Morphology of Gambierdiscus scabrosus sp. nov. (Gonyaulacales): a new epiphytic toxic dinoflagellate from coastal areas of Japan

A new epiphytic dinoflagellate is described, G ambierdiscus scabrosus sp. nov., from tidal pools and rocky shores along the coastal areas of Japan. Cells are 63.2 ± 5.7 μm in depth, 58.2 ± 5.7 μm in width, and 37.3 ± 3.5 μm in length. The plate formula of G . scabrosus is Po, 4′, 0a, 6′′, 6c, ?s, 5′′′, 0p, and 2′′′′. Morphologically, G . scabrosus resembles G . belizeanus as follows: anterioposteriorly compressed cell shape, narrow 2′′′′ plate, and areolated surface. Despite this similarity, the cells of G . scabrosus can be distinguishable by the presence of the asymmetric shaped 3′′ plate and the rectangular shaped 2′ plate.     

GAMBIERDISCUS YASUMOTOI SP. NOV. (DINOPHYCEAE), A TOXIC BENTHIC DINOFLAGELLATE FROM SOUTHEASTERN ASIA

A new, toxin-producing, benthic dinoflagellate named Gambierdiscus yasumotoi sp. nov. was isolated from macroalgae from the fringing coral reef surrounding the Singapore island of Pulau Hantu. The plate formula of G. yasumotoi is P_o , 3', 7", 6c, 6s, 5"', and 2"". Gambierdiscus yasumotoi has a globular shape and is not anterior-posteriorly compressed as are the two other known species in this genus, G. toxicus Adachi et Fukuyo 1979 and G. belizeanus Faust 1995. The girdle descends one to two girdle widths without overhang in contrast to the ascending girdles of G. toxicus and G. belizeanus. The dimensions of cultured G. yasumotoi were 45–63 μm in length, 38–50 μm in transdiameter and 43–61 μm in dorsoventral diameter. The thecae are smooth without areolae. The apical pore plate has the characteristic fishhook shape of Gambierdiscus, but it is significantly longer than G. toxicus. Cells from young cultures of G. yasumotoi are positively phototropic.     

Heavy metals, lipid peroxidation, and ciguatera toxicity in the liver of the caribbean barracuda (Sphyraena barracuda)

Human consumption of over 400 species of tropical fish containing polyether toxins (e.g. ciguatoxins, maitotoxins) causes ciguatera fish poisoning. The Caribbean barracuda (Sphyraena barracuda) is one of the most potent ciguatoxic fish. The objective of this study was to determine whether toxicity of 14 barracuda livers was correlated with lipid peroxidation. A significant correlation (p = 0.015, Pearson’s correlation) between lipid peroxidation and toxicity of barracuda liver was found. Because iron and copper are well-known catalysts of hydroxyl radical production and lipid peroxidation in biological systems, the correlation between the concentrations of these metals in barracuda liver and lipid peroxidation and toxicity was also investigated. Cadmium was significantly correlated (p = 0.014) with the toxicity of barracuda livers. This study provides the first data concerning the concentration of iron, copper, and cadmium in the liver of the Caribbean barracuda. Of the three metals studied in barracuda liver, iron was the most abundant, followed by copper and cadmium. Lipid peroxidation was highly variable and detected in five (36%) of the liver samples. Lipid peroxidation was not statistically significantly correlated (p > 0.05) with concentrations of iron, copper, and cadmium in barracuda liver. Collectively, these findings provide additional evidence that lipid peroxidation can be a mechanistic component of ciguatera toxicity in the Caribbean barracuda.     

NO EVIDENCE FOR AN ALLELOPATHIC ROLE OF OKADAIC ACID AMONG CIGUATERA-ASSOCIATED DINOFLAGELLATES

Serine/threonine protein phosphatases are regulatory enzymes critical to growth and replication in eukaryotes. Okadaic acid (OA), a potent serine/ threonine protein phosphatase inhibitor, has been well studied in vertebrates; however, little is known about the role this phycotoxin plays in the ecology of its producer, the benthic dinoflagellate Prorocentrum lima Ehrenberg. The frequency and diversity of toxins produced by benthic dinoflagellates suggests that toxin production might play a role in competition among algal species. To assess the role of OA in growth competition, dinoflagellate species that co-occur with P. lima were grown in medium preconditioned by P. lima. Exudates from P. lima inhibited the growth of three of the four co-occurring species. All four dinoflagellate species were found to possess protein phosphatases that are inhibited by low concentrations of OA (IC₅₀∼5 nM). Furthermore, when treated in culture for 24 h with either purified OA or medium preconditioned by P. lima, their protein phosphatase activity was substantially inhibited. In contrast, P. lima 's protein phosphatase activity was refractory to OA both in vitro and in culture. To determine whether its growth inhibitory action was dependent on its phosphatase inhibitory activity, the P. lima -preconditioned medium was fractionated by HPLC and fractions tested for growth-inhibitory and protein phosphatase–inhibitory activity. We found that the two activities reside in different fractions. These results suggest that although OA has growth-inhibitory potential against other microalgae, it does not represent the major growth-inhibitory activity found in P. lima 's medium.     

