Comparative pathoadaptation of Mycobacterium canettii and Mycobacterium tuberculosis: insights from assays on phagosome acidification, cytosolic access, and transcriptomics.

Genetic and molecular differences between Mycobacterium tuberculosis (Mtb) and its ancestral counterpart, Mycobacterium canettii (Mcan), remain poorly known. Our study aimed to compare their modulation of phagosome acidification and cytosolic access in macrophages, and their in vitro transcriptomes. Using spectrofluorometry, we tracked pH changes in mycobacteria-containing vacuoles in THP-1 macrophages. A single-cell FRET protocol evaluated cytosolic access of mycobacteria in these cells. Similar to Mtb, Mcan inhibits phagosome acidification and accesses the cytosol. Transcriptomic and genetic analyses reveal mutations in two-component systems (PhoPR, SenX3-RegX3, and DevRS/DosRS) and in specific genes (e.g., lactate dehydrogenase and espACD) driving variations in gene expression between pathogens. Moreover, Mcan upregulates genes of iron and molybdopterin metabolism compared to Mtb, suggesting a role for metals in the evolution of tuberculous mycobacteria. The upregulation of the termination factor Rho in Mtb also suggests differences in antisense transcription and/or gene expression regulation. In conclusion, phagosome modulation and cytosolic access in macrophages are ancestral traits predating the emergence of the MTBC and not exclusive to Mtb's strict pathogenic lifestyle. Additionally, gene expression regulation likely shaped the phenotypic differences between Mcan and Mtb, contributing to the evolutionary transition from an environmental Mcan-like ancestor to the MTBC's host-adapted lifestyle.