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Actinophrys Sol (Actinophry + sol)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Ca2+ -dependent in vitro contractility of a precipitate isolated from an extract of the heliozoon Actinophrys sol

CYTOSKELETON, Issue 2 2006
Mikihiko Arikawa
Abstract Contraction of axopodia in actinophrid heliozoons (protozoa) is induced by a unique contractile structure, the "contractile tubules structure (CTS)". We have previously shown that a cell homogenate of the heliozoon Actinophrys sol yields a precipitate on addition of Ca2+ that is mainly composed of filamentous structures morphologically identical to the CTS. In this study, to further characterize the nature of the CTS in vitro, biochemical and physiological properties of the precipitate were examined. SDS-PAGE analysis showed that the Ca2+ -induced precipitate was composed of many proteins, and that no proteins in the precipitate showed any detectable changes in electrophoretic mobility on addition of Ca2+. Addition of extraneous proteins such as bovine serum albumin to the cell homogenate resulted in cosedimentation of the proteins with the Ca2+ -induced precipitate, suggesting that the CTS has a high affinity for other proteins that are not related to precipitate formation. Appearance and disappearance of the precipitate were repeatedly induced by alternating addition of Ca2+ and EGTA, and its protein composition remained unchanged even after repeated cycles. When adhered to a glass surface, the precipitate showed Ca2+ -dependent contractility with a threshold of 10,100 nM, and this contractility was not inhibited by colchicine or cytochalasin B. The precipitate repeatedly contracted and relaxed with successive addition and removal of Ca2+, indicating that the contraction was controlled by Ca2+ alone with no need for any other energy supply. From our characterization of the precipitate, we concluded that its Ca2+ -dependent formation and contraction are associated with the unique contractile organelle, the "contractile tubules structure". Cell Motil. Cytoskeleton 2006. © 2005 Wiley-Liss, Inc. [source]

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

FRESHWATER BIOLOGY, Issue 6 2006
ELANOR M. BELL
Summary 1. The in situ abundance, biomass and mean cell volume of Actinophrys sol (Sarcodina: Heliozoa), the top predator in an extremely acidic German mining lake (Lake 111; pH 2.65), were determined over three consecutive years (spring to autumn, 2001,03). 2. Actinophrys sol exhibited pronounced temporal and vertical patterns in abundance, biomass and mean cell volume. Increasing from very low spring densities, maxima in abundance and biomass were observed in late June/early July and September. The highest mean abundance recorded during the study was 7 × 103 Heliozoa L,1. Heliozoan abundance and biomass were higher in the epilimnion than in the hypolimnion. Actinophrys sol cells from this acidic lake were smaller than individuals of the same species found in other aquatic systems. 3. We determined the growth rate of A. sol using all potential prey items available in, and isolated and cultured from, Lake 111. Prey items included: single-celled and filamentous bacteria of unknown taxonomic affinity, the mixotrophic flagellates Chlamydomonas acidophila and Ochromonas sp., the ciliate Oxytricha sp. and the rotifers Elosa worallii and Cephalodella hoodi. Actinophrys sol fed over a wide-size spectrum from bacteria to metazoans. Positive growth was not supported by all naturally available prey. Actinophrys sol neither increased in cell number (k) nor biomass (kb) when starved, with low concentrations of single-celled bacteria or with the alga Ochromonas sp. Positive growth was achieved with single-celled bacteria (k = 0.22 ± 0.02 d,1; kb = ,0.06 ± 0.02 d,1) and filamentous bacteria (k = 0.52 ± <0.01 d,1; kb = 0.66 d,1) at concentrations greater than observed in situ, and the alga C. acidophila (up to k = 0.43 ± 0.03 d,1; kb = 0.44 ± 0.04 d,1), the ciliate Oxytricha sp. (k = 0.34 ± 0.01 d,1) and in mixed cultures containing rotifers and C. acidophila (k = 0.23 ± 0.02,0.32 ± 0.02 d,1; maximum kb = 0.42 ± 0.05 d,1). The individual- and biomass-based growth of A. sol was highest when filamentous bacteria were provided. 4. Existing quantitative carbon flux models for the Lake 111 food web can be updated in light of our results. Actinophrys sol are omnivorous predators supported by a mixed diet of filamentous bacteria and C. acidophila in the epilimnion. Heliozoa are important components in the planktonic food webs of ,extreme' environments. [source]