Effects of nocodazole and latrunculin B on locomotion of amoeboid cells of Rhizochromulina sp. strain B44 (Heterokontophyta, Dictyochophyceae).

Rhizochromulina is a genus of unicellular dictyochophycean algae (Heterokontophyta), comprising a single species R. marina and numerous strains. Recently, we described the first arctic rhizochromuline-Rhizochromulina sp. strain B44. Amoeboid cells of this algae are able to transform into flagellates, and this transition can be triggered by prolonged mechanical disturbance. Thin branching pseudopodia of the neighboring rhizochromuline cells fuse to form a meroplasmodium. The pseudopodia contain microtubules, but do not contain actin microfilaments; actin forms the cytoplasmic cytoskeleton and extends only to the bases of the pseudopodia. Microtubule-driven pseudopodia are characteristic to a plethora of eukaryotes, but the role of microtubular and actin cytoskeleton in locomotion of these organisms remains poorly understood. We conducted a series of experiments where amoeboid cells of Rhizochromulina sp. B44 were treated with either 10 µM nocodazole, 10 µM latrunculin B, or both drugs simultaneously. Cellular locomotion was captured on camera, tracked, and then analyzed with the help of the generalized additive mixed model. The obtained results indicate that both drugs, when applied separately, decrease the motility of the studied cells. Unexpectedly, the combined treatment had the opposite effect, as the cells became more motile. The analysis also revealed a non-linear pattern of relationship between motility of amoeboid cells of rhizochromulines and density of their population.