Small Chromosome

Image: Circular representation of the small chromosome Vibrio cholerae

Caption: In 2000, the genomes of the two chromosomes possessed by V. cholerae were sequenced. The toxin genes, of which there are fifty, reside on the large chromosome. The sequencing data confirm that V. cholerae is a versatile organism, able to live in several habitat types, as well as to infect the human gastrointestinal tract.
Further information: As S. Sozhamannan and others have reported, Vibrio cholerae has a gene acquisition system located on its small chromosome as well as hot spots for DNA rearrangement. Lateral transfer of genetic material is clearly occurring in this organism.
The complete genome of Vibrio cholerae El Tor N16961 consists of two circular chromosomes (2,961,146 and 1,072,313 base pair) with 3,890 predicted open reading frames (2,775 and 1,115 on each chromosome respectively). The majority of recognizable genes for essential cell functions (such as DNA replication, transcription, translation, etc.) and pathogenicity (such as toxin, surface antigens, and adhesion) are located on the large chromosome. The small chromosome contains a large percentage of hypothetical genes, more genes that appear to have origins other than the Proteobacteria, a gene capture system (integron island) that suggests this may have been a mega-plasmid captured by an ancestral Vibrio species. The Vibrio cholerae genome sequence provides a starting point for understanding how a free living, environmental microorganism is also a human pathogen.

Source: The Institute for Genomic Research


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