Screening of microalgae for species excreting norharmane, a manifold biologically active indole alkaloid

A screening of microalgae strains is described, with the objective to discover more species besides the known cyanobacterium Nodularia harveyana which excrete the manifold biologically active and co-mutagenic indole alkaloid norharmane (9H-pyrido(3,4-b)indole) into their environment. Seven more cyanobacterial species, Anabaena cylindrica, Anabaena inaequalis, Anabaenopsis siamensis, Chroococcus minutus, Nostoc carneum, Nostoc commune and Phormidium foveolarum, were newly discovered. The norharmane concentrations detected for cyanobacterial culture media varied in a species-dependent manner from less than 1 up to 525 μg l⁻¹. The risk for humans and livestock, resulting from the natural appearance of norharmane as an extracellular metabolite of various cyanobacteria, is discussed.