Comparative genomics analysis of Mycoplasma leachii reveals genes involved in host specificities

Background Mycoplasma leachii (formerly Mycoplasma sp. bovine group 7) is a pathogen of ruminants causing pleuropneumonia, polyarthritis, mastitis and abortion in cattle, goats and sheep. It belongs to the “M. mycoides cluster” and phylogenetically takes a position between Mycoplasma mycoides subsp. mycoides Small Colony (SC) and Mycoplasma capricolum subsp. capricolum. Results We sequenced the genome of a virulent strain of M. leachii taking advantage of the Ultra High Throughput Sequencing technologies. The strain was isolated from the joint of a severely diseased arthritic calf belonging to a dairy cattle herd, which suffered from an outbreak of mycoplasmosis with polyarthritis, mastitis and abortion. The genome assembly and the annotation were done combining available bioinformatics tools and scripts that were developed for this purpose. The genome consists of a chromosome of approximately 1.016 Mbp with 902 predicted protein coding genes. Comparative genomic analysis with the most closely related Mycoplasma species revealed that the genome of M. leachii is composed of a majority of genes showing strong similarity to M. capricolum subsp. capricolum, spiked with segments that are highly similar with M. mycoides subsp. mycoides SC. In particular, several genes known to be involved as virulence attributes of M. mycoides subsp. mycoides SC are found in M. leachii. Furthermore, M. leachii harbours 5 full and 3 partial IS elements that are present at high copy numbers in M. mycoides subsp. mycoides SC and might have played a role in horizontal gene transfer between the two species. The mosaic structure of the genome of M. leachii underlines its phylogenetic position between M. capricolum subsp. capricolum and M. mycoides subsp. mycoides SC and sets genetic basis for the ability of this pathogen to colonize bovine, as well as caprine hosts causing a broad spectrum of clinical symptoms. Conclusions The comparative genomic analysis of M. leachii with related Mycoplasma species permits to unravel both the conserved potential pathogenic mechanisms shared by them and the broad host range of this pathogen. The data are of paramount importance for the development of specific and sensitive methods to diagnose the closely related and highly pathogenic species M. mycoides subsp. mycoides as well as well as to the design of novel vaccines against CBPP.