Introduction-Mycobacterium (M.) avium subsp. avium (MAA) and M. avium subsp. hominissuis (MAH) belongs to non-tuberculous mycobacteria group induce different courses of disease after mice infection. Previously we have shown that severe disease caused by MAA, but not MAH, was due to the accumulation of nitric oxide (NO) expressing splenic monocytic myeloid derived suppressor cells (M-MDSC). The mechanisms by which MAA induces M-MDSC and persists in the NO-rich environment is unknown. We hypothesized the subspecies-specific genes of MAA might mediate these unique features. In the present study, we identified putative phenotypic features that enable MAA to survive in the NO environment after infection of mice and after in vitro NO exposure.

Materials and methods-C57BL/6J mice were infected intraperitoneally with ∼10⁸ colony-forming units of MAA 44156 or MAH 104 per mouse and mice were sacrificed on 29 day post-infection. Both MAA and MAH were purified from spleens and ex vivo proteomic analyses were performed using mass spectrometry.

Results-Our proteomic analyses identified a total of 2729 MAA proteins. Among these 78.7% were detected in both the MAA infection input and MAA from mice. 19.3% MAA proteins were detected only in input and 1.9% were detected in MAA from mice only. The latter group is suggested to be involved in the adaption of MAA to the host milieu. Interestingly, some of the MAA proteins differentially abundant in mice, such as a paralog of a predicted nitric oxide reductase subunit B, an iron-sulfur cluster repair di-iron protein and ferredoxin paralogs were found to be encoded from genes located on MAA-specific genomic islands. To further investigating the functional relevance of the ex vivo expressed MAA-specific proteins, we monitored the mRNA expression of the above MAA proteins upregulated in mice after MAA exposed to NO in vitro. Interestingly, we found the upregulation of the respective genes which indicates a role of such proteins for MAA defense against NO stress.

Conclusions-Our proteomic and gene expression analyses provide new insights for a specific ability of MAA to respond to NO supporting its persistence in NO producing cells.