The acid-induced operon Rv3083–Rv3089 is required for growth of Mycobacterium tuberculosis in macrophages

SummaryThe Rv3083–Rv3089 operon of Mycobacterium tuberculosis has been shown to be induced 17–33-fold when tubercle bacilli were exposed in vitro to acidic conditions which may mimic those that the bacilli encounter early during the infection and it is induced during growth in macrophages. To understand the role of this operon in intracellular survival, we constructed a knockout of the operon in the M. tuberculosis H37Rv strain. No differences were observed in the growth of mutant and wild-type mycobacteria on axenic media. Though the uptake of mutant and wild-type bacteria by eukaryotic cells was similar, the mutant failed to grow subsequently. By 192 h post-infection, the fold differences between the wild-type and mutant bacteria were significant thus leading to the conclusion that the mutant is defective for intracellular growth in these cell lines. Complementation of the knockout restored intracellular growth to wild-type levels. During the first 24–48 h post-infection, mutant bacteria also stimulated production of significantly less IL-1β, IL-6, IL-8, RANTES, and MCP-1 by THP-1 cells than wild-type bacteria. Overall, the data indicate that the operon plays an important role in the ability of M. tuberculosis to grow inside host cells.