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Osmotic stress triggers toxin production by the dinoflagellate Karenia brevis.

ABSTRACT: With the increase in frequency of harmful algal blooms (HABs) worldwide, a better understanding of the mechanisms that influence toxin production is needed. Karenia brevis, the major HAB dinoflagellate in the Gulf of Mexico, produces potent neurotoxins, known as brevetoxins. Human health is directly impacted by blooms of K. brevis through consumption of shellfish contaminated by accumulated brevetoxins (neurotoxic shellfish poisoning) or from aerosolized brevetoxins in sea spray (reduced respiratory function); however, the reason for brevetoxin production has remained a mystery. Here we show that brevetoxin production increased dramatically in response to osmotic stress in three of the four K. brevis clones examined. By rapidly changing salinity to simulate a shift from oceanic conditions to a decreased salinity typical of coastal conditions, brevetoxin production was triggered. As a result, brevetoxin cell quota increased by >14-fold, while growth rate remained unchanged. Live images of K. brevis cells were also examined to assess changes in cell volume. In the K. brevis Wilson clone, cells responded quickly to hypoosmotic stress by increasing their brevetoxin cell quota from ?10 to 160 pg of brevetoxin per cell, while cell volume remained stable. In contrast, the K. brevis SP1 clone, which has a consistently low brevetoxin cell quota (<1 pg per cell), was unable to balance the hypoosmotic stress, and although brevetoxin production remained low, average cell volume increased. Our findings close a critical gap in knowledge regarding mechanisms for toxin production in K. brevis by providing an explanation for toxin production in this harmful dinoflagellate.

SUBMITTER: Errera RM

PROVIDER: S-EPMC3127906 | biostudies-other | 2011 Jun

REPOSITORIES: biostudies-other

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Osmotic stress triggers toxin production by the dinoflagellate Karenia brevis.

Errera Reagan M RM Campbell Lisa L

Proceedings of the National Academy of Sciences of the United States of America 20110613 26

With the increase in frequency of harmful algal blooms (HABs) worldwide, a better understanding of the mechanisms that influence toxin production is needed. Karenia brevis, the major HAB dinoflagellate in the Gulf of Mexico, produces potent neurotoxins, known as brevetoxins. Human health is directly impacted by blooms of K. brevis through consumption of shellfish contaminated by accumulated brevetoxins (neurotoxic shellfish poisoning) or from aerosolized brevetoxins in sea spray (reduced respira ...[more]

PMID: 21670286

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Project description:BackgroundKarenia brevis is a harmful algal species that blooms in the Gulf of Mexico and produces brevetoxins that cause neurotoxic shellfish poisoning. Elevated brevetoxin levels in K. brevis cells have been measured during laboratory hypo-osmotic stress treatments. To investigate mechanisms underlying K. brevis osmoacclimation and osmoregulation and establish a valuable resource for gene discovery, we assembled reference transcriptomes for three clones: Wilson-CCFWC268, SP3, and SP1 (a low-toxin producing variant). K. brevis transcriptomes were annotated with gene ontology terms and searched for putative transmembrane proteins that may elucidate cellular responses to hypo-osmotic stress. An analysis of single nucleotide polymorphisms among clones was used to characterize genetic divergence.ResultsK. brevis reference transcriptomes were assembled with 58.5 (Wilson), 78.0 (SP1), and 51.4 million (SP3) paired reads. Transcriptomes contained 86,580 (Wilson), 93,668 (SP1), and 84,309 (SP3) predicted transcripts. Approximately 40% of the transcripts were homologous to proteins in the BLAST nr database with an E value ≤ 1.00E-6. Greater than 80% of the highly conserved CEGMA core eukaryotic genes were identified in each transcriptome, which supports assembly completeness. Seven putative voltage-gated Na+ or Ca2+ channels, two aquaporin-like proteins, and twelve putative VATPase subunits were discovered in all clones using multiple bioinformatics approaches. Furthermore, 45% (Wilson) and 43% (SP1 and SP3) of the K. brevis putative peptides > 100 amino acids long produced significant hits to a sequence in the NCBI nr protein database. Of these, 77% (Wilson and SP1) and 73% (SP3) were successfully assigned gene ontology functional terms. The predicted single nucleotide polymorphism (SNP) frequencies between clones were 0.0028 (Wilson to SP1), 0.0030 (Wilson to SP3), and 0.0028 (SP1 to SP3).ConclusionsThe K. brevis transcriptomes assembled here provide a foundational resource for gene discovery and future RNA-seq experiments. The identification of ion channels, VATPases, and aquaporins in all three transcriptomes indicates that K. brevis regulates cellular ion and water concentrations via transmembrane proteins. Additionally, > 40,000 unannotated loci may include potentially novel K. brevis genes. Ultimately, the SNPs identified among the three ecologically diverse clones with different toxin profiles may help to elucidate variations in K. brevis brevetoxin production.

Dataset Information

Osmotic stress triggers toxin production by the dinoflagellate Karenia brevis.

Publications

Osmotic stress triggers toxin production by the dinoflagellate Karenia brevis.

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