An experimental study of the interaction between the soil amoeba Naegleria gruberi and a glass substrate during amoeboid locomotion

Abstract

The amoeboid locomotion of the soil protozoon Naegleria gruberi has been studied using reflexion-interference microscopy. Two types of contact are made with a planar glass substrate. One, formed at a considerable distance from the substrate in deionized water (congruent to 100 nm) has been termed ‘associated contact’ and usually involves a considerable surface area (of the order of 100 micrometer2), i.e. about a third of the cell profile. From this broad platform filopodia are produced which form close contacts (‘focal contacts’). In locomotion the area of associated contact is very mobile, in contrast to the focal contacts which, once established, are stable. Focal contact sites are left behind on the glass surface (‘footprints’) when the amoeba moves away. The cell-substrate gap in the associated contact is greatly affected by the ionic strength of the medium and particularly the valency of the cation component. This suggests that long-range forces of attraction play an important role in keeping the amoeba close to a substrate and thus allow the production of filopodia from the ventral surface to form focal contacts.