Paralytic shellfish poisoning (PSP) is a serious human illness caused by the ingestion of seafood contaminated with paralytic shellfish toxins, composed of saxitoxin and its derivatives (STXs). These toxins are also produced by marine dinoflagellate Alexandrium spp. STXs can affect the human neuro-vegetative system leading to muscular paralysis and death. These toxins are a family of neurotoxins produced by some freshwater prokaryotic cyanobacteria and marine eukaryotic dinoflagellates. The first two genes that start the biochemical synthesis of STX, also those best characterized, are the sxtA (coding for a polyketide synthase) and sxtG (coding for an amidinotransferase). STXs mainly affect the marine trophic web accumulating in many organisms. The accumulation of these compounds in seafood has a major economic impact on aquaculture industries. Due to the increased risks posed to human health by PSP toxins worldwide, including also the Mediterranean Sea, it is crucial to investigate the potential correlation between STX-production and sxt gene content in environmental samples during toxic blooms. This study aimed to illustrate a potential scenario of STX producing harmful Alexandrium minutum and to investigate STX-related risk in the Mediterranean Sea. Field samples were collected in Syracuse Bay (Ionian Sea) on May 2014 during a bloom event. Field samples were processed for quantitative molecular qPCR and LC-HRMS analyses. Firstly, the sxtA gene content, as well as toxin profile and content, were investigated in the Mediterranean A. minutum populations. The median sxtA1 gene copy number/cell was 2.2 and no difference in the sxtA1 gene copy number was found among A. minutum populations. A qPCR assay was applied to quantify the sxtA1 gene copy number in A. minutum strains in relation to STX production and rapidly quantify the abundance of sxtA1 gene in field samples. In field samples, a positive correlation was found between cell densities determined by microscopy and sxtA1 gene copies by qPCR in surface water (n=29, Pearson's r=0.978 p<<0.0001). The range of sxtA1 gene content was 2.55x108±3.08x107-1.38x105±1.80x103 copies/L. Further, the sxtA1 gene content was correlated with toxin presence in environmental samples to provide an indication of PSP risk during a bloom. The amount of sxtA1 gene was in the range of 1.38x105-2.55x108 copies/L and the STX concentrations ranged from 41-201 nmol/L. This scenario illustrates the potential risk of real PSP occurrences, even though the toxin amount on a per cell basis was lower than in other areas worldwide, but in high biomass blooming events, the potential risk of toxin accumulation in shellfish is likely. Efficient monitoring strategies by combined molecular and chemical methodologies could play a fundamental role in preventing and managing health and economic risks related to STX-producing Alexandrium spp. blooms in coastal and marine farm areas.
The SXT gene and paralytic shellfish poisoning toxins as markers for the monitoring of HAB dinoflagellate blooms
2016-01-01
Abstract
Paralytic shellfish poisoning (PSP) is a serious human illness caused by the ingestion of seafood contaminated with paralytic shellfish toxins, composed of saxitoxin and its derivatives (STXs). These toxins are also produced by marine dinoflagellate Alexandrium spp. STXs can affect the human neuro-vegetative system leading to muscular paralysis and death. These toxins are a family of neurotoxins produced by some freshwater prokaryotic cyanobacteria and marine eukaryotic dinoflagellates. The first two genes that start the biochemical synthesis of STX, also those best characterized, are the sxtA (coding for a polyketide synthase) and sxtG (coding for an amidinotransferase). STXs mainly affect the marine trophic web accumulating in many organisms. The accumulation of these compounds in seafood has a major economic impact on aquaculture industries. Due to the increased risks posed to human health by PSP toxins worldwide, including also the Mediterranean Sea, it is crucial to investigate the potential correlation between STX-production and sxt gene content in environmental samples during toxic blooms. This study aimed to illustrate a potential scenario of STX producing harmful Alexandrium minutum and to investigate STX-related risk in the Mediterranean Sea. Field samples were collected in Syracuse Bay (Ionian Sea) on May 2014 during a bloom event. Field samples were processed for quantitative molecular qPCR and LC-HRMS analyses. Firstly, the sxtA gene content, as well as toxin profile and content, were investigated in the Mediterranean A. minutum populations. The median sxtA1 gene copy number/cell was 2.2 and no difference in the sxtA1 gene copy number was found among A. minutum populations. A qPCR assay was applied to quantify the sxtA1 gene copy number in A. minutum strains in relation to STX production and rapidly quantify the abundance of sxtA1 gene in field samples. In field samples, a positive correlation was found between cell densities determined by microscopy and sxtA1 gene copies by qPCR in surface water (n=29, Pearson's r=0.978 p<<0.0001). The range of sxtA1 gene content was 2.55x108±3.08x107-1.38x105±1.80x103 copies/L. Further, the sxtA1 gene content was correlated with toxin presence in environmental samples to provide an indication of PSP risk during a bloom. The amount of sxtA1 gene was in the range of 1.38x105-2.55x108 copies/L and the STX concentrations ranged from 41-201 nmol/L. This scenario illustrates the potential risk of real PSP occurrences, even though the toxin amount on a per cell basis was lower than in other areas worldwide, but in high biomass blooming events, the potential risk of toxin accumulation in shellfish is likely. Efficient monitoring strategies by combined molecular and chemical methodologies could play a fundamental role in preventing and managing health and economic risks related to STX-producing Alexandrium spp. blooms in coastal and marine farm areas.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
