Engineering a bioluminescent bioreporter from an environmentally sourced mercury-resistant Enterobacter cloacae strain for the detection of bioavailable mercury.

Abstract

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. 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 0·2µgl-1 with a linear response profile being maintained between a range of 0·4-1600µgl-1 (R2 =0·9604) with a peak bioluminescent response occurring within 1h 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). The results indicated that E. cloacae DWH4lux could detect mercury in quantities below the US Environmental Protection Agency's permitted limit values (2µgl-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. 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.