Hydrogen sulfide (H2S) production by mycobacteria.
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Date
2020
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Abstract
The gasotransmitter hydrogen sulfide (H2S) has been recognized as a physiological mediator with a
variety of functions across all domains of life. Many prokaryotic bacterial species endogenously
generate H2S in their natural environments. However, to date, it is not known whether Mycobacterium
tuberculosis (Mtb) is an endogenous producer of H2S. In this study, we tested the hypothesis that Mtb
endogenously produces H2S to modulate respiration, central metabolism, oxidative stress, and drug
susceptibility. We demonstrated that fast-growing non-pathogenic, slow-growing pathogenic
mycobacterial species, as well as drug resistant clinical strains of Mtb species produce H2S. Here we
demonstrate that fast-growing non-pathogenic M. smegmatis produces barely detectable quantities of
H2S, whereas MDR Mtb produces large quantities of H2S. We have also developed a native PAGEbased
assay for the rapid screening of H2S producing enzymes in the lysates of mycobacterial species.
Using LC-MS/MS, we identified the protein, Rv3684 as an H2S-producing enzyme in Mtb. Disruption
of rv3684, demonstrated using the genetic knock out of rv3684, reduces, but does not eliminate, H2S
production, suggesting the involvement of multiple genes in H2S production. Whole Mtb cell-based
and lysate assays showed reduced levels of H2S production in the Mtb knockout strain compared to the
wild-type strain. Noticeably, we demonstrated that the Mtb mutant is resistant to oxidative stress and
the anti-TB drugs clofazimine and rifampicin. We also found that endogenous H2S is an effector
molecule that maintains bioenergetic homeostasis by regulating Mtb respiration, and that H2S also plays
a key role in central metabolism by modulating the balance between oxidative phosphorylation
(OXPHOS) and glycolysis. In summary, our findings reveal previously unknown concepts of Mtb
physiology with respect to Mtb-derived H2S and energy metabolism which has significant implication
for routine laboratory culturing, understanding susceptibility and TB disease.
Description
Doctoral Degree. University of KwaZulu-Natal, Durban.