Dataset Information

Paralytic shellfish toxin content is related to genomic sxtA4 copy number in Alexandrium minutum strains.

ABSTRACT: Dinoflagellates are microscopic aquatic eukaryotes with huge genomes and an unusual cell regulation. For example, most genes are present in numerous copies and all copies seem to be obligatorily transcribed. The consequence of the gene copy number (CPN) for final protein synthesis is, however, not clear. One such gene is sxtA, the starting gene of paralytic shellfish toxin (PST) synthesis. PSTs are small neurotoxic compounds that can accumulate in the food chain and cause serious poisoning incidences when ingested. They are produced by dinoflagellates of the genera Alexandrium, Gymnodium, and Pyrodinium. Here we investigated if the genomic CPN of sxtA4 is related to PST content in Alexandrium minutum cells. SxtA4 is the 4th domain of the sxtA gene and its presence is essential for PST synthesis in dinoflagellates. We used PST and genome size measurements as well as quantitative PCR to analyze sxtA4 CPN and toxin content in 15 A. minutum strains. Our results show a strong positive correlation between the sxtA4 CPN and the total amount of PST produced in actively growing A. minutum cells. This correlation was independent of the toxin profile produced, as long as the strain contained the genomic domains sxtA1 and sxtA4.

SUBMITTER: Stuken A

PROVIDER: S-EPMC4416454 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Paralytic shellfish toxin content is related to genomic sxtA4 copy number in Alexandrium minutum strains.

Stüken Anke A Riobó Pilar P Franco José J Jakobsen Kjetill S KS Guillou Laure L Figueroa Rosa I RI

Frontiers in microbiology 20150501

Dinoflagellates are microscopic aquatic eukaryotes with huge genomes and an unusual cell regulation. For example, most genes are present in numerous copies and all copies seem to be obligatorily transcribed. The consequence of the gene copy number (CPN) for final protein synthesis is, however, not clear. One such gene is sxtA, the starting gene of paralytic shellfish toxin (PST) synthesis. PSTs are small neurotoxic compounds that can accumulate in the food chain and cause serious poisoning incid ...[more]

PMID: 25983733

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Project description:Paralytic shellfish poisoning (PSP) is a human foodborne syndrome caused by the consumption of shellfish that accumulate paralytic shellfish toxins (PSTs, saxitoxin group). In PST-producing dinoflagellates such as Alexandrium spp., toxin synthesis is encoded in the nuclear genome via a gene cluster (sxt). Toxin production is supposedly associated with the presence of a 4th domain in the sxtA gene (sxtA4), one of the core genes of the PST gene cluster. It is postulated that gene expression in dinoflagellates is partially constitutive, with both transcriptional and post-transcriptional processes potentially co-occurring. Therefore, gene structure and expression mode are two important features to explore in order to fully understand toxin production processes in dinoflagellates. In this study, we determined the intracellular toxin contents of twenty European Alexandrium minutum and Alexandrium pacificum strains that we compared with their genome size and sxtA4 gene copy numbers. We observed a significant correlation between the sxtA4 gene copy number and toxin content, as well as a moderate positive correlation between the sxtA4 gene copy number and genome size. The 18 toxic strains had several sxtA4 gene copies (9-187), whereas only one copy was found in the two observed non-toxin producing strains. Exploration of allelic frequencies and expression of sxtA4 mRNA in 11 A. minutum strains showed both a differential expression and specific allelic forms in the non-toxic strains compared with the toxic ones. Also, the toxic strains exhibited a polymorphic sxtA4 mRNA sequence between strains and between gene copies within strains. Finally, our study supported the hypothesis of a genetic determinism of toxin synthesis (i.e., the existence of several genetic isoforms of the sxtA4 gene and their copy numbers), and was also consistent with the hypothesis that constitutive gene expression and moderation by transcriptional and post-transcriptional regulation mechanisms are the cause of the observed variability in the production of toxins by A. minutum.

Dataset Information

Paralytic shellfish toxin content is related to genomic sxtA4 copy number in Alexandrium minutum strains.

Publications

Paralytic shellfish toxin content is related to genomic sxtA4 copy number in Alexandrium minutum strains.

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