Plasticity of <i>Mycobacterium tuberculosis</i> NADH dehydrogenases and their role in virulence.

Abstract

Worldwide control of the tuberculosis (TB) epidemic has not been achieved, and the latest statistics show that the TB problem might be more endemic than previously thought. Although drugs and a TB vaccine are available, TB eradication faces the challenges of increasing occurrences of multidrug-resistant and extensively drug-resistant <i>Mycobacterium tuberculosis</i> (<i>Mtb</i>) strains. To forestall this trend, the development of drugs targeting novel pathways is actively pursued. Recently, enzymes of the electron transport chain (ETC) have been determined to be the targets of potent antimycobacterial drugs such as bedaquiline. We focused on the three NADH dehydrogenases (Ndh, NdhA, and Nuo) of the <i>Mtb</i> ETC with the purpose of defining their role and essentiality in <i>Mtb</i> Each NADH dehydrogenase was deleted in both virulent and BSL2-approved <i>Mtb</i> strains, from which the double knockouts Δ<i>ndh</i>Δ<i>nuoAN</i> and Δ<i>ndhA</i>Δ<i>nuoAN</i> were constructed. The Δ<i>ndh</i>Δ<i>ndhA</i> double knockout could not be obtained, suggesting that at least one type II NADH dehydrogenase is required for <i>Mtb</i> growth. Δ<i>ndh</i> and Δ<i>ndh</i>Δ<i>nuoAN</i> showed growth defects in vitro and in vivo, susceptibility to oxidative stress, and redox alterations, while the phenotypes of Δ<i>ndhA,</i> Δ<i>nuoAN</i>, and Δ<i>ndhA</i>Δ<i>nuoAN</i> were similar to the parental strain. Interestingly, although Δ<i>nuoAN</i> had no phenotype in vivo, Δ<i>ndh</i>Δ<i>nuoAN</i> was the most severely attenuated strain in mice, suggesting a key role for Nuo in vivo when Ndh is absent. We conclude that Ndh is the main NADH dehydrogenase of <i>Mtb</i> and that compounds that could target both Ndh and Nuo would be good candidates for TB drug development.