Effects of pH and Aeration Conditions on Xylitol Production by Candida and Hansenula Yeasts

During the fermentative production of xylitol the following environmental parameters have a controlling effect on the xylitol yield: concentration of monosaccharides, temperature, aeration and pH. The purpose of the present work was to evaluate xylitol production by four yeast strains at different pH values and oxygen transfer rates (OTRs). The highest xylitol yields were obtained under the following conditions: Candida parapsilosis: pH 5.0, OTR 6.1 mmol L-1 h-1;Candida guilliermondii: pH 4.5, OTR 5.7 mmol L-1 h-1; Candida boidinii: pH 6.0, OTR 5.7 mmol L-1 h-1; Hansenula anomala: pH 4.5, OTR 2.8 mmol L-1 h-1 using 50 g L-1 initial xylose concentration

Relevance of the light signaling machinery for cellulase expression in trichoderma reesei (hypocrea jecorina)

<p>Abstract</p> <p>Background</p> <p>In nature, light is one of the most important environmental cues that fungi perceive and interpret. It is known not only to influence growth and conidiation, but also cellulase gene expression. We therefore studied the relevance of the main components of the light perception machinery of <it>Trichoderma reesei </it>(<it>Hypocrea jecorina</it>), ENV1, BLR1 and BLR2, for production of plant cell wall degrading enzymes in fermentations aimed at efficient biosynthesis of enzyme mixtures for biofuel production.</p> <p>Findings</p> <p>Our results indicate that despite cultivation in mostly dark conditions, all three components show an influence on cellulase expression. While we found the performance of the enzyme mixture secreted by a deletion mutant in <it>env1 </it>to be enhanced, the higher cellulolytic activity observed for <it>Δblr2 </it>is mainly due to an increased secretion capacity of this strain. <it>Δblr1 </it>showed enhanced biomass accumulation, but due to its obviously lower secretion capacity still was the least efficient strain in this study.</p> <p>Conclusions</p> <p>We conclude that with respect to regulation of plant cell wall degrading enzymes, the blue light regulator proteins are unlikely to act as a complex. Their regulatory influence on cellulase biosynthesis involves an alteration of protein secretion, which may be due to adjustment of transcription or posttranscriptional regulation of upstream factors. In contrast, the regulatory function of ENV1 seems to involve adjustment of enzyme proportions to environmental conditions.</p