Construction of luminescent Escherichia coli via expressing lux operons and their application on toxicity test

Recombinant luminescent Escherichia coli strains could be used to detect the toxicity of pure or mixed contaminants as a light-off sensor. In this work, the lux operon of Photobacterium phosphoreum T3 was identified for the first time. Recombinant luminescent E. coli strains were constructed via expressing the lux operons of P. phosphoreum T3 and Vibrio qinghaiensis Q67 in E. coli MG1655, and the optimal protectant containing 10% (w/v) trehalose and 4% sucrose was used to prepare the freeze-dried recombinant luminescent E. coli cells. Then, these freeze-dried E. coli cells were subjected to acute toxicity detection. The results showed that luminescent E. coli strains displayed sensitive toxic responses to BPA, nFe₂O₃, Cd, Pb, As, and Hg, for example, the EC₅₀ values of BPA and nFe₂O₃ to luminescent E. coli strains ranged from 1.54 to 50.19 mg/l and 17.50 to 21.52 mg/l, respectively. Indeed, luminescent E. coli strains exhibited more sensitive responses to Cd, Pb, and Hg than the natural strain Q67. The results suggested that recombinant luminescent E. coli strains could be used for the detection of acute toxicity. Furthermore, the combined toxicities of BPA and nFe₂O₃, Hg, and Pb were measured, and the joint effects of these mixtures were evaluated with luminescent E. coli. The results indicated that the joint effects of BPA and nFe₂O₃ suggested to be synergistic or additive to luminescent E. coli, while the joint effects of heavy metals and nFe₂O₃ exhibited additivities. The cellular endocytosis for Fe₂O₃ nanoparticles was not observed, which could explain the additive instead of synergistic effects between heavy metals and nFe₂O₃. KEY POINTS: • Sequence of the lux operon from P. phosphoreum T3 was reported for the first time. • Recombinant luminescent E. coli was more sensitive to Cd, Pb, and Hg than Q67. • Joint effects of BPA and nFe₂O₃ were synergistic or additive to luminescent E. coli.