Genetic diversity of Gambierdiscus spp. (Gonyaulacales, Dinophyceae) in Japanese coastal areas

The genetic diversity of the ciguatera fish poisoning-related dinoflagellate distributed in Japanese coastal areas was investigated. The entire sequence of the 5.8S rRNA gene and two internal transcribed (ITS) regions were determined, which included putative pseudogenes, from 19 strains of dinoflagellates assigned to the genus Gambierdiscus Adachi et Fukuyo collected from Japanese subtropical and temperate coastal areas. The sequences obtained from the 19 strains were divided into two types based on sequence similarity. Here we designate the two types as type 1 and type 2. For the relationship between the genotypes and origins of the strains used, the strains collected from subtropical areas possessed the type 1 sequence; whereas those from temperate areas possessed the type 2. This observation led us to question former reputations that Gambierdiscus cells observed in Japanese temperate areas are immigrants from Japanese subtropical areas. Subsequently, we sequenced a part of the 18S rRNA gene from two strains from subtropical areas and two from temperate areas. Unfortunately, phylogenetic analysis including the sequences obtained from various gonyaulacales dinoflagellates failed to determine the species phylogenetically closely related to and possible origin(s) of the Gambierdiscus sp. from the Japanese coastal areas.     

DEVELOPMENT OF SEMI‐QUANTITATIVE PCR ASSAYS FOR THE DETECTION AND ENUMERATION OF GAMBIERDISCUS SPECIES (GONYAULACALES,DINOPHYCEAE)1

Ciguatera fish poisoning (CFP) is a serious health problem in tropical regions and is caused by the bioaccumulation of lipophilic toxins produced by dinoflagellates in the genus Gambierdiscus. Gambierdiscus species are morphologically similar and are difficult to distinguish from one another even when using scanning electron microscopy. Improved identification and detection methods that are sensitive and rapid are needed to identify toxic species and investigate potential distribution and abundance patterns in relation to incidences of CFP. This study presents the first species‐specific, semi‐quantitative polymerase chain reaction (qPCR) assays that can be used to address these questions. These assays are specific for five Gambierdiscus species and one undescribed ribotype. The assays utilized a SYBR green format and targeted unique sequences found within the SSU, ITS, and the D1/D3 LSU ribosomal domains. Standard curves were constructed using known concentrations of cultured cells and 10‐fold serial dilutions of rDNA PCR amplicons containing the target sequence for each specific assay. Assay sensitivity and accuracy were tested using DNA extracts purified from known concentrations of multiple Gambierdiscus species. The qPCR assays were used to assess Gambierdiscus species diversity and abundance in samples collected from nearshore areas adjacent to Ft. Pierce and Jupiter, Florida USA. The results indicated that the practical limit of detection for each assay was 10 cells per sample. Most interestingly, the qPCR analysis revealed that as many as four species of Gambierdiscus were present in a single macrophyte sample.     

Did ciguatera prompt the late Holocene Polynesian voyages of discovery?

The famous Polynesian voyages characterized an intensive network of cultural exchange and colonization that was particularly active from ad 1000 to 1450. But, why would large groups of people leave their homelands to voyage into the unknown? Oceanic voyages are risky, albeit less so today than in the past. Landfalls were not guaranteed improvements over ports of departure. Taking the Cook Islands as an example, we ask whether harmful algal blooms that result in ciguatera fish poisoning in humans prompted past and present emigration pulses of peoples from within Polynesia. We take a multipronged approach to examine our hypothesis, involving: (1) archaeological evidence, (2) ciguatera fish poisoning reports since the 1940s, and (3) climate and temperature oscillations using palaeodatasets. The archaeological records of fish bones and hooks show abrupt changes in fishing practices in post‐ad 1450 records. Sudden dietary shifts are not linked to overfishing, but may be a sign of ciguatera fish poisoning and adjustment of fishing preference. While fishes form the staple diet of Polynesians, such poisoning renders fishes unusable. We show that ciguatera fish poisoning events coincide with Pacific Decadal Oscillations and suggest that the celebrated Polynesian voyages across the Pacific Ocean may not have been random episodes of discovery to colonize new lands, but rather voyages of necessity. A modern analogue (in the 1990s) was the shift towards processed foods in the Cook Islands during ciguatera fish poisoning events, and mass emigration of islanders to New Zealand and Australia.     

Isolation and Structure of Ciguatoxin-4A,a New Ciguatoxin Precursor,from Cultures of Dinoflagellate Gambierdiscus toxicus and Parrotfish Scarus gibbus

A new ciguatoxin congener, ciguatoxin-4A (CTX4A), was isolated from cultures of marine dinoflagellate Gambierdiscus toxicus, and its structure was elucidated to be 52-epiciguatoxin-4B on the basis of spectroscopic data. Chromatographic and spectral comparisons indicated that CTX4A was identical with a structurally unelucidated congener known as scaritoxin or SGI.