Engineering a bioluminescent bioreporter from an environmentally sourced mercury‐resistantEnterobacter cloacaestrain for the detection of bioavailable mercury

Abstract

Aim Escherichia coli is the conventional choice as the host strain for whole‐cell bioreporter construction due to its well‐understood genetics and well‐established cloning protocols. However, for real‐world environmental biosensing applications, it is often beneficial to use a bacterial strain derived directly from the environment under study to better ensure chemical target specificity and optimal response time. The aim of this study was to develop a whole‐cell bioreporter for detection of bioavailable mercury by replacing E. coli with a wild‐type bacterial host derived from a soil environment. Materials and Results In this study, an Enterobacter cloacae strain isolated from soil derived from a municipal and electronic waste dumping site was engineered to serve as a bioluminescent bioreporter for mercury toxicity by linking its merR‐like gene and promoter sequence to a reorganized luxABCDE gene cassette from Photorhabdus luminescens. This bioreporter, designated as E. cloacae DWH4lux, detected mercury (HgCl2) at a minimum concentration of 0·2 µg l−1 with a linear response profile being maintained between a range of 0·4–1600 µg l−1 (R2 = 0·9604) with a peak bioluminescent response occurring within 1 h after exposure. No significant synergistic or antagonistic influences were observed on the bioluminescent response by other contaminating metal elements. Enterobacter cloacae DWH4lux was also demonstrated to detect mercury effectively in artificially contaminated water sample with linear correlation (R2 = 0·9623). Conclusions The results indicated that E. cloacae DWH4lux could detect mercury in quantities below the US Environmental Protection Agency’s permitted limit values (2 µg l−1). Hence, it is concluded that E. cloacae DWH4lux has the potential to serve as an effective whole‐cell bioreporter for the environmental monitoring of mercury contamination. Significance and Impact of the Study This study provides new insight into the recruitment of mercury‐tolerant bacterial hosts derived from environmental samples over the conventional lab‐based E. coli host for the construction of mercury bioreporters. With improved response time and selectivity, the environmentally sourced bacteria can serve as an alternative host choice to improve biosensing technology in the near future.

Use of whole-cell bioreporters to assess bioavailability of contaminants in aquatic systems

“…This is because the sensitivity and response of individual strains vary under the stress of different contaminants (Phyo et al, 2021). For example, for the construction of WCB to detect mercury, Din et al (2019) isolated mercury-resistant bacteria, an Enterobacter cloacae strain, from a contaminated soil environment. They reported that their bioreporter was both more sensitive and faster than other bireporters constructed with model E. coli bacterial strains.…”

“…Chemical instrumental methods are used to analyze the total concentrations of pollutants (Kolpin et al, 2002). However, the total concentration of a contaminant is not always related to its toxicity, it has been demonstrated that bioavailability is a prerequisite for toxicity (Wells et al, 2005a;Fairbrother et al, 2007;Din et al, 2019). In other words, the chemical analysis data are inadequate to efficiently reflect the biological impacts of toxic substances (Axelrod et al, 2016).…”

Metabolic engineering of the carotenoid biosynthetic pathway toward a specific and sensitive inorganic mercury biosensor

“…15 In previous studies, only luciferase-based whole-cell biosensors could respond to Hg(II) in the nanomolar range. 38,39 Due to the signal amplication effect, the LOD of a pigment-based biosensor is comparable to a biosensor employing enzymatic reporters, including b-galactosidase and luciferase. However, its advantage over these traditional biosensors is its independence from expensive substrates and instruments.…”

Differential Detection of Bioavailable Mercury and Cadmium Based on a Robust Dual-Sensing Bacterial Biosensor

“…However, the biosensor sensitivity is usually determined by genetic circuit engineering and types of reporter genes ( Gupta et al, 2019 ; Hui et al, 2020 ). Metalloregulator MerR is a Hg(II)-responsive transcriptional factor, which has been employed to develop bacterial whole-cell biosensors using luciferase ( Din et al, 2019 ), β-galactosidase ( Hansen and Sorensen, 2000 ), fluorescence protein ( Zhang et al, 2021 ), and visual pigments ( Guo et al, 2021a ; Hui et al, 2021a ) as the signal outputs. All of these above bacterial biosensors responded to Hg(II) with high selectivity and variable sensitivity.…”