Phenotypic analysis of Arthrospira (Spirulina) strains (cyanobacteria)

An analysis was made of the phenotypic characters of 33 helical and 2 straight Arthrospira strains, together with 5 apparently duplicate strains (4 helical, 1 straight), all axenic and clonal. The 28 characters showed morphological (14), ultrastructural (1), physiological (7) and biochemical (6) features. Multivariate analysis using the simple matching coefficient resolved the 33 helical strains into two clusters. The four helical strains and their apparent duplicates group within the same major phenotypic cluster. The two phenotypic clusters show a high correlation to the characters describing the helical trichome shape. Strains in phenotypic cluster I have an irregular, mainly dumbbell-shaped trichome helix, while strains in phenotypic cluster II have a regular trichome helix. These phenotypic clusters also show a high correlation to the molecular clusters of the same strains reported in the literature. On the basis of a comparison of the trichome morphology of these isolates with descriptions in the literature for the species name used in the original culture collection, it seems likely that several had been assigned the wrong name. The phenotypic analysis presented here plus a comparison with the molecular taxonomy of the same strains together suggest that the genus Arthrospira falls into at least two groups, with A. maxima, A. fusiformis and A. indica forming cluster I, and most strains designated A. platensis belonging to cluster II.