Microbial valorization of E-waste: Bacterial recycling and synthesis of technology-critical metal nanoparticles.

Electronic waste (E-waste) is one of the fastest growing waste streams worldwide, posing serious challenges for environmental and human health, while representing a rich secondary source of valuable metals. Among these technology-critical metals (TCMs) are those, which are essential for renewable energy systems, electronics and low carbon technologies, yet face increasingly disrupted supply chains. This chapter explores the role of E-waste as an urban mine within a circular economy framework and highlights the emerging bio-based strategies for sustainable metal recovery, with particular emphasis on bacterial systems. Bacteria employ versatile mechanisms such as biosorption, bioaccumulation, bioleaching and biomineralization to capture, dissolve and transform metals, offering a green alternative to conventional physical and chemical methods for metal recovery. Beyond recovery, bacteria can upcycle the recovered metals into value added nanoparticles with diverse biomedical, environmental and catalytic applications. Advanced omics approaches including transcriptomics, metabolomics and proteomics provide key insights for the rational design of synthetic biology strategies aimed to enhance metal recovery and enable controlled, efficient synthesis of metal nanoparticles with tailored properties. Overall, the chapter combines E-waste management with microbial biotechnology and nanotechnology presenting a sustainable way to secure technology-critical metals, reducing environmental impact and promoting the transition to a green circular economy.