MALDI-TOF-MS detection of the low molecular weight neurotoxins anatoxin-a and homoanatoxin-a on lyophilized and fresh filaments of axenic Oscillatoria strains

Anatoxin-a (ANTX) and homoanatoxin-a (HANTX) are low molecular weight neurotoxic secondary amines of 165 and 179 Da, respectively. We applied matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) for the detection of ANTX and HANTX directly on lyophilized and fresh filaments of axenic strains of the genus Oscillatoria, using 2,5-dihydroxybenzoic acid as matrix and purified ANTX and HANTX as references. To counteract the span of low molecular mass ions (< m/z 1000) generated by the matrix, we induced the matrix-suppression effect to obtain high quality ANTX/HANTX MALDI signals. MALDI desorption/ionization of the matrix-ANTX and the matrix-HANTX generated protonated molecules [M+H](+) at m/z 166.12322 and 180.1372, respectively. The masses obtained from the analysis of lyophilized filaments of the ANTX-producer Oscillatoria sp. strain PCC 9240 (m/z 166.15) and of fresh filaments of the HANTX-producers Oscillatoria sp. strains PCC 6506 (m/z 180.1375), PCC 9029 (m/z 180.1334) and PCC 10111 (m/z 180.13996) corresponded to the protonated molecular ions of ANTX and HANTX, respectively. Therefore, the application of MALDI-TOF-MS for the detection of cyanobacterial anatoxins in clonal and axenic strains of the cyanobacterial culture collections worldwide may help to assess ANTX/HANTX incidence among cyanobacteria.