Toxicity Screening of a Gambierdiscus australes Strain from the Western Mediterranean Sea and Identification of a Novel Maitotoxin Analogue.

Pablo Estevez,Angels Tudó,José Manuel Leão-Martins,Ana Gago-Martinez,Manoëlla Sibat,Robert Dickey,David Castro,Jorge Diogene,Philipp Hess

doi:10.3390/md19080460

Abstract

Dinoflagellate species of the genera Gambierdiscus and Fukuyoa are known to produce ciguatera poisoning-associated toxic compounds, such as ciguatoxins, or other toxins, such as maitotoxins. However, many species and strains remain poorly characterized in areas where they were recently identified, such as the western Mediterranean Sea. In previous studies carried out by our research group, a G. australes strain from the Balearic Islands (Mediterranean Sea) presenting MTX-like activity was characterized by LC-MS/MS and LC-HRMS detecting 44-methyl gambierone and gambieric acids C and D. However, MTX1, which is typically found in some G. australes strains from the Pacific Ocean, was not detected. Therefore, this study focuses on the identification of the compound responsible for the MTX-like toxicity in this strain. The G. australes strain was characterized not only using LC-MS instruments but also N2a-guided HPLC fractionation. Following this approach, several toxic compounds were identified in three fractions by LC-MS/MS and HRMS. A novel MTX analogue, named MTX5, was identified in the most toxic fraction, and 44-methyl gambierone and gambieric acids C and D contributed to the toxicity observed in other fractions of this strain. Thus, G. australes from the Mediterranean Sea produces MTX5 instead of MTX1 in contrast to some strains of the same species from the Pacific Ocean. No CTX precursors were detected, reinforcing the complexity of the identification of CTXs precursors in these regions.

Highlights

Species of dinoflagellates of the genera Gambierdiscus and Fukuyoa are known to produce toxic metabolites [1]
C and D detected in G. australes from the Balearic Islands (Spain) were identified and confirmed by LC-HRMS and LC-MS/MS in previous studies; and a mixture of these compounds, and P-CTXs and C-CTX1, was used as a qualitative laboratory reference material [33]
The results obtained using this combined approach allowed the identification for the first time of the presence of a new MTX analogue—MTX5—in an extract of G. australes from the Balearic Islands

Summary

Introduction

Species of dinoflagellates of the genera Gambierdiscus and Fukuyoa are known to produce toxic metabolites [1]. CTXs are cyclic polyethers of around 1100 Da and considered the main compounds responsible for ciguatera poisoning (CP) due to their lipophilic nature and their accumulation in fish tissue [7]. Depending on their structural differences, CTXs are classified as P-CTXs, C-CTXs or I-CTXs [8,9,10]. The algal precursors of P-CTXs were identified in dinoflagellate cultures from the Pacific Ocean, being oxidized when accumulated in fish [11]. CTX precursors were not identified in dinoflagellate cultures from the Indian or Atlantic

Methods

Discussion

Conclusion