Abstract
Cyanobacteria are ubiquitous in marine environments and play an important role as primary producers. Some cyanobacteria, the so-called cyanobionts (cyanobacterial symbionts), have a symbiotic relationship with unicellular organisms. Among these relationships, in particular, the nature (e.g., genetic diversity, host or cyanobiont specificity, and cyanobiont seasonality) of the cyanobiont-dinoflagellate host consortia remains poorly understood. In this study, 16S rDNA of cyanobionts in 138 single host cells isolated over four seasons from temperate waters were sequenced using the MiSeq platform. Genetic analysis of cyanobionts from the dinoflagellate host Ornithocercus revealed that three genetic types of Synechococcales cyanobionts occurred in a wide range of water temperatures (11–24 °C), and their distribution seemed to be closely associated with variations in salinity. Furthermore, a certain degree of host (or cyanobiont) specificity in cyanobionts (or the host) among Ornithocercus species as well as among other dinophysoid species (i.e. Amphisolenia, Citharistes, and Histioneis), was observed. In addition to the Synechococcales cyanobionts, this study identified OTU sequences affiliated with Vampirovibrionales and Chroococcidiopsidales in some Ornithocercus cells, suggesting that Ornithocercus species are an additional habitat for these bacterial groups.
Highlights
Cyanobacteria are ubiquitous in marine environments and play an important role as primary producers
Genetic analysis of cyanobionts from the dinoflagellate host Ornithocercus isolated from samples obtained over four seasons from temperate waters revealed that dinoflagellate hosts harbor moderately host-specific and consistent types of cyanobionts throughout the year
The present study has shown that Type 1 Synechococcales cyanobionts can be further subdivided into Type 1a and 1b when based on internal transcribed spacer (ITS) sequences, revealing the presence of four genetic types of Ornithocercus cyanobionts (Supplemental Fig. S2a,b)
Summary
Cyanobacteria are ubiquitous in marine environments and play an important role as primary producers. The so-called cyanobionts (cyanobacterial symbionts), have a symbiotic relationship with unicellular organisms Among these relationships, in particular, the nature (e.g., genetic diversity, host or cyanobiont specificity, and cyanobiont seasonality) of the cyanobiont-dinoflagellate host consortia remains poorly understood. Cyanobionts have been found in numerous protist groups, including dinoflagellates, tintinnids, radiolarians, amoebae, diatoms, and haptophytes[9,10] Among these cyanobionts, little is known regarding the nature (e.g., genetic diversity, host or cyanobiont specificity, and cyanobiont seasonality) of the symbiosis involved, in relation to dinoflagellate host. Free-living picocyanobacteria, such as Synechococcus and Prochlorococcus, are widely distributed, including in temperate waters undergoing seasonal changes in water temperature As such, they can be subdivided into cold/warm types associated with variations in water temperature[22]. To identify the genetic type of Ornithocercus cyanobionts present, the cyanobacterial 16S rDNA (V3–V4 regions) sequences of whole cyanobionts from individual host cells were verified using the Illumina MiSeq sequencing platform
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