Reduction of phosphite to phosphate for growth (ptxABCD)
| Phosphite utilization (ptxABCD) |
|---|
| Approach: culture growth assay with phosphite as sole P source |
| Context: incubation, lab |
| Spatial scale: culture flask (point) |
| Temporal scale: days |
| Units: d-1 (growth rate) |
| Community captured: cyanobacteria and heterotrophic bacteria |
| Co-measurements: (none specified) |
Method Overview
Phosphite (HPO32-) is a reduced form of phosphorus found at trace concentrations in marine environments. The ptxABCD operon encodes a phosphite oxidoreductase system that oxidizes phosphite to phosphate, allowing certain microorganisms (including some cyanobacteria and heterotrophic bacteria) to use phosphite as a sole phosphorus source. Utilization capacity is assessed by growing candidate organisms or environmental assemblages in media where phosphite is the only P source and comparing growth rates to phosphate-amended controls. Growth (optical density, cell counts, or Chl fluorescence) is tracked over time, and the growth rate (d-1) indicates whether the community can access phosphite[1].
Scale of measurement
Laboratory culture or controlled incubation; single species or enriched communities. Days-long incubations to observe growth responses.
Data generated
Growth rate (d-1) on phosphite vs. phosphate, indicating the capacity for phosphite-supported growth. Does not directly provide a phosphite oxidation rate in the field.
Units & currency
Units are d-1 (growth rate). The currency is cells (growth).
Sample size
Typical samples are < 1 L in volume.
Repositories & databases
Limitations
Growth responses in culture may not represent the behavior of natural assemblages in low-phosphorus environments. The assumption that a positive growth response on phosphite in culture applies to mixed natural assemblages is a simplification. The method does not quantify phosphite uptake or oxidation rates directly.
Example Applications & Protocols
Classic examples
- Polyviou et al. (2015) Phosphite utilisation by the globally important marine diazotroph Trichodesmium [1]
Recent applications
Common calculations/conversions
- Growth rate µ (d-1) = ln(Nfinal / Ninitial) / incubation time.
References
- ↑ 1.0 1.1 Polyviou, D., Hitchcock, A., Baylay, A. J., Moore, C. M., & Bibby, T. S. (2015). Phosphite utilization by the globally important marine diazotroph Trichodesmium. Environmental Microbiology Reports, 7(6), 824–830. https://doi.org/10.1111/1758-2229.12308