Complete mitochondrial genome of Coscinodiscus granii (Coscinodiscophyceae, Bacillariophyta).

Coscinodiscus is a genus common in marine phytoplankton, with some species thought to have a significant negative ecological impact. However, the availability of their genome sequences is rather limited. Here, we assembled and annotated the first complete mitochondrial genome (mtDNA) of the species Coscinodiscus granii L.F.Gough 1905, as part of our efforts to gain a better understanding of the genetic characteristics of Coscinodiscus taxa at a genomic level. The circular mtDNA was 34,970 bp in length and encoded 60 genes, including 32 protein-coding genes (PCGs), 24 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes, and two conserved open reading frames (orfs). The overall GC content of C. granii mtDNA was 24.30%, which was slightly lower than that of C. wailesii (25.00%), the first species in the genus Coscinodiscus whose mtDNA has been reported, and higher than that of Melosira undulata (21.60%), the first species in the class Coscinodiscophyceae whose mtDNA has been reported. As expected for congeneric species, phylogenetic analysis using concatenated amino acid sequences of 27 shared PCGs suggested that C. granii has a closer evolutionary relationship with C. wailesii. Coscinodiscus was found to be monophyletic in the phylogeny. The complete mtDNAs of more Coscinodiscus species will facilitate the exploration of the evolutionary relationships of species in the Class Coscinodiscophyceae.