The Amoeba
Hartmannella veriformis

Hartmannella belongs to the so-called limax - "slug-like" - amoebae, ~30 µm long and 6 µm wide. Amoeboid movement involves the formation of pseudopodia ("false feet"). Hartmannella is characteristically monopodial ("single foot"). The advancing end of the pseudopodium is called the hyaline cap. There is still some debate on how pseudopodia work. The process involves converting the cytoplasm from a fluid endoplasm to solid ectoplasm, a process in which the muscle proteins actin and myosin are involved. One of the more recent models proposes that actin is prevented from forming filaments by the presence of regulatory proteins attached to each actin molecule. When actin and regulatory protein stream forward and reach the hyaline cap, the regulatory proteins are removed and the actin forms filaments connecting into a solid mesh that forms the ectoplasm. At the trailing edge of the cytoplasm, the presence of calcium dissolves the mesh and the actin filaments are now free to interact with myosin filaments. This causes the shape of the trailing edge of the pseudopod to change, or contract, and this propels the endoplasm toward the hyaline cap:

Hartmannella is capable of encysting, forming the round, resistant cells seen at the beginning of the video. After the amoeba hatches from the cyst it becomes mobile. This is a non-pathogenic, free-living amoeba. Older isolates of Hartmannella suspected of being opportunistic pathogens (like Acanthamoeba and Naegleria) have now been reclassified as Acanthamoeba.

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