Bolidomonas

Introduction

The class Bolidophyceae includes a single genus Bolidomonas and two species (Bolidomonas pacifica and B. mediterranea) described from marine waters.

The Bolidophyceae was established by Guillou et al. (1999), as a new class of picoplankton isolated from both the equatorial Pacific and the Mediterranean Sea. One genus, Bolidomonas, and two species, Bolidomonas pacifica and B. mediterranea, have been described. Guillou et al. also proposed a subspecies of B. pacifica: B. pacifica var. eleuthra.

Bolidomonas pacifica swims differently than B. mediterranea, and their flagella are oriented differently with respect to one another (Fig. 1). B. pacifica swims in a consistently straight pattern, and the flagella are oriented at a 90° angle with respect to one another. In contrast, B. mediterranea demonstrates frequent changes in swimming direction, and flagella are oriented at a 180° angle with respect to one another.

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Figure 1: The two flagella are oriented differently to one another in Bolidomonas mediterranea and B. pacifica.  © J. Craig Bailey

Characteristics

• Unicellular, picoplanktonic golden-brown colored    photosynthetic eukaryotes; flagellate and rapidly motile.
• Cells are naked, with no walls, and are spherical to ovoid in shape with cell diameters of ~1.2 µm.
• Two unequal, laterally inserted flagella are present. The long flagellum is ~4-7 µm in length, with mastigonemes (tubular hairs) and three terminal filaments; lateral filaments are absent. The short flagellum is ~0.9-2.2 µm in length, naked and acronematic.
  
• Single chloroplast with a distinct ring genophore and girdle lamellae; photosynthetic lamella composed of three adpressed thylakoids; eyespot unknown.
  
• Photosynthetic pigments are similar to those of diatoms and include chlorophylls a and c, fucoxanthin, diadinoxanthin, diatoxanthin, and beta carotene.
  
• Part of the picoplankton community, with cell diameter of ~1.2 µm.
  
• Individual cells possess a single mitochondrion with tubular cristae and a single Golgi apparatus which is located near the basal bodies.
  
• Reduced flagellar root system consisting only of two basal bodies; transitional helix absent; two transitional plates present, with lower plate thinner and more difficult to observe than upper plate.
  
• Thought to undergo unusual flagellar duplication, as the long flagellum may be incorporated by an invagination of the cell membrane and emerges at the opposite side of its normal insertion.
  
• Ploidy level of motile cels, sexual reproduction, and the existence of siliceous forms in the life cycle are as yet unknown.
  
• Described from the equatorial Pacific Ocean and the Mediterranean Sea; found in both mesotrophic and oligotrophic waters.

Relationship of Bolidophytes to other Stramenopiles

Phylogenetic analyses of nuclear 18S rRNA and plastid-encoded rbcL sequences indicate – with robust support – that Bolidomonas spp. are sister to the diatoms (Bacillariophyceae).

Other Names for Bolidomonas

• Bolidophytes