Scalable bio-platform to recover critical metals from complex waste sources

Abstract

Chemical methods for extraction and refinement of technologically critical rare earth elements (REEs) are energy intensive, hazardous, and environmentally destructive. Current bio-based extraction systems rely on extremophilic organisms and generate many of the same detrimental effects as chemical methodologies. The mesophilic methylotrophic bacteriumMethylobacterium extorquensAM1 was previously shown to grow using electronic waste by naturally acquiring REEs to power methanol metabolism. Here we show that growth using electronic waste as a sole REE source is scalable up to 10 L with consistent metal yields without the use of harsh acids or high temperatures. Addition of organic acids increases REE leaching in a nonspecific manner. REE-specific bioleaching can be engineered through the overproduction of REE-binding ligands (called lanthanophores) and pyrroloquinoline quinone. REE bioaccumulation increases with leachate concentration and is highly specific. REEs are stored intracellularly in polyphosphate granules, and genetic engineering to eliminate exopolyphosphatase activity increases metal accumulation, confirming the link between phosphate metabolism and biological REE use. Finally, we report the innate ability ofM. extorquensto grow using other complex REE sources including pulverized smart phones, demonstrating the flexibility and potential for use as a recovery platform for these critical metals.

Discovery and characterization of the first known biological lanthanide chelator

“…It is known that M. extorquens AM1 is responsive to Ln levels as low as 2.5 nM, but it is not yet known why Ln are bioaccumulated at much higher levels. 41 M. extorquens AM1 is a candidate to recover lanthanides selectively from electronic waste and old magnets 42 . Previously it has been shown that M. extorquens AM1 can selectively bioaccumulate Nd from NdFeB magnets, hence neodymium salts were chosen in this study.…”

“…We have shown elsewhere that Fe bioaccumulation remains unaffected by overexpression of mll . 42 The Ln affinity of methylolanthanin may be stalled at a local fitness peak, where evolving greater affinity for Ln binding would incur a fitness disadvantage that cannot occur under selection. Siderophores, zincophores, and other metallophores exhibit convergent evolution, where biosynthetically unrelated molecules share the same function.…”

Rare earth elements in biology: From biochemical curiosity to solutions for extractive industries

“…Several biotechnologies have the potential to address issues relating to REE extraction and recycling through their concentration and separation. These technologies have been shown to work well at bench scale, but only one study to date addressing the issue of scalability (Good et al., 2023 ). In addition to scalability, technoeconomic and life cycle analyses will be required to demonstrate that these biotechnologies can compete with existing extraction methods, both from an economic and environmental perspective.…”

“…A similar approach has been used to reclaim/remediate gadolinium (a highly toxic medical imaging agent) from medical waste (Good et al., 2022 ). Notably, hyperaccumulating mutants of M. extorquens have been identified, potentially allowing the development of more efficient REE bioextraction processes (Good et al., 2023 ). Another promising approach has been to engineer the capability to accumulate REEs into a range of microorganisms ( E. coli , Caulobacter crescentus , Yarrowia lipolytica , and Acidithiobacillus ferrooxidans ) by the heterologous expression of lanmodumin targeted to their periplasmic space (Brewer et al., 2019 ; Chang et al., 2020 ; Jung et al., 2023 ; Park et al., 2020 ; Xie et al., 2022 ).…”