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Title: Co-cultures of Yeasts and Zygomycetes in the Form of Pellets Methods for the Preparation of Pellets and Biocapsules, Their Properties and Applications
Authors: Nyman, Jonas
Lacintra, Michael
Department: Högskolan i Borås/Ingenjörshögskolan (IH)
Issue Date: 16-Aug-2013
Series/Report no.: Magisteruppsats
Programme: MSc in Resource Recovery - Industrial Biotechnology
Publisher: University of Borås/School of Engineering
Media type: text
Keywords: Zygomycetes
Saccharomyces cerevisiae
Fungal Pellets
Abstract: Many industrially important fungi can grow in the form of small spherical pellets. Such pellets reduce the viscosity and enhances mass transfer rates in culture broths. The pelleted morphology also influences the fungus’s metabolism, directing it to specific metabolites. The pellets are easily harvested from the broth and recycled. These properties makes pelleted morphology very attractive. The pelleted morphology of four Zygomycetes strains was studies. Several different nutrient media used by other researchers for achieving pelleted growth was tested. The influence of eight factors on pelletization of Rhizopus sp. in a completely defined medium was determined using a fractional central composite design and logistic regression. Pelleted growth of all four Zygomycetes was achieved, with very good results for two Rhizomucor sp. strains. A simple medium containing calcium carbonate was found to induce pelletization with very high reproducibility. Immobilization of yeast cells was attempted in pellets of Rhizomucor. It was found that a flocculating yeast can be immobilized inside pellets of fungal mycelium, forming ”biocapsules”. This is accomplished by first using a medium that induces pelletization of the filamentous fungus and does not allow for growth of the yeast. The pellets are then inoculated into a second medium that induces growth and flocculation of the yeast and inhibits further growth of the filamentous fungus. Non-flocculating yeasts could not be immobilized, suggesting that the flocculin proteins in the cell wall of flocculating strains are important for proper immobilization. The flocculation and immobilization arises due to expression of several different FLO-genes and the importance of these genes for successful immobilization is discussed. The results demonstrate that the morphology of Zygomycetes can be controlled and that this may be useful in industrial fermentation. The new immobilization technique reveals the great importance of flocculation and cell surface hydrophobicity. Using yeast strains that express certain FLO-genes may be beneficial in fermentation of lignocellulosic hydrolysates. Microscopy techniques were developed that allows for high quality microphotography of pellets and thin cross-sections of pellets and biocapsules.
Appears in Collections:Magisteruppsatser (IH)

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