Construction and Analysis of the Complete Genome Sequence of Leprosy Agent Mycobacterium lepromatosis.

Leprosy is caused by Mycobacterium leprae and Mycobacterium lepromatosis. We report construction and analyses of the complete genome sequence of M. lepromatosis FJ924. The genome contained 3,271,694 nucleotides to encode 1,789 functional genes and 1,564 pseudogenes. It shared 1,420 genes and 885 pseudogenes (71.4%) with M. leprae but differed in 1,281 genes and pseudogenes (28.6%). In phylogeny, the leprosy bacilli started from a most recent common ancestor (MRCA) that diverged ~30 million years ago (Mya) from environmental organism Mycobacterium haemophilum. The MRCA then underwent reductive evolution with pseudogenization, gene loss, and chromosomal rearrangements. Analysis of the shared pseudogenes estimated the pseudogenization event ~14 Mya, shortly before species bifurcation. Afterwards, genomic changes occurred to lesser extent in each species. Like M. leprae, four major types of highly repetitive sequences were detected in M. lepromatosis, contributing to chromosomal rearrangements within and after MRCA. Variations in genes and copy numbers were noted, such as three copies of the gene encoding bifunctional diguanylate cyclase/phosphodiesterase in M. lepromatosis, but single copy in M. leprae; 6 genes encoding the TetR family transcriptional regulators in M. lepromatosis, but 11 such genes in M. leprae; presence of hemW gene in M. lepromatosis, but absence in M. leprae; and others. These variations likely aid unique pathogenesis, such as diffuse lepromatous leprosy associated with M. lepromatosis, while the shared genomic features should explain the common pathogenesis of dermatitis and neuritis in leprosy. Together, these findings and the genomic data of M. lepromatosis may facilitate future research and care for leprosy. IMPORTANCE Leprosy is a dreaded infection that still affects millions of people worldwide. Mycobacterium lepromatosis is a recently recognized cause in addition to the well-known Mycobacterium leprae. M. lepromatosis is likely specific for diffuse lepromatous leprosy, a severe form of the infection and endemic in Mexico. This study constructed and annotated the complete genome sequence of M. lepromatosis FJ924 and performed comparative genomic analyses with related mycobacteria. The results afford new and refined insights into the genome size, gene repertoire, pseudogenes, phylogenomic relationship, genome organization and plasticity, process and timing of reductive evolution, and genetic and proteomic basis for pathogenesis. The availability of the complete M. lepromatosis genome may prove to be useful for future research and care for the infection.

On the age of leprosy.

Leprosy is a chronic infection of the skin and nerves caused by Mycobacterium leprae and the newly discovered Mycobacterium lepromatosis. Human leprosy has been documented for millennia in ancient cultures. Recent genomic studies of worldwide M. leprae strains have further traced it along global human dispersals during the past ∼ 100,000 years. Because leprosy bacilli are strictly intracellular, we wonder how long humans have been affected by this disease-causing parasite. Based on recently published data on M. leprae genomes, M. lepromatosis discovery, leprosy bacilli evolution, and human evolution, it is most likely that the leprosy bacilli started parasitic evolution in humans or early hominids millions of years ago. This makes leprosy the oldest human-specific infection. The unique adaptive evolution has likely molded the indolent growth and evasion from human immune defense that may explain leprosy pathogenesis. Accordingly, leprosy can be viewed as a natural consequence of a long parasitism. The burden of leprosy may have affected minor selection on human genetic polymorphisms.

La dos especies de micobacterias causantes de la lepra y su emergencia como enfermedad humana / No disponible

Mycobactyerium leprae y Mycobacterium lepromatosis son dos especies de bacterias causantes de la lepra cuya divergencia ocurrió hace varios millones de años. El genoma de M. leprae contiene más de mil pseudogenes que reflejan un fenómeno de inactivación génica masiva probablemente asociado a un cambio en el estilo de vida del ancestro de estas bacterias. El análisis de unos pocos pseudogenes presentes en ambas bacterias indica que este fenómeno tuvo lugar antes de la divergencia de las dos especies. Con el objeto de reconciliar la divergencia antigua entre estas dos especies y la reciente colonización de los continentes por los seres humanos se plantea un posible escenario evolutivo en el que una micobacteria, ancestro de ambas especies, se asoció como patógeno a una especie animal desconocida. En el nuevo ambiente muchos genes se volvieron dispensables lo que permitió su inactivación. Durante la coevolución entre hospedador y patógeno se originaron las dos especies de bacterias de la lepra M. leprae saltó a los seres humanos en África oriental emergiendo como nuevo patógeno humano, mientras M. lepromatosis saltó a los seres humanos en América antes de la llegada de europeos y africanos a partir del siglo XV (AU)

