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.