Chen_2023_bioRxiv__

Mycobacterium tuberculosis ( Mtb ), the pathogenic bacterium that causes tuberculosis, has evolved sophisticated defense mechanisms to counteract the cytotoxicity of reactive oxygen species (ROS) generated within host macrophages during infection. The melH gene in Mtb and Mycobacterium marinum ( Mm ) plays a crucial role in defense mechanisms against ROS generated during infection. We demonstrate that melH encodes an epoxide hydrolase and contributes to ROS detoxification. Deletion of melH in Mm resulted in a mutant with increased sensitivity to oxidative stress, a minor increase in the bacterium's sensitivity to NO exposure. This heightened vulnerability is attributed to the increased expression of whiB3 , subsequently leading to decreased production of mycothiol and ergothioneine. Our study elucidated profound effects on the bioenergetic metabolism of Mm upon disruption of melH . The absence of melH resulted in reduced intracellular levels of NAD (+) , NADH, and ATP, and accumulation of aldehydes within Mm. Bacterial growth was impaired, even in the absence of external stressors, and was carbon-source-dependent. Taken together, these results highlight the essential role of melH in mycobacterial metabolism and provide new insights into the complex interplay between redox homeostasis and carbon utilization in mycobacteria. IMPORTANCE: This study unveils the pivotal role played by the melH gene in Mycobacterium tuberculosis and Mycobacterium marinum in combatting the detrimental impact of oxidative conditions during infection. This investigation revealed notable alterations in level of cytokinin-associated aldehyde, para -hydroxybenzaldehyde, as well as the redox buffer ergothioneine, upon deletion of melH . Moreover, changes in crucial cofactors responsible for electron transfer highlighted melH 's crucial function in maintaining a delicate equilibrium of redox and bioenergetic processes. These findings collectively emphasize the potential of melH as an attractive target for the development of novel antitubercular therapies, offering new avenues for combating tuberculosis.