1. Introduction
One of the problems associated with simultaneous saccharification and fermentation (SSF) of cellulose is the different optimum temperatures for saccharification (45–50 ◦C) and fermentation (25–35 ◦C). The microorganisms employed in the fermentation of sugars from lignocellulose into ethanol are principally bacteria and yeasts [1,2]. The Saccharomyces cerevisiae yeast has proved to be
more robust than bacteria, being more tolerant to ethanol and inihibitors present in hydrolysates of lignocellulosic materials [3]. Due to their potential applications, thermotolerant yeasts at temperatures
above 35 ◦C have been the object of numerous studies [4–7].
Tolerance to high temperatures and high ethanol concentrations are important properties of microorganisms of interest to industry. The fermentation efficiency of S. cerevisiae at high temperatures
is very low due to increased fluidity in membranes to which the yeast responds by changing its fatty acids composition [8–10]. For an efficient conversion of lignocellulosic biomass to ethanol, another desirable microorganism characteristic is the capacity to ferment other sugars besides glucose, such as d-xylose and cellobiose obtained from hydrolysis of the material [11–14].