First Report of Microcystis Strains Producing MC-FR and -WR Toxins in Japan.

Tsuyoshi Ikehara,Naomasa Oshiro,Kyoko Kuniyoshi,Tomoharu Sano,Mina Yasumoto-Hirose,Haruyo Yamaguchi,Yuuhiko Tanabe,Masahiro Yoshimoto,Shihoko Nakashima

doi:10.3390/toxins11090521

Abstract

Microcystins (MCs) are a group of cyclic heptapeptide hepatotoxins produced by Microcystis and several other genera of cyanobacteria. Many structural variants have been characterized using various methods such as liquid chromatography–mass spectrometry (LC-MS) analysis, enzyme-linked immunosorbent assay (ELISA) and protein phosphatase 2A (PP2A) inhibition assay. The representative MC, MC-LR, and related cyanobacterial toxins strongly inhibit PP2A activity and can therefore be assayed by measuring the extent of PP2A inhibition. However, these methods require reference toxin standards for the quantification and identification of known MCs. To obtain various MC-producing cyanobacterial strains, we surveyed and collected MC-producing cyanobacteria from environmental sources of water in Okinawa, Japan. Using a dual assay (LC-MS analysis and PP2A inhibition assay), we identified and isolated Microcystis strains producing five MC variants (MC-LR, -RR, -LA, -FR and -WR). Approximately 4 mg of MC-WR and -FR toxins were purified from the laboratory culture of the Microcystis isolate NIES-4344. Pure MC-WR and -FR variants were prepared for future use as toxin standards in LC-MS analysis. Phylogenetic analysis based on ftsZ revealed that the NIES-4344 strain belongs to the identified groups in Microcystis aeruginosa. This is the first report of Microcystis strains producing mainly MC-WR and -FR toxins in Japan.

Highlights

IntroductionWorldwide blooms of toxic cyanobacteria (blue-green algae) commonly occur in fresh, brackish and marine waters
Worldwide blooms of toxic cyanobacteria commonly occur in fresh, brackish and marine waters
Microcystins (MCs) are a group of cyclic heptapeptide hepatotoxins produced by Microcystis and several other genera of cyanobacteria

Summary

Introduction

Worldwide blooms of toxic cyanobacteria (blue-green algae) commonly occur in fresh, brackish and marine waters. Microcystins (MCs) are a group of cyclic heptapeptide hepatotoxins produced by Microcystis and several other genera of cyanobacteria. MCs are composed of five common amino acids plus a pair of variable L-amino acids. More than 250 structural variants of MCs have been. Toxins 2019, 11, 521 characterized in bloom samples and cultured strains of cyanobacteria to date [1,2,3]. The structural variation in MCs is based on either the two variable amino acids or chemical modifications around the molecules. All MCs are highly toxic to many life forms, including aquatic organisms, wildlife, livestock and humans, and MC-LR, the representative MC variant, is the most toxic. Given the toxicity of MCs, the World

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Conclusion