Development of an Improved Thiosulfate-Utilizing Denitrifying Bacteria-Based Ecotoxicity Test with High Detection...

Area of Science:

• Environmental Science
• Microbiology
• Ecotoxicology

Background:

• Microorganism-based ecotoxicity assessments are crucial for understanding contaminant impacts on ecosystems.
• Existing thiosulfate-utilizing denitrifying bacteria (TUDB) toxicity tests require improvement in sensitivity and reproducibility.
• Developing sensitive and reproducible ecotoxicity tests is vital for environmental monitoring and risk assessment.

Purpose of the Study:

• To develop an optimized thiosulfate-utilizing denitrifying bacteria (TUDB)-based ecotoxicity test with enhanced detection sensitivity and reproducibility.
• To identify optimal test conditions, including microbial biomass, temperature, and pH, for the TUDB assay.
• To evaluate the performance of the optimized TUDB test for diverse toxic metals.

Main Methods:

• Utilized a pure culture of *Thiobacillus thioparus* ATCC 8158 for the TUDB ecotoxicity test.
• Optimized key parameters: initial bacterial biomass (20 mg VSS/L), incubation temperature (25 °C), and operational pH (6).
• Determined a 4-hour processing time for the TUDB test kits and assessed toxic metal toxicity using EC50 values.

Main Results:

• Optimal conditions (20 mg VSS/L biomass, 25 °C, pH 6) significantly enhanced TUDB test sensitivity and reproducibility.
• Achieved low 4-hour EC50 values for various toxic metals (e.g., Ag+, As3+, Cd2+, Cr6+, Cu2+, Hg2+, Ni2+, Pb2+), indicating high sensitivity.
• Demonstrated excellent reproducibility with low coefficient of variation (CV) values (1.6-6.3%) for EC50 determinations.

Conclusions:

• The optimized TUDB ecotoxicity test provides a highly sensitive and reproducible method for assessing toxic metals.
• The refined TUDB assay offers advantages such as versatility, no need for advanced equipment, and clear endpoint measurements.
• This improved TUDB test is a valuable tool for environmental ecotoxicity assessment, offering enhanced performance over previous methods.