Fermentation of lignocellulosic hydrolysate by the alternative industrial ethanol yeast Dekkera bruxellensis.

AIM: Testing the ability of the alternative ethanol production yeast Dekkera bruxellensis to produce ethanol from lignocellulose hydrolysate and comparing it to Saccharomyces cerevisiae. METHODS AND RESULTS: Industrial isolates of D. bruxellensis and S. cerevisiae were cultivated in small-scale batch fermentations of enzymatically hydrolysed steam exploded aspen sawdust. Different dilutions of hydrolysate were tested. None of the yeasts grew in undiluted or 1:2 diluted hydrolysate [final glucose concentration always adjusted to 40 g l⁻¹ (0.22 mol l⁻¹)]. This was most likely due to the presence of inhibitors such as acetate or furfural. In 1:5 hydrolysate, S. cerevisiae grew, but not D. bruxellensis, and in 1:10 hydrolysate, both yeasts grew. An external vitamin source (e.g. yeast extract) was essential for growth of D. bruxellensis in this lignocellulosic hydrolysate and strongly stimulated S. cerevisiae growth and ethanol production. Ethanol yields of 0.42 ± 0.01 g ethanol (g glucose)⁻¹ were observed for both yeasts in 1:10 hydrolysate. In small-scale continuous cultures with cell recirculation, with a gradual increase in the hydrolysate concentration, D. bruxellensis was able to grow in 1:5 hydrolysate. In bioreactor experiments with cell recirculation, hydrolysate contents were increased up to 1:2 hydrolysate, without significant losses in ethanol yields for both yeasts and only slight differences in viable cell counts, indicating an ability of both yeasts to adapt to toxic compounds in the hydrolysate. CONCLUSIONS: Dekkera bruxellensis and S. cerevisiae have a similar potential to ferment lignocellulose hydrolysate to ethanol and to adapt to fermentation inhibitors in the hydrolysate. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study investigating the potential of D. bruxellensis to ferment lignocellulosic hydrolysate. Its high competitiveness in industrial fermentations makes D. bruxellensis an interesting alternative for ethanol production from those substrates.

Dose distribution from a degraded 60Co gamma field.

Dose distribution in two cylindrical phantoms, a small phantom (12.8 cm in diameter and 39.4 cm in length) and a large phantom (25.2 cm and 35.1 cm in length), exposed to a degraded 60Co gamma field was studied. The angular distribution and energy spectrum of the 60Co radiation was changed by ground and air scattering. The dose was measured using thermoluminescent dosimeters (LiF and CaF2). The energy-dependent responses of the dosimeters were corrected using a method developed by Momeni et al. which is based on differential responses of the two types of dosimeters. The dose distribution was calculated from a three-dimensional interpolation-extrapolation of the measured doses. Analysis of the data suggests that the half-value layer concept for a determination of depth dose is not applicable to exposures where the angular distributions and the energy spectra are field variables. Application of thermoluminescent dosimeters for personnel dosimetry in compliance with federal regulations requires correction for the energy dependence of the dosimeters. In exposure cases where the radiation field is nonuniform, use of multiple badges should be considered.

Measurement of bone density by gas displacement.

Small bone volumes, porous and irregular structured objects with volumes 0.05-2 cm3, were measured by differential pressure of displaced air. The differential air pressure was measured by a piezoelectric resistor pressure gauge. The gas-displacement system was used to measure the volumes of 234 bone specimens for calculation of bone density. The operation of the system, calibration, sensitivity, and errors of measurement are described.