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PubMed2003

New insights on trehalose: a multifunctional molecule.

Trehalose is a nonreducing disaccharide in which the two glucose units are linked in an alpha,alpha-1,1-glycosidic linkage. This sugar is present in a wide variety of organisms, including bacteria, yeast, fungi, insects, invertebrates, and lower and higher plants, where it may serve as a source of energy and carbon. In yeast and plants, it may also serve as a signaling molecule to direct or control certain metabolic pathways or even to affect growth. In addition, it has been shown that trehalose can protect proteins and cellular membranes from inactivation or denaturation caused by a variety of stress conditions, including desiccation, dehydration, heat, cold, and oxidation. Finally, in mycobacteria and corynebacteria, trehalose is an integral component of various glycolipids that are important cell wall structures. There are now at least three different pathways described for the biosynthesis of trehalose. The best known and most widely distributed pathway involves the transfer of glucose from UDP-glucose (or GDP-glucose in some cases) to glucose 6-phosphate to form trehalose-6-phosphate and UDP. This reaction is catalyzed by the trehalose-P synthase (TPS here, or OtsA in Escherichia coli ). Organisms that use this pathway usually also have a trehalose-P phosphatase (TPP here, or OtsB in E. coli) that converts the trehalose-P to free trehalose. A second pathway that has been reported in a few unusual bacteria involves the intramolecular rearrangement of maltose (glucosyl-alpha1,4-glucopyranoside) to convert the 1,4-linkage to the 1,1-bond of trehalose. This reaction is catalyzed by the enzyme called trehalose synthase and gives rise to free trehalose as the initial product. A third pathway involves several different enzymes, the first of which rearranges the glucose at the reducing end of a glycogen chain to convert the alpha1,4-linkage to an alpha,alpha1,1-bond. A second enzyme then releases the trehalose disaccharide from the reducing end of the glycogen molecule. Finally, in mushrooms there is a trehalose phosphorylase that catalyzes the phosphorolysis of trehalose to produce glucose-1-phosphate and glucose. This reaction is reversible in vitro and could theoretically give rise to trehalose from glucose-1-P and glucose. Another important enzyme in trehalose metabolism is trehalase (T), which may be involved in energy metabolism and also have a regulatory role in controlling the levels of trehalose in cells. This enzyme may be important in lowering trehalose concentrations once the stress is alleviated. Recent studies in yeast indicate that the enzymes involved in trehalose synthesis (TPS, TPP) exist together in a complex that is highly regulated at the activity level as well as at the genetic level.

Cell Wall↗
PubMed2003

Effect of trehalose on survival of Bradyrhizobium japonicum during desiccation.

AIMS: A major reason for the ineffectiveness of legume inoculants in the field is the rapid death of rhizobia because of desiccation. The major purpose of this study was to identify conditions under which alpha,alpha-trehalose would improve survival of Bradyrhizobium japonicum during desiccation. METHODS AND RESULTS: Trehalose was added to cultures just prior to desiccation or was supplied to bacteria during the 6-day growth period. A wide variety of trehalose concentrations was tested. Trehalose added to cultures at the time of desiccation improved survival slightly, but trehalose loading during growth was much more effective in protection against desiccation. Growth of bacteria with 3 mmol l-1 trehalose increased trehalose concentration in cells by about threefold and increased survival of cells placed on soya bean [Glycine max (L.) Merr.] seeds by two- to four-fold after 2 or 24 h. Average of overall results indicate that growth of bacteria with trehalose in the medium resulted in a 294% increase in survival after 24 h of desiccation. The concentration of trehalose in cells was very highly correlated with survival of bacteria. When trehalose-loaded cells were suspended in buffer or water, 60-85% of cellular trehalose was lost in about 1 h and, in spite of these losses, survival during desiccation was not reduced. CONCLUSIONS: Accumulation of trehalose in the cytoplasm is critical to the survival of B. japonicum during desiccation. Increasing the periplasmic concentration of trehalose is also beneficial but is not so critical as the concentration of trehalose in the cytoplasm. Because B. japonicum cannot utilize trehalose as a carbon source, cells can be loaded with trehalose by providing the disaccharide during the growth period. SIGNIFICANCE AND IMPACT OF THE STUDY: Although it may not be practical to use trehalose as a carbon source in inoculant production, it may be possible to engineer greater trehalose accumulation in rhizobia. Trehalose concentration in cells should be a useful predictor of survival during desiccation.

Bacteriological Techniques↗
PubMed1993

Induction of the lambda receptor is essential for effective uptake of trehalose in Escherichia coli.

Trehalose transport in Escherichia coli after growth at low osmolarity is mediated by enzyme IITre of the phosphotransferase system (W. Boos, U. Ehmann, H. Forkl, W. Klein, M. Rimmele, and P. Postma, J. Bacteriol. 172:3450-3461, 1990). The apparent Km (16 microM) of trehalose uptake is low. Since trehalose is a good source of carbon and the apparent affinity of the uptake system is high, it was surprising that the disaccharide trehalose [O-alpha-D-glucosyl(1-1)-alpha-D-glucoside] has no problems diffusing through the outer membrane at high enough rates to allow full growth, particularly at low substrate concentrations. Here we show that induction of the maltose regulon is required for efficient utilization of trehalose. malT mutants that lack expression of all maltose genes, as well as lamB mutants that lack only the lambda receptor (maltoporin), still grow on trehalose at the usual high (10 mM) trehalose concentrations in agar plates, but they exhibit the half-maximal rate of trehalose uptake at concentrations that are 50-fold higher than in the wild-type (malT+) strain. The maltose system is induced by trehalose to about 30% of the fully induced level reached when grown in the presence of maltose in a malT+ strain or when grown on glycerol in a maltose-constitutive strain [malT(Con)]. The 30% level of maximal expression is sufficient for maximal trehalose utilization, since there is no difference in the concentration of trehalose required for the half-maximal rate of uptake in trehalose-grown strains with the wild-type gene (malT+) or with strains constitutive for the maltose system [malT(Con)]. In contrast, when the expression of the lambda receptor is reduced to less than 20% of the maximal level, trehalose uptake becomes less efficient. Induction of the maltose system by trehalose requires metabolism of trehalose. Mutants lacking amylotrehalase, the key enzyme in trehalose utilization, accumulate trehalose but do not induce the maltose system.

Bacterial Outer Membrane Proteins↗