Synthetic symbiotic bacteria reduces the toxicity of mercury ingested via contaminated food.

Mercury contamination in food poses a significant threat to human health. In this article, we propose a novel approach to solve this problem by enhancing the function of gut microbiota against mercury using a synthetically engineered bacterial strain. An engineered Escherichia coli biosensor MerR with mercury binding function was introduced into the intestines of mice for colonization, whereafter the mice were challenged with oral mercury. Compared with the control mice and mice colonized with unengineered Escherichia coli, the mice with biosensor MerR cells in their gut showed significantly stronger mercury resistance. Furthermore, mercury distribution analysis revealed that biosensor MerR cells promoted the excretion of oral mercury with feces, thereby blocking the entry of mercury into the mice, decreasing the concentration of mercury in the circulatory system and organs, and, thus, attenuating the toxicity of mercury to the liver, kidneys and intestines. Colonization with the biosensor MerR did not result in significant health problems in the mice, nor were genetic circuit mutations or lateral transfers identified during the experiments, thus demonstrating the safety of this approach. This study elucidates the remarkable promise of synthetic biology for modulating gut microbiota function.

A gas reporting whole-cell microbial biosensor system for rapid on-site detection of mercury contamination in soils.

As optical reporting elements, fluorescent proteins are extensively used in whole-cell microbial biosensors. However, the use of these optical reporters is limited in opaque media such as soil. This study described a method utilizing gas as a reporting signal that could be used for the rapid on-site detection of mercury in soil. In this biosensor, the MerR protein could capture mercury ions and then bind the promoter of the efe gene to initiate the synthesis of the ethylene (C2H4)-forming enzyme that produced the gas. The research showed that the mercury ion concentrations could be converted into C2H4 gas signals, which were quantified using a handheld C2H4 sensor. By optimizing the biosensor to improve its anti-interference ability in the system, it could detect mercury ion concentrations in the soil ranging from 0.2 to 20 mg/kg within 45 min, effectively reflecting whether the mercury pollution in the soil exceeded the limit standard. This study provides a simple, inexpensive, and portable method for the on-site detection of soil pollutants.

A test strip platform based on a whole-cell microbial biosensor for simultaneous on-site detection of total inorganic mercury pollutants in cosmetics without the need for predigestion.

Mercury pollutants such as mercuric chloride (HgCl2), mercurous chloride (Hg2Cl2) and mercuric ammonium chloride (Hg(NH2)Cl) are often found in cosmetics. Previous attempts at the on-site detection of mercury were hindered by the complicated and dangerous pretreatment procedure of converting various forms of mercury to Hg (II) ions. In this study, a test strip platform was developed based on a whole-cell microbial biosensor for the simultaneous detection of soluble and insoluble inorganic mercury pollutants in cosmetics without the need for predigestion. The genetic circuits with constitutively expressed MerR as sensor proteins and inducible red fluorescent protein (RFP) as the reporter were introduced into Escherichia coli to construct the mercury detection biosensor. The RFP fluorescence intensity of this biosensor showed a excellent linear relationship (R2 = 0.9848) with the Hg (II) concentration ranging from 50 nM to 10 µM in Luria-Bertani (LB) broth. Further research indicated that this biosensor could respond not only to Hg (II) ions but also to insoluble Hg2Cl2 and Hg2Cl2. The transcriptomic results confirmed the mercury conversion ability of the whole-cell biosensor from a gene expression perspective. This biosensor was embedded on filter paper to form a test strip, which could be used to determine whether the total inorganic mercury pollutants in cosmetics exceeded 1 mg/kg. Therefore, this strip provided a low cost, easy-to-use, and instrument-independent method for the detection of mercury pollution in cosmetics, while this study revealed the unique advantages of microbial biosensors in the automatic bioconversion of targets.