Title: Interaction of Penicillium Purpurogenum fungus with bentonite and kaolin clays
Τίτλος: Αλληλεπίδραση του μύκητα Penicillium με μπεντονιτικές και καολινιτικές αργίλους
Χρηστίδης Γεώργιος, Καθηγητής ΜΗΧ.Ο.Π. (Επιβλέπων)
Βενιέρη Δανάη Αναπλ. Καθηγήτρια ΧΗ.ΜΗ.ΠΕΡ
Charles W. Knapp, Dr (Reader in Environmental Science, University of Strathclyde,U.K.)
The present Thesis investigates the impact of the surface properties and specifically the isoelectric point (IEP) of clay minerals, on the production of antimicrobial, extracellular metabolites by the fungus Penicillium Purpurogenum. The tested materials were KGa-2 kaolinite and SWy-2 Na-smectite reference samples (CMS Source Clay Project) and a white Ca-smectite (B3) derived from the Greek island of Kimolos. The materials underwent chemical and mineralogical characterization. Also, their electrokinetic properties were investigated, by determining the IEP of each material with acid titration. The results were confirmed by measuring the zeta potential, electrophoretic mobility and particle size. The resulted IEPs for KGa-2, SWy-2 and B3 samples were 2.81 ± 0.03, 6.71 ± 0.01 and 6.40 ± 0.02 respectively. The fungus was cultivated in potato dextrose for 14 days, in presence of each of the aforementioned clay minerals. The pH was regulated at the IEP of each sample. For reference purposes, the culture was repeated in different pH, above and below the IEP of each material to observe possible variations in the antimicrobial performance of the leachates. The antimicrobial performance of the extracellular metabolites was determined by the Minimum Inhibitory Concentration (MIC) test. According to MIC, the extracellular leachates were introduced into bacterial colonies of Staphylococcus Aureus to obtain the minimum concentration of leachates capable of reducing 60% of the initial bacterial population. The results proved that the isoelectric point of clay minerals is not a stimulation factor for the fungus, since the former produced antimicrobial, extracellular metabolites under the influence of Na-smectite (SWy-2) regardless of the pH. Furthermore, Ca-smectite stimulated the fungus at pH=7.5, which is above the observed IEP. Kaolinite did not affect the microorganism in any way, since the antibacterial activity of the leachates was absent in lower concentrations.