Highly Reduced Genome of the New Species Mycobacterium uberis, the Causative Agent of Nodular Thelitis and Tuberculoid Scrotitis in Livestock and a Close Relative of the Leprosy Bacilli

Nodular thelitis is a chronic enzootic infection affecting dairy cows and goats. The causative agent was recently shown to be related to the leprosy-causing bacilli Mycobacterium leprae and Mycobacterium lepromatosis. In this study, the genome of this pathogen was sequenced and analyzed. Phylogenomic analyses confirmed that the pathogen present in nodular thelitis and tuberculoid scrotitis is a distinct species related to the leprosy bacilli and Mycobacterium haemophilum. Because the pathogen was originally isolated from a bovine udder, it was named "Mycobacterium uberis." The genome of "M. uberis" is only 3.12 Mb in length, which represents the smallest mycobacterial genome identified so far but which is close to that of leprosy bacilli in size. The genome contains 1,759 protein-coding genes and 1,081 pseudogenes, indicative of extensive reductive evolution and likely the reason that M. uberis cannot be grown axenically. The pseudogenization and genome reduction in M. uberis seem to have been to some extent independent from the results determined for the genomes of the leprosy bacilli.