Influence of biogenic iodide-iodine lixiviant and laccase enzyme produced by two-step conditioning of Acinetobacter baumannii on gold, copper, and nickel bioleaching from gold fingers in used card edge connectors

The study emphasizes Acinetobacter baumannii's impressive capacity to efficiently extract metals from gold finger substrates. It delves into the bacterium's distinctive characteristics as both an iodide-iodine oxidizer and a producer of laccase enzymes, which play crucial roles in extracting valuable metals such as gold, copper, and nickel. A. baumannii showcases its prowess in metal oxidation through iodide-oxidizing enzymes, employing biogenic iodide-iodine lixiviants (specifically triiodide) as powerful complexing agents that form stable metal complexes. This process results in the formation of gold (I) diiodide [AuI2]- or gold (III) tetraiodide [AuI4]- species, particularly in environments lacking laccase activity. Moreover, the addition of commercial lignin notably boosts bacterial laccase activity, a key factor in oxidizing iodide to dissolve insoluble metals into soluble metal-iodide complexes. Additionally, A. baumannii's encoded multicopper oxidase serves a vital function in metal homeostasis, supporting the bacterium's survival under conditions of metal excess, where trace metal elements are indispensable for bacterial growth. These compelling findings underscore A. baumannii's effectiveness and strategic approach in bioleaching gold, copper, and nickel from electronic waste, specifically gold fingers, through the application of biogenic iodide-iodine lixiviants and the facilitation of laccase-mediated reaction mechanisms. Importantly, the study highlights the potential of microbial bioleaching as a sustainable method for metal recovery and waste management in electronic industries.