Identification of genes of Mycobacterium tuberculosis upregulated during anaerobic persistence by fluorescence and kanamycin resistance selection.

Molecular mechanisms involved in maintaining the latent infection of Mycobacterium tuberculosis are least understood. We have applied principles of in vivo expression technology (IVET) to identify upregulated genes in an in vitro simulated condition of anaerobic persistence likely to be encountered by the pathogen in lung granulomas. A promoter library of M. tuberculosis constructed in plasmid pLL192 was subjected to hypoxic condition (dissolved oxygen <1%) in a controlled fermenter. On the basis of green fluorescent protein fluorescence and kanamycin resistance the upregulated promoters were selected, identified by nucleotide sequence and the genes were confirmed by RT-PCR. The upregulated genes include Rv0050 (penicillin binding protein), Rv1511 (GDP-d-mannose dehydratase), Rv1489, Rv2257, Rv2258 (all conserved hypothetical proteins), Rv0467 (isocitrate lyase) and Rv2031c (alpha-crystalline homolog). The involvement of the last four genes in latency has been suggested before. The functional role of Rv0050 and Rv1511 may be important in determining cell wall characteristics controlling permeability of nutrients and antibiotics.