Project description:The present study focused on the characterization of a glycoside hydrolase 51 family α-l-arabinofuranosidase named TtAbf51 from thermophile Thermoanaerobacterium thermosaccharolyticum DSM 571. The recombinant TtAbf51 with 497 amino acids was successfully expressed in Escherichia coli BL21(DE3) and purified via nickel affinity chromatography, and native protein was a dimer verified by size exclusion chromatography. The TtAbf51 showed an optimum pH and temperature of 5.5 and 55 °C, and was relatively stable at pH 5.0-8.0 and up to 60 °C for 2 h of incubation. In addition, TtAbf51 was significantly inhibited by Cu2+, Zn2+ and 1 mM or 10 mM SDS. In the presence of 800 mM arabinose, the residual activity remained over 40% of the initial activity. In addition, the recombinant enzyme possessed a good catalytic effect for both synthesized and natural substrates, and the specific enzyme activity toward CM-linear arabinan reached 426.5 μmol min-1 mg-1. In summary, this study provides an α-l-arabinofuranosidase with potential in the synergistic hydrolysis of hemicellulose to fermentable sugars in applications such as liquid biofuels, food and beverages, and related industries.
Project description:Characterizing and engineering microbial communities for lignocellulosic biofuel production has received widespread attention. Previous research has established that Clostridium thermocellum JN4 and Thermoanaerobacterium thermosaccharolyticum GD17 coculture significantly improves overall cellulosic biofuel production efficiency. Here, we investigated this interaction and revealed the mechanism underlying the improved efficiency observed. In contrast to the previously reported mutualistic relationship, a harmful effect toward C. thermocellum JN4 was observed in these microbial consortia. Although T. thermosaccharolyticum GD17 relieves the carbon catabolite repression of C. thermocellum JN4 regarding obtaining more cellobiose or glucose released from lignocellulose, T. thermosaccharolyticum GD17 significantly hampers the growth of C. thermocellum JN4 in coculture. The increased formation of end products is due to the strong competitive metabolic advantage of T. thermosaccharolyticum GD17 over C. thermocellum JN4 in the conversion of glucose or cellobiose into final products. The possibility of controlling and rebalancing these microbial consortia to modulate cellulose degradation was achieved by adding T. thermosaccharolyticum GD17 stimulants into the system. As cellulolytic bacteria are usually at a metabolic disadvantage, these discoveries may apply to a large proportion of cellulosic biofuel-producing microbial consortia. These findings provide a reference for engineering efficient and modular microbial consortia for modulating cellulosic conversion.
Project description:Unusual di- and trideoxysugars are often found on the O-antigens of Gram-negative bacteria, on the S-layers of Gram-positive bacteria, and on various natural products. One such sugar is 3-acetamido-3,6-dideoxy-D-glucose. A key step in its biosynthesis, catalyzed by a 3,4-ketoisomerase, is the conversion of thymidine diphosphate (dTDP)-4-keto-6-deoxyglucose to dTDP-3-keto-6-deoxyglucose. Here we report an X-ray analysis of a 3,4-ketoisomerase from Thermoanaerobacterium thermosaccharolyticum. For this investigation, the wild-type enzyme, referred to as QdtA, was crystallized in the presence of dTDP and its structure solved to 2.0-Å resolution. The dimeric enzyme adopts a three-dimensional architecture that is characteristic for proteins belonging to the cupin superfamily. In order to trap the dTDP-4-keto-6-deoxyglucose substrate into the active site, a mutant protein, H51N, was subsequently constructed, and the structure of this protein in complex with the dTDP-sugar ligand was solved to 1.9-Å resolution. Taken together, the structures suggest that His 51 serves as a catalytic base, that Tyr 37 likely functions as a catalytic acid, and that His 53 provides a proton shuttle between the C-3' hydroxyl and the C-4' keto group of the hexose. This study reports the first three-dimensional structure of a 3,4-ketoisomerase in complex with its dTDP-sugar substrate and thus sheds new molecular insight into this fascinating class of enzymes.
