Title: Engineering Acidithiobacillus ferrooxidans for metal corrosion and recovery
Description: Biomining technologies have been developed to use acidophilic microorganisms and the reactions that they catalyze to extract metals from ores in the mining industry. This biological processing through hydrometallurgy is responsible for the production of a significant portion of the world’s copper and gold supplies. Acidithiobacillus ferrooxidans is one of the better-studied and important chemolithotrophic bacterial species that is a part of the natural consortia found in mines across the world. This acidophile is unique in the array of redox reactions it participates in as it is capable of oxidizing both iron and reduced inorganic sulfur species, enabling dissolution of metal from minerals. As the transition to renewable energy continues and the demand for electronic devices grows, more copper and other valuable metals will need to be extracted from increasingly low-grade ores, such as chalcopyrite. Additionally, there has been a growing interest in further developing this biotechnology for the leaching and the recovery of valuable metals from scrap alloys and electronic waste as these feedstock streams can contain rare metals at concentrations above those found in the earth.

However, the challenge in deploying biomining to these applications involves understanding the interactions that can potentially inhibit the extraction of these metals. In this dissertation, we expanded the genetic toolbox for A. ferrooxidans by using a transposition technique for the chromosomal integration of exogenous genes. The ability to permanently modify the genome enables engineering of strains that can be used in industry without the need of maintaining selective pressure for plasmid-based expression. Next, we investigated the potential role of A. ferrooxidans in microbially influenced corrosion. We focused on finding conditions that would enable the corrosion of stainless steel, which is resistant to the medium typically used for the growth of the bacterium. Additionally, the further optimization of the corrosive environment and the introduction of genetically engineered cells led to additional corrosion of a higher-grade stainless steel. Then, we explored how altering the bioavailability of sulfur in different formulations could shift the population phenotypes in A. ferrooxidans.

We found that a unified description with a few parameters could describe the wide range of behaviors observed in the presence of iron and sulfur. Thus, using this improved understanding of A. ferrooxidans, we are able to engineer phenotypes of interest to generate robust strains that can modulate leaching conditions.