Characterization of endogenous promoters for control of recombinant gene expression in Acidithiobacillus ferrooxidans

Acidithiobacillus ferrooxidans is an important iron- and sulfur-oxidizing acidophilic chemolithoautotroph that is used extensively in metal extraction and refining, and more recently in the bioproduction of chemicals. However, a lack of genetic tools has limited the further development of this organism for industrial bioprocesses. Using prior microarray studies that identified genes, which may express differentially in response to the availability of iron and sulfur, the cycA1 and tusA promoter sequences have been characterized for their ability to drive green fluorescent protein expression. The promoters exhibited opposite control behavior, where the cycA1 sequence was repressed and the tusA promoter was induced by the presence of sulfur in the growth medium. Sulfur was found to be the dominant signal. The sulfur IC₅₀ for cycA1 was 0.56 mM (18 mg/L), whereas the sulfur EC₅₀ of tusA was 2.5 mM (80 mg/L). Together these sequences provide two new tools to selectively induce or repress gene expression in A. ferrooxidans. Acidithiobacillus ferrooxidans is an important industrial organism; however, genetic tools for control of gene expression do not exist. Here, we report the identification of promoter sequences that allow for the development of control of gene expression for engineering this organism.