Heterologous Expression of a Hyperthermophilic α-Amylase in Xanthan Gum Producing Xanthomonas campestris Cells

A hyperthermophilic α-amylase encoding gene from Pyrococcus woesei was transferred and expressed in Xanthomonas campestris ATCC 13951. The heterologous α-amylase activity was detected in the intracellular fraction of X. campestris and presented similar thermostability and catalytic properties with the native P. woesei enzyme. The recombinant α-amylase was found to be stable at 90 °C for 4 h and within the same period it retained more than 50% of its initial activity at 110 °C. Furthermore, X. campestris transformants produced similar levels of recombinant α-amylase activity regardless of the carbon source present in the growth medium, whereas the native X. campestris α-amylase production was highly dependent on starch availability and it was suppressed in the presence of glucose or other reducing sugars. On the other hand, xanthan gum yield, which appeared to be similar for both wild type and recombinant X. campestris strains, was enhanced at higher starch or glucose concentrations. Evidence presented in this study supports that X. campestris is a promising cell factory for the co-production of recombinant hyperthermophilic α-amylase and xanthan gum.     

Thermal dissociation of molten KHSO4: temperature dependence of Raman spectra and thermodynamics

Raman spectroscopy is used to study the thermal dissociation of molten KHSO4 at temperatures of 240-450 degrees C under static equilibrium conditions. Raman spectra obtained at 10 different temperatures for the molten phase and for the vapors thereof exhibit vibrational wavenumbers and relative band intensities inferring the occurrence of the temperature-dependent dissociation equilibrium 2HSO4(-)(l) <--> S2O7(2-)(l) + H2O(g). The Raman data are adequate for determining the partial pressures of H2O in the gas phase above the molten mixtures. A formalism for correlating relative Raman band intensities with the stoichiometric coefficients, the equilibrium constant, and the thermodynamics of the reaction equilibrium is derived. The method is used along with the temperature-dependent features of the Raman spectra to show that the studied equilibrium 2HSO4(-)(l) <--> S 2O7(2-)(l) + H2O(g) is the only process taking place to a significant extent in the temperature range of the investigation and for determining its enthalpy to be DeltaH degrees=64.9+/-2.9 kJ mol(-1). The importance of these findings for the understanding of the performance of the industrially important sulfuric acid catalyst under "wet" conditions is briefly addressed.     

A strongly blue-emitting heptametallic [Dy(III)7] centered-octahedral single-molecule magnet

The employment of 2-(β-naphthalideneamino)-2-(hydroxymethyl)-1-propanol and 2-aminoisobutyric acid in dysprosium chemistry has led to the isolation of a novel heptanuclear [Dy(III)(7)] cluster displaying single-molecule-magnetism behavior and blue-emitting properties.