The DosR regulon of Mycobacterium avium and adaptation to hypoxia

Like other tuberculous and nontuberculous mycobacterial pathogens of human lung such as <i>Mycobacterium tuberculosis</i> and <i>M. abscessus</i>, <i>M. avium</i> is likely exposed to a variety of stressors during infection, including hypoxic conditions inside activated macrophages and in the avascular necrotic regions of granulomas. How <i>M. avium</i> survives hypoxic stress to establish a chronic infection is currently not well understood. Using RNA-sequencing, we here show that <i>M. avium</i> grown under progressive microaerophilic conditions activates more than 4-fold a subset of 16 genes, the expression of 13 of which is dependent on the two-component system regulator DosRS. A subset of <i>M. avium</i> DosR regulon genes was confirmed to also be activated upon exposure to nitric oxide. Although a second sensor kinase besides DosS has been proposed to function with the transcriptional regulator DosR in <i>M. avium</i>, we show that this other kinase cannot compensate for a deficiency in DosS. Loss of <i>dosRS</i> expression in <i>M. avium</i> led to a significant reduction in viability under hypoxia that was more marked at acidic than at neutral pH. Unlike the situation in <i>M. abscessus</i>, however, loss of DosRS did not significantly impact the ability of <i>M. avium</i> to establish a drug tolerant state <i>in vitro</i> or form biofilms under host relevant conditions. Collectively, these results are suggestive of a lesser impact of DosRS on the ability of <i>M. avium</i> to develop antibiotic tolerance compared to other nontuberculous mycobacteria. The <i>M. avium dosRS</i> mutant further showed no signs of virulence attenuation in murine macrophages and in chronically infected immunocompetent BALB/c mice.