Food capture and adhesion by the heliozoonActinophrys sol

Abstract

The heliozoon Actinophrys sol is characterized by needie-like axopodia radiating from the spherical cell body. When heliozoons capture food organisms, the prey is caught by adhesion to the surface of axopodia where numerous extrusomes are present close to the plasma membrane. To understand the molecular mechanism by which the heliozoons capture prey organisms, crude isolation and characterization of the adhesive substance was carried out. Prey flagellates (Chlorogonium elongatum) adhered and aggregated to remnants of heliozoon cells which had been killed by freezing or treatment at high temperature (80 ~ for 10 min). Isolated extrusomes, which were prepared as the supernatant of cells homogenized and centrifuged after freezing and thawing, showed strong adhesion to the prey flagellates which responded to the supernatant by adhering their flagella and cell bodies to each other to form bouquet-like cell clusters. The adhesive substance was further extracted from heattreated A. sol. This fraction contained filamentous material similar to the secreted contents of the extrusomes observed during feeding. Its adhesive activity was not inhibited by trypsin treatment.

Temporal dynamics and growth of Actinophrys sol (Sarcodina: Heliozoa), the top predator in an extremely acidic lake

“…cultures to stimulate bacterial growth and to support bacterivorous species. Once established, heliozoan cells were harvested from the cultures by micropipetting, fixed with EM grade glutaraldehyde (final concentration 1%) and examined under a scanning electron microscope to confirm their identity (method described in Sakaguchi et al. , 1998).…”

“…The majority of published literature concerning Heliozoa describes ultra‐structural and molecular aspects of their physiology (e.g. Hausmann & Patterson, 1982; Grębecki & Hausmann, 1993; Sakaguchi, Hausmann & Suzaki, 1998) or taxonomy (e.g. Croome, van den Hoff & Burton, 1987; Croome, 1987a,b; Mikrjukov & Patterson, 2001).…”

“…Food organisms make contact with the axopodia and are immobilised at the cell surface by an extracellular adhesive secreted by extrusomes beneath the cell membrane (Suzaki et al. , 1980; Hausmann & Patterson, 1982; Sakaguchi & Hausmann, 1997; Sakaguchi et al. , 1998).…”

The Ultrastructure of Contractile Tubules in the Heliozoon Actinophrys sol and Their Possible Involvement in Rapid Axopodial Contraction

“…In Echinosphaeriurn, the driving force for axopodial contraction is considered to be conformational changes in a bundle of contractile tubules (formerly called X-bodies: Shigenaka and Kaneda 1979), which are located alongside the axonemal microtubules (Ando and Shigenaka 1989;Suzaki et al 1980Suzaki et al , 1994. The smaller, single-nucleated heliozoon Actinophrys also uses axopodia when it captures prey organisms Ockleford and Tucker 1973;Patterson and Hausmann 1981;Sakaguchi et al 1997Sakaguchi et al , 1998Sakaguchi et al , 2001. Similar axopodial contraction has been reported to occur in this species (Ockleford and Tucker 1973).…”

Ca2+- and glycoconjugates-dependent prey capture in the heliozoon Actinophrys sol

“…The prey flagellate Chlorogonium sp. was cultured axenically as described by Sakaguchi et al (1998). Both cell types were collected by centrifugation and washed with 10% artificial seawater (10% ASW; 47 mM NaCl, 1.1 mM KCl, 1.1 mM CaCl 2 , 2.5 mM MgCl 2 , 2.5 mM MgSO 4 and 1 mM Tris-HCl at pH 7.8) or with Ca 2+ -free 10% ASW before they were used for experiments.…”