The Construction of an Engineered Bacterial Strain and Its Application in Accumulating Mercury from Wastewater

Shenghe Chang,Zhengjing Wu,Wei Sun,Haiyan Shu

doi:10.3390/app8091572

Abstract

To remove organic and inorganic mercury from wastewater, an engineered bacterial strain, BL21-7, was constructed that contained the artificial operon P16S-g10-merT-merP-merB1-merB2-ppk-rpsT. For BL21-7, the minimum inhibitory concentrations of mercuric chloride, methylmercury chloride and phenylmercury chloride in Luria-Bertani (LB) medium were 100 µmol/L, 60 µmol/L and 80 µmol/L, respectively. After being cultured in three media (liquid LB containing 80 µmol/L mercuric chloride, 40 µmol/L methylmercury chloride or 60 µmol/L phenylmercury chloride) for 72 h, the engineered bacteria accumulated up to 70.5 ± 1.5 µmol/L, 33.5 ± 3.2 µmol/L and 45.3 ± 3.7 µmol/L of mercury, respectively. In the presence of 10 µmol/L Cd2+, 10 µmol/L Pb2+ or 10 µmol/L Cu2+, the accumulation of mercurial derivatives by BL21-7 was not affected. BL21-7 could accumulate mercury well in media with pH values ranging from 5 to 8 and it could work well at temperatures from 25 °C to 37 °C. After BL21-7 was added to wastewater and cultured for 24 h, approximately 43.7% of the Hg in the wastewater was removed.

Highlights

An In-Fusion HD Cloning Kit, T4 DNA ligase, HgCl2, methylmercury chloride (MMC), phenylmercury chloride (PMC) and other chemicals were purchased from TAKARA (Dalian, China)
The results showed that the transcripts of ppk-rpsT in BL21-1, BL21-2 and BL21-7 were 1373 ± 62 copies/ng, 8245 ± 119
The results showed that after BL21-7 was cultured in LB medium containing 80 μmol/L HgCl2 for 72 h, HgCl2 for 72 h, the Hg content in the bacterial pellet was 70.5 ± 1.5 μmol/L (Figure 6)

Summary

Introduction

Hg exists in three forms: elemental (Hg(0)), inorganic (Hg2+ or Hg+ ) and organic forms (R-Hg+ or R-Hg-X, where “R” is methyl or phenyl and “X” is acetate) [1]. All the forms are hazardous but the extent of toxicity varies among different forms of Hg. Organic Hg is the most toxic and elemental is the least toxic. The Hg in agricultural soil can enter the human body through crops and Hg mainly comes from irrigated-polluted water released from factories [5]. A.M.; Rodrigues, S.; Mieiro, C.; Ferreira da Silva, E.; Pereira, E.; Duarte, A.C. Controlling factors and environmental implications of mercury contamination in urban and agricultural soils under a long-term influence of a chlor-alkali plant in the North–West Portugal.

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