Mycobacterium leprae and Mycobacterium lepromatosis, which are the causative agents of leprosy, are two bacterial species that diverged several million years ago. The genome of M. leprae contains more than 1,000 pesudogenes that reflect a mass gene inactivation event, probably associated with a change in the lifestyle of the ancestor of these bacteria. The analysis of a few shared pseudogenes showed that the divergence of both species took place prior to this inactivation event. With the aim of reconciling the old divergence of these species to the recent colonization of the continents by the human beings, a putative evolutionary scenario is proposed in which a mycobacterial ancestor of both species became associated as a pathogen to an unknown animal species. In the new environment many genes became disposables, leading to their inactivation. During the co-evolution of host and pathogen lineages, the two species, causative agents of leprosy, were originated. M. leprae emerged as a new human pathogen in East Africa, while M. lepromatosis emerged as a new pathogen in America before the arrival of Europeans and Africans in the 15th century (AU)

Comparative sequence analysis of Mycobacterium leprae and the new leprosy-causing Mycobacterium lepromatosis.

Mycobacterium lepromatosis is a newly discovered leprosy-causing organism. Preliminary phylogenetic analysis of its 16S rRNA gene and a few other gene segments revealed significant divergence from Mycobacterium leprae, a well-known cause of leprosy, that justifies the status of M. lepromatosis as a new species. In this study we analyzed the sequences of 20 genes and pseudogenes (22,814 nucleotides). Overall, the level of matching of these sequences with M. leprae sequences was 90.9%, which substantiated the species-level difference; the levels of matching for the 16S rRNA genes and 14 protein-encoding genes were 98.0% and 93.1%, respectively, but the level of matching for five pseudogenes was only 79.1%. Five conserved protein-encoding genes were selected to construct phylogenetic trees and to calculate the numbers of synonymous substitutions (dS values) and nonsynonymous substitutions (dN values) in the two species. Robust phylogenetic trees constructed using concatenated alignment of these genes placed M. lepromatosis and M. leprae in a tight cluster with long terminal branches, implying that the divergence occurred long ago. The dS and dN values were also much higher than those for other closest pairs of mycobacteria. The dS values were 14 to 28% of the dS values for M. leprae and Mycobacterium tuberculosis, a more divergent pair of species. These results thus indicate that M. lepromatosis and M. leprae diverged approximately 10 million years ago. The M. lepromatosis pseudogenes analyzed that were also pseudogenes in M. leprae showed nearly neutral evolution, and their relative ages were similar to those of M. leprae pseudogenes, suggesting that they were pseudogenes before divergence. Taken together, the results described above indicate that M. lepromatosis and M. leprae diverged from a common ancestor after the massive gene inactivation event described previously for M. leprae.

Reconstructing the ancestor of Mycobacterium leprae: the dynamics of gene loss and genome reduction.

We have reconstructed the gene content and order of the last common ancestor of the human pathogens Mycobacterium leprae and Mycobacterium tuberculosis. During the reductive evolution of M. leprae, 1537 of 2977 ancestral genes were lost, among which we found 177 previously unnoticed pseudogenes. We find evidence that a massive gene inactivation took place very recently in the M. leprae lineage, leading to the loss of hundreds of ancestral genes. A large proportion of their nucleotide content ( approximately 89%) still remains in the genome, which allowed us to characterize and date them. The age of the pseudogenes was computed using a new methodology based on the rates and patterns of substitution in the pseudogenes and functional orthologous genes of closely related genomes. The position of the genes that were lost in the ancestor's genome revealed that the process of function loss and degradation mainly took place through a gene-to-gene inactivation process, followed by the gradual loss of their DNA. This suggests a scenario of massive genome reduction through many nearly simultaneous pseudogenization events, leading to a highly specialized pathogen.