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UBC Theses and Dissertations

Antibiotic secondary metabolities of bacteria isolated from the marine environment Gerard, Jeffery M.


Bioassay guided fractionation of the organic extracts obtained from cultures of several bacteria strains from the marine environment led to the isolation of twelve new and nine previously described secondary metabolites. The structures of these metabolites were determined by extensive chemical and spectroscopic analysis. Stable isotope incorporation experiments were also performed using one of the isolated strains to investigate the biosynthetic origins of the atoms in the principle active secondary metabolite. A culture of a Bacillus sp. isolated from the tissues of a marine worm collected near Loloata Island in Papua New Guinea produced a mixture of novel cyclic decapeptide antibiotics. Loloatins A (1), B (2), and C (3) were isolated and their structures were elucidated through NMR and mass spectrometric analysis. Peptides 1, 2, and 3 showed potent gram-positive antibiotic activity, including activity against drug resistant strains of Staphylococcus aureus, Streptococcus pneumoniae and Enterococcus spp. Loloatin C (3) also showed strong Gram-negative antibiotic activity. Massetolides A - H (4 - 11), novel cyclic depsipeptides, as well as the known compound viscosin (12), were isolated from cultures of two Pseudomonas sp. isolated from a marine alga and a marine tube worm each collected near Masset Inlet, B.C. and Moira Island, B.C. respectively. Massetolide A (4) and viscosin (12) exhibited in vitro antimicrobial activity against Mycobacterium tuberculosis and Mycobacterium avium-intracellulare. The known compounds, AI77-B (13), AI77-F (14) as well as AI77-H (15), a new diastereomer of AI77-F(14), were isolated from several species of Bacillus pumilus isolated from various marine sources. AI77-B (13) exhibited cytotoxic and Gram-positive antibiotic activity. The absolute configuration of AI77-H (15) was determined by chemical modification and NMR analysis of the (R)- and (S)- a-methoxy-a-(trifluoromethyl)phenylacetate esters. Finally, stable isotope incorporation experiments were performed using a selected strain of Bacillus pumilus which demonstrated that AI77-B (13) is of mixed polyketide/amino acid biosynthetic origin.

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