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. 2023 Jul 27;14:1218933. doi: 10.3389/fmicb.2023.1218933

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Copyright © 2023 Zhu, Guo, Ma, Lin, Wang, Gao, Liu, Zhang, Luo and Hui.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Pb(II) triggers the biosynthesis of proviolacein, which can be converted into two colored substances under non-oxidizing and oxidizing conditions. (A) Design of PV-based whole-cell biosensor toward Pb(II). The PV biosynthetic module is artificially synthesized and genetically fused downstream of the Pb(II) sensory module. A tetracistronic unit is transcribed upon exposure to intracellular bioavailable Pb(II). PV biosynthesis is based on the branched violacein biosynthetic pathway catalyzed by VioA, VioB, VioE, and VioD. After n-butanol extraction accompanied by oxidation and non-oxidation treatments, PV in the organic phase was converted into two colored substances. PbrR, Pb(II) responsive metalloregulator; IPA, indole-3-pyruvate acid imine; oxy, oxidizing condition; non-oxy, non-oxidizing condition. (B) After non-oxidation and oxidation treatment, the n-butanol phase containing PV was placed at 25°C for 8 h. Representative photos from three independent experiments are shown. Visible absorption spectra of PV derivatives after non-oxidation (C) and oxidation (D) treatment were scanned at 1-h intervals. The wavelength range is from 400 to 700 nm in 1 nm intervals. Representative results from three independent assays are shown.