Novel bioactive bacterial metabolites from a marine derived bacterium Nocardia Sp. Merv 21695

The marine environment may contain more than 80% of world's species. Marine microorganisms constitute the largest and yet most poorly explored source of new biologically active secondary metabolites. Marine microbiology is still under utilized as a starting point field for academic drug discovery and biological programs. We have recently started a program aimed to investigate the bioactive secondary metabolites of marine derived microbial strains. We report here the isolation, structure elucidation and antimicrobial activities of the secondary metabolites isolated from the Egyptian actinobacterial strain as well as the taxonomy of the producing strain.

Egyptian marine strain Merv 21695, which was found to be the most promising bioactive strain, was isolated from the marine algae Laurencia spectablilis of Ras – Gharib beach of the Red Sea, Egypt. Merv 21695 strain was identified according to detailed identification studies: morphological; culture-based; physiological; biochemical and 16 S rDNA sequencing, as a new species of Nocardia.

The cultivation and chemical analysis of this species yielded four structurally related compounds namely, asphodelin [1], justicidin B [2], chrysophanol 8-methyl ether [3] and 1,1-dicloro-4-ethyl-5-(4-nitro-phenyl)-hexan-2-one by a series of steps: solvent extraction; silica gel column chromatography; sephadex LH-20 column chromatography and semipreparative HPLC. The structures were secured by detailed spectroscopic analysis of the MS and NMR data and single crystal x-ray diffraction studies. By using the serial dilution technique [4], these compounds displayed antimicrobial activity against both Gram-positive and Gram-negative bacteria as well as antifungal activity with minimum inhibitory concentration (MIC) ranged from 0.5 ˜ 10µg/ml.

References: [1] Ulubelen A. and Tuzlaci E. (1985) Phytochemistry 24: 2923. [2] Yang M. et al. (2006) Magn. Reson. Chem. 44: 727. [3] Hongzhu G. et al. (1998) Phytochemistry 49: 1623. [4] Egorov, N. S. (1985) Antibiotics. A scientific approach. Mirpublishers. Moscow. (translated from the russian by Alexander Poshinkin).