Carbon metabolism modulates the efficacy of drugs targeting the cytochrome bc(1):aa(3) in Mycobacterium tuberculosis

The influence of carbon metabolism on oxidative phosphorylation is poorly understood in mycobacteria. M. tuberculosis expresses two respiratory terminal oxidases, the cytochrome bc(1):aa(3) and the cytochrome bd oxidase, which are jointly required for oxidative phosphorylation and mycobacterial viability. The essentiality of the cytochrome bc(1):aa(3) for optimum growth is illustrated by its vulnerability to chemical inhibition by the clinical drug candidate Q203 and several other chemical series. The cytochrome bd oxidase is not strictly essential for growth but is required to maintain bioenergetics when the function of the cytochrome bc(1):aa(3) is compromised. In this study, we observed that the potency of drugs targeting the cytochrome bc(1):aa(3) is influenced by carbon metabolism. The efficacy of Q203 and related derivatives was alleviated by glycerol supplementation. The negative effect of glycerol supplementation on Q203 potency correlated with an upregulation of the cytochrome bd oxidase-encoding cydABDC operon. Upon deletion of cydAB, the detrimental effect of glycerol on the potency of Q203 was abrogated. The same phenomenon was also observed in recent clinical isolates, but to a lesser extent compared to the laboratory-adapted strain H37Rv. This study reinforces the importance of optimizing in vitro culture conditions for drug evaluation in mycobacteria, a factor which appeared to be particularly essential for drugs targeting the cytochrome bc(1):aa(3) terminal oxidase.