Query: NC_017058:497500 Rickettsia australis str. Cutlack chromosome, complete genome Lineage: Rickettsia australis; Rickettsia; Rickettsiaceae; Rickettsiales; Proteobacteria; Bacteria General Information: Animal pathogen in Mammalia (intracellular obligate). Rickettsiae are obligate intracellular Gram-negative bacteria mostly found in arthropods, some of which cause mild to severe diseases in humans. Rickettsia australis causes a medical condition called Queensland tick typhus. The probable vectors are the tick species, Ixodes holocyclus and Ixodes tasmani. Small marsupials are suspected reservoirs of this bacterium.
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General Information: This strain is the symbiont of the aphid Schizaphis graminum and contains a large circular chromosome. 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.