Abstract
Mycobacteria contain high levels of the disaccharide trehalose in free form as well as within various immunologically relevant glycolipids such as cord factor and sulfolipid-1. By contrast, most bacteria use trehalose solely as a general osmoprotectant or thermoprotectant. Mycobacterium tuberculosis and Mycobacterium smegmatis possess three pathways for the synthesis of trehalose. Most bacteria possess only one trehalose biosynthesis pathway and do not elaborate the disaccharide into more complex metabolites, suggesting a distinct role for trehalose in mycobacteria. We disabled key enzymes required for each of the three pathways in M. smegmatis by allelic replacement. The resulting trehalose biosynthesis mutant was unable to proliferate and enter stationary phase unless supplemented with trehalose. At elevated temperatures, however, the mutant was unable to proliferate even in the presence of trehalose. Genetic complementation experiments showed that each of the three pathways was able to recover the mutant in the absence of trehalose, even at elevated temperatures. From a panel of trehalose analogs, only those with the native alpha,alpha-(1,1) anomeric stereochemistry rescued the mutant, whereas alternate stereoisomers and general osmo- and thermoprotectants were inactive. These findings suggest a dual role for trehalose as both a thermoprotectant and a precursor of critical cell wall metabolites.
Highlights
Trehalose (␣-D-glucopyranosyl-(1,1)-␣-D-glucopyranoside, Fig. 1) is a non-reducing disaccharide that is abundant in mycobacteria in free form and in glycoconjugates that are found in the cytosol and the cell wall [1]
Other trehalose-containing glycolipids include diacyl trehaloses substituted at the 2- and 3-positions, which have been isolated from Mycobacterium tuberculosis [14] (Fig. 1B) and Mycobacterium fortuitum [9], pyruvylated glycolipids found in M. smegmatis [15,16,17], monomethylated acyltrehaloses of Mycobacterium gordonae [18], and the complex lipooligosaccharides of Mycobacterium kansasii, the oligosaccharide core of which is shown in Fig. 1C [19]
Homologs of the M. tuberculosis OtsB and TreZ genes were found, suggesting that these pathways for trehalose biosynthesis are intact in M. smegmatis
Summary
OtsA, trehalose-6-phosphate synthase; OtsB, trehalose-6-phosphate phosphatase; TreY, maltooligosaccharyltrehalose synthase; TreZ, maltooligosaccharyltrehalose trehalohydrolase; TreS, trehalose synthase; TreϪ mutant, trehalose biosynthesis mutant of M. smegmatis; DIG, digoxigenin; cfu, colony forming unit. In the TreY-TreZ pathway, first identified in Rhizobia [27], Arthrobacter [28], and Sulfolobus acidocaldarius [29], ␣-(1,4)-glucose polymers are converted to trehalose by isomerizing the terminal ␣-(1,4)-linkage to an ␣,␣-(1,1)-linkage This is accomplished by the product of the treY gene, maltooligosaccharyltrehalose synthase. We demonstrate that trehalose is vital both for growth and for entry into stationary phase and is not an osmo/thermoprotectant as in other bacteria
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
