Dilution incubation experiments
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| Viral lysis rate (virus dilution method) |
|---|
| Approach: dilution of viruses with 0.2 µm filtered seawater; host abundance tracked by FCM |
| Context: incubation |
| Spatial scale: point sample |
| Temporal scale: hours |
| Units: cell L-1 d-1; d-1 |
| Community captured: size-fractionated host populations (FCM-resolvable) |
| Co-measurements: time (h); host cell counts at t0 and tf |
Method Overview
The virus dilution method is analogous to the microzooplankton dilution method but targets viral lysis rather than grazing as the loss term. Whole seawater (containing both hosts and viruses) is diluted with 0.2 µm filtered seawater (containing the host community but no viruses). Lower dilutions reduce the virus-to-host encounter rate, reducing viral lysis. Any grazers are simultaneously removed by the filtration. By comparing host net growth rates across dilution levels, the viral lysis rate can be inferred from the regression of apparent growth rate vs. dilution factor[1]. Flow cytometry tracks specific host cell populations (e.g., Synechococcus, Prochlorococcus, picoeukaryotes) over the incubation period.
Scale of measurement
Discrete samples incubated for hours after collection.
Data generated
Viral lysis rate (d-1) for specific host populations. Combined with host growth rates from paired dilution experiments, the relative contributions of viral lysis and grazing to total phytoplankton mortality can be estimated.
Units & currency
Units are d-1 (viral lysis rate) or cells L-1 d-1. The currency is Chl-a or cell counts.
Sample size
Typical samples are 1–2 L per dilution treatment.
Repositories & databases
Limitations
The method assumes that viral lysis is the only density-dependent process removed by dilution; if predation also scales with dilution, the two effects are confounded. Viral production during the incubation (from newly lysed cells) partially re-populates the viral pool at higher dilutions, potentially underestimating viral lysis rates. No other factors beyond viral infection should affect host cell abundance change over time.
Example Applications & Protocols
Classic examples
- Wilhelm et al. (2002) A dilution technique for the direct measurement of viral production: a comparison in stratified and tidally mixed coastal waters [1]
Recent applications
- Cram et al. (2016) Dilution reveals how viral lysis and grazing shape microbial communities [2]
Common calculations/conversions
- As for the microzooplankton dilution method: regression of k vs. dilution factor, but now the slope represents viral lysis rate rather than grazing.
References
- ↑ 1.0 1.1 Wilhelm, S. W., Brigden, S. M., & Suttle, C. A. (2002). A dilution technique for the direct measurement of viral production: a comparison in stratified and tidally mixed coastal waters. Microbial Ecology, 43(1), 168–173. https://doi.org/10.1007/s00248-001-1021-9
- ↑ Cram, J. A., Chow, C.-E. T., Sachdeva, R., Needham, D. M., Parada, A. E., Steele, J. A., & Fuhrman, J. A. (2016). Seasonal and interannual variability of the marine bacterioplankton community throughout the water column over ten years. Limnology and Oceanography, 61(3), 889–905. https://doi.org/10.1002/lno.10259