Re-evaluation of three Chlorogonium (Volvocales, Chlorophyceae) species based on 18S ribosomal RNA gene phylogeny

We sequenced the nuclear 18S ribosomal RNA (rRNA) genes of 23 strains of the genus Chlorogonium, to re-evaluate the status of C. euchlorum, C. elongatum, and C. capillatum, which had previously been classified using morphological criteria and gene sequence data from the large subunit of chloroplast Rubisco (rbcL). Although C. capillatum CCAP 12/2A and SAG 12-2a had been considered parts of the same strain of C. capillatum, we identified SAG 12-2a as C. euchlorum. We observed no intraspecific variation of the 18S rRNA gene sequence within C. euchlorum and C. capillatum. Some variations in 18S rRNA gene sequences were observed among strains of C. elongatum, but these sequences constituted a monophyletic group. Thus, taxonomic delimitation using chloroplast rbcL gene sequences produced monophyletic groupings of Chlorogonium species, which are supported by nuclear gene sequence analysis.

Keywords

• Chlorogonium ,
• Chlorophyceae,
• culture strain,
• molecular phylogeny,
• monophyletic species,
• 18S rRNA,
• species taxonomy