Isolation and identification of a new antibacterial entity from the Antarctic cyanobacterium Nostoc CCC 537

The present study was aimed at the isolation, purification and structural elucidation of an antibacterial entity/lead molecule from the Antarctic cyanobacterium Nostoc CCC 537. A methanolic extract of the cyanobacterium was bioassayed with Enterobacter aerogenes as a target. The extract was purified by TLC, and the most active band was subjected to HPLC. The fraction (retention time 15.7 min) designated as the active principle was antibacterial towards Gram positive Mycobacterium tuberculosis H37Rv, Staphylococcus aureus ATCC 25923, Gram negative Salmonella typhi MTCC 3216, Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25992, Enterobacter aerogenes MTCC 2822 and multi-drug resistant strains of Escherichia coli GS 2003/01, 02, 03. Based on UV, IR, ¹H NMR, EIMS, and ESIMS data, the structure of the active principle is proposed as 4-(5-carboxy-2-hydroxy)-benzyl]-1,10-dihydroxy-3,4,7,11,11-pentamethyloctahydrocyclopenta<a>naphthalene (Mr 428, Mp 243–249°C). This intracellular biomolecule is similar to anthraquinone and indane derivatives of a diterpenoid. The rate of production of the active principle currently corresponds to 1.70 mg g⁻¹ biomass dry weight. The inherent property of Nostoc sp. to synthesise niche-specific biomolecules/lead molecules may be exploited for future drug development.