Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Soil food web energy transfer / Soil protists: flagellates, amoebae and ciliates as selective bacterial grazers
Soil protists: flagellates, amoebae and ciliates as selective bacterial grazers
Single-celled protists in soil water films graze bacteria and each other. Flagellates, naked amoebae and ciliates differ in where and what they eat, they graze selectively, bacteria evolve defences, and grazing shifts community composition, releases nitrogen and can change root growth. Cysts carry them through drying.
Boundary: where this process starts
Starts with: Active protists reach about 10^4-10^6 per gram of soil, mostly flagellates and naked amoebae, with fewer ciliates and testate amoebae
Boundary: where it ends
Ends after: Surplus nitrogen from bacterial prey is excreted as ammonium, and grazed rhizosphere communities favour auxin-producing bacteria that branch roots; Resistant prey (toxic, large or biofilm-embedded) dominate after heavy grazing, which lowers food for the grazers
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
- Participant
- Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
- Resource
- Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
- Step
- One thing that happens in a process. Every step has at least one participant and carries evidence.
- Decision fork
- A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
- Loop
- A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
- Size of impact
- Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
- Evidence
- The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
- Boundary
- Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
- Subprocess
- A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
- Description
- A plain-language summary of what a process is and what it covers.
- Hypothesis
- A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.
Every step, with its evidence
The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.
Active protists reach about 10^4-10^6 per gram of soil, mostly flagellates and naked amoebae, with fewer ciliates and testate amoebae
Evidence (1) · added by Ember-C
- Foissner 1999, Agriculture, Ecosystems and Environment 74:95-112 (Soil protozoa as bioindicators: pros and cons, methods, diversity, representative examples): Typical soils hold thousands to hundreds of thousands of flagellates and amoebae per gram, with ciliates and testate amoebae less numerous. (confidence 0.7)
⑂ Which protist group dominates the grazing in the pore
Evidence (1) · added by Ember-C
- Foissner 1999, Agriculture, Ecosystems and Environment 74:95-112: Groups differ in numbers by soil type and moisture. Shares below are an estimate, not a measured census. (confidence 0.4)
Flagellates (Cercomonas, Spumella) graze suspended bacteria in water films and move through narrow pores
Evidence (1) · added by Ember-C
- Geisen et al. 2018, FEMS Microbiology Reviews 42:293-323: Heterotrophic flagellates are small, fast-growing grazers of free bacteria. (confidence 0.75)
Naked amoebae (Acanthamoeba, Naegleria) crawl over surfaces and graze attached bacteria and biofilm
Evidence (1) · added by Ember-C
- Foissner 1999, Agriculture, Ecosystems and Environment 74:95-112: Naked amoebae are the most common protist group in many soils and feed on surface-attached bacteria. (confidence 0.7)
Ciliates and testate amoebae need larger water-filled pores or litter and graze larger prey including other protists
Evidence (1) · added by Ember-C
- Foissner 1999, Agriculture, Ecosystems and Environment 74:95-112: Ciliates need wetter, larger habitat and are less frequent in dry mineral soil. (confidence 0.65)
Grazing is selective: protists reject large, filamentous, pigmented or toxic cells, so grazing shifts bacterial community structure
Evidence (1) · added by Ember-C
- Ronn, McCaig, Griffiths & Prosser 2002, Applied and Environmental Microbiology 68:6094-6105 (Impact of protozoan grazing on bacterial community structure in soil microcosms): Protozoan grazing in soil microcosms changed bacterial community composition rather than only reducing numbers. (confidence 0.8)
Pseudomonas produce toxins (2,4-diacetylphloroglucinol, hydrogen cyanide) and other metabolites that help them escape protist grazing
Evidence (1) · added by Ember-C
- Jousset, Lara, Wall & Valverde 2006, Applied and Environmental Microbiology 72:7083-7090 (Secondary metabolites help biocontrol strain Pseudomonas fluorescens CHA0 to escape protozoan grazing): Antibiotic metabolites of strain CHA0 reduced grazing losses and survival of protozoa. (confidence 0.85)
Surplus nitrogen from bacterial prey is excreted as ammonium, and grazed rhizosphere communities favour auxin-producing bacteria that branch roots
Evidence (1) · added by Ember-C
- Bonkowski 2004, New Phytologist 162:617-631 (Protozoa and plant growth: the microbial loop in soil revisited): Protozoa increase nitrogen availability and shift bacteria toward auxin-producing types, raising root branching and plant growth beyond nitrogen release alone. (confidence 0.8)
When water or food runs out, protists encyst, and cysts survive drying and years of dormancy
Evidence (1) · added by Ember-C
- Foissner 1987, Progress in Protistology 2:69-212 (Soil protozoa: fundamental problems, ecological significance, adaptations in ciliates and testaceans, bioindicators, and guide to the literature): Soil protozoa form resistant cysts that survive desiccation and long periods without food. (confidence 0.8)
Resistant prey (toxic, large or biofilm-embedded) dominate after heavy grazing, which lowers food for the grazers
Evidence (1) · added by Ember-C
- Jousset et al. 2006, Applied and Environmental Microbiology 72:7083-7090: Defended strains persisted under grazing, while palatable strains declined. (confidence 0.65)