Genetic engineering of extremely acidophilic Acidithiobacillus species for biomining: Progress and perspectives

With global demands for mineral resources increasing and ore grades decreasing, microorganisms have been increasingly deployed in biomining applications to recover valuable metals particularly from normally considered waste, such as low-grade ores and used consumer electronics. Acidithiobacillus are a genus of chemolithoautotrophic extreme acidophiles that are commonly found in mining process waters and acid mine drainage, which have been reported in several studies to aid in metal recovery from bioremediation of metal-contaminated sites. Compared to conventional mineral processing technologies, biomining is often cited as a more sustainable and environmentally friendly process, but long leaching cycles and low extraction efficiency are main disadvantages that have hampered its industrial applications. Genetic engineering is a powerful technology that can be used to enhance the performance of microorganisms, such as Acidithiobacillus species. In this review, we compile existing data on Acidithiobacillus species' physiological traits and genomic characteristics, progresses in developing genetic tools to engineer them: plasmids, shutter vectors, transformation methods, selection markers, promoters and reporter systems developed, and genome editing techniques. We further propose genetic engineering strategies for enhancing biomining efficiency of Acidithiobacillus species and provide our perspectives on their future applications.