Search

Low molecular weight (LMW) thiols are molecules with a functional sulfhydryl group that enable them to detoxify reactive oxygen species, reactive nitrogen species and other free radicals. Their roles range from their ability to modulate the immune system to their ability to prevent damage of biological molecules such as DNA and proteins by protecting against oxidative, nitrosative and acidic stress. LMW thiols are synthesized and found in both eukaryotes and prokaryotes. Due to their beneficial role to both eukaryotes and prokaryotes, their specific functions need to be elucidated, most especially in pathogenic prokaryotes such as Mycobacterium tuberculosis (M.tb), in order to provide a rationale for targeting their biosynthesis for drug development. Ergothioneine (ERG), mycothiol (MSH) and gamma-glutamylcysteine (GGC) are LMW thiols that have been shown to interplay to protect M.tb against cellular stress. Though ERG, MSH and GGC seem to have overlapping functions, studies are gradually revealing their unique physiological roles. Understanding their unique physiological role during the course of tuberculosis (TB) infection, would pave the way for the development of drugs that target their biosynthetic pathway. This review identifies the knowledge gap in the unique physiological roles of LMW thiols and proposes their mechanistic roles based on previous studies. In addition, it gives an update on identified inhibitors of their biosynthetic enzymes., (Copyright © 2019. Published by Elsevier Ltd.)

The emerging resistance of tuberculosis (TB) to current first line drugs (isoniazid, rifampicin, pyrazinamide, ethambutol) warrants alternative treatment approaches with broad-spectrum efficacy. Previously, we have shown that sulfamethoxazole (SMX) has synergestic activity with rifampicin against Mycobacterium tuberculosis. The primary target of SMX is folP1 in mycobacteria; however, SMX may affect other secondary targets in M. tuberculosis. This study investigated the potential additional targets of SMX in a clinical isolate of M. tuberculosis using Orbitrap mass spectrometry to identify differentially expressed proteins following treatment with a sub-lethal concentration of SMX. Raw data have been deposited as ProteomeXchange accession PXD009315. Our proteomic analysis identified approximately 1500 proteins in total of which 45 proteins were differentially regulated as a result of SMX treatment. These included 25 upregulated and 20 downregulated proteins. The oxidative stress proteins (Rv2428, AhpC and Rv2394, GgtB) and an enzyme from the electron transport chain (Ndh-II, Rv1854c) were found to be upregulated. Gene expression analysis correlated with the observed proteomic changes. In conclusion our results show that SMX treatment of a drug sensitive M. tuberculosis clinical isolate resulted in the regulation of proteins involved in the oxidative stress response, indicating the induction of oxidative stress by SMX in mycobacteria., (Copyright © 2018. Published by Elsevier Ltd.)

The culturing of mycobacteria is a standard procedure that is consistent world-wide, with little variation in the growth media constituents, particularly those found in liquid and solid media. Before the 1940s however, the aggregating nature of mycobacteria as well as the characteristic slow growth-rate saw mycobacterial research delay considerably. Dubos and colleagues addressed both these issues and observed that a very small volume of Tween detergent was sufficient to greatly improve the culturing of mycobacteria. Over the years however, evidence of the unfavourable effects of this detergent on a number of morphological, biochemical, pathogenic and host-interacting properties of mycobacteria surfaced. For the first time we bring together literature, past and present to comprehensively review the mycobacterial properties which are, and are not affected by the use of this detergent. We also address other detergents and methods which may circumvent the need to include Tween compounds in mycobacterial culture media., (Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Setting: DNA repair genes assist the organism in maintaining DNA integrity in the face of environmental (mutagenic) stress. The genome sequences of M. tuberculosis and M. bovis demonstrate sequences suggestive of an O(6)-alkylguanine-DNA alkyltransferase DNA repair activity similar to that seen in almost all other bacterial and eukaryotic organisms. The near ubiquitousness of this gene implies an important function., Objective: Our aim was to ascertain whether mycobacteria exert an alkyltransferase response to mutagen (streptozotocin) stimulation and whether alkyltransferase activity is essential for mycobacterial survival., Design: Alkyltransferase activity in slow- and fast-growing mycobacterial species was determined in the presence and absence of sublethal concentrations of an alkylating agent streptozotocin. The intracellular survival and response to anti-tuberculosis drugs of an alkyltransferase knockout strain of M. bovis BCG was also determined., Results: We demonstrate the presence of O(6)-alkylguanine alkyltransferase (cellular methyltransferase activity) in mycobacterial species and that there is an inducible and constitutive form in fast-growing mycobacteria (M. smegmatis), whereas only the constitutive form exists in the pathogenic or slow-growing species (M. bovis BCG) under the conditions tested. The overall activity of the constitutive form is high. We also show that intracellular growth of M. bovis BCG in macrophages is reduced when the alkyltransferase gene is absent. The presence of alkyltransferase activity appears to assist the organism in reducing the effects of isoniazid, since interruption of the gene confers sensitivity to the drug., Conclusions: We conclude that for the slow-growing mycobacteria, an inducible response is not essential as their ecological niche is stable and protected, but that the presence of the alkyltransferase activity confers a growth advantage in macrophages and offers some protection against antibiotics.