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Kiørboe T. Predation in a Microbial World: Mechanisms and Trade-Offs of Flagellate Foraging. ANNUAL REVIEW OF MARINE SCIENCE 2024; 16:361-381. [PMID: 37368955 DOI: 10.1146/annurev-marine-020123-102001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/29/2023]
Abstract
Heterotrophic nanoflagellates are the main consumers of bacteria and picophytoplankton in the ocean and thus play a key role in ocean biogeochemistry. They are found in all major branches of the eukaryotic tree of life but are united by all being equipped with one or a few flagella that they use to generate a feeding current. These microbial predators are faced with the challenges that viscosity at this small scale impedes predator-prey contact and that their foraging activity disturbs the ambient water and thus attracts their own flow-sensing predators. Here, I describe some of the diverse adaptations of the flagellum to produce sufficient force to overcome viscosity and of the flagellar arrangement to minimize fluid disturbances, and thus of the various solutions to optimize the foraging-predation risk trade-off. I demonstrate how insights into this trade-off can be used to develop robust trait-based models of microbial food webs.
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Affiliation(s)
- Thomas Kiørboe
- Centre for Ocean Life, DTU Aqua, Technical University of Denmark, Kongens Lyngby, Denmark;
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Chin NE, Wu TC, O'Toole JM, Xu K, Hata T, Koehl MAR. Formation of multicellular colonies by choanoflagellates increases susceptibility to capture by amoeboid predators. J Eukaryot Microbiol 2022; 70:e12961. [PMID: 36578145 DOI: 10.1111/jeu.12961] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2022] [Revised: 11/10/2022] [Accepted: 12/13/2022] [Indexed: 12/30/2022]
Abstract
Many heterotrophic microbial eukaryotes are size-selective feeders. Some microorganisms increase their size by forming multicellular colonies. We used choanoflagellates, Salpingoeca helianthica, which can be unicellular or form multicellular colonies, to study the effects of multicellularity on vulnerability to predation by the raptorial protozoan predator, Amoeba proteus, which captures prey with pseudopodia. Videomicrography used to measure the behavior of interacting S. helianthica and A. proteus revealed that large choanoflagellate colonies were more susceptible to capture than were small colonies or single cells. Swimming colonies produced larger flow fields than did swimming unicellular choanoflagellates, and the distance of S. helianthica from A. proteus when pseudopod formation started was greater for colonies than for single cells. Prey size did not affect the number of pseudopodia formed and the time between their formation, pulsatile kinematics and speed of extension by pseudopodia, or percent of prey lost by the predator. S. helianthica did not change swimming speed or execute escape maneuvers in response to being pursued by pseudopodia, so size-selective feeding by A. proteus was due to predator behavior rather than prey escape. Our results do not support the theory that the selective advantage of becoming multicellular by choanoflagellate-like ancestors of animals was reduced susceptibility to protozoan predation.
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Affiliation(s)
- Nicole E Chin
- Department of Integrative Biology, University of California, Berkeley, Berkeley, California, USA
| | - Tiffany C Wu
- Department of Integrative Biology, University of California, Berkeley, Berkeley, California, USA
| | - J Michael O'Toole
- Department of Integrative Biology, University of California, Berkeley, Berkeley, California, USA
| | - Kevin Xu
- Department of Integrative Biology, University of California, Berkeley, Berkeley, California, USA.,Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Tom Hata
- Department of Integrative Biology, University of California, Berkeley, Berkeley, California, USA
| | - Mimi A R Koehl
- Department of Integrative Biology, University of California, Berkeley, Berkeley, California, USA
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Kumler WE, Jorge J, Kim PM, Iftekhar N, Koehl MAR. Does Formation of Multicellular Colonies by Choanoflagellates Affect Their Susceptibility to Capture by Passive Protozoan Predators? J Eukaryot Microbiol 2020; 67:555-565. [PMID: 32455487 DOI: 10.1111/jeu.12808] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Revised: 04/17/2020] [Accepted: 05/14/2020] [Indexed: 01/20/2023]
Abstract
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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Affiliation(s)
- William E Kumler
- Department of Integrative Biology, University of California, Berkeley, California, 94720-3140.,School of Oceanography, University of Washington, Seattle, Washington, 98105
| | - Justin Jorge
- Department of Integrative Biology, University of California, Berkeley, California, 94720-3140.,Department of Biology, Duke University, Durham, North Carolina, 27708-0338
| | - Paul M Kim
- Department of Integrative Biology, University of California, Berkeley, California, 94720-3140
| | - Noama Iftekhar
- Department of Integrative Biology, University of California, Berkeley, California, 94720-3140
