Borrelia burgdorferi sensu stricto

Borrelia burgdorferi sensu stricto

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A Microbial Biorealm page on the genus Borrelia burgdorferi sensu stricto

Classification

Bacteria; Spirochaetes; Spirochaetes; Spirochaetales; Spirochaetacae; Borrelia burgdorferi; Borrelia burgdorferi sensu stricto. (1, 2)

Description and significance

Borrelia burgdorferi sensu stricto is a strain of Borrelia burgdorferi, the causative agent of Lyme borreliosis (also known as Lyme disease). The size and structure of this pathogenic spirochete (See Cell Structure, metabolism, & life cycle) allows it to easily invade tissue as well as cross the blood brain barrier, causing a multitude of negative symptoms in both the peripheral nervous system and the central nervous system of humans. As a tick-borne disease (TBD), B. burgdorferi sensu stricto is transmitted to mammals via a tick vector, which releases the bacteria into the bloodstream of its own host. (Again, see Cell Structure, metabolism, & life cycle for the full explanation.) The most common manifestations of Lyme disease are arthritis, carditis, and neurological symptoms related to the inflammatory response of the host to the invading B. burgdorferi (migraines, deficits in memory and attention, cognitive deficits, and seizures). Since its discovery in Lyme, Connecticut in 1982 by Willy Burgdorfer, Lyme disease has become the number one TBD in North America and has been the subject of much controversy and debate in the medical world. This controversy mainly revolves around the accepted treatment of Lyme disease and the possible existence of chronic Lyme disease, meaning Lyme disease not cured by the standard one-month treatment of antibiotics recommended by the Infectious Diseases Society of America (IDSA). It is likely that the cost of long-term antibiotic treatment as well as the heterogeneity of the disease symptoms and severity has led to the conflicting opinions regarding the existence of chronic Lyme. Lyme disease has caused a fundamental divide between doctors and scientists who believe it exists and those who believe it is a convenient “catch-all” diagnosis. Like the AIDS virus and the other well-known spirochete Treponema pallidum subspecies pallidum (causative agent of syphillus), B. burgdorferi represents the human fear of unpredictable pathogens and how this fear of the unknown can result in stigmatization of those with the resulting disease. (3, 4).

==Genome structure==(molecular typing article, B. burgdorferi sensu stricto is one of ten species whose genome sequences suggest they belong to the B. burgdorferi sensu lato complex. It contains a linear chromosome as well as circular plasmids. While the genome sequence of this particular strain is incomplete; the completed genomes of similar strains provide insight into the complexity of this organism. The strain B. burgdorferi B31 for example, contains a linear chromosome of 910, 725 base pairs and 17 plasmids, both linear and circular, that total approximately 533,000 base pairs. The plasmids of B. burgdorferi typically replicate in low numbers. Of these plasmids, only 71% encode functional proteins. This suggests that many of the ORFs contain “stops.” The diversity of B. burgdorferi’s plasmids provides protection from the host immune response, as they encode for 63 different membrane lipoproteins; this allows for a wide variety of combinations making the bacteria difficult to identify. B. burgdorferi contains tRNAs for all 20 amino acids but its genome seems to lack the necessary genes for their synthesis. It is capable of homologous recombination but does not have genes encoding DNA restriction enzymes. (5, 6, 7).

Cell structure, metabolism & life cycle

Cell Structure It contains seven flagella on each end, and it is the structure and location of these periplasmic flagella that allow the bacteria to be so invasive. The rotation of the filaments of the flagella within the periplasmic space causes the corkscrew-like motion characteristic of spirochetes. In other words, the bacteria is able to move forward by simply rotating in place. It also allows the bacteria to hide its flagella inside, preventing its discovery by its host's immune system. The flagella's location inside the periplasm of the cell and its complexity (it is the most complex bacterial flagella, containing both FlaA sheath proteins and FlaB core proteins) allow the bacteria to move in gel-like, liquid material (i.e. connective tissue) that prohibits the movement of most bacteria.

They are much longer than they are wide, another structural aspect which allows them to burrow through otherwise impenetrable tissue. This also prohibits observation by standard light microscopy; dark field microscopy is used instead. This focuses the light at an angle and the organism is therefore seen as a light object while the background is dark (See Figure 1).

Dark-field microscopy must be used to view spirochetes. Dark field microscopy utilizes a special condenser which directs light toward an object at a angle, rather than from the bottom. As a result, particles or cells are seen as light objects against a dark background. (1, 8, 9, 13)

Metabolism This spirochete is microaerophilic and uses glucose as its primary energy source. Like similar bacteria, Borrelia burgdorferi have limited systems of metabolism; they do not encode proteins required for the TCA cycle or for oxidative phosphorylation. They do use substrate-level phosphorylation for the production of ATP. It has been suggested that their association with ticks is due to their use of N-acetylglucosamine (NAG) for energy, as NAG is located in the chitin of tick cuticles. Despite its limited metabolic processes, B. burgdorferi can survive well in a host due to their impressive ability to avoid the host immune system. (5, 10)

Life Cycle B. burgdorferi sensu stricto, as a tick-borne disease (TBD), cycles through two main hosts: deer ticks and rodents. B. burgdorferi can live in both transmission-competent hosts and transmission incompetent hosts, providing a wide variety of host organisms. Transmission to humans is possible through tick bites, but the minimum amount of time required for transmission is not definitively known. Transmission to humans most often occurs from tick bites of the nymph life stage of the tick, meaning a young tick. Tick eggs are laid in the winter and develop first into the nymph stage and then into the adult stage during spring. This is why transmission of B. burgdorferi to new hosts occurs most often in spring. (11, 12)

Ecology (including pathogenesis)

Describe its habitat, symbiosis, and contributions to environment. If it is a pathogen, how does this organism cause disease? Human, animal, plant hosts? Describe virulence factors and patient symptoms.

Interesting feature

Describe in detail one particularly interesting aspect of your organism or it's affect on humans or the environment.

References

1. http://www.textbookofbacteriology.net/Lyme.html 2. http://www.ncbi.nlm.nih.gov/genome?Db=genome&Cmd=ShowDetailView&TermToSearch=23501