Palytoxin and Analogs: Biological and Ecological Effects

Palytoxin (PTX) is a potent marine toxin that was originally found in soft corals from tropical areas of the Pacific Ocean. Soon after, its occurrence was observed in numerous other marine organisms from the same ecological region. More recently, several analogs of PTX were discovered, remarkably all from species of the dinoflagellate genus Ostreopsis. Since these dinoflagellates are also found in other tropical and even in temperate regions, the formerly unsuspected broad distribution of these toxins was revealed. Toxicological studies with these compounds shows repeatedly low LD50 values in different mammals, revealing an acute toxic effect on several organs, as demonstrated by different routes of exposure. Bioassays tested for some marine invertebrates and evidences from environmental populations exposed to the toxins also give indications of the high impact that these compounds may have on natural food webs. The recognition of its wide distribution coupled with the poisoning effects that these toxins can have on animals and especially on humans have concerned the scientific community. In this paper, we review the current knowledge on the effects of PTX and its analogs on different organisms, exposing the impact that these toxins may have in coastal ecosystems

Prymnesins: Toxic Metabolites of the Golden Alga, Prymnesium parvum Carter (Haptophyta)

Increasingly over the past century, seasonal fish kills associated with toxic blooms of Prymnesium parvum have devastated aquaculture and native fish, shellfish, and mollusk populations worldwide. Protracted blooms of P. parvum can result in major disturbances to the local ecology and extensive monetary losses. Toxicity of this alga is attributed to a collection of compounds known as prymnesins, which exhibit potent cytotoxic, hemolytic, neurotoxic and ichthyotoxic effects. These secondary metabolites are especially damaging to gill-breathing organisms and they are believed to interact directly with plasma membranes, compromising integrity by permitting ion leakage. Several factors appear to function in the activation and potency of prymnesins including salinity, pH, ion availability, and growth phase. Prymnesins may function as defense compounds to prevent herbivory and some investigations suggest that they have allelopathic roles. Since the last extensive review was published, two prymnesins have been chemically characterized and ongoing investigations are aimed at the purification and analysis of numerous other toxic metabolites from this alga. More information is needed to unravel the mechanisms of prymnesin synthesis and the significance of these metabolites. Such work should greatly improve our limited understanding of the physiology and biochemistry of P. parvum and how to mitigate its blooms

Automated detection and enumeration for toxic algae by solid-phase cytometry and the introduction of a new probe for Prymnesium parvum (Haptophyta: Prymnesiophyceae)

Harmful algal blooms have a severe impact on aquaculture and fishery and can be caused by toxic haptophytes and dinoflagellates. Different toxic species, which are not easy to distinguish from their morphologically similar and non-toxic relatives, occur in both groups. Sequencing of the large subunit ribosomal RAA of different strains and taxonomic relatives allowed the design of a probe specific to the toxic Prymnesium parvum spp. For the rapid detection and enumeration of Prymnesium and Alexandrium cells in cultures and environmental samples, respectively, protocols for fluorescence in situ hybridization were adapted for automated detection by a solid-phase cytometer, the ChemScan. This cytometer enables the automated counting of fluorescently labelled cells on a membrane filter and subsequently a microscopic verification of these results by the user, because the motorized stage of the microscope is driven to each positive signal by the computer software to localize that cell on the filter. With this fast detection method, it was possible to detect, enumerate and verify microalgal cells on a filter, with a detection limit of one cell per membrane filter

Investigations into the role of bacteria/dinoflagellate interactions in paralytic shellfish poisoning

The interactions of purportedly toxic bacteria with dinoflagellates in the occurrence of Paralytic Shellfish Poisoning (PSP) were investigated. Dinoflagellates of the genus Alexandrium were examined to determine their bacterial population by the use of fluorescently labelled probes. Extracellular associated bacteria were shown to be associated with A. andersonii, A. tamarense and A. lusitanicum. Intracellulae bacteria were found in A. tamarense. Cyanoditolyltetrazolium chloride was used to detect endocytic metabolically active bacteria in these dinoflagellates. Intracellular bacteria were detected in A. tamarense and A. lusitanicum. In field studies, the occurrence of putatively toxic bacteria together with Alexandrium spp. and PSP in mussels was investigated. Lugol's fixed field samples from the Orkney Islands were screened for these bacteria in two sequential years. For the first time, fluorescently labelled probes were successfully applied to Lugol's fixed environmental samples. The bacteria were detected in high numbers in the samples, when both Alexandrium spp. were present and absent in the water column and when mussels contained PSP. The effect of purportedly toxic bacteria on mussel toxicity was examined with feeding experiments. The bacteria were detected in situ in tissue sections of the mussels gut. Mussel flesh did not show toxification after feeding upon the putatively toxic bacteria, although the blue mussels have filtered the bacteria in high numbers. The physical interactions between bacteria and dinoflagellates were investigated by conducting reassociation experiments with purportedly toxic bacteria which were originally isolated from the Alexandrium tamarense clone used in this experiments, or isolated from another related A. tamarense clone, respectively. No intracellular reassociated PTB-bacteria were detected in the dinoflagellates. However, a preferred extracellular attachment of the PTB-1 bacteria to the A. tamarense strain was observed