A novel gas production bioassay of thiosulfate utilizing denitrifying bacteria (TUDB) for the toxicity assessment of heavy metals contaminated water

Response mechanism of extracellular polymers in the remediation of chromium pollution by carbonate mineralizing bacteria

This study examines the adaptability of carbonate mineralizing bacteria in Cr(iii)-contaminated environments with varying Cr(iii) concentrations and their response mechanism via EPS. Cr(iii) removal efficiency declined with concentrations exceeding 1000 mg L-1, while the removal amount continued to rise, indicating strong Cr(iii) tolerance in the bacterium. Analysis of dynamic changes in EPS revealed a significant increase in production, with polysaccharides and proteins playing key roles in Cr(iii) binding. A notable increase in mannose in the monosaccharide composition of EPS suggests its involvement in Cr(iii) binding. Moreover, alterations in the protein secondary structure, such as a reduction in α-helix content and an increase in β-sheet and random coil structures, may enhance EPS interaction with Cr(iii). These findings demonstrate that EPS contributes to heavy metal remediation not only through its polysaccharide components but also through changes in protein structure, offering a new theoretical foundation for Cr(iii) bioremediation.

Development of an Improved Thiosulfate-Utilizing Denitrifying Bacteria-Based Ecotoxicity Test with High Detection Sensitivity and Reproducibility

Microorganism-based ecotoxicity assessment has been widely used as a reliable tool showing direct biochemical impacts of contaminants on ecosystems and the environment. The present study aimed at developing a thiosulfate-utilizing denitrifying bacteria (TUDB)-based ecotoxicity test with high detection sensitivity and favorable reproducibility. To achieve this goal, existing TUDB toxicity tests were improved by employing a pure culture of Thiobacillus thioparus ATCC 8158 and optimizing test conditions, particularly in terms of inoculated microbial biomass, incubating temperature, and operational pH. From control tests, it was found that 4 h is a sufficient processing time for TUDB test kits. As a result of optimization, 20 mg VSS/L of initial bacterial biomass, 25 °C of incubating temperature, and 6 of operational pH were determined as the most favorable test conditions, providing enhanced detection sensitivity and reproducibility. Under these optimal test conditions, I conducted toxicity tests for diverse toxic metals and obtained 0.65 ± 0.03, 1.09 ± 0.04, 1.21 ± 0.07, 0.13 ± 0.01, 0.56 ± 0.04, 1.42 ± 0.03, 0.98 ± 0.02, and 2.12 ± 0.05 mg/L of 4 h EC50 values for Ag+, As3+, Cd2+, Cr6+, Cu2+, Hg2+, Ni2+, and Pb2+, respectively. These EC50 values are substantially lower than those from earlier TUDB tests, demonstrating the high detection sensitivity of the current TUDB tests. Moreover, the present TUDB tests attained very low coefficient of variation (CV) values (1.6-6.3%) for the EC50, showing favorable reproducibility of the test methodology. In addition, the current TUDB toxicity tests offer numerous advantages for ecotoxicity assessment, including versatility for diverse test samples, no requirement for advanced equipment, and no distortion of end-point measurement. These refinements render the TUDB tests a favorable ecotoxicity assessment with enhanced sensitivity and reproducibility.

Assessing the toxicity of contaminated soils via direct contact using a gas production bioassay of thiosulfate utilizing denitrifying bacteria (TUDB)

A direct contact bioassay of thiosulfate utilizing denitrifying bacteria (TUDB) based on inhibition of gas production was deployed to assess the toxicity of naturally contaminated field soils and soils artificially contaminated with heavy metals. Test procedure producing optimal conditions responsible for maximum gas production was 0.5 mL test culture, 1 g soil sample, 80 RPM, and 48 h reaction time. Similarly, the concentrations which generated a 50% reduction in gas production by TUDB for the tested heavy metals were 3.01 mg/kg Cr⁶⁺; 15.30 mg/kg Ni²⁺;15.50 mg/kg Cu²⁺;16.60 mg/kg Ag⁺; 20.60 mg/kg As³⁺; 32.80 mg/kg Hg²⁺; 54.70 mg/kg Cd²⁺; and 74.0 mg/kg Pb²⁺. Because soil toxicity is usually influenced by various physicochemical characteristics, ten reference soils were used to determine the toxicity threshold for evaluating the toxicity of naturally contaminated field soils. All eight contaminated soils were toxic to the TUDB bioassay because their levels of inhibition ranged between 72% and 100% and exceeded the determined toxicity threshold of 10%. Compared to other direct contact assays, the newly developed assay TUDB proved to be very robust, producing highly sensitive data while the different soil physicochemical properties exerted minimal influence on the gas production activity of TUDB. Additionally, the simplicity of the developed methodology coupled with the elimination of pretreatment procedures such as elutriation, and ability to perform generate sensitive data in turbid and highly colored samples makes it, cost-effective, and easily adaptable for the assessment of heavy metal and field contaminated soils when compared with other conventional assays which require sophisticated instrumentation and prolonged testing procedures and times.

Recent and Emerging Trends in Remediation of Methylene Blue Dye from Wastewater by Using Zinc Oxide Nanoparticles

Due to the increased demand for clothes by the growing population, the dye-based sectors have seen fast growth in the recent decade. Among all the dyes, methylene blue dye is the most commonly used in textiles, resulting in dye effluent contamination. It is carcinogenic, which raises the stakes for the environment. The numerous sources of methylene blue dye and their effective treatment procedures are addressed in the current review. Even among nanoparticles, photocatalytic materials, such as TiO2, ZnO, and Fe3O4, have shown greater potential for photocatalytic methylene blue degradation. Such nano-sized metal oxides are the most ideal materials for the removal of water pollutants, as these materials are related to the qualities of flexibility, simplicity, efficiency, versatility, and high surface reactivity. The use of nanoparticles generated from waste materials to remediate methylene blue is highlighted in the present review.