Cylindrospermopsin and Saxitoxin Synthetase Genes in Cylindrospermopsis raciborskii Strains from Brazilian Freshwater

Abstract

The Cylindrospermopsis raciborskii population from Brazilian freshwater is known to produce saxitoxin derivatives (STX), while cylindrospermopsin (CYN), which is commonly detected in isolates from Australia and Asia continents, has thus far not been detected in South American strains. However, during the investigation for the presence of cyrA, cyrB, cyrC and cyrJ CYN synthetase genes in the genomes of four laboratory-cultured C. raciborskii Brazilian strains, the almost complete cyrA gene sequences were obtained for all strains, while cyrB and cyrC gene fragments were observed in two strains. These nucleotide sequences were translated into amino acids, and the predicted protein functions and domains confirmed their identity as CYN synthetase genes. Attempts to PCR amplify cyrJ gene fragments from the four strains were unsuccessful. Phylogenetic analysis grouped the nucleotide sequences together with their homologues found in known CYN synthetase clusters of C. raciborskii strains with high bootstrap support. In addition, fragments of sxtA, sxtB and sxtI genes involved in STX production were also obtained. Extensive LC-MS analyses were unable to detect CYN in the cultured strains, whereas the production of STX and its analogues was confirmed in CENA302, CENA305 and T3. To our knowledge, this is the first study reporting the presence of cyr genes in South American strains of C. raciborskii and the presence of sxt and cyr genes in a single C. raciborskii strain. This discovery suggests a shift in the type of cyanotoxin production over time of South American strains of C. raciborskii and contributes to the reconstruction of the evolutionary history and diversification of cyanobacterial toxins.

Sporadic Distribution and Distinctive Variations of Cylindrospermopsin Genes in Cyanobacterial Strains and Environmental Samples from Chinese Freshwater Bodies

“…However, Cylindrospermopsis-like cyr fragments except cyrJ were detected in Cylindrospermopsis strains from Brazil and water samples from Florida (34,36). The Brazilian C. raciborskii cyDB-1 showed the presence of both cyr genes and CYNs and thus provides strong evidence for the distribution of CYN-producing Cylindrospermopsis in the American continent.…”

“…CYN-producing Cylindrospermopsis from Australia and Asia have been reported, whereas Cylindrospermopsis strains isolated from Europe and America are incapable of CYN production (32)(33)(34)(35)(36). However, no conclusion can be drawn about the geographic distribution of the CYN-producing genotype of Cylindrospermopsis before additional samples from each continent are investigated by molecular and chemical methods.…”

Variability in the sxt Gene Clusters of PSP Toxin Producing Aphanizomenon gracile Strains from Norway, Spain, Germany and North America

“…SxtI has also been detected in the non PSP toxin producing C . raciborskii strain CENA 303 [7], although only a 589 bp long section was investigated by Hoff-Risettii et al [7]. The sxtI gene is therefore most likely not suitable as a selective marker gene for the detection of PSP toxin producers.…”

Molecular Verification of Bloom-forming Aphanizomenon flos-aquae and Their Secondary Metabolites in the Nakdong River

“…In contrast, sxtI has been detected only in STX-producing strains to date in genus Aphanizomenon with exception in genus Cylindrospermopsis and Lyngbya [42,43]; therefore, it was suggested as a marker for verification of STX-producing Aphanizomenon strains [11]. To date, various filamentous cyanobacterial species including A. gracile , Cuspidothrix issatschenkoi , C. raciborskii , D. circinale , and Geitlerinema spp.…”