Laboratory-cultured Red Sea cyanobacteria as a source of biologically active natural products

Abstract

The Red Sea represents an unexplored repository of diverse cyanobacteria, although in low abundance. This may result from the low annual rainfall, minimal freshwater input and high evaporation rate that make the Red Sea one of the most saline and pristine water bodies in the world. Despite these conditions, we have collected specimens from a range of cyanobacterial genera that have been maintained in laboratory culture and produce several biosynthetically distinct metabolites to date. Notably, a cultured black Lyngbya sp. collected from the Nabq mangroves near Sharm El-Sheikh, Egypt produces two new apratoxin analogues along with several known apratoxin and lyngbyabellin analogues. Additionally, cultures of a phormidolide-producing Red Sea Leptolyngbya sp. have led to the isolation of three new macrolides. Finally, cultures of a newly identified Symploca sp. collected from the Excalibur shipwreck have yielded a series of uncharacterized metabolites that show nanomolar toxicity to NCI-H460 lung cancer cells. Molecular characterization of the component metabolites has been achieved using a combination of NMR spectroscopy and mass spectrometry. Although the organisms in this study were collected from a relatively isolated habitat, the compounds reported here show biosynthetic capabilities comparable to cyanobacteria collected pantropically, which poses additional questions as to the biogenetic origin of these metabolites.