Phylogenetic relationships of Arthrospira strains inferred from 16S rRNA gene and cpcBA-IGS sequences

$Arthrospira$ $platensis$ and $Arthrospira$ $maxima$ are species of cyanobacteria used in health foods, animal feed, food additives, and fine chemicals. This study conducted a comparison of the 16S rRNA gene and $cpcBA$-intergenic spacer ($cpcBA$-IGS) sequences in $Arthrospira$ strains from culture collections around the world. A cluster analysis divided the 10 $Arthrospira$ strains into two main genotypic clusters, designated I and II, where Group I contained $A.$ $platensis$ SAG 86.79, UTEX 2340, $A.$ $maxima$ KCTC AG30054, and SAG 49.88, while Group II contained $A.$ $platensis$ PCC 9108, NIES 39, NIES 46, and SAG 257.80. However, although $A.$ $platensis$ PCC 9223 belonged to Group II-2 based on its $cpcBA$-IGS sequence, this strain also belonged to Group I based on its 16S rRNA gene sequence. Phylogenetic analyses based on the 16S rRNA gene and $cpcBA$-IGS sequences showed no division between $A.$ $platensis$ and $A.$ $maxima$, plus the 16S rRNA gene and $cpcBA$-IGS sequence clusters did not indicate any well-defined geographical distribution, instead overlapping in a rather interesting way. Therefore, the current study supports some previous conclusions based on 16S rRNA gene and $cpcBA$-IGS sequences, which found that $Arthrospira$ taxa are monophyletic. However, when compared with 16S rRNA sequences, $cpcBA$-IGS sequences may be better suited to resolve close relationships and intraspecies variability.