A Genomic View of Sugar Transport inMycobacterium smegmatisandMycobacterium tuberculosis

Abstract

We present a comprehensive analysis of carbohydrate uptake systems of the soil bacterium Mycobacterium smegmatis and the human pathogen Mycobacterium tuberculosis. Our results show that M. smegmatis has 28 putative carbohydrate transporters. The majority of sugar transport systems (19/28) in M. smegmatis belong to the ATP-binding cassette (ABC) transporter family. In contrast to previous reports, we identified genes encoding all components of the phosphotransferase system (PTS), including permeases for fructose, glucose, and dihydroxyacetone, in M. smegmatis. It is anticipated that the PTS of M. smegmatis plays an important role in the global control of carbon metabolism similar to those of other bacteria. M. smegmatis further possesses one putative glycerol facilitator of the major intrinsic protein family, four sugar permeases of the major facilitator superfamily, one of which was assigned as a glucose transporter, and one galactose permease of the sodium solute superfamily. Our predictions were validated by gene expression, growth, and sugar transport analyses. Strikingly, we detected only five sugar permeases in the slow-growing species M. tuberculosis, two of which occur in M. smegmatis. Genes for a PTS are missing in M. tuberculosis. Our analysis thus brings the diversity of carbohydrate uptake systems of fast-and a slow-growing mycobacteria to light, which reflects the lifestyles of M. smegmatis and M. tuberculosis in their natural habitats, the soil and the human body, respectively.The growth and nutritional requirements of mycobacteria have been intensely studied since the discovery of Mycobacterium tuberculosis (32). This resulted in an overwhelming body of literature on the physiology of mycobacterial metabolism in the years before the dawn of molecular biology (20,53,54). Carbon metabolism of mycobacteria has attracted renewed interest since the discovery that M. tuberculosis relies on the glyoxylate cycle for survival in mice (36,41). This observation indicates that M. tuberculosis uses lipids as the main carbon source during infection. On the other side, genes that encode a putative disaccharide transporter were essential for M. tuberculosis during the first week of infection, indicating that M. tuberculosis may switch its main carbon source from carbohydrates to lipids with the onset of the adaptive immune response (61). However, the nutrients and the corresponding uptake proteins are unknown for M. tuberculosis inside the human host. Surprisingly, this is also true for M. tuberculosis growing in vitro and for Mycobacterium smegmatis, which is often used as a fast-growing, nonpathogenic model organism to learn more about basic mycobacterial physiology. There is no doubt that the uptake pathways have been adapted to the habitats of M. tuberculosis and M. smegmatis, the human body and soil, respectively. Thus, much can be learned about the lifestyles of both organisms by a comparison of the complements of specific nutrient uptake proteins. Previously, 38 ATP-binding cassette (ABC) transport proteins...

Trehalose-recycling ABC transporter LpqY-SugA-SugB-SugC is essential for virulence of Mycobacterium tuberculosis

“…This locus encodes an ABC transporter highly conserved in mycobacteria comprised of the periplasmic sugar-binding lipoprotein LpqY, the ATP-binding protein SugC, and the transmembrane proteins SugA and SugB (Fig. 1A) (11,16). In contrast to suppressor mutations in treS, transposon insertions in lpqY or sugC did not prevent conversion of endogenous trehalose to M1P, as revealed by TLC analysis (Fig.…”

“…Despite the lack of substrate in its niche, the Mtb genome encodes four carbohydrate ATP-binding cassette (ABC) importers and one import system belonging to the major facilitator super family. These Mtb sugar importers were identified based on reasonable homology to carbohydrate transporters characterized in other bacteria, but the substrate for none of them is known (11). It has been a paradox that even though there appear to be no exogenous sugars available to transport, genome-wide screens of saturated transposon mutant libraries have implicated sugar uptake systems in the virulence of Mtb.…”

Novel regulatory roles of cAMP receptor proteins in fast-growing environmental mycobacteria

“…These included operons for five carbon sugar transporters (namely MSMEG_1370-1374, MSMEG_1704-1706, MSMEG_ 1713-1715), a glucose, trehalose, N-acetylglucosamine transporter belonging to the sugar PTS family (MSMEG_2116-2119) and a glycerol transporter of the PTS family encoded by MSMEG_2121-2124 (Table S2) (functions reviewed by Titgemeyer et al, 2007). To determine the physiological effect of the de-repression of genes involved in transport and catabolism of carbohydrates, growth analysis was performed using HdB minimal medium supplemented with either arabinose, xylose or glucose (Fig.…”

Defining mycobacteria: Shared and specific genome features for different lifestyles

“…• Recently, a comprehensive genome based study by Titgemeyer et al predicts and validates genes involved in sugar transport in M. smegmatis and M. tuberculosis [174]. The distinct excess of carbohydrate uptake systems in M. smegmatis (28) over that in M. tuberculosis (5), refl ect saprophytic versus host dependent pathogenic lifestyles.…”