The causative agent of human tuberculosis, a disease with an annual death toll of three million. This human pathogen arose from a soil bacterium and may have subsequently moved to cows and then to humans, following the domestication of cattle. The H37 Rv strain was isolated in 1905, and it is the DNA of bacteria from this strain that was sequenced. The circular chromosome contains 4,411,529 base pairs and 3,924 ORFs. The demonstration that the DNA of M. tuberculosis has a high content of GC relative to AT disproved the tetranucleotide hypothesis (q.v.). The tubercle bacillus is resistant to many antibiotics, and this natural resistance is mainly due to its hydrophobic cell envelope, which acts as a permeability barrier. Many of its genes are devoted to a synthesis and breakdown of the lipoproteins in this envelope. The genome also contains at least two prophages and over 50 insertion sequences (q.v.). See Classification, Bacteria, Actinobacteria; Chronology, 1882, 1905, Koch; 1998, Cole et al.; Chargaff rule, leprosy bacterium, lysogenic cycle.
Subjects: Genetics and Genomics — Medicine and Health.