Alkaline phosphatase (AP) is a key enzyme that enables marine phytoplankton to scavenge phosphorus (P) from dissolved organic phosphorus (DOP) when inorganic phosphate is scarce in the ocean. Yet how the AP gene has evolved in phytoplankton, particularly dinoflagellates, is poorly understood. We sequenced full-length AP genes and corresponding complementary DNA (cDNA) from 15 strains (10 species), representing 4 classes of the core dinoflagellate lineage, Gymnodiniales, Prorocentrales, Suessiales and Gonyaulacales. Dinoflagellate AP gene sequences exhibited high variability, containing variable introns, pseudogenes, single nucleotide polymorphisms and consequent variations in amino acid sequence, indicative of gene duplication events and consistent with the “birth-and-death” model of gene evolution. Further sequence comparison showed that dinoflagellate APs likely belong to an atypical type AP (PhoAaty), which shares conserved motifs with counterparts in marine bacteria, cyanobacteria, green algae, haptophytes and stramenopiles. Phylogenetic analysis suggested that PhoAaty probably originated from an ancestral gene in bacteria and evolved divergently in marine phytoplankton. Because variations in AP amino acid sequences may lead to differential subcellular localization and potentially different metal ion requirements, the multiple types of APs in algae may have resulted from selection for diversifying strategies to utilize DOP in the P variable marine environment.

Hemidiscus cuneiformis, type of the family Hemidiscaceae, is a diatom with a distinctive semi-circular shape in valve view. A strain of H. cuneiformis was established from the coastal region of the tropical southwestern Atlantic Ocean off Brazil. Cells of this strain showed semi-circular to asymmetrically elliptical valves, indicating morphological plasticity. In the small subunit (SSU) rDNA phylogeny, the type species of Hemidiscus branched between two clades of Actinocyclus, one of which was a sister group, the other in a basal position. Beyond cell shape, there are no significant morphological differences between Hemidiscus and Actinocyclus. We propose the transfer of H. cuneiformis and H. kanayanus into Actinocyclus. The family Hemidiscaceae remains for the genus Actinocyclus.

Climacodium frauenfeldianum is a planktonic chain-forming diatom able to proliferate in severely oligotrophic waters of tropical seas. In this study, a strain of C. frauenfeldianum, the type of Climacodium, was established in culture from the tropical southwestern Atlantic Ocean off Brazil. SEM observations showed weakly silicified cells, without visible surface sculpturing. In the small subunit (SSU) rRNA and ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (rbcL) gene phylogeny, C. frauenfeldianum clustered with sequences of Bellerochea malleus (the type of Bellerochea) and B. horologicalis. Contrary to previous classifications that placed Climacodium in the Hemiaulaceae, Climacodium and Bellerochea should be placed in the same family, Bellerocheaceae. The species Bellerochea yucatanensis needs further research because sequences of the single strain available clustered with the genus Lithodesmioides. In adaptation to the oligotrophic open ocean environment, C. frauenfeldianum seems to have evolved an appearance closer to Hemiaulus, i.e. very lightly silicified flat cells with long elevations, and with diazotrophic cyanobionts.

Climate change disrupts the phenology of marginal coral reefs, yet our understanding of how these coral populations undergo physiological range shifts in response to seasonal disturbances...