Applied Uses Of Chitosan Layer Of Yeast Spores

In this study, we present a non-hazardous biological method of producing chitosan beadsusing the budding yeast Saccharomyces cerevisiae. Yeast cells cultured under conditions ofnutritional starvation cease vegetative growth and instead form spores. The spore wall has amulti-layer structure which consists of mannan, β-glucose, chitosan and dityrosine from theinnermost layer to the outermost layer. Thus, removal of the outermost dityrosine layer bydisruption of the DIT1gene, which is required for dityrosine synthesis, leads to exposure ofthe chitosan layer at the spore surface. In this way, spores can be made resemble chitosanbeads.Chitosan has adsorptive features and can be used to remove heavy metals and negativelycharged molecules from solution, which can clean the environment. Consistent with thispractical application, we find that spores are capable of adsorbing heavy metals such as Cr3+,Cu2+and Cd2+and removal of the dityrosine layer further improves the adsorption, whereaschs3Δ spore lacking of the dityrosine and chitosan layers decreases the adsorption, indicatingthat chitosan works as an adsorbent in the spores. Atomic absorption spectrum was used toassay the concentration of metal ions. Besides heavy metals, spores can also absorb anegatively charged cholesterol derivative, taurocholic acid. HPLC was used to investigate thefeatures of chitosan beads which can absorb taurocholic acid. The results indicate that theabsorbed amount of taurocholic acid by1mg of dit1spores, chs3spores, wt spores andvegetative cells are0.92,0.60,0.74,0.54μmol, respectively.Furthermore, glutaraldehyde was used to activate amino groups, which made exogenousenzyme cross-linked to the chitosan. Consistent with this property, dit1spores can serve as acarrier for immobilization of enzymes. β-Galactosidase was used in this study. At the sametime, the activity of immobilization enzyme, the reutilization and the thermostability weredetected. The results showed that dit1spores have a better property than other cells as thecarrier for immobilization of enzymes.Given that yeast spores are natural product, the results suggested that they, especiallydit1mutants, can be used as chitosan beads and applied for multiple purposes.