The genus Limnospira contains only two species, both unable to produce microcystins: L. maxima and L. platensis

Abstract

Spirulina is the commercial name for edible cyanobacteria of the genus <i>Limnospira</i>. The taxonomy of this genus is confusing with four species distributed in two lineages. Furthermore, the species <i>Limnospira fusiformis</i> has been cited as toxic by potentially producing microcystins. Taxonomic ambiguity combined with suspected health concerns constitute a major issue for spirulina producers. In a collection of six cultivars and one ecotype, we identified strains of the two lineages through metagenetic and morphological analyses. We demonstrated that the genus <i>Limnospira</i> only comprises two distinct species according to genomic comparisons of three genomes obtained in this study and 19 reference genomes. We showed that the V3-V4 region of the 16S rRNA gene is sufficient to identify the genus <i>Limnospira</i> and to distinguish the two species. Toxinogenesis investigations on eleven genomes from each <i>Limnospira</i> species revealed no genes involved in cyanotoxin synthesis, reflecting the inability of this genus to produce microcystins.