Growth ofMycobacterium tuberculosisat acidic pH depends on lipid assimilation and is accompanied by reduced GAPDH activity

Abstract

Acidic pH arrests the growth of Mycobacterium tuberculosis in vitro (pH < 5.8) and is thought to significantly contribute to the ability of macrophages to control M. tuberculosis replication. However, this pathogen has been shown to survive and even slowly replicate within macrophage phagolysosomes (pH 4.5 to 5) [M. S. Gomes et al., Infect. Immun. 67, 3199–3206 (1999)] [S. Levitte et al., Cell Host Microbe 20, 250–258 (2016)]. Here, we demonstrate that M. tuberculosis can grow at acidic pH, as low as pH 4.5, in the presence of host-relevant lipids. We show that lack of phosphoenolpyruvate carboxykinase and isocitrate lyase, two enzymes necessary for lipid assimilation, is cidal to M. tuberculosis in the presence of oleic acid at acidic pH. Metabolomic analysis revealed that M. tuberculosis responds to acidic pH by altering its metabolism to preferentially assimilate lipids such as oleic acid over carbohydrates such as glycerol. We show that the activity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is impaired in acid-exposed M. tuberculosis likely contributing to a reduction in glycolytic flux. The generation of endogenous reactive oxygen species at acidic pH is consistent with the inhibition of GAPDH, an enzyme well-known to be sensitive to oxidation. This work shows that M. tuberculosis alters its carbon diet in response to pH and provides a greater understanding of the physiology of this pathogen during acid stress.

Reliable detection of pyrazinamide antitubercular activity in vitro

“…To quantify PZA activity in vitro, wild-type Mtb was grown in 7H9 media containing Gly or OA as a main carbon source at either neutral (pH7) or acidic pH (pH5) (Fig 1 A). 100 µg/mL PZA did not affect growth of Mtb at pH7 and as previously described, Mtb did not grow with Gly at pH5 independently of the presence of PZA [8]. In contrast, 100 µg/mL PZA completely inhibited the growth of Mtb with OA at pH5.…”

“…The reliability of PPST in the clinic is reduced by the high frequency of false positive results caused by large inoculum sizes increasing the pH of the media to a pH at which PZA is not active [7]. Moreover, growth of Mtb is inhibited at pH<5.8 in standard media containing glycerol (Gly) and glucose as main carbon sources, which prevents the use of media at pH lower than 5.9 [8]. Consequently, PPST is not routinely conducted in the clinic which prevents optimal treatment of patients infected with PZA-resistant Mtb [9].…”

Rv0500A is a transcription factor that links Mycobacterium tuberculosis environmental response with division and impacts host colonization

“…This observation has led to the concept that the slowed growth of Mtb at acidic pH is an adaptive evolutionary characteristic, a notion supported by the discovery that the growth capability of Mtb at acidic pH can be genetically manipulated (Baker & Abramovitch, 2018). Recent work has also shown that Mtb growth at acidic pH is altered depending on the carbon source available, indicating the intrinsic relationships between bacterial environmental response and metabolism (Gouzy et al, 2021). However, much remains unknown regarding how Mtb environmental cue response and growth regulation are coordinated.…”

The TbD1 Locus Mediates a Hypoxia-Induced Copper Response in Mycobacterium bovis

“…Furthermore, acidic pH and hypoxia are known to be a common stresses imposed on tubercle bacilli during infection ( Wayne and Sohaskey, 2001 ). Notably, in vitro assays that seek to mimic in vivo stresses commonly encountered by M. tuberculosis have been shown to alter carbon metabolic flux, i.e., a recent study showed that lipids are the preferred primary carbon source in an acidic environment ( Gouzy et al, 2021 ). GO analysis revealed an induction of genes involved in lipid metabolism in M. bovis AF2122/97 WT cultured under standing conditions.…”