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

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

doi:10.3389/fmicb.2022.834293

Zijie Zhou, Yixuan Dong + Show 5 more

Open Access

https://doi.org/10.3389/fmicb.2022.834293

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Abstract

A ferredoxin protein (AAY72_06850, named FesR) was identified to associate with chromate [Cr(VI)] resistance in Alishewanella 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 in vivo showed that the mutant strain ΔfesR had lost partial Cr(VI) and Se(IV) reduction capacities compared to the wild-type and complemented strains. Furthermore, overexpression in Escherichia coli and enzymatic tests in vitro 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–1 mg–1, 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.

Highlights

IntroductionThe transition metal chromium (Cr) is widely used in industry (Lunk, 2015; Xia et al, 2021)
The amino acid sequence of FesR was blasted in the NCBI conserved domain database
No transmembrane motifs or signal peptides were predicted in the sequence of FesR. These results indicated that FesR might be an intracellular reductase

Summary

Introduction

The transition metal chromium (Cr) is widely used in industry (Lunk, 2015; Xia et al, 2021). The wide applications and long mining history have led to Cr contamination. Cr(VI) (chromate) and Cr(III) are the most common and stable forms in the natural environment (Xia et al, 2021). Cr(VI) is highly toxic because its easy migrates, while Cr(III) has low toxicity as low solubility and easy immobilization (Moukarzel, 2009; Wang et al, 2017). There are four valences of Se in the natural environment: Se(IV), Se(IV) (selenite), Se(0) and Se(-II). Se(IV) is highly toxic and soluble, while Se(0) is non-toxic as low solubility (Wang et al, 2022). Cr(VI) and Se(IV) reduction is a very important way to remediate Cr and Se contamination

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