Biological and chemical characterisation of marine streptomycetes active against selected pathogenic yeasts / Mumtaz Hidayahtullah Atau @ Yatau

Streptomyces spp. have been the most abundant sources of all types of antibiotics. The success of marine natural products has promoted the marine environment as a source of novel chemical diversity for drug discovery. In Malaysia, the marine actinomycetes niche remains virtually unexplored and is a promising resource for the biotechnological applications including drug discovery. Screening for antifungal activity revealed that six out of 44 putative Streptomyces spp. isolated from sponges from Tioman Island showed strong antifungal activities against Candida albicans and Schizosaccharomyces pombe. Some physiological characterisation was done to these six potential strains to facilitate the strain identification including temperature range and optimum temperature range for growth, formation of melanoid pigment, liquefaction of gelatin, hydrolysis of starch, hydrogen sulfide production, sodium chloride tolerance, carbon sources utilization,nitrate reduction test and pH sensitivity. Fermentation of these strains was done using ISP 2 broth as growth medium prior to extraction of their bioactive components using ethyl acetate in ratio of 3:1 (filtrate broth: ethyl acetate). The crude extract of the strains were analysed using high performance liquid chromatography (HPLC) for chemical profiling. Based on the HPLC analysis, interesting compounds in three strains (X34, X42 and X77) were detected. 16S rRNA gene sequence analysis of these three strains showed 100%, 99.70% and 99.76% similarity to Streptomyces rochei (strain X34), Streptomyces albidoflavus (strain X42) and Streptomyces cavourensis (strain X77), respectively. When crude extracts of these three strains were tested against S. pombe, only strain X34 was positive and was further profiled, purified and isolated by column chromatography, thin layer chromatography (TLC), HPLC and preparative thin layer chromatography (PTLC). Six fractions (F1-F6) were obtained after column chromatography was done to strain X34, and were tested against S. pombe. As only iv fraction F5 was positive, this fraction was subjected to PTLC. Another six sub-fractions (F5.1-F5.6) obtained after PTLC (of fraction F5) which were then tested against S. pombe. As a result, two out of six sub-fractions (F5.1 and F5.4) showed antifungal activity against the tested fungi but based on their 1H-NMR chromatogram, only subfraction F5.1 was further analysed by nuclear magnetic resonance (NMR) and fourier transformation infrared spectroscopy (FTIR) for structure identification. Both NMR and FTIR analyses showed that the active sub-fraction (F5.1) was belonging to 2-(3- hydroxybutan-2-yloxy) propanoic acid. This is the first report of antifungal activity of this compound isolated from Streptomyces rochei