M. tuberculosis H37Rv (wt, black circles), the mutant ML163 (ΔompATb, closed red squares), the pML588 complemented mutant (+ompATb, open blue triangles) and the pML763 complemented mutant (+ompATb operon, closed blue triangles) were grown in HdB medium (pH 5.5). In parallel, 10 mM exogenous ammonia was added (pink arrows) to the mutant ML163 culture on day 8 (ΔompATb+NH3, open pink squares). The cell density (OD600) of the culture (A), pH (B) and ammonia concentration (C) were measured each day for 30 days.