The Cyclic AMP Receptor Protein, Crp, Is Required for the Decolorization of Acid Yellow 36 in Shewanella putrefaciens CN32.

Weijie Liu,Xuge Zhou,Ying Chen,Jiawen Liu,Shiwei Wang,Jingrong Zhu,Di Sun,Cong Liu

doi:10.3389/fmicb.2020.596372

Abstract

Shewanella shows good application potentials in the decolorization and detoxification of azo dye wastewater. However, the molecular mechanism of decolorization is still lacking. In this study, it was found that Shewanella putrefaciens CN32 exhibited good decolorization ability to various azo dyes, and a global regulatory protein cAMP receptor protein (Crp) was identified to be required for the decolorization of acid yellow 36 (AY) by constructing a transposon mutant library. Then, the molecular mechanism of AY decolorization regulated by Crp was further investigated. RT-qPCR and electrophoretic mobility shift assay (EMSA) results showed that Crp was able to directly bind to the promoter region of the cymA gene and promote its expression. Riboflavin acting as an electron shuttle could accelerate the AY decolorization efficiency of S. putrefaciens CN32 wild-type (WT) but did not show a promoting effect to Δcrp mutant and ΔcymA mutant, further confirming that Crp promotes the decolorization through regulating electron transport chains. Moreover, the mutant with cymA overexpression could slightly enhance the AY decolorization efficiency compared with the WT strain. In addition, it was found that MtrA, MtrB, and MtrC partially contribute to the electron transfer from CymA to dye molecules, and other main electron transport chains need to be identified in future experiments. This study revealed the molecular mechanism of a global regulator Crp regulating the decolorization of azo dye, which is helpful in understanding the relationship between the decolorization and other metabolic processes in S. putrefaciens CN32.

Highlights

With the rapid development of the textile, printing, and dyeing industries, more than 700,000 tons of commercial synthetic dyes are produced worldwide each year (Guo et al, 2020b), of which azo dyes account for 60–70% (Hameed and Ismail, 2018; Kong et al, 2018), mainly due to their properties of low cost, easy synthesis, high coloring efficiency, and good stability to various oxidizing agents
It can be seen that the characteristic absorption peak at around 414 nm disappeared after decolorization of 4 h, suggesting that S. putrefaciens CN32 shows good potential in the treatment of azo dye-containing wastewater
acid yellow 36 (AY) was selected as an electron acceptor to reveal the molecular mechanism of S. putrefaciens CN32 decolorization of azo dyes

Summary

Introduction

With the rapid development of the textile, printing, and dyeing industries, more than 700,000 tons of commercial synthetic dyes are produced worldwide each year (Guo et al, 2020b), of which azo dyes account for 60–70% (Hameed and Ismail, 2018; Kong et al, 2018), mainly due to their properties of low cost, easy synthesis, high coloring efficiency, and good stability to various oxidizing agents. Dyeing wastewater affects the transparency of the surrounding water and poses a serious threat to the ecological environment and even human health because azo dye molecules and their degradation products have strong mutagenic, teratogenic, and carcinogenic effects (Guo et al, 2020a; Samir et al, 2020). The most remarkable characteristic of azo dyes is that their molecules contain one or more azo groups (Yan et al, 2012). Because of their stubborn structural properties, azo dyes are very stable in nature and difficult to degrade (Liu W. et al, 2017). Decolorization and detoxification are very necessary before the discharge of azo dye-containing wastewater (Liu et al, 2017b)

Methods

Results

Conclusion