Abstract
Domoic acid (DA) is produced by almost half of the species belonging to the diatom genus Pseudo-nitzschia and causes amnesic shellfish poisoning (ASP). It is, therefore, important to investigate the diversity and toxin production of Pseudo-nitzschia species for ASP risk assessments. Between 2018 and 2020, seawater samples were collected from various sites around Aotearoa New Zealand, and 130 clonal isolates of Pseudo-nitzschia were established. Molecular phylogenetic analysis of partial large subunit ribosomal DNA and/or internal transcribed spacer regions revealed that the isolates were divided into 14 species (Pseudo-nitzschia americana, Pseudo-nitzschia arenysensis, Pseudo-nitzschia australis, Pseudo-nitzschia calliantha, Pseudo-nitzschia cuspidata, Pseudo-nitzschia delicatissima, Pseudo-nitzschia fraudulenta, Pseudo-nitzschia galaxiae, Pseudo-nitzschia hasleana, Pseudo-nitzschia multiseries, Pseudo-nitzschia multistriata, Pseudo-nitzschia plurisecta, Pseudo-nitzschia pungens, and Pseudo-nitzschia cf. subpacifica). The P. delicatissima and P. hasleana strains were further divided into two clades/subclades (I and II). Liquid chromatography-tandem mass spectrometry was used to assess the production of DA and DA isomers by 73 representative strains. The analyses revealed that two (P. australis and P. multiseries) of the 14 species produced DA as a primary analogue, along with several DA isomers. This study is the first geographical distribution record of P. arenysensis, P. cuspidata, P. galaxiae, and P. hasleana in New Zealand coastal waters.
Highlights
Genotype screening using molecular phylogenetic analysis based on the nuclearencoded ribosomal RNA gene, internal transcribed spacer (ITS) 1–5.8S
The screening revealed that the strains could be separated into 14 species: P. americana [number of strains (n) = 6], P. arenysensis (n = 7), P. australis (n = 14), P. calliantha (n = 3), P. cuspidata (n = 1), P. delicatissima (n = 28), P. fraudulenta (n = 13), P. galaxiae (n = 2), P. hasleana (n = 6), P. multiseries (n = 4), P. multistriata (n = 13), P. plurisecta (n = 1), P. pungens (n = 27), and
As the sequences of the strains of each species/clade/subclade had high levels of identity, selected representative sequences from each species/clade/subclade were used for the molecular phylogenetic analysis using the maximum likelihood (ML) and Bayesian inference (BI) methods
Summary
Multiseries) was identified as the causative species [1,2,3,4] It produced a biotoxin, domoic acid (DA) [2], which has been monitored in Aotearoa New Zealand shellfish since 1993 [5], and is currently the only DA analogue regulated in New Zealand [6,7]. As well as shellfish being tested, seawater samples are analysed to determine the presence and quantity of Pseudonitzschia cells, which bloom regularly in the coastal waters, to allow for risk assessments for the shellfish industry and regulators [10] These assessments aid managers in their harvesting decisions and help public health officials determine whether to post warnings for recreational harvesters of potential toxins in seafood
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