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. 2025 Mar-Apr;72(2):e13065.
doi: 10.1111/jeu.13065. Epub 2024 Nov 3.

Broad-range necrophytophagy in the flagellate Orciraptor agilis (Viridiraptoridae, Cercozoa) and the underappreciated role of scavenging among protists

Jannika Moye  1 , Sebastian Hess  1
Affiliations

Broad-range necrophytophagy in the flagellate Orciraptor agilis (Viridiraptoridae, Cercozoa) and the underappreciated role of scavenging among protists

Jannika Moye et al. J Eukaryot Microbiol. 2025 Mar-Apr.

Abstract

Protists show diverse lifestyles and fulfill important ecological roles as primary producers, predators, symbionts, and parasites. The degradation of dead microbial biomass, instead, is mainly attributed to bacteria and fungi, while necrophagy by protists remains poorly recognized. Here, we assessed the food range specificity and feeding behavior of the algivorous flagellate Orciraptor agilis (Viridiraptoridae, Cercozoa) with a large-scale feeding experiment. We demonstrate that this species is a broad-range necrophage, which feeds on a variety of eukaryotic and prokaryotic algae, but fails to grow on the tested fungi. Furthermore, our microscopic observations reveal an unexpected flexibility of O. agilis in handling food items of different structures and biochemistry, demonstrating that sophisticated feeding strategies in protists do not necessarily indicate narrow food ranges.

Keywords: Rhizaria; algae; decomposition; flagellates; necrophagy; scavenger.

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Figures

FIGURE 1
FIGURE 1
Results of the feeding experiments with O. agilis. Tested organisms are listed according to their taxonomic treatment. “fast growth” indicates the impression of a rapid increase in cell number as observed with the natural food alga (Hess & Melkonian, 2013). CCAC = Central Collection of Algal Cultures; DSM = German Collection of Microorganisms and Cell Cultures; SAG = Culture Collection of Algae at Göttingen University.
FIGURE 2
FIGURE 2
Orciraptor agilis (strain OrcA03) feeding on different zygnematophytes. (A) Cell extracting the contents of a small‐celled Mougeotia species. (B) Multiple cells attacking Closterium cornu. (C) Perforations (arrows) left by O. agilis in the cell wall of Closterium cornu. Note the attached cell wall disc. (D) Two cells attacking Penium margaritaceum with discernible lysopodia. (E) Multiple well‐fed Orciraptor cells inside Penium margaritaceum. (F) Colorless cells with food remnants inside Penium margaritaceum. (G) Time series of O. agilis perforating the cell wall of Penium margaritaceum from the inside and exiting the algal cell. (H) Orciraptor extracting cell contents from a Spirogyra sp. filament. (I) Two cells inside a Spirogyra sp. filament. (J) Cell penetrating the cross wall of Spirogyra sp. (K) Cell feeding on free protoplast material of Penium margaritaceum. Scale bars: 20 μm.
FIGURE 3
FIGURE 3
Scanning electron micrographs of zygnematophytes perforated by O. agilis. (A) Roya obtusa. (B) Planotaenium ohtanii with attached cell wall discs (arrows). (C) Penium margaritaceum with multiple perforations. (D) Close‐up of the reticulate cell wall of Penium margaritaceum. (E) Planotaenium interruptum. (F) Close‐up of the perforation in Planotaenium interruptum. (G) Staurodesmus mamillatus with incomplete perforation (arrow). (H) Cosmarium tinctum with circular perforation (arrow) and cell wall disc still in place. Scale bars: 10 μm.
FIGURE 4
FIGURE 4
Orciraptor agilis feeding on gelatinous colonies and palmella. (A) Time series of O. agilis feeding on the cell contents of E. elegans after piercing the gelatinous colony. (B) Colony of E. elegans emptied by O. agilis with discernible degradation of the outer mucus layer (arrows). The staining with fluorescent wheat germ agglutinin shows the perforations and a flap of displaced mucus. (C) Close‐up of displaced mucus (arrow) from (B). (D) O. agilis removing a complete cell from Pandorina morum. (E) O. agilis removing a cell from a palmella of Chroomonas sp. Scale bars: A, B, D, E: 20 μm, C: 10 μm.
FIGURE 5
FIGURE 5
Interaction of O. agilis with euglenids, Cyanobacteria, yeast, and wheat flour. (A) O. agilis extracting the cell contents of M. pseudonordstedtii. (B, C) O. agilis extracting cell contents of Euglena deses. (D) Freeze‐killed cells of Euglena deses. (E) Remains of Euglena deses after extraction by O. agilis. (F) Time series of O. agilis incorporating and lysing a filament of an Anabaena species. Note the removed fragments (arrows). (G) Time series of O. agilis lysing and incorporating a filament of Oscillatoria amoena. (H, I) Cells of O. agilis deformed by filaments of Oscillatoria amoena (H) and Anabaena sp. (I). (J, K) O. agilis with incorporated cells of Saccharomyces cerevisiae. (L) O. agilis with incorporated amyloplast from wheat flour. Scale bars: 20 μm.
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