Phylogenetic analyses of Bolidophyceae (Heterokontophyta) using rbcL gene sequences support their sister group relationship to diatoms

Nearly complete (> 97%) chloroplast-encoded rbcL gene sequences were determined for Bolidomonas mediterranea from the eastern Mediterranean Sea and two strains of B. pacifica var. eleuthera from the equatorial Pacific Ocean. The three sequences were added to an rbcL data matrix comprising 45 taxa representing 11 of the 12 recognized classes of Hetero-kontophyta. Phylogenetic analyses that used maximum parsimony (MP), maximum likelihood (ML) and neighbour-joining (NJ) algorithms supported their sister group relationship to the Bacillariophyceae. Centric and pennate diatoms and the three novel Bolidomonas rbcL sequences share a two-amino-acid insertion at position 1336, relative to the homologous position in the complete sequence for the centric diatom Odontella sinensis. This synapomorphic character state further supports a common evolutionary history of bolidophyceans and diatoms. Chloroplast- and nuclear-encoded molecular markers thus favour the idea that the ancestor of the diatoms possessed two flagella. The Rubisco spacer region was also determined. Sequences showed no differences among the strains of B. pacifica examined but these differed by 25% from B. mediterranea. New observations are presented on the distribution of Bolidomonas and the phylogenetic relationships of bolidomonads and other heterokont algae are discussed.