Project description:BACKGROUND:?-Glucosidase is an important component of the cellulase enzyme system. It does not only participate in cellulose degradation, it also plays an important role in hydrolyzing cellulose to fermentable glucose by relieving the inhibition of exoglucanase and endoglucanase from cellobiose. Therefore, the glucose-tolerant ?-glucosidase with high specific activity for cellobiose might be a potent candidate for industrial applications. RESULTS:The ?-glucosidase gene bgl that encodes a 443-amino-acid protein was cloned and over-expressed from Thermoanaerobacterium thermosaccharolyticum DSM 571 in Escherichia coli. The phylogenetic trees of ?-glucosidases were constructed using Neighbor-Joining (NJ) and Maximum-Parsimony (MP) methods. The phylogeny and amino acid analysis indicated that the BGL was a novel ?-glucosidase. By replacing the rare codons for the N-terminal amino acids of the target protein, the expression level of bgl was increased from 6.6 to 11.2 U/mg in LB medium. Recombinant BGL was purified by heat treatment followed by Ni-NTA affinity. The optimal activity was at pH 6.4 and 70°C. The purified enzyme was stable over pH range of 5.2-7.6 and had a 1 h half life at 68°C. The activity of BGL was significantly enhanced by Fe2+ and Mn2+. The Vmax of 64 U/mg and 120 U/mg were found for p-nitrophenyl-?-D-glucopyranoside (Km value of 0.62?mM) and cellobiose (Km value of 7.9?mM), respectively. It displayed high tolerance to glucose and cellobiose. The Kcat for cellobiose was 67.7?s-1 at 60°C and pH 6.4, when the concentration of cellobiose was 290?mM. It was activated by glucose at concentrations lower that 200?mM. With glucose further increasing, the enzyme activity of BGL was gradually inhibited, but remained 50% of the original value in even as high as 600?mM glucose. CONCLUSIONS:The article provides a useful novel ?-glucosidase which displayed favorable properties: high glucose and cellobiose tolerance, independence of metal ions, and high hydrolysis activity on cellobiose.
Project description:Cocultures of engineered thermophilic bacteria can ferment lignocellulose without costly pretreatment or added enzymes, an ability that can be exploited for low cost biofuel production from renewable feedstocks. The hemicellulose-fermenting species Thermoanaerobacterium thermosaccharolyticum was engineered for high ethanol yield, but we found that the strains switched from growth-coupled production of ethanol to growth uncoupled production of acetate and 1,2-propanediol upon growth cessation, producing up to 6.7 g/L 1,2-propanediol from 60 g/L cellobiose. The unique capability of this species to make 1,2-propanediol from sugars was described decades ago, but the genes responsible were not identified. Here we deleted genes encoding methylglyoxal reductase, methylglyoxal synthase and glycerol dehydrogenase. Deletion of the latter two genes eliminated propanediol production. To understand how carbon flux is redirected in this species, we hypothesized that high ATP levels during growth cessation downregulate the activity of alcohol and aldehyde dehydrogenase activities. Measurements with cell free extracts show approximately twofold and tenfold inhibition of these activities by 10 mM ATP, supporting the hypothesized mechanism of metabolic redirection. This result may have implications for efforts to direct and maximize flux through alcohol dehydrogenase in other species.
Project description:BACKGROUND:Energy shortage and environmental pollution are two severe global problems, and biological hydrogen production from lignocellulose shows great potential as a promising alternative biofuel to replace the fossil fuels. Currently, most studies on hydrogen production from lignocellulose concentrate on cellulolytic microbe, pretreatment method, process optimization and development of new raw materials. Due to no effective approaches to relieve the inhibiting effect of inhibitors, the acid pretreated lignocellulose hydrolysate was directly discarded and caused environmental problems, suggesting that isolation of inhibitor-tolerant strains may facilitate the utilization of acid pretreated lignocellulose hydrolysate. RESULTS:Thermophilic bacteria for producing hydrogen from various kinds of sugars were screened, and the new strain named MJ1 was isolated from paper sludge, with 99% identity to Thermoanaerobacterium thermosaccharolyticum by 16S rRNA gene analysis. The hydrogen yields of 11.18, 4.25 and 2.15 mol-H2/mol sugar can be reached at an initial concentration of 5 g/L cellobiose, glucose and xylose, respectively. The main metabolites were acetate and butyrate. More important, MJ1 had an excellent tolerance to inhibitors of dilute-acid (1%, g/v) pretreated sugarcane bagasse hydrolysate (DAPSBH) and could efficiently utilize DAPSBH for hydrogen production without detoxication, with a production higher than that of pure sugars. The hydrogen could be quickly produced with the maximum hydrogen production reached at 24 h. The hydrogen production reached 39.64, 105.42, 111.75 and 110.44 mM at 20, 40, 60 and 80% of DAPSBH, respectively. Supplementation of CaCO3 enhanced the hydrogen production by 21.32% versus the control. CONCLUSIONS:These results demonstrate that MJ1 could directly utilize DAPSBH for biohydrogen production without detoxication and can serve as an excellent candidate for industrialization of hydrogen production from DAPSBH. The results also suggest that isolating unique strains from a particular environment offers an ideal way to conquer the related problems.