Evaluation of mtr cluster expression in Shewanella RCRI7 during uranium removal
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ORIGINAL PAPER
Evaluation of mtr cluster expression in Shewanella RCRI7 during uranium removal Razieh Ghasemi1 · Faezeh Fatemi2 · Mohammad Mir‑Derikvand1 · Mahsa Zarei1 Received: 1 January 2020 / Revised: 3 July 2020 / Accepted: 10 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In recent years, bioremediation is considered as an efficient method to remove the pollutants from the industrial wastewater. In this study, quantitative gene expressions (Real-time RT-PCR) of mtr gene cluster (mtrA, mtrB, mtrC, mtrD, mtrE, mtrF and omcA) in five different uranium concentrations (0.1, 0.25, 0.5, 1 and 2 mM) were performed with ICP and microscopic live cell counting analysis under anaerobic condition, by Shewanella RCRI7 as a native bacterium. The results indicated that the amount of uranium removal and live-cell counting were decreased in the higher uranium concentrations (1 and 2 mM), due to the uranium toxicity, suggesting 0.5 mM as the optimum uranium concentration for Shewanella RCRI7 resistance. The expression of mtrCED and omcA genes presented increasing trend in the lower uranium concentrations (0.1, 0.25 and 0.5 mM) and a decreasing trend in 1 and 2 mM, while mtrABF, presented an inverse pattern, proving the alternative role of mtrF for mtrC and omcA, as the substantial multiheme cytochromes in Extracellular Electron Transfer (EET) pathway. These data are a proof of these gene vital roles in the EET pathway, proposing them for genetic engineering toward EET optimization, as the certain pathway in heavy metal bioremediation process. Keywords Bioremediation · Shewanella RCRI7 · Extracellular electron transfer (EET) · Live cell counting · mtr gene cluster
Introduction Metal breathing bacteria are able to remove the pollutant (such as heavy metals) from industrial wastewater (Seyrig 2010). In situ metal deposition is the result of accepting electrons from the bacteria in anoxic media through the bioremediation process. This process requires electrontransporting released within intracellular oxidative catabolic reactions to the terminal electron acceptors through extracellular electron transfer (EET) pathway (Lovley et al. Communicated by Erko Stackebrandt. * Faezeh Fatemi [email protected] * Mohammad Mir‑Derikvand [email protected] 1
Department of Life Science Engineering, Faculty of New Sciences and Technologies, University of Tehran, Tehran, Iran
Materials and Nuclear Fuel Research School, Nuclear Science and Technology Research Institute, Tehran, Iran
2
1991; Wall and Krumholz 2006). The role of bacteria as a live electrode is passing electrons from electron donors to electron acceptors in the aqueous anoxic environments. Facultative anaerobe bacteria can couple the oxidation of carbon sources to the reduction of numerous terminal electron acceptors while producing energy from electron flowing through cytochromes (Wall and Krumholz 2006; Shi et al. 2007; Pirbadian et al. 2014). Literature reviews regarding genes involved in the extracellular electron transfer in Sh
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