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

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.