Applied Radiation and Isotopes 177 (2021) 109911 Available online 25 August 2021 0969-8043/© 2021 Published by Elsevier Ltd. Investigating the rus and petI operon expression patterns in exposed Acidithiobacillus ferrooxidans sp. FJ2 to different doses of gamma irradiation Sara Sheikh Nasiri a, b , Mona Sarabi a, c , Faezeh Fatemi d, * , Salome Dini e a Radiation Application Development Company, AEOI, Tehran, Iran b Department of Biology, Payame Noor University, Tehran, Iran c Department of Biology, Shahed University, Tehran, Iran d Nuclear Fuel Cycle Research School, Nuclear Science and Technology, Research Institute, Tehran, Iran e Young Researchers and Elite Club, Karaj Branch, Islamic Azad University, Karaj, Iran A R T I C L E INFO Keywords: Uranium bioleaching Acidithiobacillus ferrooxidans sp. FJ2 Gamma-ray rus and petI operons ABSTRACT The bioleaching process is developing as an economic and successful biotechnology method in the metallurgy industry. Acidithiobacillus ferrooxidans is one of the most important bacteria involved in uranium bioleaching which converts insoluble U 4+ to soluble U 6+ by oxidation of Fe 2+ to Fe 3+ using several periplasmic proteins encoded by the genes in rus and petI operons in its electron transport pathway. Accordingly, the purpose of this study was to consider the expression of these genes through exposed A. ferrooxidans sp. FJ2 to γ-ray in 17 different doses targeting uranium extraction yield. Acidithiobacillus ferrooxidans sp. FJ2 was irradiated by gamma rays at 25, 50, 75, 100, 150, 300, 450, 600, 750 Gy and 1, 2, 5, 10, 15, 20, 25 and 30 kGy doses. Moreover, the Eh value of 9k culture media was measured as special screening criteria to select the four treatments. The selected bacteria were cultured in 9k media, con- taining 50% uranium ore powder in the bioleaching process. Then, the value of pH & Eh of culture media, Fe 2+ and uranium concentrations in 4, 8 and 13 day’s period of incubation were measured. In followings, the expression levels of cyc1, cyc2, rus, coxB, petA, petB, petC and cycA genes at the end of each period were investigated by real-time PCR. Overall, all samples demonstrated a decrease in pH value and Fe 2+ concentration and an increase in Eh value and U concentration in time intervals. The gamma irradiation in given doses raised the expression levels of all genes encoded in rus and petI operons, except petB gene during the bioleaching process, although, it had no effect either on the pH, Eh values or on Fe 2+ and uranium concentrations. This result implies that during the oxidation of ferrous iron and formation of Jarosite sediment, the decreasing trend of pH and the increasing trend of Eh occurred in all samples. However, the differences in expression of the genes of rus and petI operons in the samples did not have an effect on uranium extraction. 1. Introduction Most of the world’s ore resources are consisted of sulfde minerals while the concentration of metals is so low that it is not economically to be extracted by conventional chemical methods. Therefore, fnding an appropriate solution for the extraction of metals from a large volume of sulfde minerals has always been a concern for researchers. In general, the bioleaching process is an applied biotechnological bioconversion of insoluble metal sulfde compounds to soluble metal ions and sulfate compounds. Accordingly, acidophilic microorganisms which oxidize ferrous or sulfur compounds are involved in this bio-oxidation process. Therefore, bioleaching is the most appropriate option commonly used to recover metals such as gold, copper, and uranium (Dong et al., 2011; Ehrlich, 2001; Tabak et al., 2005; Falag´ an et al., 2017; Rouchalova et al., 2020). This process is not only less energy demanding but also, envi- ronmentally benign manner (Sajjad et al., 2019). Acidithiobacillus ferrooxidans, the Gram-negative, chemolithotrophic bacterium which is the most known microorganism in bioleaching ob- tains energy in their respiratory chains by oxidizing Fe 2+ to Fe 3+ and reducing sulfur compounds under aerobic and acidic conditions (Priya and Hait, 2018; Gao et al., 2020; Breed et al., 2015; Ohmura et al., 2002). The ferrous oxidation divided into downhill and uphill pathways * Corresponding author. E-mail address: ffatemi@aeoi.org.ir (F. Fatemi). Contents lists available at ScienceDirect Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso https://doi.org/10.1016/j.apradiso.2021.109911 Received 15 December 2019; Received in revised form 25 May 2021; Accepted 15 August 2021