REMARKABLE CONSERVATION OF INTERNALLY TRANSCRIBED SPACER SEQUENCES OF ARTHROSPIRA (“SPIRULINA” ) (CYANOPHYCEAE, CYANOBACTERIA) STRAINS FROM FOUR CONTINENTS AND OF RECENT AND 30‐YEAR‐OLD DRIED SAMPLES FROM AFRICA¹

Abstract

The internally transcribed spacer (ITS) sequences of 21 Arthrospira clonal strains from four continents and assigned to four different species (A. platensis, A. maxima, A. fusiformis, A. indica) in the culture collections were determined. Two main clusters, I and II, were differentiated by 49 positions out of 475 nt or 477 nt, respectively. Each cluster was further subdivided into two subclusters. Subclusters I.A and I.B were separated by two substitutions, whereas subclusters II.A and II.B were distinguished by four substitutions. After direct sequencing of the PCR products, three dried samples from Chad aged between 3 months and 35 years yielded a sequence belonging to subcluster I.A, as did a recent commercial product. The strains grown in production plants belonged to the same (sub)clusters as strains from culture collections, mainly I.A and II. PCR primers specific for each cluster and subcluster were designed and tested with crude cell lysates of Arthrospira strains. One dried sample (“dihé” 1) and a herbarium sample from Lake Sonachi (Kenya) only contained I.A sequences, whereas the commercial product was a mixture of the four genotypes and the other two dried samples contained minor polymorphisms characteristic of different clusters. Five clonal Arthrospira strains, thought to be duplicates, showed the simultaneous presence of the two forms of the four diagnostic positions that distinguish subclusters genotype II.A and genotype II.B. This is likely to be caused by multiple copies of the rDNA operon, in a intermediate stage of homogenization between subcluster II.A and subcluster II.B. The high conservation of ITS sequences is in contrast with the assignment to four different species, the great morphological variability of the strains, and their wide geographic distribution.

Cyanobacterial Diversity in Natural and Artificial Microbial Mats of Lake Fryxell (McMurdo Dry Valleys, Antarctica): a Morphological and Molecular Approach

“…Since the ITS is less subject to selection pressure, it may accumulate more mutations than functional genes (39) and is therefore a variable marker. Consequently, it has been used successfully in several studies based on restriction fragment length polymorphism (49) or direct sequencing (3,7,13) to discriminate cyanobacterial strains at the intra-or interspecific level. In addition, it has proven to be useful in bacterial community studies (5).…”

“…The morphological diversity was assessed by light microscopy, and the genotypic diversity was studied by examining clone libraries and by performing denaturing gradient gel electrophoresis (DGGE) based on rRNA gene amplicons. The internal transcribed spacer (ITS) has proven to be useful for taxonomic studies of cyanobacterial cultures (3,7,13), as well as for bacterial community studies (5). Therefore, we retrieved ITS sequences from the cyanobacterial communities to complement the information obtained from the 16S rRNA gene.…”

Elucidation of the gas vesicle gene clusters in cyanobacteria of the genusArthrospira(Oscillatoriales, Cyanophyta) and correlation with ITS phylogeny

“…They also show a relatively low degree of genetic diversity based on several other, more discriminative, molecular markers (Beard et al, 1999;Scheldeman et al, 1999;Baurain et al, 2002;Manen & Falquet, 2002;Christiansen et al, 2008). The identical gene organization and the very similar sequence data for the gas vesicle gene cluster of several strains, suggest a particularly low degree of divergence among members of the genus Arthrospira.…”

“…Strains of ITS clusters I and II can be differentiated by 28 substitutions. Further subdivision was possible on the basis of a total of 16 substitutions that, depending on their positions in the gvp sequences, grouped the strains into four ITS subclusters, I.A, I.B, II.A and II.B., which are known from previous studies (Baurain et al, 2002).…”

“…Gas vacuoles, composed of numerous gas vesicles, are characteristically present, occurring throughout the cells of these organisms (Castenholz, 2001). Although several different species have been described, the members of this genus are highly related (Scheldeman et al, 1999;Baurain et al, 2002) and may thus all represent only one or two species. Arthrospira is found in tropical and semitropical regions (Vonshak & Tomaselli, 2000) and strains are mass-cultured industrially for their high nutritional values and therapeutic properties (Ciferri, 1983).…”