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Förslaget inkom 2006-02-28

Molecular characterisation of the yeast and bacterial community in industrial ethanol production

OBS! ANSÖKNINGSTIDEN FÖR DETTA EXJOBB HAR LÖPT UT.
Background
The aim of this project is to identify yeast strains and bacteria involved in the ethanol production process.
The ethanol is produced from wheat starch. Since the yeast cannot ferment starch directly, the starch must be pre-treated to release fermentable sugars.
The process is started by mixing commercial baker¿s yeast with sugar substrate. During the production, substrate is continuously added, while ethanol and solid fermentation residues (distiller¿s grain) are removed. The distiller¿s grain serves as a high-quality feed. The yeast is recycled in the process. This process involves that the yeast is challenged by significant stresses, including low pH, high cell density, oxygen and nutrient limitation and ethanol. Microscopic investigations indicate that the yeast is changing its morphology during the first three weeks of the process. However, nothing is known about the basis of these changes. It might be a physiological adaptation of the strain to the cultivation conditions, but it is also possible that cells of a more adapted strain are present on the equipment and take over the fermentation.
We will investigate the yeast succession in the process during the first three weeks, by PCR-fingerprinting. It is also planned to investigate the gene expression of isolated yeast strains in microarray experiments and/ or by 2-D-protein electrophoresis.
Infections by bacteria and, occasionally, wild yeasts is a common problem in ethanol production. Commercial baker¿s contains a certain amount of lactic acid bacteria that usually do not disturb the fermentation. However, under some circumstances, the bacteria rapidly proliferate and outcompete the yeast in the process, which can stop the fermentation and lead to huge economical losses. It is unknown where the infecting microorganisms come from or which circumstances are leading to the infection. Therefore, we will also investigate the bacterial flora in the fermentation and in the starch processing process. This will be performed by PCR-fingerprinting. Dominating strains will be identified to the species level by partial sequencing rRNA-genes.
Methods
· Cultivation of microorganisms, selective growth media, strain conservation
· DNA/RNA-isolation, PCR-techniques, RNA-analysis, gel electrophoresis
· Sequence analysis using databases and software tools (BLAST, SRS)

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