Size-fractionated extract spiking
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| Allelopathy (size-fractionated extract spiking) |
|---|
| Approach: size-fractionated culture extracts added to target species; growth or Fv/Fm response measured |
| Context: lab |
| Spatial scale: culture flask (point) |
| Temporal scale: hours to days |
| Units: cells L-1 d-1; Fv/Fm |
| Community captured: individual target species |
| Co-measurements: temperature, PAR; sometimes pH and salinity |
Method Overview
Cell-free extracts or filtrates from a potentially allelopathic species are size-fractionated by molecular weight cutoff ultrafiltration membranes (e.g., < 1 kDa, 1–10 kDa, 10–100 kDa, > 100 kDa) or by reverse-phase solid-phase extraction (SPE) into polarity fractions. Each fraction is then added separately to cultures of a target species. The effect of each fraction on target species growth rate or photosynthetic efficiency (Fv/Fm) is quantified relative to solvent controls[1]. This approach identifies the molecular size range (and sometimes polarity class) of the allelopathic compound(s), aiding in their chemical characterization.
Scale of measurement
Laboratory culture; no direct in situ spatial scale. Hours to days incubation per fraction.
Data generated
Growth rate or Fv/Fm of the target species in response to each size fraction. The fraction(s) causing significant inhibition narrow down the molecular size class of the allelopathic compound.
Units & currency
Units are cells L-1 d-1 (growth) or Fv/Fm. The currency is cell abundance or photon relaxation.
Sample size
Typical samples are < 1 L in volume per fraction.
Repositories & databases
Limitations
The size fractionation assumes that the allelopathic compound is in a specific size class and that fractionation does not alter its activity (e.g., through pH changes during ultrafiltration or solid phase extraction). Compounds may interact synergistically across fractions, making single-fraction bioassays incomplete. The assumption that a specific compound or fraction exerts the allelopathic effect must be verified by chemical identification and dose-response experiments. Longer incubations in culture flasks may introduce bottle effects, such as nutrient starvation or confinement stress, that can alter target species growth independently of the added extracts.
Example Applications & Protocols
Classic examples
- Wu et al. (2010) Allelopathic control of cyanobacterial blooms by periphyton biofilms [1]
Recent applications
Common calculations/conversions
- % inhibition per fraction = (Fv/Fmcontrol − Fv/Fmfraction) / Fv/Fmcontrol × 100; highest inhibition identifies the active size class.
References
- ↑ 1.0 1.1 Wu, J.-T., Chiang, Y.-R., Huang, W.-Y., & Jane, W.-N. (2010). Allelopathic control of cyanobacterial blooms by periphyton biofilms. Environmental Microbiology, 13(3), 604–615. https://doi.org/10.1111/j.1462-2920.2010.02363.x