Bioleaching of critical trace metals by Sphingomonas desiccabilis: substrate-driven selectivity in Earth and space...

Biotechnological advances are transforming the potential for sustainable resource utilization in space exploration. Biomining, using microorganisms to extract valuable metals, has emerged as a viable strategy for in situ resource utilization (ISRU) in extraterrestrial environments. However, an increasing body of literature is showing that selecting the most efficient bioleaching approach highly depends on the interaction between the microbial species, the type of rock and environmental conditions. In the space biomining context, the heterotrophic bacterium Sphingomonas desiccabilis has demonstrated its capacity to extract valuable metals in space.

This study harnessed a comparative bioleaching analysis to investigate the organism's ability to extract industrially relevant metals from seven terrestrial and extraterrestrial rock types, including a meteorite, a basaltic rock, and samples from the Sudbury Basin, an impact structure formed ~1.85 Ga ago.

We demonstrated that, depending on the substrate mineralogy, S. desicca bilis selectively mobilized Ce (up to 10.6%), Th (up to 1.5%), and other metals such as Pd, Pt, Mo, and W, at circum-neutral pH conditions. However, the extraction was not equal across all substrates, indicating the importance of mineralogy in bioleaching.

While extraction rates were lower compared to industrial biomining standards, these results underscore the organism's potential in low-grade rocks bioleaching, particularly relevant for sustainable terrestrial biomining and long-duration space missions. More broadly, this work demonstrates that bioleaching efficiency is shaped not only by the microbial species employed, but also by the specific characteristics of the substrate, emphasizing the need to tailor bioleaching strategies to distinct mineral contexts.