Detailed characterization of the Arthrospira type species separating commercially grown taxa into the new genus Limnospira (Cyanobacteria)

Abstract

The genus Arthrospira has a long history of being used as a food source in different parts of the world. Its mass cultivation for production of food supplements and additives has contributed to a more detailed study of several species of this genus. In contrast, the type species of the genus (A. jenneri), has scarcely been studied. This work adopts a polyphasic approach to thoroughly investigate environmental samples of A. jenneri, whose persistent bloom was noticed in an urban reservoir in Poland, Central Europe. The obtained results were compared with strains designated as A. platensis, A. maxima, and A. fusiformis from several culture collections and other Arthrospira records from GenBank. The comparison has shown that A. jenneri differs from popular species that are massively utilized commercially with regard to its cell morphology, ultrastructure and ecology, as well as its 16S rRNA gene sequence. Based on our findings, we propose the establishment of a new genus, Limnospira, which currently encompasses three species including the massively produced L. (A.) fusiformis and L. (A.) maxima with the type species Limnospira fusiformis.

Figure 1

The morphology of Arthrospira jenneri, (a) original drawing of A. jenneri by Gomont, (b–l) morphology of straight and spiral trichomes of A. jenneri’s population from Tomaszowska Reservoir in LM.

Figure 2

The morphology and ultrastructure of Arthrospira jenneri under electron microscope, (a,b) morphology of the trichomes in SEM, (c–h) ultrastructure of the trichomes in TEM, aerotopes indicated by arrows, (g) detail of an aerotope.

Figure 3

Phylogenetic tree based on 1800 bp fragment of the gene for 16S rRNA, including 291 sequences and showing the position of the genera Arthrospira and Limnospira. Branch support values (above 50 or 0.75) are shown as Maximum Likelihood, Bayesian posterior probability, and Maximum Parsimony bootstrap values, respectively. Note to Fig. 3: Quotation marks indicate the uncertainty of the real name of the sequenced organism.

Figure 4

The morphology of Limnospira, (a) original drawing of L. fusiformis (Spirulina fusiformis) by Voronichin, (b–h) morphology of the L. fusiformis reference strain SAG 85.79 in LM (i–o) morphology of the L. fusiformis strain SAG 84.79 in LM, (p–t) morphology of the L. fusiformis strain SAG 257.80 in LM; black triangles point out calyptra/thickened cell wall.

Figure 5

The ultrastructure of Limnospira in TEM, (a–c) the reference strain of L. fusiformis SAG 85.79, (d–f) the strain of L. fusiformis SAG 257.80, black arrows point out the calyptra/thickened cell wall at the end of the trichome.