Comparative study of the life cycles of Alexandrium tamutum and Alexandrium minutum (Gonyaulacales, Dinophyceae) in culture¹

Abstract

The microalgal genus Alexandrium includes species known to produce paralytic shellfish poisoning (PSP). Due to the importance of discriminating between HAB-forming species, we compared the undescribed life-cycle pattern of Alexandrium tamutum Montresor, Beran et U. John and of its toxic relative Alexandrium minutum Halim. Sexual stages, asexual and sexual division, mating type, and nuclear morphology were studied in both species. Sexual cysts are known to be morphologically identical. However, the relative size of the U-shaped nucleus may be used to differentiate between the cysts of these species since DNA packaging in the resting cysts was lower in A. tamutum than in A. minutum, species in which the planozygote nucleus was reduced to half its volume prior to encystment. The dormancy period of the cysts was <20 d for A. tamutum, but longer than 1 month for A. minutum. In both species, cyst appearance needed to be explained by the existence of more than two sexual types (+ ⁄ -), which indicates a complex heterothallic mating type. However, planozygotes of both species may divide instead of encysting. This characteristic was used for nutritional and heritage studies. Isolated planozygotes of both species encysted in larger percentages in medium deficient in both nitrates and phosphates (L ⁄ 15) than in medium without phosphates added (L-P), a medium in which most planozygotes neither divide nor encyst. Parental strains of A. minutum with and without the ventral pore formed planozygotes and, later, offspring with the ventral pore, although apparently smaller than usual. A synchronization-flow cytometry method for discriminating diploids formed by sexual fusion (planozygotes) from cells with 2C DNA content resulting from self-duplication of DNA (dividing cells) was described. The results indicated that the maximum percentage of A. minutum planozygotes (20%) was achieved only 3 to 5 d after crossing the parental strains, and that light might not be needed for the sexual fusion and formation of planozygotes.

The Life History and Cell Cycle of Kryptoperidinium foliaceum, A Dinoflagellate with Two Eukaryotic Nuclei

“…These estimates were based on a comparison with the DNA content of the dinoflagellate species Alexandrium minutum, whose DNA content was previously shown to be almost identical to that of our K. foliaceum strain (Figueroa et al 2007). Our results were obtained by a different methodology than Kite et al (1988), which may explain why these authors reported higher DNA content values for K. foliaceum than determined in this study.…”

“…Study of the dinoflagellate and endosymbiont cell cycle by flow cytometry: DNA analyses were done following the method described by Figueroa et al (2006Figueroa et al ( , 2007. Culture aliquots of 45 ml were fixed in 1% paraformaldehyde for 10 min at room temperature and washed with PBS Life History of Kryptoperidinium foliaceum (Sigma-Aldrich, USA, #P4417), pH 7.…”

Unexpected Genetic Diversity among and within Populations of the Toxic Dinoflagellate Alexandrium catenella as Revealed by Nuclear Microsatellite Markers

“…The fusion of compatible gametes from the same clone (selfing, homothallism) results in a lack of effective recombination, whereas the fusion of gametes from different clones (outcrossing, heterothallism) may result in recombination. Therefore, A. catenella from Thau Lagoon may ex- (13), and Alexandrium peruvianum (12), whose sexual stages have been well described. Such knowledge is essential for understanding the origin and occurrence of toxic events due to A. catenella.…”

Life cycle studies of the red tide dinoflagellate species complex Alexandrium tamarense

“…The initial IFCB analysis of this sample Other flow cytometry studies of dinoflagellate sexual conjugation have not detected premeiotic replication (Parrow, Burkholder et al 2002;Parrow and Burkholder 2003;Figueroa, Garces et al 2007;Figueroa, Garcés et al 2010) and some have suggested that dinoflagellates may undergo a unique meiosis that does not require premeiotic replication (Beam and Himes 1980;Kita, Fukuyo et al 1993;Elbrachter 2003;Parrow and Burkholder 2003). The notion that dinoflagellate could carry out a unique dinoflagellate meiosis stems from pioneering genetic studies of the saprobic dinoflagellate, Crypthecodinium cohnii, which showed that these cells only rarely yield tetratype sexual progeny (Beam, Himes et al 1977;Beam and Himes 1980), and also by a lack of reports of chiasmata between dinoflagellate chromosomes.…”