Abstract
Specimens of a new species of blue diatoms from the genus Haslea Simonsen were discovered in geographically distant sampling sites, first in the Canary Archipelago, then North Carolina, Gulf of Naples, the Croatian South Adriatic Sea, and Turkish coast of the Eastern Mediterranean Sea. An exhaustive characterization of these specimens, using a combined morphological and genomic approach led to the conclusion that they belong to a single new to science cosmopolitan species, Haslea silbo sp. nov. A preliminary characterization of its blue pigment shows similarities to marennine produced by Haslea ostrearia, as evidenced by UV-visible spectrophotometry and Raman spectrometry. Life cycle stages including auxosporulation were also observed, providing data on the cardinal points of this species. For the two most geographically distant populations (North Carolina and East Mediterranean), complete mitochondrial and plastid genomes were sequenced. The mitogenomes of both strains share a rare atp6 pseudogene, but the number, nature, and positions of the group II introns inside its cox1 gene differ between the two populations. There are also two pairs of genes fused in single ORFs. The plastid genomes are characterized by large regions of recombination with plasmid DNA, which are in both cases located between the ycf35 and psbA genes, but whose content differs between the strains. The two sequenced strains hosts three plasmids coding for putative serine recombinase protein whose sequences are compared, and four out of six of these plasmids were highly conserved.
Highlights
Diatoms able to synthetize blue marennine-like pigments are restricted to a few species belonging to the genus Haslea, the most famous being H. ostrearia (Gaillon) Simonsen [1,2].The naming of blue diatoms or blue Haslea comes from their remarkable ability to synthesize water soluble, blue-green, non-photosynthetic pigments, commonly called marenninelike pigments [3]
The most decisiveDiagnosis feature is the stria density, which is lower in H. silbo compared to all otherHaslea blue Haslea due a significant reduction the number of longitudinal silbo is verytosimilar to H. ostrearia, H.in karadagensis
The third major clade contains the species of pennate diatoms which were meant to be the outgroup (e.g., Trachyneis sp.) as well as numerous species listed as Haslea spp., but whose exact identities and classification have been recently linked to Navicula sensu lato [44]
Summary
Diatoms able to synthetize blue marennine-like pigments are restricted to a few species belonging to the genus Haslea, the most famous being H. ostrearia (Gaillon) Simonsen [1,2]. Nusantara are morphologically similar to H. ostrearia These four species are confused based on light microscopy (LM), they show significant differences in stria densities that are only visible using scanning electron microscopy (SEM) [19,21,22]. In 2009, we observed blue diatoms in water samples from La Gomera, an island from the Canary Archipelago Based on their morphology, they appeared to belong to a new species thereafter called Haslea silbo sp. These studies include the formal description of this new species, physico-chemical analyses of the blue pigment, evidence for auxosporulation, a molecular phylogeny as well as a genomic comparison of two sub-populations based on the sequencing of complete organellar genomes
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