Expression of the nodularin synthetase genes in the Baltic Sea bloom-former cyanobacterium Nodularia spumigena strain AV1

Abstract

Cyanobacterial blooms in the Baltic Sea are a common phenomenon and are formed by the heterocystous, filamentous species Nodularia spumigena. The toxicity of these blooms is attributed to the hepatotoxin nodularin, produced by N. spumigena. Little is known regarding the regulatory mechanisms or environmental signaling that control nodularin production. Here we report the characterization of the transcriptional expression pattern of the nodularin synthetase gene cluster (nda) during phosphate depletion, and nitrogen supplementation. Real-time PCR analysis of these genes revealed that while cells continuously expressed the nda cluster, the expression of all nda genes increased when cells were subjected to phosphate depletion, and decreased in the presence of ammonium. In contrast to the shifts in expression, the intracellular and extracellular nodularin concentrations did not vary significantly during the treatments.

Toxin-producing cyanobacterium Nodularia spumigena, potential competitors and grazers: testing mechanisms of reciprocal interactions

“…The latter is supported by findings of Møgelhøj et al (2006) and Suikkanen et al (2006), who found no evidence for pure nodularin having allelopathic properties against Rhodomonas sp. Also, Jonasson et al (2008) suggested that nodularin is not a secondary metabolite, but an important primary intracellular nitrogen compound, because N. spumigena cells continuously express the nodularin synthetase genes and maintain a threshold level of nodularin in cells. This view about a physiological role of nodularin is supported by the positive relationship between exponential growth and nodularin cellular concentration in monocultures (Lehtimäki et al 1994).…”

“…Alternatively, copepods could have caused changes in nutrient conditions, potentially affecting nodularin production. Indeed, Jonasson et al (2008) found that the expression of nodularin synthetase genes decreases in the presence of ammonium. In our experiments, all nutrients were supplied at saturating levels at the start of each experiment, which is indicated by the constant growth rate in Tetraselmis suecica (Fig.…”

“…Nodularin is a predominantly intracellular hepatotoxin that inhibits protein phosphatases in eukaryotic cells (MacKintosh et al 1990). While abiotic environmental factors affecting nodularin production have been studied rather extensively using cultures (Lehtimäki et al 1994, Jonasson et al 2008, factors affecting the toxin production and its ecological role are much less understood. Allelopathic responses of phytoplankton to N. spumigena, its cell-free filtrate and pure nodularin have been studied experimentally in algal cultures (Suikkanen et al 2004, Møgelhøj et al 2006.…”

Development of a Chip Assay and Quantitative PCR for Detecting Microcystin Synthetase E Gene Expression

“…However, in Lake Agawam, toxic Anabaena was not detected. Previously the qPCR assay for the ndaF gene of Nodularia spumigena was used to study gene expression changes in response to nutrient levels in Baltic Sea samples (15). The chip assay, although not quantitative, can be used to simultaneously identify all the main microcystin and nodularin producers present, expediting the analysis of large sample sets.…”

“…However, few studies are available in which RNA was used for identification of microcystin producers in natural environments by PCR (8,11). Expression of biosynthesis genes of nodularin, a toxin resembling microcystin but produced solely by Nodularia spumigena, was detected by qPCR in Baltic Sea samples (15).…”