Copper promotes E. coli laccase-mediated TNT biotransformation and alters the toxicity of TNT metabolites toward Tigriopus japonicus

Ecotoxicol Environ Saf. 2019 May 30;173:452-460. doi: 10.1016/j.ecoenv.2019.02.056. Epub 2019 Feb 21.

Abstract

Although laccase is involved in the biotransformation of 2,4,6-trinitrotoluene (TNT), little is known regarding the effect of E. coli laccase on TNT biotransformation. In this study, E. coli K12 served as the parental strain to construct a laccase deletion strain and two laccase-overexpressing strains. These E. coli strains were used to investigate the effect of laccase together with copper ions on the efficiency of TNT biotransformation, the variety of TNT biotransformation products generated and the toxicity of the TNT metabolites. The results showed that the laccase level was not relevant to TNT biotransformation in the soluble fraction of the culture medium. Conversely, TNT metabolites varied in the insoluble fraction analyzed by thin-layer chromatography (TLC). The insoluble fraction from the laccase-null strain showed fewer and relatively fainter spots than those detected in the wild-type and laccase-overexpressing strains, indicating that laccase expression levels were interrelated determinants of the varieties and amounts of TNT metabolites produced. In addition, the aquatic invertebrate Tigriopus japonicus was used to assess the toxicity of the TNT metabolites. The toxicity of the TNT metabolite mixture increased when the intracellular laccase level in strains increased or when purified E. coli recombinant Laccase (rLaccase) was added to the culture medium. Thus, our results suggest that laccase activity must be considered when performing microbial TNT remediation.

Keywords: Copper ion; Laccase; Remediation; TNT transformation; Toxicity.

MeSH terms

  • Animals
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Biotransformation
  • Chromatography, Thin Layer
  • Copepoda / drug effects*
  • Copper / pharmacology*
  • Escherichia coli / genetics
  • Escherichia coli / metabolism*
  • Laccase / metabolism*
  • Trinitrotoluene / metabolism
  • Trinitrotoluene / toxicity*

Substances

  • Bacterial Proteins
  • Trinitrotoluene
  • Copper
  • Laccase