Morphology and phylogeny of a non-toxic invasive Cylindrospermopsis raciborskii from a Mediterranean Lake

Abstract

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.

Molecular separation of two long taxonomically debated cyanobacterial genera Cylindrospermopsis and Raphidiopsis (Nostocales) based on the ITS-L phylogeny

“…1). Previous efforts to identify genetic markers that can distinguish between genera Cylindrospermopsis and Raphidiopsis have been unsatisfactory (Gugger et al, 2005;Stucken et al, 2009;Alster et al, 2010). In the present study, based on the ITS-L alignment, a fragment of 7 bp (RAGAAACT) in ITS-L labeled in the box was conserved for the Raphidiopsis strains but was more variable in the Cylindrospermopsis strains (Fig.…”

“…They mainly differ in terms of heterocytes, which are absent in Raphidiopsis strains. However, distinction between these two genera is difficult when heterocytes are not shown in Cylindrospermopsis strains (Li et al, 2001;Moustaka-Gouni et al, 2009;Alster et al, 2010). The coexistance of Cylindrospermopsis and Raphidiopsis in the same waters has been widely reported (McGregor and Fabbro, 2000;Moustaka-Gouni et al, 2009;Wu et al, 2011).…”

“…In previous studies, genetic markers have been explored to distinguish between genera Cylindrospermopsis and Raphidiopsis, but the results are always unsatisfactory (Gugger et al, 2005;Stucken et al, 2009;Alster et al, 2010). Wu et al (2011) concatenated a set of seven gene loci sequences (i.e., psbA, 16S rDNA, rbcL, rbcS, rpoC1, cpcB, and ITS1 between 16S and 23S rDNA) but failed to distinguish Cylindrospermopsis and Raphidiopsis.…”

“…This genus morphologically resembles another cyanobacterial bloom-forming genus, Raphidiopsis Fritsch et Rich (Li et al, 2001;Moustaka-Gouni et al, 2009;Alster et al, 2010;Wu et al, 2011;Komá rek, 2013). These two genera mainly differ in terms of heterocytes, which are absent in Raphidiopsis.…”

“…These two heterocytous cyanobacterial genera Raphidiopsis and Cylindrospermopsis, are difficult to distinguish, especially in cases where heterocytes are not present in Cylindrospermopsis strains (Li et al, 2001;Moustaka-Gouni et al, 2009;Alster et al, 2010). They share similar ecological niches, in which Raphidiopsis species have been found to co-occur with Cylindrospermopsis raciborskii (Woloszyń ska) Seenayya et Subba Raju in a range of waters (Moustaka-Gouni et al, 2009;Wu et al, 2011;Hill, 1970).…”