and two decades afterwards. During World War II, Japan conducted research on the bacteria for its potential as a biological weapon. Francisella tularensis has the potential to be a biological weapon because it is very infectious (a small number, about 10-50 organisms, can cause disease). As a biological weapon it is most effective when spread airbrone, and the United States developed weapons that can deliver aerosol Francisella tularensis in the 1950s-60s. The Soviet Union, along with using Francisella tularensis as a weapon, also developed antibiotic and vaccine resistant strains against the bacteria.
The effects of the biological weapon are severe respiratory illness including pneumonia and systemic infection that if not treated, can result in death.
1. This research deals with the genetic manipulation of Francisella tularensis . This bacteria is a "category A bioterror pathogen" that can cause fatal human infection, however, very few virulence factors are known in this species due to lack of tools for genetic manipulation and difficulty working with it. In this research, a vector that can replicate in E. Coli and F. tularensis is created that allows the research of the bacteria by identifying the promoters that are activated during intracellular growth and survival of the bacteria.
2. This research investigated the virulence of different strains of F. tularensis on chicken embryos. The experiments are conducted by infecting 7 day old chicken embryos with different strains (a wild strain and a live vaccine strain (LVS). The wild strain is determined to be more virulent. Later, more mutant strains of the bacteria are tested, and it is determined that they all have a wide range of virulence in chicken embryos.
3. This research attempts to identify F. tularensis mutants that can be useful in the developmental of a vaccine for tularemia in humans and other animals. F novicida transposon mutants are screened to identify mutants that showed reduced growth in mouse microphages. Results yielded 16 F. novicida mutants that were "100-fold more attenuated for virulence in a mouse model than the wild0type parental strain". The mutants are then tested for their ability to protect the mice against high doses of wild type strains. 5 of the 16 mutants exhibit protection for the mice. This is believed to be valuable in designing a vaccine against tularemia.
1. Rasko DA, Esteban CD, Sperandio V, Development of novel plasmid vectors and a promoter trap system in Francisella tularensis compatible with the pFLN10 based plasmids. 2007 http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=17459476&itool=iconabstr&query_hl=1&itool=pubmed_docsum
2. Eli B. Nix,1 Karen K. M. Cheung,1 Diana Wang,2 Na Zhang,1 Robert D. Burke,1,2 and Francis E. Nano Virulence of Francisella spp. in Chicken Embryos, 2006 http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1539577
3. Rebecca Tempel,†* Xin-He Lai,† Lidia Crosa, Briana Kozlowicz, and Fred Heffron. Attenuated Francisella novicida Transposon Mutants Protect Mice against Wild-Type Challenge, 2006 http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&rendertype=abstract&artid=1594869
Edited by Dan Su of Rachel Larsen and Kit Pogliano