AUTHOR=Zhou Zijie , Zhu Lin , Dong Yixuan , You Lexing , Zheng Shixue , Wang Gejiao , Xia Xian 

TITLE=Identification of a Novel Chromate and Selenite Reductase FesR in Alishewanella sp. WH16-1

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.834293

DOI=10.3389/fmicb.2022.834293

ISSN=1664-302X

ABSTRACT=<p>A ferredoxin protein (AAY72_06850, named FesR) was identified to associate with chromate [Cr(VI)] resistance in <italic>Alishewanella</italic> sp. WH16-1. FesR and its similar proteins were phylogenetically separated from other reductase families. Unlike the reported Cr(VI) and selenite [Se(IV)] reductases, two 4Fe-4S clusters and one flavin adenine dinucleotide (FAD) -binding domain were found in the FesR sequence. The experiment <italic>in vivo</italic> showed that the mutant strain Δ<italic>fesR</italic> had lost partial Cr(VI) and Se(IV) reduction capacities compared to the wild-type and complemented strains. Furthermore, overexpression in <italic>Escherichia coli</italic> and enzymatic tests <italic>in vitro</italic> showed FesR were involved in Cr(VI) and Se(IV) reduction. 4Fe-4S cluster in purified FesR was detected by ultraviolet-visible spectrum (UV-VIS) and Electron Paramagnetic Resonance (EPR). The Km values of FesR for Cr(VI) and Se(IV) reduction were 1682.0 ± 126.2 and 1164.0 ± 89.4 μmol/L, and the Vmax values for Cr(VI) and Se(IV) reduction were 4.1 ± 0.1 and 9.4 ± 0.3 μmol min<sup>–1</sup> mg<sup>–1</sup>, respectively. Additionally, site-directed mutagenesis and redox potential analyses showed that 4Fe-4S clusters were essential to FesR, and FAD could enhance the enzyme efficiencies of FesR as intracellular electron transporters. To the best of our knowledge, FesR is a novel Cr(VI) and Se(IV) reductase.</p>