Physiological characterization of thermotolerant yeast for cellulosic ethanol production.

The conversion of lignocellulose into fermentable sugars is considered a promising alternative for increasing ethanol production. Higher fermentation yield has been achieved through the process of simultaneous saccharification and fermentation (SSF). In this study, a comparison was performed between the yeast species Saccharomyces cerevisiae and Kluyveromyces marxianus for their potential use in SSF process. Three strains of S. cerevisiae were evaluated: two are widely used in the Brazilian ethanol industry (CAT-1 and PE-2), and one has been isolated based on its capacity to grow and ferment at 42 °C (LBM-1). In addition, we used thermotolerant strains of K. marxianus. Two strains were obtained from biological collections, ATCC 8554 and CCT 4086, and one strain was isolated based on its fermentative capacity (UFV-3). SSF experiments revealed that S. cerevisiae industrial strains (CAT-1 and PE-2) have the potential to produce cellulosic ethanol once ethanol had presented yields similar to yields from thermotolerant strains. The industrial strains are more tolerant to ethanol and had already been adapted to industrial conditions. Moreover, the study shows that although the K. marxianus strains have fermentative capacities similar to strains of S. cerevisiae, they have low tolerance to ethanol. This characteristic is an important target for enhancing the performance of this yeast in ethanol production.

Nematicidal activity of three novel extracellular proteases of the nematophagous fungus Monacrosporium sinense.

Extracellular proteases are an important virulence factor for the nematophagous fungi Monacrosporium. The objective of this study was to optimize, purify, partially characterize, and to evaluate the nematicidal activity of the proteases produced by the nematophagous fungus Monacrosporium sinense (SF53) by solid-state fermentation. Wheat bran was used as substrate for protease production. The variables moisture, pH, incubation time, temperature, glucose, yeast extract, and the number of conidia were tested for their influences on protease production by SF53. To determine the optimal level of the selected variables the central composite design was applied. The crude extract obtained was purified in two steps, an ion exchange chromatography and a gel excision. SDS-PAGE and zymogram were performed for analysis of the purification process. Proteolytic activity was also tested at different pHs and temperatures. In the in vitro assay, the nematicidal activity of the three proteases was evaluated. pH and incubation time showed a significant effect (p<0.05) on production of protease. The highest value of activity was 38.0 (U/ml) under the conditions of pH 5.0 and incubation time of 211 h. SF53 produced three different proteases (Ms1, Ms2, and Ms3) which were directly purified from the zymogram. Ms1, Ms2, and Ms3 showed the following percentage of reduction (p<0.05) on the number of Panagrellus redivivus compared to control after 24 h: 76.8, 68.1, and 92.1%. This is the first report of the use of proteases of the isolate SF53 on a phytonematode, which may be a research tool in future works.