Some Observations on <i>Actinosphaerium nucleofilum</i> n. sp., a New Fresh Water Actinophryid.*

Barrett, James M.

doi:10.1111/j.1550-7408.1958.tb02553.x

Cited by 14 publications

(2 citation statements)

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“…THE ORGANISMS: Originally a culture of Actinosphaerium nudeofilum (Barrett, 1958) was obtained from the Carolina Biological Supply Co) and serially subcultured in a wheat medium (Looper, 1928). Small amounts of a rich culture of mixed ciliates were added from time to time as food for the Actinosphaerium.…”

Section: Methodsmentioning

confidence: 99%

Studies on the Microtubules in Heliozoa

Tilney

Hiramoto

Marsland

1966

The Journal of Cell Biology

221

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Electron microscope preparations were made of specimens of Actinosphaerium nucleofilum fixed in glutaraldehyde before, during, and after exposure to high pressures (4,000 to 8,000 psi). A study of this material showed that, although other organelles were relatively stable, the microtubular elements of the axopodia and cytosome became unstable under pressure. Their rapid disintegration under pressure was correlated with beading and retraction of the axopodia. Moreover, after the release of pressure, microtubules reappeared as soon as, or sooner than the reextension of the axopodia. The rate of disintegration increased as the pressure was raised. At 4,000 psi, few if any tubules remained after 10 min, whereas at 6,000 and 8,000 psi the disintegration was much more rapid. Some adaptational reorganization of the microtubules and axopodia occurred while relatively low pressures were maintained. This was accompanied by an actual elongation of the axopodia in specimens maintained for 20 min at 4,000 psi, but was confined to knoblike axopodial remnants in animals kept at 6,000 psi. No regeneration of tubules or axopodia occurred at 8,000 psi. The presence of fibers and a finely fibrillar material in pressurized animals suggests that these may be derivatives of microtubular disintegration. This evidence, though purely morphological, is consistent with the hypothesis that microtubules play an important role not only in maintaining the formstability of the axopodia, but also in the active process by which the axopodia reextend themselves after retraction.

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Section: Methodsmentioning

confidence: 99%

Studies on the Microtubules in Heliozoa

Tilney

Hiramoto

Marsland

1966

The Journal of Cell Biology

221

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“…1C) was chosen for this study because it is ecologically important, is easy to maintain in culture, and readily eats choanoflagellates in the laboratory. This heliozoan ("sun animalcule") is found in freshwater habitats worldwide where it consumes a wide variety of other protozoans (Barrett 1958;Leidy 1879). Heliozoans can be found in concentrations of more than 5,000 cells/liter and likely exert a large grazing pressure on protozoans in lakes and ponds (Pierce and Coats 1999).…”

Section: Research Systemmentioning

confidence: 99%

Does Formation of Multicellular Colonies by Choanoflagellates Affect Their Susceptibility to Capture by Passive Protozoan Predators?

Kumler

Jorge

Kim

et al. 2020

J Eukaryotic Microbiology

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Microbial eukaryotes, critical links in aquatic food webs, are unicellular, but some, such as choanoflagellates, form multicellular colonies. Are there consequences to predator avoidance of being unicellular vs. forming larger colonies? Choanoflagellates share a common ancestor with animals and are used as model organisms to study the evolution of multicellularity. Escape in size from protozoan predators is suggested as a selective factor favoring evolution of multicellularity. Heterotrophic protozoans are categorized as suspension feeders, motile raptors, or passive predators that eat swimming prey which bump into them. We focused on passive predation and measured the mechanisms responsible for the susceptibility of unicellular vs. multicellular choanoflagellates, Salpingoeca helianthica, to capture by passive heliozoan predators, Actinosphaerium nucleofilum, which trap prey on axopodia radiating from the cell body. Microvideography showed that unicellular and colonial choanoflagellates entered the predator's capture zone at similar frequencies, but a greater proportion of colonies contacted axopodia. However, more colonies than single cells were lost during transport by axopodia to the cell body. Thus, feeding efficiency (proportion of prey entering the capture zone that were engulfed in phagosomes) was the same for unicellular and multicellular prey, suggesting that colony formation is not an effective defense against such passive predators.

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Stabilizing effects of D₂O on the microtubular components and needle‐like form of heliozoan axopods: A pressure‐temperature analysis

Marsland

Tilney

Hirshfield

1971

Journal Cellular Physiology

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A systematic study of the resistance of heliozoan axopodia to pressure-induced disintegrational changes has shown that progressively higher concentrations of DzO in the environing medium produce a progressively greater stability, not only as to the needle-like form of the whole axopodia, but also as to their microtubular components. Also it was found that a higher temperature (25°C) yielded significantly higher stability values with identical degrees of deuteration, as compared with experiments performed at a lower temperatureHigh hydrostatic pressure, in the range between 4000 and 8000 psi, has provided a useful tool for studying the stability of the elongate needlelike pseudopodia ( axo-

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Some Observations on Actinosphaerium nucleofilum n. sp., a New Fresh Water Actinophryid.*

Cited by 14 publications

References 1 publication

Studies on the Microtubules in Heliozoa

Studies on the Microtubules in Heliozoa

Does Formation of Multicellular Colonies by Choanoflagellates Affect Their Susceptibility to Capture by Passive Protozoan Predators?

Stabilizing effects of D₂O on the microtubular components and needle‐like form of heliozoan axopods: A pressure‐temperature analysis

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Some Observations on Actinosphaerium nucleofilum n. sp., a New Fresh Water Actinophryid.*

Cited by 14 publications

References 1 publication

Studies on the Microtubules in Heliozoa

Studies on the Microtubules in Heliozoa

Does Formation of Multicellular Colonies by Choanoflagellates Affect Their Susceptibility to Capture by Passive Protozoan Predators?

Stabilizing effects of D2O on the microtubular components and needle‐like form of heliozoan axopods: A pressure‐temperature analysis

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Stabilizing effects of D₂O on the microtubular components and needle‐like form of heliozoan axopods: A pressure‐temperature analysis