Chemical pretreatment of Arundo donax L. for second-generation ethanol production

Background: Pretreatment of lignocellulosic biomass is essential for using it as a raw material for chemical and biofuel production. This study evaluates the effects of variables in the chemical pretreatment of the Arundo biomass on the glucose and xylose concentrations in the final enzymatic hydrolysate. Three pretreatments were tested: acid pretreatment, acid pretreatment followed by alkaline pretreatment, and alkaline pretreatment. Results: The amounts of glucose and xylose released by the enzymatic hydrolysis of the Arundo biomass obtained from acid pretreatment ranged from 6.2 to 19.1 g/L and 1.8 to 3.1 g/L, respectively. The addition of alkaline pretreatment led to a higher yield from the enzymatic hydrolysis, with the average glucose concentration 3.5 times that obtained after biomass hydrolysis with an acid pretreatment exclusively. The use of an alkaline pretreatment alone resulted in glucose and xylose concentrations similar to those obtained in the two-step pretreatment: acid pretreatment followed by alkaline pretreatment. There was no significant difference in 5-hydroxymethylfurfural, furfural, or acetic acid concentrations among the pretreatments. Conclusion: Alkaline pretreatment was essential for obtaining high concentrations of glucose and xylose. The application of an alkaline pretreatment alone resulted in high glucose and xylose concentrations. This result is very significant as it allows a cost reduction by eliminating one step.

Adaptative response to enhanced basal oxidative damage in sod mutants from Saccharomyces cerevisiae.

We investigated the adaptative response of S. cerevisiae in sod mutants (sod 1 Delta, sod 2 Delta and sod 1 Deltasod 2 Delta) after H(2)O(2) treatment in the stationary phase. sod 2 Delta and sod 1 Deltasod 2 Delta demonstrated the highest levels of GSH in the control, suggesting that pathways which include GSH protect these double mutants against oxidative stress. In addition, sod 1 Delta and sod 1 Deltasod 2 Delta had higher iron levels than the wild-type, independently of H(2)O(2) stress. Fe levels were increased in sod 2 Delta following H(2)O(2) In addition, the sod 2 Delta mutant was more sensitive to H(2)O(2) treatment than the wild-type. These results suggest that sod 2 Delta sensibility may be associated with *OH production by the Fenton reaction. This increased iron demand in the sod 2 Delta mutant may be a reflection of the cells' efforts to reconstitute proteins that are inactivated in conditions of excess superoxide. MDA levels were assayed by HPLC in these mutants. The highest MDA levels could be observed after 10mM H(2)O(2) treatment in the sod 1 Deltasod 2 Delta double mutant. After treatment with a GSH inhibitor, the MDA level was still higher in the same strain. Thus, both direct and indirect GSH pathways are involved in the protection of lipid membranes and proteins in these mutants and may constitute an adaptative response to enhanced basal oxidative damage produced by superoxide.