Molecular phylogeny suggests the affinity of the planktonic diatoms Climacodium and Bellerochea (Lithodesmiales, Mediophyceae)

Abstract

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.

Keywords:

• Bacillariophyceae
• Bacillariophyta
• DNA barcoding
• molecular phylogenetics
• phylogeny

ORCID

Fernando Gómez http://orcid.org/0000-0002-5886-3488

Lu Wang http://orcid.org/0000-0003-4559-3607

Senjie Lin http://orcid.org/0000-0001-8831-6111

Additional information

Funding

This work was supported by the Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tecnologico [grant number BJT 370646/2013–14 to F.G]; MEL Senior Fellowship at Xiamen University, China [grant number MELRS1711 to F.G.]; Chinese Visiting Scholarship Council and the National Natural Science Foundation of China [grant number #41330959 to L.W. and S.L.]. This is contribution #2018303 of MEL, Xiamen University.