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  • 11
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    Growing degree-day measurement of cyst germination rates in the toxic dinoflagellate Alexandrium catenella (2022)
    American Society for Microbiology
    Details
    Publication Date: 2022-09-01
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Fischer, A., & Brosnahan, M. Growing degree-day measurement of cyst germination rates in the toxic dinoflagellate Alexandrium catenella. Applied and Environmental Microbiology, 88(12), (2022): e02518-21, https://doi.org/10.1128/aem.02518-21.
    Description: Blooms of many dinoflagellates, including several harmful algal bloom (HAB) species, are seeded and revived through the germination of benthic resting cysts. Temperature is a key determinant of cysts’ germination rate, and temperature–germination rate relationships are therefore fundamental to understanding species’ germling cell production, cyst bed persistence, and resilience to climate warming. This study measured germination by cysts of the HAB dinoflagellate Alexandrium catenella using a growing degree-day (DD) approach that accounts for the time and intensity of warming above a critical temperature. Time courses of germination at different temperatures were fit to lognormal cumulative distribution functions for the estimation of the median days to germination. As temperature increased, germination times decreased hyperbolically. DD scaling collapsed variability in germination times between temperatures after cysts were oxygenated. A parallel experiment demonstrated stable temperature–rate relationships in cysts collected during different phases of seasonal temperature cycles in situ over three years. DD scaling of the results from prior A. catenella germination studies showed consistent differences between populations across a wide range of temperatures and suggests selective pressure for different germination rates. The DD model provides an elegant approach to quantify and compare the temperature dependency of germination among populations, between species, and in response to changing environmental conditions.
    Description: We gratefully acknowledge support to A.D.F. and M.L.B. through the Woods Hole Center for Oceans and Human Health (National Science Foundation grants OCE‐0430724, OCE‐0911031, OCE‐1314642, and OCE-1840381 and National Institutes of Health grants NIEHS‐1P50‐ES02192301 and P01ES028938).
    Keywords: dinoflagellate cyst bed ; population comparison ; microbial resting stages ; temperature-dependent phenology
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 12
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    Horizontal gene transfer is a significant driver of gene innovation in dinoflagellates (2014)
    Oxford University Press
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    Publication Date: 2022-05-26
    Description: © The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Genome Biology and Evolution 5 (2013): 2368-2381, doi:10.1093/gbe/evt179.
    Description: The dinoflagellates are an evolutionarily and ecologically important group of microbial eukaryotes. Previous work suggests that horizontal gene transfer (HGT) is an important source of gene innovation in these organisms. However, dinoflagellate genomes are notoriously large and complex, making genomic investigation of this phenomenon impractical with currently available sequencing technology. Fortunately, de novo transcriptome sequencing and assembly provides an alternative approach for investigating HGT. We sequenced the transcriptome of the dinoflagellate Alexandrium tamarense Group IV to investigate how HGT has contributed to gene innovation in this group. Our comprehensive A. tamarense Group IV gene set was compared with those of 16 other eukaryotic genomes. Ancestral gene content reconstruction of ortholog groups shows that A. tamarense Group IV has the largest number of gene families gained (314–1,563 depending on inference method) relative to all other organisms in the analysis (0–782). Phylogenomic analysis indicates that genes horizontally acquired from bacteria are a significant proportion of this gene influx, as are genes transferred from other eukaryotes either through HGT or endosymbiosis. The dinoflagellates also display curious cases of gene loss associated with mitochondrial metabolism including the entire Complex I of oxidative phosphorylation. Some of these missing genes have been functionally replaced by bacterial and eukaryotic xenologs. The transcriptome of A. tamarense Group IV lends strong support to a growing body of evidence that dinoflagellate genomes are extraordinarily impacted by HGT.
    Description: J.H.W. was supported by the NSF IGERT Program in Comparative Genomics at the University of Arizona (grant number DGE-0654435). This work was supported by grants from the National Science Foundation (grant numbers OCE-0723498, EF-0732440) and funding provided by the BIO5 Institute at the University of Arizona to J.D.H.
    Keywords: Gene innovation ; Alexandrium tamarense Group IV ; Phylogenetic profile ; Phylogenomics ; De novo transcriptome assembly ; Mitochondrial metabolism
    Repository Name: Woods Hole Open Access Server
    Type: Article
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    Format: application/vnd.ms-excel
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  • 13
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    A red tide of Alexandrium fundyense in the Gulf of Maine (2014)
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 103 (2014): 174-184, doi:10.1016/j.dsr2.2013.05.011.