| | - M A R Koehl
- Department of Integrative Biology, University of California, Berkeley, California, 94720-3140
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Ireland EV, Woznica A, King N. Synergistic Cues from Diverse Bacteria Enhance Multicellular Development in a Choanoflagellate. Appl Environ Microbiol 2020; 86:e02920-19. [PMID: 32220848 PMCID: PMC7237790 DOI: 10.1128/aem.02920-19] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Accepted: 03/23/2020] [Indexed: 02/07/2023] Open
Abstract
Bacteria regulate the life histories of diverse eukaryotes, but relatively little is known about how eukaryotes interpret and respond to multiple bacterial cues encountered simultaneously. To explore how a eukaryote might respond to a combination of bioactive molecules from multiple bacteria, we treated the choanoflagellate Salpingoeca rosetta with two sets of bacterial cues, one that induces mating and another that induces multicellular development. We found that simultaneous exposure to both sets of cues enhanced multicellular development in S. rosetta, eliciting both larger multicellular colonies and an increase in the number of colonies. Thus, rather than conveying conflicting sets of information, these distinct bacterial cues synergize to augment multicellular development. This study demonstrates how a eukaryote can integrate and modulate its response to cues from diverse bacteria, underscoring the potential impact of complex microbial communities on eukaryotic life histories.IMPORTANCE Eukaryotic biology is profoundly influenced by interactions with diverse environmental and host-associated bacteria. However, it is not well understood how eukaryotes interpret multiple bacterial cues encountered simultaneously. This question has been challenging to address because of the complexity of many eukaryotic model systems and their associated bacterial communities. Here, we studied a close relative of animals, the choanoflagellate Salpingoeca rosetta, to explore how eukaryotes respond to diverse bacterial cues. We found that a bacterial chondroitinase that induces mating on its own can also synergize with bacterial lipids that induce multicellular "rosette" development. When encountered together, these cues enhance rosette development, resulting in both the formation of larger rosettes and an increase in the number of rosettes compared to rosette development in the absence of the chondroitinase. These findings highlight how synergistic interactions among bacterial cues can influence the biology of eukaryotes.
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Affiliation(s)
- Ella V Ireland
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, USA
| | - Arielle Woznica
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, USA
| | - Nicole King
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, USA
- Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, California, USA
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Koehl MAR. Selective factors in the evolution of multicellularity in choanoflagellates. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2020; 336:315-326. [PMID: 32198827 DOI: 10.1002/jez.b.22941] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Revised: 02/12/2020] [Accepted: 02/17/2020] [Indexed: 11/10/2022]
Abstract
Choanoflagellates, unicellular eukaryotes that can form multicellular colonies by cell division and that share a common ancestor with animals, are used as a model system to study functional consequences of being unicellular versus colonial. This review examines performance differences between unicellular and multicellular choanoflagellates in swimming, feeding, and avoiding predation, to provide insights about possible selective advantages of being multicellular for the protozoan ancestors of animals. Each choanoflagellate cell propels water by beating a single flagellum and captures bacterial prey on a collar of microvilli around the flagellum. Formation of multicellular colonies does not improve the swimming performance, but the flux of prey-bearing water to the collars of some of the cells in colonies of certain configurations can be greater than for single cells. Colony geometry appears to affect whether cells in colonies catch more prey per cell per time than do unicellular choanoflagellates. Although multicellular choanoflagellates show chemokinetic behavior in response to oxygen, only the unicellular dispersal stage (fast swimmers without collars) use pH signals to aggregate in locations where bacterial prey might be abundant. Colonies produce larger hydrodynamic signals than do single cells, and raptorial protozoan predators capture colonies while ignoring single cells. In contrast, ciliate predators entrain both single cells and colonies in their feeding currents, but reject larger colonies, whereas passive heliozoan predators show no preference. Thus, the ability of choanoflagellate cells to differentiate into different morphotypes, including multicellular forms, in response to variable aquatic environments might have provided a selective advantage to the ancestors of animals.
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Affiliation(s)
- M A R Koehl
- Department of Integrative Biology, University of California, Berkeley, California
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