Fundamentals of Microbiology

1.3.1.1 Flagella and Motility in eukaryotes

Many eukaryotic microorganisms also move by means of flagella and cilia. Cilia are shorter than flagella but structurally similar. Eukaryotic flagella are long, flexible structures which move in a whiplash fashion. They have a complex structure consisting of a number of microtubules. Both consist of 9 fused pairs of protein microtubules (tubulin) with side arms of the motor molecule dynein that originate from a centriole. These form a ring around an inner central pair of microtubules that arise from a plate near the cell surface. The arrangement of microtubules is known as a 2X9+2 arrangement. This complex of microtubules is surrounded by a sheath continuous with the cytoplasmic membrane. Each microtubule is composed of protein, tubulin, with subunits arranges in a helical fashion along the tubule axis. Eukaryotic microbes move at a rate of 30 to 250 µm per second. In contrast to flagella, cilia are more in numbers, more or less rigid and beat in a coordinated fashion called metachronal rhythm.

Amoeba and slime moulds do not possess flagella or cilia but show a movement produced by their cytoplasm, called cytoplasmic streaming. Such cytoplasmic flow produces projections, called pseudopodia which cause the cell to move.