Transposase-Mediated Chromosomal Integration of Exogenous Genes in Acidithiobacillus ferrooxidans

The development of Acidithiobacillus ferrooxidans as a non-model host organism for synthetic biology is hampered by a lack of genetic tools and techniques. New plating and liquid-based selection methods were developed to improve the identification of transformed cell lines. Enabled by these methods, a hyperactive transposase was used to generate mutants with integrated genes for the expression of the superfolder green fluorescent protein (sfGFP) gene or a 2-keto decarboxylase (KDC) gene, which enabled the production and secretion of isobutyric acid (IBA). An inverse PCR method was used to identify the insertion sites of the KDC gene in several mutants, leading to the identification of a region on the chromosome that may be suitable for future genetic insertions. These results demonstrate that functional exogenous metabolic genes have been chromosomally integrated into A. ferrooxidans, and this advance will facilitate the future development of these cells for new biotechnology applications.IMPORTANCEAcidithiobacillus ferrooxidans is an iron- and sulfur-oxidizing chemolithoautotroph and is a key member of the microbial consortia used in industrial biomining applications. There is interest in exploiting these cells for other metal recovery applications as well as in developing them as unique nonmodel microbial cell factories. Plasmid-driven expression of exogenous genes has been reported, and homologous recombination has been used to knock out some gene expression. Here, new selection protocols facilitated the development of a transposition method for chromosomal integration of exogenous genes into A. ferrooxidans This greatly expands the available genetic toolbox, which will open the door to greater metabolic engineering efforts for these cells.