Abstract

Soumaya El Herry , Hichem Nasri , and Noureddine Bouaïcha

The toxic potential, morphological characteristics and sequences of the 16S rRNA gene, and restriction fragment length polymorphisms (RFLPs) of the amplified 16S-23S rDNA internal transcribed spacer (ITS) regions were investigated in three Microcystis morphospecies (MCYS-LB01, -LB02 and -LB03) isolated from Lebna dam in Tunisia, and compared to the reference strain Microcystis aeruginosa PCC 7806 and different known Microcystis species described in the literature. Based on their morphology, morphospecies MCYS-LB01 and -LB02 were assigned to Microcystis aeruginosa and morphospecies MCYS -LB03 to Microcystis wesenbergii. The phylogenic tree based on 16S rDNA sequences showed that these three morphospecies are indistinguishable from each other, from the reference strain PCC 7806 and from many other known Microcystis species and, therefore, this tree did not necessarily correlate to the distinctions between morphospecies. Furthermore, when using PCR amplification and restriction fragment length polymorphism (RFLP) analysis of the 16S-23S rRNA spacer region of these three morphospecies of Microcystis, a similar pattern type was obtained, even though they had been assigned to two distinct morphospecies on the basis of their morphological characteristics. This implies that some of the morphological distinctions between the Microcystis morphospecies isolated from the same reservoir must be viewed as intraspecific or phenotypic variations.