Abstract
Microcystins (MCs) are cyclic peptides produced by cyanobacteria, which can be harmful to humans and animals when ingested. Differences in the coding of the non-ribosomal peptide synthetase/polyketide synthase enzyme complex responsible for microcystin production have resulted in more than 100 microcystin variants being reported to date. The microcystin diversity of Microcystis CAWBG11 was investigated using matrix-assisted laser desorption/ionization-time of flight mass spectrometry and liquid chromatography-mass spectrometry. This revealed that CAWBG11 simultaneously produced 21 known microcystins and six new congeners: [Asp3] MC-RA, [Asp3] MC-RAba, [Asp3] MC-FA, [Asp3] MC-WA, MC-FAba and MC-FL. The new congeners were putatively characterized by tandem mass spectrometry and chemical derivatization. A survey of the microcystin congeners produced by 49 cyanobacterial strains documented in scientific literature showed that cyanobacteria generally produce four microcystin congeners, but strains which produce up to 47 microcystin congeners have been reported. Microcystis CAWBG11 (which produces at least 27 congeners) was positioned in the top ten percentile of the strains surveyed, and showed fluidity of the amino acids incorporated into both position two and position four.
Highlights
Cyanobacteria are a group of ancient prokaryotic organisms which use chlorophyll-a to harness energy from the sun with water as the reductant [1]
A methanol extract of Microcystis CAWBG11 was analyzed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS)
Assessment of Microcystis CAWBG11 indicated the presence of numerous oligopeptides including aeruginosins, microviridins and microcystins
Summary
Cyanobacteria (blue-green algae) are a group of ancient prokaryotic organisms which use chlorophyll-a to harness energy from the sun with water as the reductant [1]. A single strain of cyanobacteria can produce more than one microcystin congener, which is mainly due to at least one adenylation domain possessing relaxed substrate specificity and being able to incorporate different amino acids into the structure [12,13]. The different microcystin congeners range in toxicity from non-toxic (e.g., [(6Z)-Adda5] MC-LR, LD50 > 1200 μg/kg) to highly toxic (e.g., MC-LR, LD50 = 50 μg/kg) by mouse bioassay [7] Despite their toxicity, microcystins have been proposed as drug candidates for cancer treatment, due to the preferential expression of organic anion transporting polypeptides (OATPs, which actively transport microcystins into mammalian cells) in a number of cancer tissues [20].
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