Degradation of dissolved organic phosphorus (P-diesters): Phosphodiesterase activity (PDE)

• Page authors: PRIMO
• Responsible curator: Hagen Buck-Wiese

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Phosphodiesterase activity (PDE)
Approach: fluorescent bis-MUF-phosphate substrate assay
Context: incubation, lab
Spatial scale: point sample
Temporal scale: hours to days
Units: mol fluorescent tag L-1 h-1
Community captured: heterotrophic bacteria
Co-measurements: cell abundance

Method Overview

Phosphodiesterase (PDE) activity is measured using a fluorogenic bis-phosphate substrate (e.g., bis-MUF-phosphate or MUF-bis(p-nitrophenyl)phosphate). PDE cleaves phosphodiester bonds in dissolved organic phosphorus compounds such as nucleic acid fragments, releasing fluorescent MUF and liberating phosphate. The fluorescence release rate is measured over time in a flow-through fluorimeter or plate reader, calibrated against a MUF standard, and expressed as a V_max rate. PDE is complementary to alkaline phosphatase (which targets monoesters) and together they characterize the community's capacity to access the full dissolved organic phosphorus pool.

Scale of measurement

Point sample; hours to days incubation.

Data generated

Potential PDE rate at V_max (mol MUF L^-1 h^-1), reflecting the community's enzymatic capacity to hydrolyze phosphate diester bonds. Comparing PDE to APA reveals whether microbial phosphorus acquisition is constrained by diester or monoester hydrolysis.

Units & currency

Units are mol fluorescent tag L^-1 h^-1. The currency is phosphorus.

Sample size

Typical samples are < 1 L in volume.

Limitations

Rates represent V_max at saturating substrate. The synthetic substrate may not represent the chemical diversity of natural phosphate diesters in dissolved organic matter. Bottle effects may arise.

Example Applications & Protocols

Classic examples

• Thomson et al. (2020) Relative importance of phosphodiesterase vs. phosphomonoesterase (alkaline phosphatase) activities for DOP hydrolysis in epi- and mesopelagic waters

Common calculations/conversions

• PDE (nmol MUF L^-1 h^-1) = ΔRFU / incubation time / MUF calibration slope.