Genetic diversity and bioactive metabolites of yeasts associated with fermented milk in selected regions of Tanzania

This thesis reports on genetic diversity of yeasts associated with both industrially (yoghurt) and traditionally fermented milk (mtindi), bioactivity of secondary metabolites of yeast from mtindi for potentially valuable yeasts of medicinal value as well as spoilage proteinase production. A total of 25 yeasts isolated from fermented milk sampled from Dar es Salaam, Kilimanjaro, Morogoro and Mwanza, Tanzanian were included in this study. Partial sequencing of the D1/D2 domain of the 26S rDNA (rDNA) was used to establish their diversity. Yeasts belonging to seven genera namely Galactomyces (9), Pichia (5), Candida (4), Clavispora (1), Issatchenkia (1), Yarrowia (3) and Debaryomyces (2) were identified. Fourteen extracts were found to be non-toxic against brine shrimps naupalii and were found to have weak to strong antimicrobial activities against Escherichia coli, Vibrio cholera, Pseudomonas aureginosa and Staphylococcus aureaus while C. tropicalis, P. kudriavzevii, C. pararugosa, Cl. lusitaniae and I. Orientalis, P. guilliermondii were found to possess strong antifungal activity against Cryptococcus neoformans and moderate antimycobacterial activity against Mycobacterium smegmatis. The highest proteinase activity was exhibited by C. pararugosa and Y. lipolytica. UsingTLC and HPTLC; Alkaloids, Terpenoids and Flavonoids were detected. The findings of this study revealed for the first time the potential of the yeasts from fermented milk from Tanzania as a source of antimicrobials and proteases with potential for research in the pharmaceutical and in dairy industries.