The enhancement of <i>mtrABDEF</i> gene expressions in <i>Shewanella azerbaijanica,</i> through acclimation in high uranium concentrations

Abstract Shewanella azerbaijanica can transfer electrons to uranium in its respiratory system and maintain the efficient growth through bioreduction process. MtrABDEF are some of the main cytochromes involving in Extracellular Electron Transfer of Shewanella . This work attempts to investigate how these genes are affected by various respiratory conditions, and make an effort to enhance their expression through a series of incubations at increasing uranium concentrations. Mtr gene expressions and the uranium removal were analyzed by Real Time RT-PCR and ICP-AES respectively. Uranium threshold concentration, (1 mM uranium for anaerobic electron donor free samples, and 2 mM uranium for electron donor containing samples), the ratio of electron donor to electron acceptor, and the presence of Oxygen, were found to be some of the most important factors affecting the mtr gene expressions during bioreduction. During the acclimation procedure mtr gene expressions were well enhanced, demonstrating that acclimation is a suitable strategy to improve Mtr pathway. Less uranium removal percentage by acclimated bacteria, however, indicates that mtrABDEF are not the most significant agents in bacterial uranium respiration. This work can serve as a model for more advanced research in uranium bioreduction and acclimation-based reduction improvement.