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Some diatoms of the genera Pseudo-nitzschia and Nitzschia produce the neurotoxin domoic acid (DA), a compound that caused amnesic shellfish poisoning (ASP) in humans just over 30 years ago (December 1987) in eastern Canada. This review covers new information since two previous reviews in 2012. Nitzschia bizertensis was subsequently discovered to be toxigenic in Tunisian waters. The known distribution of N. navis-varingica has expanded from Vietnam to Malaysia, Indonesia, the Philippines and Australia. Furthermore, 15 new species (and one new variety) of Pseudo-nitzschia have been discovered, bringing the total to 52. Seven new species were found to produce DA, bringing the total of toxigenic species to 26. We list all Pseudo-nitzschia species, their ability to produce DA, and show their global distribution. A consequence of the extended distribution and increased number of toxigenic species worldwide is that DA is now found more pervasively in the food web, contaminating new marine organisms (especially marine mammals), affecting their physiology and disrupting ecosystems. Recent findings highlight how zooplankton grazers can induce DA production in Pseudo-nitzschia and how bacteria interact with Pseudo-nitzschia. Since 2012, new discoveries have been reported on physiological controls of Pseudo-nitzschia growth and DA production, its sexual reproduction, and infection by an oomycete parasitoid. Many advances are the result of applying molecular approaches to discovering new species, and to understanding the population genetic structure of Pseudo-nitzschia and mechanisms used to cope with iron limitation. The availability of genomes from three Pseudo-nitzschia species, coupled with a comparative transcriptomic approach, has allowed advances in our understanding of the sexual reproduction of Pseudo-nitzschia, its signaling pathways, its interactions with bacteria, and genes involved in iron and vitamin B 12 and B 7 metabolism. Although there have been no new confirmed cases of ASP since 1987 because of monitoring efforts, new blooms have occurred. A massive toxic Pseudo-nitzschia bloom affected the entire west coast of North America during 2015-2016, and was linked to a 'warm blob' of ocean water. Other smaller toxic blooms occurred in the Gulf of Mexico and east coast of North America. Knowledge gaps remain, including how and why DA and its isomers are produced, the world distribution of potentially toxigenic Nitzschia species, the prevalence of DA isomers, and molecular markers to discriminate between toxigenic and non-toxigenic species and to discover sexually reproducing populations in the field., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The commercial demand for domoic acid (DA), the phycotoxin responsible for Amnesic Shellfish Poisoning, is currently met by extraction from a diminishing supply of stockpiled contaminated mussels (Mytilus edulis). As this supply becomes scarce, a more reliable source is needed. Purification of the toxin from an algal source would be easier and more economical than from shellfish tissue if algal growth and yield of toxin were maximized. This project was initiated to determine if DA could be produced using large-scale semi-continuous algal cultures, which should reduce labour and shorten the time required for biomass production. Pseudo-nitzschia multiseries was grown in 300-L fibreglass photobioreactors called a Brite-Box™. The effect of temperature and nutrient depletion on the yield of DA by P. multiseries was examined. A decline in maximum cell number without a substantial increase in cellular DA was associated with increased temperature. Maximum total cellular DA (8.8 pg cell -1 ) was achieved at 20 °C. Semi-continuous culture of P. multiseries is accompanied by increasing amounts of DA lost to the medium. The process was deemed to be feasible for growing P. multiseries but methods to recover this extracellular DA are necessary for this process to be economical., (Crown Copyright © 2018. Published by Elsevier B.V. All rights reserved.)