Wednesday, August 24, 2011

Genome structure of Pseudomonas aeruginosa

Ps. aeruginosa has the genome size of about 5.2 to 7 million base pairs (Mbp) with 65% Guanine + Cytosine content. It is a combination of variable accessory segments and a conserved core. The variable accessory genome is characterized by a set of genomic islands and islets from a primeval tRNA-integrated island type. The core genome consists of a low level of nucleotide divergence of 0.5% and a conserved synteny of genes, which means two or more genes, whether they are linked or not, are on the same chromosome (Wiehlmann et al., ‎2007‎).
Ps. aeruginosa has a single and supercoiled circular chromosome in the cytoplasm. It also carries a lot of chromosome-mobilizing plasmids that are very significant to the organism’s lifestyle as a pathogen. The plasmids, TEM, OXA, and PSE, for instance, are encoded for β-lactamases production, which is necessary for its resistance to antibiotics, thus allowing Ps. aeruginosa to be a formidable pathogen. The two strains that have the complete genome sequence are Pseudomonas aeruginosa PA01 and Pseudomonas aeruginosa PA014 (Pseudomonas Genome Database). Knowing the complete genome sequence of Pseudomonas aeruginosa PAO1 would provide new information about this bacterium as a pathogen and about its ecological versatility and genetic complexity. At 6,264,403 base pairs, its bacterial genome is the largest to ever be sequenced. It also contains 5,570 predicted open reading frames (ORFs). Using whole-genome-shotgun sampling, the complete 6.3 Mbp genome of Pseudomonas aeruginosa PA01 is very much similar to the Ps. aeruginosa’s physical map, with only one major exception, which is the inversion of about a quarter of the Pseudomonas aeruginosa PA01 genome (Stover et al., 2000).

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