TOC Measurements of Photosynthetic Bacteria

Importance of the Topic

The quantification of total organic carbon (TOC) is a rapid and efficient approach to assess microbial biomass generated via CO2 fixation. Accurate TOC analysis supports the development of carbon capture bioprocesses by enabling evaluation of microorganism growth and the corresponding CO2 uptake.

Objectives and Study Overview

This study demonstrates the application of the Shimadzu TOC-L analyzer, equipped with a high suspension kit and ASI-L autosampler, to measure TOC in suspensions of purple photosynthetic bacteria. Key aims include:

• Validating the repeatability of TOC measurements in high-sedimentation samples.
• Establishing correlation between TOC concentration and bacterial concentration.
• Illustrating simultaneous determination of CO2 absorbed via inorganic carbon (IC) measurement.

Methodology and Instrumentation

Sample Preparation:

• Commercially obtained purple photosynthetic bacteria isolated by centrifugation.
• Resuspension in water and dilution at ratios of undiluted, 2/3, and 1/3.

Measurement Procedure:

• Use of high suspension kit to transfer entire sample volume into the combustion tube, minimizing sedimentation bias.
• Consecutive analysis enabled by magnetic stirring option on the ASI-L autosampler.
• Determination of TOC by subtracting IC (measured separately) from total carbon (TC).

Instrumental Setup

Key components and conditions:

• Analyzer: Shimadzu TOC-LCPH total organic carbon analyzer with high suspension kit.
• Catalyst: TC standard catalyst.
• Calibration: TC via one-point curve (100 mgC/L potassium hydrogen phthalate), IC via two-point curve (0–30 mgC/L sodium carbonate/bicarbonate).
• Injection volume: 80 µL.

Main Results and Discussion

TOC measurements for undiluted, 2/3, and 1/3 samples yielded concentrations of approximately 80.0, 52.7, and 26.1 mgC/L, respectively. Repeatability was excellent, with coefficients of variation below 2% for all dilutions. A linear correlation (R≥0.999) between dilution ratio and TOC confirmed the method's accuracy for quantifying microbial biomass.

Benefits and Practical Applications

• Reliable quantification of suspended microorganisms despite high sedimentation rates.
• Simultaneous assessment of organic carbon content and CO2 uptake through combined TOC/IC measurements.
• High sample throughput enabled by ASI-L autosampler and magnetic stirring.
• Applicable to screening and breeding of CO2-fixing strains and optimization of cultivation protocols.

Future Trends and Potential Applications

Advancements may include integration of real-time online sampling, coupling TOC analysis with spectroscopic or genomic tools for deeper metabolic insights, and expansion to diverse microbial consortia. Miniaturized analyzers and automation will further enhance screening capacity for synthetic biology and environmental monitoring.

Conclusion

The Shimadzu TOC-L analyzer with a high suspension kit delivers precise and reproducible TOC measurements in photosynthetic bacterial suspensions. The strong correlation between TOC and cell concentration, combined with simultaneous CO2 uptake estimation, makes this approach valuable for advancing CO2 capture bioprocesses and microbial cultivation strategies.

References

• Shimadzu Corporation. TOC Measurements of Photosynthetic Bacteria. Application News, First Edition Feb. 2023, Document No. 01-00462-EN.