Genetic variation in bloom-forming ichthyotoxicPseudochattonellaspecies (Dictyochophyceae, Heterokonta) using nuclear, mitochondrial and plastid DNA sequence data

Abstract

This study reports on genetic variation within bloom-forming ichthyotoxic algae in the genus Pseudochattonella. One aim of this study was to search for further molecular evidence to separate the two species, Pseudochattonella farcimen and Pseudochattonella verruculosa using DNA sequences with different levels of variability and from three different cell compartments (the nucleus, mitochondria and plastids). Secondly, the genetic variability among Pseudochattonella strains within a bloom and between blooms in successive years in the Skagerrak was assessed. We also aimed to determine the identity of Pseudochattonella strains from two other geographical locations. Using molecular data (LSU and SSU rDNA, rbcL, psbA and cox1) our results demonstrate clear delineation of the two Pseudochattonella species. The barcoding marker cox1 was well suited to separating the two closely related dictyochophyte species. Pseudochattonella strains from Germany and New Zealand were almost identical in five DNA regions to the P. verruculosa reference strain, NIES 670, suggesting that blooms in these geographical areas consisted of P. verruculosa. Comparison of DNA sequences from P. farcimen-strains within a bloom and between blooms in the Skagerrak in 2001 and 2006 suggests the existence of a homogeneous and stable population over a 5-year period. Intraspecific and intraclonal variations in the ITS rDNA were revealed within both P. farcimen and P. verruculosa eliminating ITS rDNA as a marker to differentiate among individuals and/or populations of Pseudochattonella.

The fish-killing dictyochophyte Pseudochattonella farcimen: Adaptations leading to bloom formation during early spring in Scandinavian waters

“…in Scandinavian waters takes place during February and March, where the water temperatures ranges from 1 to 5 8C (Andersen, 2008;Naustvoll et al, 2002;Riisberg and Edvardsen, 2008) and April to May where the water temperature ranges from 5 to 10 8C (Andersen, 2008). However, the Danish blooms occurring in 2009 and 2011 took place in February and March when the water temperature was around 1-2 8C and at a salinity around 17 psu.…”

The use of partialcox1,rbcL and LSU rDNA sequences for phylogenetics and species identification within theNitzschia paleaspecies complex (Bacillariophyceae)

“…For such taxa the effect is that direct sequencing currently yields poor quality or unreadable sequences, which will undermine the use of ITS regions for barcoding until the predominant copy can be reliably and easily sequenced without cloning. Riisberg & Edvardsen (2008) also found ITS to be less suitable than other markers in the dictyochophyte Pseudochattonella, both because of intragenomic variation (making cloning essential) and because ITS sequences from P. farcimen Eikrem, Edvardsen & Throndsen and P. verruculosa (Y. Hara & Chihara) Eikrem did not assort according to species, nor even according to individual isolate. In contrast, although LSU (Beszteri et al, 2005) and even SSU rDNA (Alverson & Kolnick, 2005) can also display intragenomic variation in diatoms, this seems rarely to cause any practical difficulties for direct sequencing (e.g.…”

“…They found that cox1 performed better than the other genes tested (SSU and ITS rDNA, rbcL) because it (1) could be amplified and directly sequenced in most cases using a single pair of primers, (2) gave unambiguous reads (reflecting the rarity of intragenomic variants) and (3), for a span of 624 base-pairs (bp), gave divergences of c. 20 bp between isolates that were thought to represent sister species. Cox1 has also been found to be an effective identifier in Pseudochattonella (Riisberg & Edvardsen, 2008) and Fucus (Kucera & Saunders, 2008), which represent two other major groups of heterokonts (dictyochophytes and brown algae, respectively), and in the red algae (e.g. Le Gall & Saunders, 2010).…”

Toxicity of the ichthyotoxic marine flagellate Pseudochattonella (Dictyochophyceae, Heterokonta) assessed by six bioassays

“…verruculosa occurred in April-May 1998 (Aure et al, 2001). Pseudochattonella has since then been held responsible for several fish mortality events in the North Sea and Skagerrak (Lu and Gö bel, 2000;Aure et al, 2001;Backe-Hansen et al, 2001;Edvardsen et al, 2007;Riisberg and Edvardsen, 2008). Since 2001, the blooms in Skagerrak and Kattegat have developed earlier (January-March) and in colder water (2-6 8C) (Edvardsen et al, 2007;Riisberg and Edvardsen, 2008) than previous blooms in European and Japanese waters.…”

“…Pseudochattonella has since then been held responsible for several fish mortality events in the North Sea and Skagerrak (Lu and Gö bel, 2000;Aure et al, 2001;Backe-Hansen et al, 2001;Edvardsen et al, 2007;Riisberg and Edvardsen, 2008). Since 2001, the blooms in Skagerrak and Kattegat have developed earlier (January-March) and in colder water (2-6 8C) (Edvardsen et al, 2007;Riisberg and Edvardsen, 2008) than previous blooms in European and Japanese waters. Strains isolated from the Skagerrak bloom in 2001 and from the Skagerrak in 2006 were found to belong to a new species, Pseudochattonella farcimen (Eikrem, Edvardsen et Throndsen) Eikrem, Edvardsen et Throndsen which differ both genetically and morphologically from P. verruculosa isolates from Japan and elsewhere (Edvardsen et al, 2007;Riisberg and Edvardsen, 2008;Eikrem et al, 2009).…”