Isolates identifiable as Arthrospira maxima and Arthrospira fusiformis (Oscillatoriales, Cyanobacteria) appear identical on the basis of a morphological study in culture and 16S rRNA gene sequences
Two single filament isolates of Arthrospira (Cyanobacteria), one with tightly coiled trichomes and the other with freely coiled trichomes, were isolated from water samples obtained at Lake Chitu, Ethiopia. On the basis of accepted morphological criteria, they were initially identified as A. fusiformis and A. maxima, respectively. In laboratory culture their morphological characteristics and 16S rRNA gene sequences were examined. After two months, a mixture of both morphological forms was observed in each isolate. 16S rRNA gene sequence similarity between the two Arthrospira isolates was 100%. These morphological and genetic results allow us to conclude that the degree of coiling is an unreliable taxonomic character and strongly suggest that A. maxima and A. fusiformis are the same species.