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bioRxiv · 10.64898/2025.12.06.692726

Integrated Detoxification, Bioremoval and Ohmic-Heating Recovery of Lead and Cadmium by Escherichia coli K-12 MG1655

Nnaji, N. D.·Anyanwu, C. U.·Miri, T.·Onyeaka, H.
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Abstract

Lead (Pb) and cadmium (Cd) remain among the most persistent and hazardous heavy-metal contaminants in industrial effluents, posing severe risks to ecosystems and human health due to their non-biodegradable nature and high toxicity. In response to the limitations of conventional chemical remediation technologies, this study evaluates the potential of Escherichia coli K-12 MG1655 to function as a microbially driven system for the detoxification, sequestration and recovery of Pb and Cd. Emphasis is placed on oxalic acid production as a mechanistic basis for metal tolerance. High-performance liquid chromatography confirmed that E. coli K-12 MG1655 synthesises oxalic acid under metal stress, with Pb exposure eliciting the highest oxalate output, providing biochemical evidence for metal-oxalate complexation as a key detoxification strategy. Bioaccumulation studies using inductively coupled plasma-optical emission spectrometry revealed exceptional metal removal efficiencies, reaching 99.94% for Pb and 97.77% for Cd at 1000 ppm, while Pb + Cd mixed-metal systems maintained high overall uptake (98.19%). These results demonstrate that E. coli can sequester metals across a wide concentration range with minimal inhibition from competitive ion interactions. Metal recovery from loaded biomass was evaluated through acid desorption and Ohmic heating. Nitric acid (0.1 M HNO3) achieved the highest recovery efficiencies (Pb: 98.5%; Cd: 91.5%), whereas Ohmic heating yielded moderate (Pb: 45.38%; Cd: 45.83%) but environmentally favourable recovery without chemical additives. The integrated findings illustrate a complete microbial remediation-recovery cycle encompassing detoxification via oxalic acid, high-efficiency metal sequestration and effective downstream recovery. This integrative study establishes E. coli K-12 MG1655 as a promising candidate for closed-loop bioremediation systems linking detoxification, sequestration and recovery of heavy metals. Impact statementThis study addresses a major gap in microbial bioremediation research by integrating the interconnected processes of detoxification, metal bioaccumulation and metal recovery within a single microbial platform. By demonstrating that oxalic-acid-driven detoxification directly enhances bioaccumulation performance and enables subsequent metal release through either dilute acid or ohmic-heating regeneration, this work provides a unified framework linking microbial physiology with practical recovery technologies. The study advances the field by showing how microbial systems can be engineered into circular, regenerable bioprocesses, reducing dependency on chemically intensive methods and offering scalable, sustainable solutions for the remediation of metal-contaminated environments.

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Nnaji, N. D., Anyanwu, C. U., Miri, T., Onyeaka, H.. 2025-12-07. Integrated Detoxification, Bioremoval and Ohmic-Heating Recovery of Lead and Cadmium by Escherichia coli K-12 MG1655. https://doi.org/10.64898/2025.12.06.692726

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