Fermentation at high temperature with application of thermotolerant microorganisms is a technological advantage in bioethanol production. Among the yeasts, K. marxianus has outstanding thermotolarance. The industrial application of the IMB3 strain occurs usually at 45C. The final aim of our project is the genetic modification of the K. marxianu...s CBS712 strain in order to achieve ethanol production at higher temperature than the currently applied. This requires the characterization of the CBS712 strain, with special attention to the determination of the temperature limit of its growth and the amount of the ethanol produced. The temperature limit of growth was 48C in YPD medium. Elevation of the temperature above 45C led to an exponential drop of the cell viability. Ethanol production was tested in shaking flasks, in MYFM medium, under oxigene limited conditions, applying variable concentrations of glucose (12–20%) and different temperatures (45–47 ºC). Preliminary results have revealed that the elevation of glucose concentration increased the amount of ethanol produced. The amount of ethanol (appr. 5%)+ produced at the highest glucose concentration was not different at the tested temperatures (45, 46 and 47 ºC). The observation indicates the potential in raising the thermotolerance of the strain.
The aim of the current experiment was to optimize the creation process of single cell protein on plant-based substrate solution with the intention to improve end-product turn out by means of adding vitamin solution. Based on the results of the fermentation processes of yeast strains, it was concluded that the vitamin-supplementation produced it...s greatest effect on the dry matter production, primarily on the K. marxianus DSM 4908 strain, while it was less beneficent when it comes to the figures of wet cell mass. In addition, it can be assumed that vitamin supplementation increased the maximum specific rate of growth (μmax) and decreased the generation time (tg) significantly. In the case of the K. marxianus yeast strain on corn steep liquor treated with vitamin-supplementation, the highest (μmax) and the lowest (tg) data were observed [(0.226 h-1) and (4.4 h), respectively]. Based on the results it was found that K. marxianus DSM 4908 is expedient to be applied on corn steep liquor medium in order to determine its suitability to produce additive for feeding.