Effects of UV stress on Shewanella azerbaijanica bioremediation response

Abstract

Shewanella azerbaijanica roles as a live electrode, passing electrons from electron donors to electron acceptors, to gain energy from the extracellular electron transfer (EET) pathway. The present study, considered the quantitative expressions of the major EET reductase genes (mtr cluster), together with uranium removal, live-cell counting, and spectrophotometry in UV-C treated bacteria (0, 60, 120 and 180 s). The simultaneous decline in the uranium removal and cell counting, along with major mtr gene expression patterns (mtrABDEF), approved the negative effects of UV-C radiation on uranium bioreduction in S. azerbaijanica. Uranium removal and cell counting decreased to 25.49% and 0.45 × 109 cells/mL in the 180s UV-C treated sample, respectively at 2 mM uranium concentration, while no decline trend found in 0.5 mM for the counted cells and uranium removal tests. No considerable expression of omcA and omcB (mtrC) genes were traced due to spontaneous mutagenesis during the in vitro serial passages, proposing a novel alternative EET pathway in S. azerbaijanica during uranium bioreduction process. The results could pave the way for further researches to modify the bioremediation process through genetic manipulation.