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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|
|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|
|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
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
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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