Uptake of Sulfate but Not Phosphate by Mycobacterium tuberculosis Is Slower than That for Mycobacterium smegmatis

Abstract

Knowledge of the metabolic pathways used by Mycobacterium tuberculosis during infection is important for understanding its nutrient requirements and host adaptation. However, uptake, the first step in the utilization of nutrients, is poorly understood for many essential nutrients, such as inorganic anions. Here, we show that M. tuberculosis utilizes nitrate as the sole nitrogen source, albeit at lower efficiency than asparagine, glutamate, and arginine. The growth of the porin triple mutant M. smegmatis ML16 in media with limiting amounts of nitrate and sulfate as sole nitrogen and sulfur sources, respectively, was delayed compared to that of the wild-type strain. The uptake of sulfate was 40-fold slower than that of the wild-type strain, indicating that the efficient uptake of these anions is dependent on porins. The uptake by M. tuberculosis of sulfate and phosphate was approximately 40-and 10-fold slower than that of M. smegmatis, respectively, which is consistent with the slower growth of M. tuberculosis. However, the uptake of these anions by M. tuberculosis is orders of magnitude faster than diffusion through lipid membranes, indicating that unknown outer membrane proteins are required to facilitate this process. In 2009, Mycobacterium tuberculosis caused 9.4 million cases of tuberculosis, resulting in the deaths of approximately 1.7 million people (53). After inhalation, M. tuberculosis is phagocytosed by alveolar macrophages and resides in nutrient-limited phagosomes. M. tuberculosis can prevent the phagosome acidification and influx of many toxic compounds into the phagosome by blocking fusion with late endosomes and lysosomes. This mechanism is critical for the survival of M. tuberculosis in macrophages and is a key feature of its virulence in the host environment (34). However, it is obvious that the acquisition of essential nutrients also is required for the replication of M. tuberculosis in macrophages. Recently, carbon metabolism has received increased attention due to its importance for the virulence of M. tuberculosis (5, 23), but knowledge about the metabolism of other essential nutrients is scarce (25). On a molecular level, the uptake of nutrients precedes any intracellular metabolism and often is the target of regulatory mechanisms.In this study, we examined the uptake of inorganic anions, in particular nitrate, sulfate, and phosphate, by M. tuberculosis and Mycobacterium smegmatis. A possible source of nitrate for M. tuberculosis in vivo is the oxidation of nitric oxide, which is generated in large amounts within macrophages and restricts the growth of M. tuberculosis (13). The activity of nitrate reductase drastically increases upon the entry of M. tuberculosis into the dormant state (49, 50), indicating that M. tuberculosis uses nitrate as an alternative terminal electron acceptor under anaerobic conditions. Sohaskey demonstrated that nitrate enhances the survival of M. tuberculosis during a sudden shift from aerobic to anaerobic respiration (39). NarK2 is a putative nitrate/nitrite transp...

New Targets and Inhibitors of Mycobacterial Sulfur Metabolism

“…It has recently been established that mycobacteria have an outer membrane [91], which is the primary permeability barrier to overcome the transport of any nutrient molecule. In line with these findings, recent studies conducted by Song et al demonstrate that specific outer membrane proteins, called porins, are responsible for transport of inorganic anions like sulfate and nitrate in M. tuberculosis [93, 94] and in M. bovis BCG [92, 95]. From these findings, it can be inferred that the porins and cysTWA SubI should align to allow the transport of anions from outside the cell to inside of the cell.…”

“…In contrast, little is known about the Rv1707 gene product [62]. However these gene products are believed to be associated with inner membrane of M. tuberculosis [78, 91, 92]. It has recently been established that mycobacteria have an outer membrane [91], which is the primary permeability barrier to overcome the transport of any nutrient molecule.…”

“…Recent studies demonstrated that mycobacterium possesses an outer membrane, which is the primary barrier for transport of molecules across the membrane [91]. The outer membrane was shown to contain specific channels called porins which allow the passage of specific anions through the inner membrane [92–95]. The primary sulfate transporter is an ABC transporter encoded by subI-cysTWA1 operon [78] located at the inner membrane and is expressed in response to oxidative stress and phagocytosis.…”

Disulfiram and Copper Ions Kill Mycobacterium tuberculosis in a Synergistic Manner

“…2). Both strains have comparable susceptibilities to Cu II (DETC) 2 despite the up to 40-fold lower membrane permeability of M. tuberculosis for small and hydrophilic solutes (58).…”

Antibacterial photodynamic therapy: overview of a promising approach to fight antibiotic-resistant bacterial infections

“…Nevertheless, encouraging findings of porin-like beta-barrel membrane proteins such as OmpATb [152] and Rv1698 [153] in the outer membrane of M. tuberculosis, which are proposed to transport small hydrophilic molecules [154] (albeit at significantly lower efficiency than other Gramnegative species such as E. coli [155]), may act as a transport channel for PSs, and cationic PSs in particular [151]. Furthermore, APDT was also shown to be effective in vitro against other Mycobacterium species that cause MDR-TB jointly, such as M. smegmatis.…”