Display of the peroxiredoxin Bcp1 of Sulfolobus solfataricus on probiotic spores of Bacillus megaterium.

Bacterial spores displaying heterologous proteins have been proposed as a safe and efficient method for delivery of antigens and enzymes to animal mucosal surfaces. Initial studies have been performed using Bacillus subtilis spores, but other spore forming organisms have also been considered. B. megaterium spores have been shown capable of displaying large amounts of a model heterologous protein (Discosoma red fluorescent protein mRFP) that in part crossed the exosporium to localize in the space between the outer coat layer and the exosporium. Here, B. megaterium spores have been used to adsorb Bcp1 (bacterioferritin comigratory protein 1), a peroxiredoxin of the archaeon Sulfolobus solfataricus, known to have an antioxidant activity. The spores were highly efficient in adsorbing the heterologous enzyme which, once adsorbed, retained its activity. The adsorbed Bcp1 localized beneath the exosporium, filling the space between the outer coat and the exosporium. This unusual localization contributed to the stability of the enzyme-spore interaction and to the protection of the adsorbed enzyme in simulated intestinal or gastric conditions.

Biochemical characterization of a novel thermostable ß-glucosidase from Dictyoglomus turgidum.

Dtur_0462 gene from the hypertermophilic bacterium Dictyoglomus turgidum, encoding a ß-glucosidase, was synthetically produced and expressed in Escherichia coli BL21(DE3)-RIL. DturßGlu was purified to homogeneity by affinity chromatography and its homotetrameric structure was determined by gel filtration. The monomer is composed by 418 amino acidic residues and showed high sequence similarity with Glycoside Hydrolases (GHs) belonging to GH1 family. The maximum activity of DturßGlu was observed at 80°C and at pH5.4. DturßGlu was stable in the range of pH5-8 and retained 70% of its activity after 2h of incubation at 70°C. Metal ions and chemical reagents differently influenced the ß-glucosidase activity; furthermore, DturßGlu displays a good ethanol and glucose tolerance (Ki 750mM). The enzyme is active on p-nitrophenyl-ß-d-glucopyranoside (pNPGlu) (Km 0.84mM) and p-nitrophenyl-ß-d-galactopyranoside (pNPGal) (Km 1.36mM) and shows a broad substrate specificity towards natural compounds as salicin, cellobiose and genistin. The ability to hydrolyze different substrates, the activation in the presence of surfactants, the good thermal resistance, and finally the high glucose and ethanol tolerance make this enzyme a good candidate for industrial applications.

A thermophilic enzymatic cocktail for galactomannans degradation.

The full utilization of hemicellulose sugars (pentose and exose) present in lignocellulosic material, is required for an efficient bio-based fuels and chemicals production. Two recombinant thermophilic enzymes, an endo-1,4-ß-mannanase from Dictyoglomus turgidum (DturCelB) and an α-galactosidase from Thermus thermophilus (TtGalA), were assayed at 80 °C, to assess their heterosynergystic association on galactomannans degradation, particularly abundant in hemicellulose. The enzymes were tested under various combinations simultaneously and sequentially, in order to estimate the optimal conditions for the release of reducing sugars. The results showed that the most efficient degree of synergy was obtained in simultaneous assay with a protein ratio of 25% of DturCelB and 75% of TtGalA, using Locust bean gum as substrate. On the other hand, the mechanism of action was demonstrated through the sequential assays, i.e. when TtGalA acting as first to enhance the subsequent hydrolysis performed by DturCelB. The synergistic association between the thermophilic enzymes herein described has an high potential application to pre-hydrolyse the lignocellulosic biomasses right after the pretreatment, prior to the conventional saccharification step.

Biochemical characterization of a thermostable endomannanase/endoglucanase from Dictyoglomus turgidum.

Dictyoglomus turgidum is a hyperthermophilic, anaerobic, gram-negative bacterium that shows an array of putative glycoside hydrolases (GHs) encoded by its genome, a feature that makes this microorganism very interesting for biotechnological applications. The aim of this work is the characterization of a hyperthermophilic GH5, Dtur_0671, of D. turgidum, annotated as endoglucanase and herein named DturCelB in agreement to DturCelA, which was previously characterized. The synthetic gene was expressed in Escherichia coli. The purified recombinant enzyme is active as a monomer (40 kDa) and CD structural studies showed a conserved α/ß structure at different temperatures (25 and 70 °C) and high thermoresistance (Tm of 88 °C). Interestingly, the enzyme showed high endo-ß-1,4-mannanase activity vs various mannans, but low endo-ß-1,4 glucanase activity towards carboxymethylcellulose. The K M and V max of DturCelB were determined for both glucomannan and CMC: they were 4.70 mg/ml and 473.1 µmol/min mg and 1.83 mg/ml and 1.349 µmol/min mg, respectively. Its optimal activity towards temperature and pH resulted to be 70 °C and pH 5.4, respectively. Further characterization highlighted good thermal stability (~ 50% of enzymatic activity after 2 h at 70 °C) and pH stability over a broad range (> 90% of activity after 1 h in buffer, ranging pH 5-9); resistance to chemicals was also observed.