Quantification of phosphorus in single cells using synchrotron X-ray fluorescence

Area of Science:

• Biogeochemical cycles
• Cellular elemental composition
• Microbial ecology

Background:

• Phosphorus is vital for cellular functions and serves as a proxy for biomass.
• Single-cell analysis by synchrotron X-ray fluorescence (SXRF) offers high sensitivity for elemental composition.
• Accurate quantification of phosphorus (P) in single cells is challenging due to a lack of suitable standards.

Purpose of the Study:

• To develop and validate a method for quantifying phosphorus in individual phytoplankton cells using SXRF.
• To compare SXRF-derived phosphorus cell quotas with bulk measurements.
• To evaluate different grid substrates for their suitability in SXRF-based phosphorus analysis.

Main Methods:

• Utilized empirical phosphorus conversion factors derived from certified thin-film element standards.
• Quantified phosphorus in the model diatom Thalassiosira pseudonana using SXRF on gold (Au), nickel (Ni), and nylon grids.
• Compared SXRF single-cell phosphorus measurements with bulk spectrophotometry.
• Assessed grid substrates for spectral interferences and background concentrations.

Main Results:

• SXRF-quantified cellular phosphorus quotas were not significantly different from spectrophotometric bulk measurements.
• No significant differences were observed in phosphorus quantification across Au, Ni, and nylon grids.
• Nylon grids exhibited lower background concentrations and limits of detection for phosphorus compared to Ni and Au grids.
• Typical inter-cell variability within the phytoplankton population was observed.

Conclusions:

• SXRF, using empirical conversion factors, provides accurate single-cell phosphorus quantification in phytoplankton.
• Nylon grids are recommended for SXRF analysis of phosphorus due to lower background interference.
• The method is suitable for studying elemental composition and biomass in individual microbial cells.