M.tb adaptation to human alveolar lining fluid (ALF)
Superbugs such as drug-resistant Mycobacterium tuberculosis (DR-M.tb) poses a serious global health threat. Upon infection, M.tb reaches the alveolar space and comes in close contact with soluble components of the human alveolar lining fluid (ALF) for an uncertain period of time prior to and following its encounter with alveolar compartment cells. Homeostatic ALF hydrolases, which main function is maintaining lung health, modify the M.tb cell envelope, driving M.tb-host cell interactions. Still, the contribution of human ALF to M.tb adaptation to the host during infection is poorly understood. Here, we exposed 4 M.tb strains (H37Rv, HN878, CDC1551, W-7642) with different levels of virulence, transmissibility, and drug resistance to human ALF for shorter (15 min) and longer (12 h) periods of time. RNA sequencing was performed to determine the strains' transcriptional profiles in response to ALF exposure. Gene expression analysis showed a clear temporal and strain-specific adaptation to human ALF. When comparing ALF-exposed vs. unexposed bacteria for each M.tb strain, differential expression (DE) analysis revealed a total of 397 DE genes associated with lipid metabolism, cell envelope and processes, intermediary metabolism and respiration, and regulatory proteins, among others. Most DE was detected at 12 h post-ALF exposure, with DR-M.tb strain W-7642 having the highest number of DE genes. Interestingly, genes from the KstR2 regulon, which controls the degradation of cholesterol C and D rings, were significantly upregulated early in all strains post-ALF exposure. These results indicate that M.tb-ALF contact (15 min to 12 h prior to M.tb recognition by host cells in the alveolar space) drives global metabolic and physiologic changes in M.tb during the initial stages of the infection, with potential implications in infection outcome. Overall design: RNAseq data of 4 different M.tb strains exposed to human Alveolar Lining Fluid (ALF) for 15min and 12h, 2 replicates each, control sample is unexposed bacteria for each of the strains. Total: 32 samples