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, increased accumulation of aldehyde species, and decreased production of mycothiol and ergothioneine. This heightened vulnerability is attributed to the increased expression of
whiB3
, a universal stress sensor. The absence of
melH
also resulted in reduced intracellular levels of NAD
+
, NADH, and ATP. Bacterial growth was impaired, even in the absence of external stressors, and the impairment was carbon source dependent. Initial MelH substrate specificity studies demonstrate a preference for epoxides with a single aromatic substituent. Taken together, these results highlight the role of
melH
in mycobacterial bioenergetic metabolism and provide new insights into the complex interplay between redox homeostasis and generation of reactive aldehyde species in mycobacteria.
IMPORTANCE
This study unveils the pivotal role played by the
melH
gene in
Mycobacterium tuberculosis
and in
Mycobacterium marinum
in combatting the detrimental impact of oxidative conditions during infection. This investigation revealed notable alterations in the 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. MelH prefers epoxide small substrates with a phenyl substituted substrate. These findings collectively emphasize the potential of
melH
as an attractive target for the development of novel antitubercular therapies that sensitize mycobacteria to host stress, offering new avenues for combating tuberculosis.