A Biosystematics Study of Microcystis (Cyanobacteria), A Bloom-Forming Cyanobacterium from Aras Reservoir (North-West Iran)

Today, harmful cyanobacerial bloom is considered as a main problem in freshwater ecosystems all over the world. The Microcystis is an important genus in cyanobacteria composed of about 23 species. This genusforms various shaped colonies including spherical or oblong cells which whole colony is surrounded by a mucilage sheath. Many populations and species of the genus produce sever blooms and often toxins in eutrophic freshwaters. The genus Microcystis has been defined based on morphological, morphometrical and genetical criteria, however, its classification under the genus level is still indistinct and presence of traditional morphological species within the genus is doubtful. Therefore, determining of the natural diversity under the genus level in Microcystis has a crucial importance. The purpose of this study was to determine the species of Microcystis in Aras reservoir. The samples were collected from 6 sampling sites on 18 August 2013. Morphological and morphometrical studies of Microcystis was carried out by Nikon 50i microscope equipped with Nikon DSFi camera and Nikon monitor with length measurment software. Principal Component Analysis (PCA) and two-way Unweighted Pair Group Method with Arithmetic Mean (UPGMA) by PAleontological STatistics (PAST) version 3.04 were performed to determine biosystematics variations between Microcystis populations. The results indicated that Microcystis from Aras reservoir was composed of two distinct groups based on the shape and size of cells, colony form, presence and absence of gelatinous sheath around the colonies, etc).These two groups may be considered as two morphospecies of M. botrys which are separated due to different ecological factors.