    Description: In early July 2009, an unusually high concentration of the toxic dinoflagellate Alexandrium fundyense occurred in the western Gulf of Maine, causing surface waters to appear reddish brown to the human eye. The discolored water appeared to be the southern terminus of a large-scale event that caused shellfish toxicity along the entire coast of Maine to the Canadian border. Rapid-response shipboard sampling efforts together with satellite data suggest the water discoloration in the western Gulf of Maine was a highly ephemeral feature of less than two weeks in duration. Flow cytometric analysis of surface samples from the red water indicated the population was undergoing sexual reproduction. Cyst fluxes downstream of the discolored water were the highest ever measured in the Gulf of Maine, and a large deposit of new cysts was observed that fall. Although the mechanisms causing this event remain unknown, its timing coincided with an anomalous period of downwelling-favorable winds that could have played a role in aggregating upward-swimming cells. Regardless of the underlying causes, this event highlights the importance of short-term episodic phenomena on regional population dynamics of A. fundyense.
    Description: The R/V Tioga sampling effort was facilitated by event response funding from the National Oceanic Atmospheric Administration (NOAA), National Ocean Service, Center for Sponsored Coastal Ocean Research, through NOAA Cooperative Agreement NA17RJ1223. Additional support for follow-up analysis and synthesis was provided by NOAA grant NA06NOS4780245 for the Gulf of Maine Toxicity (GOMTOX) program and the Woods Hole Center for Oceans and Human Health through National Science Foundation grants OCE- 0430724 and OCE-0911031 and National Institute of Environmental Health Sciences grant 1P50-ES01274201.
    Keywords: Phytoplankton ; Population dynamics ; Red tides ; Cysts ; Paralytic shellfish poisoning ; USA ; Gulf of Maine
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 14
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    Evaluation of sxtA and rDNA qPCR assays through monitoring of an inshore bloom of Alexandrium catenella Group 1 (2019)
    Nature Research
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Murray, S. A., Ruvindy, R., Kohli, G. S., Anderson, D. M., & Brosnahan, M. L. Evaluation of sxtA and rDNA qPCR assays through monitoring of an inshore bloom of Alexandrium catenella Group 1. Scientific Reports, 9(1), (2019): 14532, doi:10.1038/s41598-019-51074-3.
    Description: Alexandrium catenella (formerly A. tamarense Group 1, or A. fundyense) is the leading cause of Paralytic Shellfish Poisoning in North and South America, Europe, Africa, Australia and Asia. The quantification of A.catenella via sxtA, a gene involved in Paralytic Shellfish Toxin synthesis, may be a promising approach, but has not been evaluated in situ on blooms of A. catenella, in which cell abundances may vary from not detectable to in the order of 106 cells L−1. In this study, we compared sxtA assay performance to a qPCR assay targeted to a species-specific region of ribosomal DNA (rDNA) and an established fluorescent in situ hybridization (FISH) microscopy method. Passing-Bablok regression analyses revealed the sxtA assay to overestimate abundances when 〈5 cell equivalents A. catenella DNA were analysed, but otherwise was closer to microscopy estimates than the rDNA assay, which overestimated abundance across the full range of concentrations analysed, indicative of a copy number difference between the bloom population and a culture used for assay calibration a priori. In contrast, the sxtA assay performed more consistently, indicating less copy number variation. The sxtA assay was generally reliable, fast and effective in quantifying A. catenella and was predictive of PST contamination of shellfish.
    Description: We thank the Australian Research Council for Funding (FT120100704). We thank Chowdhury Sarowar for the toxicity measurements, at the Sydney Institute of Marine Science. Support to MB and DA was provided by MIT Sea Grant (NA14OAR4170077) and the Woods Hole Center for Oceans and Human Health (National Science Foundation award OCE-1840381 and National Institute of Environmental Health Sciences award 1-P01-ES028938–01). We are grateful for assistance from David Kulis, Claire Mullen, and Isaac Rosenthal for assistance in the collection and processing of Salt Pond samples.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 15
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    Morphological and phylogenetic data do not support the split of Alexandrium into four genera (2020)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 98, pp. 101902, ISSN: 1568-9883
    Details
    Publication Date: 2023-03-13
    Description: A recently published study analyzed the phylogenetic relationship between the genera Centrodinium and Alexandrium, confirming an earlier publication showing the genus Alexandrium as paraphyletic. This most recent manuscript retained the genus Alexandrium, introduced a new genus Episemicolon, resurrected two genera, Gessnerium and Protogonyaulax, and stated that: “The polyphyly [sic] of Alexandrium is solved with the split into four genera”. However, these reintroduced taxa were not based on monophyletic groups. Therefore this work, if accepted, would result in replacing a single paraphyletic taxon with several non-monophyletic ones. The morphological data presented for genus characterization also do not convincingly support taxa delimitations. The combination of weak molecular phylogenetics and the lack of diagnostic traits (i.e., autapomorphies) render the applicability of the concept of limited use. The proposal to split the genus Alexandrium on the basis of our current knowledge is rejected herein. The aim here is not to present an alternative analysis and revision, but to maintain Alexandrium. A better constructed and more phylogenetically accurate revision can and should wait until more complete evidence becomes available and there is a strong reason to revise the genus Alexandrium. The reasons are explained in detail by a review of the available molecular and morphological data for species of the genera Alexandrium and Centrodinium. In addition, cyst morphology and chemotaxonomy are discussed, and the need for integrative taxonomy is highlighted.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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