Three pathways for trehalose biosynthesis in mycobacteria, ..

Effect of osmotic stress was studied extensively in bacterial systems. Bacteria accumulate compatible solutes trehalose, glutamate and other osmoprotectants during osmotic stress (Truper and Galinski, ). In particular, effects of osmotic stress on Escherichia coli, Corynebacterium sp. and Propionibacterium freudenreichii were reported previously (Strøm and Kaasen, ; Carpinelli etal., ; Cardoso etal., ; Ruhal and Choudhury, ,). Altogether, prominent role of trehalose biosynthesis against stress conditions was clearly demonstrated in these bacteria and yeast (Argüelles, ,). In yeast, a strong correlation between trehalose content and stress resistance was demonstrated for a variety of stresses such as heat, osmotic stress and ethanol (Hottiger etal., ; Zancan and Sola-Penna, ; Conlin and Nelson, ). Similarly, bacteria are subjected to succession of stress conditions during fermentation, which affects their viability and production efficiency. Thus, when the bacterial cell faces stress conditions, dynamic variation arises in the complex metabolic networks (comprise genes, proteins, metabolites, etc.) that subsequently underlie different cellular functions (Belloch etal., ). Furthermore, the stress response is mediated at the level of transcription, and a number of stress-induced transduction pathways concerning trehalose were reported (Ruis and Schuller, ; Estruch, ). The research including such molecular responses (like trehalose accumulation) can help us to understand the molecular mechanisms by which cells adapt to fermentation conditions. The advantage of accumulation of compatible solutes is rehydration of bacterial cell (reduction of water activity, restoration of cell volume and turgor pressure) without interfering cellular functions. Trehalose and proline are neutral solutes and hence these are preferred osmoregulator in contrast to potassium ion or glutamate (Csonka and Hanson, ). Several studies have reported that trehalose is better as a protein stabilizer than any of compatible solutes because of its unusual ability to alter the water environment surrounding a protein and stabilize the protein in its native conformation (Kaushik and Bhat, ; Magazù etal., ).

The Trehalose Synthesis Pathway Is an Integral Part of …

The trehalose synthesis pathway is an integral part of …

Three pathways for trehalose biosynthesis in …

Apart from direct physiological measurements, Ins/IGF-mutant metabolism was also studied by analyzing transcriptional profiles of metabolism-related genes. ) found that, in mutants, gluconeogenesis, glyoxylate pathway activity and trehalose biosynthesis were upregulated relative to the appropriate controls ( versus adults). These authors found similar qualitative changes in dauer larvae compared to recovered dauer larvae. Unlike dauer stage animals, TCA-cycle and respiratory chain activities were not downregulated in mutants, supporting the physiological data discussed above (). In addition, in part explanation for the high ATP levels found in these mutants, the mitochondrial F1-ATPase inhibitor protein (IF1), which specifically inhibits the ATPase activity of ATP synthase under anoxic conditions, was found to be upregulated in .

Plant-type trehalose synthetic pathway in …

One of most interesting trehalose synthesis pathways studied in Mycobacterium includes trehalose synthase (TreS). It has been extensively studied as it interconnects in vivo synthesis of glycogen and trehalose (Pan etal., ; Chandra etal., ). Previously, in a study with Corynebacterium, intracellular glycogen was used in vivo via TreYZ pathway as a source for trehalose biosynthesis as discussed in above section, but in Mycobacterium TreS was reported to be involved in trehalose biosynthesis from glycogen. It was proposed that trehalose synthase, maltokinase and α 1,4 glucan:maltose-1-P maltosyltransferase (GPMT) were involved in synthesis of glycogen when trehalose was present in higher concentration (Elbein etal., ). Alternatively, role of maltokinase to provide maltose-1-phosphate was considered as metabolic interconnection between trehalose, maltose and glycogen (Mendes etal., ). Trehalose synthase was purified from Mycobacterium and was considered as valuable in synthetic carbohydrate chemistry (Pan etal., ). Furthermore, isotope exchange studies demonstrated intramolecular mechanism of active site of trehalose synthase and suggested that protein conformational changes were rate-limiting (Zhang etal., ). The physiological interconnection of these three substrates in Mycobacterium has been extensively studied which can be seen altogether in .

we believe that this is the only active trehalose synthesis pathway in ..
One pathway for trehalose synthesis is ..

