Figure 3: Borrelia burgdorferi; Magnified 400x
Species: B. burgdorferi 
Why does this organism belong to this Domain?
Bacteria cells are found to only be unicellular and prokaryotic. The bacteria moves with the help of flagella in the lash-like movement it uses.  There are two types of bacteria, beneficial and pathogenic organisms. Borrelia burgdorferi found in the Domain Bacteria is a prokaryotic, single cell organism that lives mostly as an extracellular pathogen.  The main function of this organism leaves an infection in the human’s body causing a disease. Therefore, this organism would be considered a pathogenic organism. Inthas flagella on its cell wall to help it move around within an organism’s blood stream. These are characteristic that would be found in the Domain Bacteria. As most prokaryotes, it has two membranes, an inner , and outer membrane. With these two layers the Borrelia burgdorferi has a periplasmic space which contains a layer of peptidoglycan.  This characteristic makes this organism only fit into only the Domain Bacteria. In the Domain bacteria the organisms contain peptidoglycan, which is something that the Domain Archaea does not have.  Finally, Borrelia burgdorferi can only be categorized in the Domain Bacteria because of all these characteristic it consists of.
Borrelia burgdorferi is a long strand. This organism barely has any width to it and is not able to be seen with a light microscope, which is why a dark-field microscope is used to see this organism. It is about 20- 30 μm in length and about .2-.3 μm in width. It has an optimal growth at 32 C° with a low amount of oxygen environment. Even though it has an optimal growth temperature, it still grows very slow, in the time of 12-24 hours.  Many of the unique characteristics of this organism are found in its replication. It first replicates specific genes and then sends them into its cell wall, pinching that part off. When this is complete it is sent to the host cell. Making the process of reproduction very long. Most bacteria organisms grow and divide in about 20 minutes.  Borrelia burgdorferi is not considered gram-positive nor gram-negative. However, it is weakly gram-negative and does show characteristics of gram-negative bacteria, although there are differences between a gram-negative bacteria and this organism.
Borrelia burgdorferi is usually made in a certain type of tick and is then spread to other ticks. This pathogenic bacteria likes to target the blood of different animals.  The kind of ticks it is found in, is in deer ticks and wood ticks.  When Borrelia burgdorferi is in a blood of an animal and a tick comes for its first feeding, it can get infected with this bacteria too. An infection of this bacteria can cause the disease, called Lyme disease. 
The video below will tell you more about the disease the bacteria causes, and why this bacteria is categorized in the pathogenic bacterial organisms. This organism is commonly known because of the disease it causes, Lyme disease.
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