Query: NC_010263:167450 Rickettsia rickettsii str. Iowa, complete genome Lineage: Rickettsia rickettsii; Rickettsia; Rickettsiaceae; Rickettsiales; Proteobacteria; Bacteria General Information: Causative agent for Rocky Mountain Spotted Fever. This organism was first identified by Dr. Howard Rickets as the causative agent of Rocky Mountain Spotted Fever, which was originally named for its geographic distribution at the time, it is now known to be widespread throughout the North American continent. This bacterium is an obligate intracellular pathogen that infects primarily the vascular endothelium, and occasionally smooth muscle tissue. It is passed to the human host from a tick bite, and the tick acts as both a natural reservoir and a vector for disease transmission. Once the organism is endocytosed by the host cell, it quickly escapes the phagozome, and replicates intracellularly, causing cell death and tissue damage. The disease is characterized by a spotted rash and has a high mortality rate if left untreated.
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General Information: This strain is found in the pea aphid, Acyrthosiphon pisum.Aphid endosymbiont. Almost all aphids contain maternally transmitted bacteriocyte cells, which themselves contain bacteria called Buchnera. The aphids live on a restricted diet (plant sap), rich in carbohydrates, but poor in nitrogenous or other essential compounds. It is believed that the Buchnera provide the essential nutrients the host lacks. Besides a nutritional co-dependence, due to a co-existence of millions of years, Buchnera have lost the ability to produce cell surface components such as lipopolysaccharides. This makes for an obligate endosymbiont relationship between host and Buchnera. Buchnera are prokaryotic cells which belong to the gamma-Proteobacteria, closely related to the Enterobacteriaceae family. Phylogenetic studies using 16S rRNA indicate that the symbiotic relationship was established around 200-250 million years ago. Since Buchnera are closely related to Escherichia coli and Haemophilus influenzae, comparative genomic studies can shed light on the evolutionary mechanisms of intracellular endosymbiosis as well as the different underlying molecular basis between organisms with parasitic behavior and symbionts.