Mycobacterium riyadhense is a non-tuberculoid Mycobacteria (NTM) that was first isolated in a clinical facility in Riyadh, Saudi Arabia in 2009. M. riyadhense causes pulmonary disease primarily in immunocompromised individuals and the clinical symptoms are strikingly similar to clinical symptoms caused by the human TB pathogen Mycobacterium tuberculosis. To illustrate the similarity and difference of these organisms, we have sequenced the genomes of M. riyadhense strains of nine clinical cases from Riyadh. The representative assembly contains one circular chromosome of 6.25Mbp length, one 0.55Mbp linear plasmid pMRLP01 and one circular plasmid pMR01 which is 94Kb. We conducted a comparative genomic study of M. riyadhense with the M. tuberculosis complex (MTBC) and revealed that they share a large number of conserved orthologs for the five ESX secretion systems. The phylogenomic position of M. riyadhense is closer to MTBC complex than both closely related M. kansasii and M. marinum - often used as experimental models to study M. tuberculosis infection biology. M. riyadhense has 49 toxin/antitoxin pairs that resemble members of the MTBC complex. To help the diagnostics of M. riyadhense from infections caused by members of the MTBC complex including M. tuberculosis, we have developed a set of discriminatory PCR primers based on comparative genome information which is currently being tested in other samples suspected of having M. riyadhense DNA present. Together, we provide data that suggest that M. riyadhense is the likely closest known environmental ancestor of the human pathogen M. tuberculosis and potentially could be used as the model organism to study M. tuberculosis.
Qingtian Guan received his BSc from Jilin University (JLU),China in Biotechnology and received his MSc degree in Bioscience from King Abdullah University of Science and Technology and is currently pursuing a Ph.D. under the supervision of Professor Arnab Pain. His research work is in the comparative genomic/pangenome study of Mycobacteria.