A study on antimicrobial and antimalarial activities of marine actinomycetes secondary metabolites

The aim of this thesis was to investigate antimicrobial and antimalarial potentials of metabolites from Actinomycetes isolated from mangrove and seagrass sediments of Dar es Salaam, Tanzanian. Foremost, the diversity of Actinomycetes in the sediments was investigated by employing both culture-dependent and culture-independent analyses with the later based on environmental rDNA fragments. Results showed that the isolates belong to two genera namely Nocardiopsis and Streptomyces. Subsequently, out of 85 rDNA clones, 28 phylotypes were clustered in three known genera of Actinomycetes including Nocardiopsis, Streptomyces and Actinoalloteichus. Thereafter, ten selected Streptomyces species were investigated for the cytotoxic and antimicrobial activities. All extracts were found to possess cytotoxic activities with the LC50 values ranging from 236.86 – 1231.65 μg/ml. In addition, three isolates (RM-14, RM-20 and MM10) were found to posses antimicrobial activities against pathogenic bacteria and fungi. Furthermore, upon screening for larvicidal one isolate MS1 showed 100% antilarval activity after 21 hours of incubation with mosquito Culex quinquefascintus larvae.Upon evaluation of the bioactive metabolites using the hypothanxamine method for antimalarial parasite activity, three crude extracts showed strong growth inhibition of malarial parasites with an IC50 in the low microgram range (0.44 – 7.98µg/ml). The most potent crude extract in this study was from the genus Streptomyces and had a cytostatic effect on P. falciparum. The findings of this study reveal for the first time the potential of the marine actinobacterial diversity of Tanzania as a source of antimicrobials and antiplasmodials with potential for development in the pharmaceutical industry.