Plant-Type Trehalose Synthetic Pathway in …

Monosaccharides (glucose), disaccharides (sucrose), polysaccharides (starch) and gluconeogenic (glycerol) were used for trehalose accumulation. Besides, the carbon channelizes through three important nodes of metabolic pathway – glucose-6-P, glucose-1-P and NDP-glucose as shown in . Since trehalose is synthesized with NDP-glucose and glucose-6-P, these can be significant nodes. Similar to trehalose biosynthesis, microbial production of polysaccharides (like exopolysaccharides, pullulan, glucan) too requires substrate nucleotide sugar (NDP-glucose). Moreover, an insight into these studies explained how enzymes at the different nodes of central metabolic pathway influenced nucleotide sugar synthesis and henceforth exopolysaccharides. Similarly, trehalose biosynthesis may be influenced by enzymes at these nodes. In several previous reports, carbon source influenced synthesis of nucleotide sugars and consequently production of exopolysaccharides, as described by measuring enzyme activities in Lactobacillus delbrueckii (Grobben etal., ) and Lactobacillus casei (Mozzi etal., ). Likewise, exopolysaccharides biosynthesis was correlated to enzyme activities of phosphoglucomutase, epimerase and UDP-glucose pyrophosphorylase in Streptococcus thermophilus (Degeest and Vuyst, ). Metabolic pathway for β-glucan was proposed in Pediococcus parvulus in relation to carbon source by measuring enzyme activities at these three nodes (Velasco etal., ). This work reported new insight regarding activity of enzymes involved in sugar transport, sugar nucleotide biosynthesis and energy generation. Similarly, metabolic pathway was proposed with the help of enzyme activities in Lactobacillus helveticus for exopolysaccharide synthesis which involved enzyme at the branch point of three nodes glucose-6-P, glucose-1-P and UDP-glucose (Torino etal., ). In fact, in a study with pullulan production in Aureobasidium, an analysis of enzyme activities at these nodes and measurement of metabolite UDP-glucose gave some new insight that when more pullulan was synthesized less UDP-glucose was left in cell extract and higher activities of phosphoglucomutase, UDP-glucose pyrophosphorylase and glycosyl transferase were observed in different carbon sources (Duan etal., ). In conclusion, availability of nucleotide sugars and hence sugar synthesis were correlated to enzyme activities of these three nodes glucose-6-P, glucose-1-P and UDP-glucose which are also affected by numerous environmental conditions including carbon source. Since trehalose biosynthesis involves nucleotide sugar as an important substrate, regulation of these nucleotide sugars through their corresponding enzymes was expected.

Background The trehalose synthetic pathway is present in bacteria, ..

Unfortunately, limited metabolic flux studies linked with trehalose biosynthesis were reported. Metabolic flux and elementary mode analysis in Corynebacterium glutamicum indicated increased flux towards trehalose formation and it was principle osmolyte in low dilution rate (Rajvanshi and Venkatesh, ; Wiitmann and Heinzle, ). In addition, carbon flux towards trehalose increased under oxidative stress after deleting transcription repressor McbR (Krömer etal., ). Thus branches of different nodes of metabolic pathway in relation to trehalose biosynthesis are significant to study. Three important nodes of central metabolic pathway are glucose-6-phosphate (pathway towards glycolysis and pentose phosphate pathway), glucose-1-phosphate and NDP-glucose node (UDP-glucose/ADP-glucose/GDP-glucose) as shown in . Several studies on influences of these various enzymes have been reported previously as discussed above. Hence, it was discussed further how the enzymes at these nodes may have influence on trehalose metabolism as reported in literature.

Trehalose induces autophagy via an mTOR independent pathway

Although enzymes at branch of glucose-6-P node () do not have direct control on trehalose metabolism, channelization of carbon (from different carbon source) at these branches can impact trehalose synthesis. This can be more important when carbon source has influence on trehalose synthesis. Effect of carbon source on trehalose biosynthesis was reported in Propionibacterium freudenreichii, as higher trehalose accumulated in lactose and lower in lactic acid in comparison with glucose (Cardoso etal., ). In yeast, it was proposed that the effect of glucose-6-phosphate dehydrogenase was insignificant while in Corynebacterium overexpression of glucose-6-phosphate dehydrogenase reduced the trehalose yield (Voit, ; Becker etal., ). This was probably due to reduction of glucose-6-phosphate which is a substrate for trehalose biosynthesis (Becker etal., ). Similarly, at low osmolality 90 % of flux moves from glucose-6-P node to PPP while it increases towards trehalose synthesis under high osmolality (Varela etal., ). Alternatively, with gluconeogenic carbon source (like glycerol) fructose 1,6 diPase may be regulatory for trehalose biosynthesis, since carbon enters metabolic pathway through this enzyme. In a similar study with Propionibacterium freudenreichii, lactic acid was considered poor for trehalose accumulation and lower activity of gluconeogenic pathway was proposed as probable reason (Cardoso etal., ). Alternatively, in Corynebacterium overexpression of fructose 1,6 biphosphotase led to higher yield of lysine but there was a decrease in trehalose content in the recombinant strain (Becker etal., ). Thus influence of one enzyme can differ in dissimilar bacteria.