AUTHOR=Johnson Matthew D. , Beaudoin David J. , Laza-Martinez Aitor , Dyhrman Sonya T. , Fensin Elizabeth , Lin Senjie , Merculief Aaron , Nagai Satoshi , Pompeu Mayza , Setälä Outi , Stoecker Diane K. 

TITLE=The Genetic Diversity of Mesodinium and Associated Cryptophytes

JOURNAL=Frontiers in Microbiology

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2016.02017

DOI=10.3389/fmicb.2016.02017

ISSN=1664-302X

ABSTRACT=<p>Ciliates from the genus <italic>Mesodinium</italic> are globally distributed in marine and freshwater ecosystems and may possess either heterotrophic or mixotrophic nutritional modes. Members of the <italic>Mesodinium major/rubrum</italic> species complex photosynthesize by sequestering and maintaining organelles from cryptophyte prey, and under certain conditions form periodic or recurrent blooms (= red tides). Here, we present an analysis of the genetic diversity of <italic>Mesodinium</italic> and cryptophyte populations from 10 environmental samples (eight globally dispersed habitats including five <italic>Mesodinium</italic> blooms), using group-specific primers for <italic>Mesodinium</italic> partial 18S, ITS, and partial 28S rRNA genes as well as cryptophyte large subunit RuBisCO genes (<italic>rbcL</italic>). In addition, 22 new cryptophyte and four new <italic>M. rubrum</italic> cultures were used to extract DNA and sequence <italic>rbcL</italic> and 18S-ITS-28S genes, respectively, in order to provide a stronger phylogenetic context for our environmental sequences. Bloom samples were analyzed from coastal Brazil, Chile, two Northeastern locations in the United States, and the Pribilof Islands within the Bering Sea. Additionally, samples were also analyzed from the Baltic and Barents Seas and coastal California under non-bloom conditions. Most blooms were dominated by a single <italic>Mesodinium</italic> genotype, with coastal Brazil and Chile blooms composed of <italic>M. major</italic> and the Eastern USA blooms dominated by <italic>M. rubrum</italic> variant B. Sequences from all four blooms were dominated by <italic>Teleaulax amphioxeia</italic>-like cryptophytes. Non-bloom communities revealed more diverse assemblages of <italic>Mesodinium</italic> spp., including heterotrophic species and the mixotrophic <italic>Mesodinium chamaeleon</italic>. Similarly, cryptophyte diversity was also higher in non-bloom samples. Our results confirm that <italic>Mesodinium</italic> blooms may be caused by <italic>M. major</italic>, as well as multiple variants of <italic>M. rubrum</italic>, and further implicate <italic>T. amphioxeia</italic> as the key cryptophyte species linked to these phenomena in temperate and subtropical regions.</p>