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The cylindrospermopsin (CYN)-producing cyanobacterium Aphanizomenon ovalisporum is currently known from the Mediterranean area of Europe and the Middle East and from North America and Australia. Aphanizomenon ovalisporum was observed for the first time in Lake Kinneret (Sea of Galilee, Israel) in 1994. It appeared with an exceptional bloom and has persisted since then. To gain further insight into biodiversity and chemotype composition of this invasive cyanobacterium, we isolated, cultured and analyzed six putative A. ovalisporum strains from Lake Kinneret in 2010. In a polyphasic approach, the strains were investigated for their morphology and phylogeny (based on 16S rRNA gene and PC-IGS) as well as for CYN production [by enzyme-linked immunosorbent assay (ELISA) and LC-MS] and the presence of four fragments of the CYN-encoding gene cluster (aoaA/cyrA, aoaB/cyrB, aoaC/cyrC and cyrJ). Two isolated strains were assigned to A. ovalisporum, whereas four strains were identified as Anabaena bergii. Unlike previous reports of toxic A. ovalisporum from Lake Kinneret, all strains isolated in this study tested negative for CYN by ELISA and LC-MS. All strains contained aoaA/cyrA, aoaB/cyrB and aoaC/cyrC fragments of the CYN gene cluster. The cyrJ fragment was not detected in any of the isolated strains. This is the first report describing non-CYN-producing A. ovalisporum strains and the presence of the cyanobacterium A. bergii in L. Kinneret. [ABSTRACT FROM AUTHOR]

A member of the cyanobacterial genus Cylindrospermopsis Seenayya et Subba Raju (Order Nostocales) invaded Lake Kinneret (Israel) in 1998. Since then it has been found in the water column nearly every summer, initially at low concentrations, but since 2003 it formed major summer blooms. The goals of the present study were to identify the invading species based on its morphology, annual life cycle, toxicity, genetic markers, and its phylogeny, and to examine its range of morphological variability. Cell counts, allometric measurements, and filament morphology were determined on samples collected weekly from a mid-lake station throughout 2005. Akinetes, heterocytes, filament end types, cellular contents, and the annual cycle of filament morphology were described, supporting the identification as Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju. Cells had many small, few large, or no dark granules presumed to be polyphosphate bodies. Filament fragmentation was observed and six types of filament ends were described. Sequence analysis of the 16S rRNA and ITS-L DNA fragment from a laboratory isolate of the cyanobacterium also confirmed the identification as C. raciborskii. Biomass of this species collected from Lake Kinneret during a bloom did not show toxicity in Artemia bioassays, and the toxin cylindrospermopsin was not detected in a methanolic extract of the isolate. Genetic examination indicated that C. raciborskii from Lake Kinneret lacked the cyrJ component of the cylindrospermopsin synthase cluster and, thereby, was incapable of producing the toxin. Due to the morphological plasticity of this species, the identification of C. raciborskii from Lake Kinneret was not straight forward and required taking multiple approaches, including microscopic observations over a full annual cycle, culture isolation, and molecular taxonomy. [ABSTRACT FROM AUTHOR]