Diatoms are unicellular algae distributed throughout marine and freshwater environments. They play an important role in global carbon cycles as they are estimated to be responsible for about 20% of global primary productivity. Diatoms are members of the heterokont algae and first appeared in the fossil record about 180 million years ago. There are three major classes of diatoms, traditionally distinguished by morphology: the Coscinodiscophyceae and Mediophyceae, characterized by radial or bi-/multi-polar symmetry, and the Bacillariophyceae, also known as the pennates, characterized by bilateral symmetry. The pennates are the more derived form, with their first appearance in the fossil record in the Late Cretaceous.
Pseudo-nitzschia is a cosmopolitan genus of pennate diatoms that can become very abundant in the plankton. Pseudo-nitzschia species commonly bloom in coastal waters and in the large-scale open ocean iron fertilization experiments, emphasizing the global importance of this genus. At least 12 of the 30 described species of Pseudo-nitzschia can produce the neurotoxin domoic acid (DA), which is biomagnified through the food web. Shellfish or finfish that have fed upon Pseudo-nitzschia cells producing DA can concentrate the toxin in their tissues. Consumption of high levels of DA-contaminated seafood is lethal to birds, marine mammals, and humans. Toxic blooms of Pseudo-nitzschia result in major economic losses due to the closure of fisheries. Pseudo-nitzschia multiseries has been detected in many estuaries and coastal regions around the world and is a known DA-producing species. The strain chosen for sequencing, CLN-47, produced DA in the laboratory when growth was arrested by depletion of nutrients such as silicate or phosphate or when cells are grown exponentially on urea as a sole nitrogen source.
Pseudo-nitzschia multiseries CLN-47 was obtained from Stephen Bates and Claude Leger of Fisheries Oceans Canada. The strain is the product of a cross between two field isolates: CL-147 (isolated from Caribou Harbor, Nova Scotia, Canada) and CL-191 (isolated from Deadman’s Harbor, Bay of Fundy, Canada).