Reactive oxygen species (ROS) generated by host macrophages and antioxidant defense mechanisms-mediated by Mycobacterium tuberculosis (Mtb) play significant roles during Mtb infection and treatment. Previous studies suggested a role for the Mtb mel2 locus in resistance to oxidative stress and in silicoanalysis identified melgenes as close homologs of lux genes which may have evolved from oxidative defense mechanisms. melH encodes epoxide hydrolase b (EHB), which presumably catalyzes hydrolysis of epoxides involved in the ROS detoxification process. Therefore, understanding the molecular role of melHand how it interacts with Mtb metabolism is important for developing new therapeutic targets in Mtb. In this study, we discovered that the Mtb melH knockout mutant is more susceptible to oxidants such as cumulene hydroperoxide (CHP) and H2O2 than wild type, suggesting that Mtb melH plays a role in Mtb’s defense against ROS. Mtb can utilize different carbon sources for its survival. Interestingly, Mtb cultured in minimal medium containing glycerol or propionate as a single carbon source exhibits a growth arrest phenotype upon melH knockout compared to wild type, indicating a potential link of melHto central carbon metabolism during Mtb growth. An untargeted metabolomics strategy was employed to understand the impact of melH knockout on the M. marinum metabolome using three different carbon sources. The metabolomics data revealed that the melHmutant has reduced levels of oxidized nicotinamide adenine dinucleotide (NAD+), reduced NAD (NADH) and adenosine (ATP), accompanied by an accumulation of succinate. Mtb employs multiple mechanisms to modulate its lipid biosynthetic pathways, and to ensure survival within the host. We found the melH mutant accumulates the storage lipid triacylglycerol (TAG). Here, we demonstrate that Mtb melH contributes to withstanding ROS stress, which is generated by the host upon infection, and melH is required for transfer of reducing equivalents from Mtb primary metabolism to the electron transport chain. This study has uncovered a dynamic imbalance caused by melH deficiency between Mtb redox and bio-energetic homeostasis, which may influence Mtb immune system susceptibility. Our findings demonstrate that disruption of melH dysregulates Mtb central metabolism, and increases Mtb sensitivity to ROS. Thus targeting MelH may provide a new mechanism for anti-TB therapy.

Influence of melH epoxide hydrolase b on mycobacterium tuberculosis response to oxidative stress and drug resistance

ACS Spring 2022

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