Isolation and identification of homoanatoxin-a from a toxic strain of the cyanobacterium Raphidiopsis mediterranea Skuja isolated from Lake Biwa, Japan

Abstract

A neurotoxin, homoanatoxin-a, was isolated and characterized from a strain of the cyanobacterium Raphidiopsis mediterranea (from the Lake Biwa Research Institute, designated as LBRI 48) isolated from Lake Biwa, Japan. The toxicity of the lyophilized cells was estimated at 330 mg kg−1 by intraperitoneal injection in mice. A toxic substance was extracted with a methanol–water mixture (4:1) and separated by an octadecylsilanated silica gel (ODS) cartridge, followed by high-performance liquid chromatography purification (ODS, 17% methanol–water containing 0.05% trifluoroacetic acid). Signs of toxicity observed following lethal doses of the cell extract and the toxin were intense body paralysis, convulsions, gasping, dyspnea, and death in 5–10 min. The toxin was identified, based on its ultraviolet absorption spectrum (maximum at 230 nm), fast atom bombardment mass [(M + H)+ at m/z 180], and 1H-nuclear magnetic resonance spectral data, as homoanatoxin-a, which has previously been identified only from Oscillatoria formosa strain NIVA-CYA 92. This is the first report demonstrating that R. mediterranea produces cyanotoxins.