Estimation of Hg(II) in Soil Samples by Bioluminescent Bacterial Bioreporter E. coli ARL1, and the Effect of Humic Acids and Metal Ions on the Biosensor Performance

Abstract

Mercury is a ubiquitous environmental pollutant of dominantly anthropogenic origin. A critical concern for human health is the introduction of mercury to the food chain; therefore, monitoring of mercury levels in agricultural soil is essential. Unfortunately, the total mercury content is not sufficiently informative as mercury can be present in different forms with variable bioavailability. Since 1990, the use of bioreporters has been investigated for assessment of the bioavailability of pollutants; however, real contaminated soils have rarely been used in these studies. In this work, a bioassay with whole-cell bacterial bioreporter Escherichia coli ARL1 was used for estimation of bioavailable concentration of mercury in 11 soil samples. The bioreporter emits bioluminescence in the presence of Hg(II). Four different pretreatments of soil samples prior to the bioassay were tested. Among them, laccase mediated extraction was found to be the most suitable over water extraction, alkaline extraction, and direct use of water-soil suspensions. Nevertheless, effect of the matrix on bioreporter signal was found to be severe and not possible to be completely eliminated by the method of standard addition. In order to elucidate the matrix role, influences of humic acid and selected metal ions present in soil on the bioreporter signal were tested separately in laboratory solutions. Humic acids were found to have a positive effect on the bioreporter growth, but a negative effect on the measured bioluminescence, likely due to shading and Hg binding resulting in decreased bioavailability. Each of the tested metal ions solutions affected the bioluminescence signal differently; cobalt (II) positively, iron (III) negatively, and the effects of iron (II) and nickel (II) were dependent on their concentrations. In conclusion, the information on bioavailable mercury estimated by bioreporter E. coli ARL1 is valuable, but the results must be interpreted with caution. The route to functional bioavailability bioassay remains long.

Applications of bioluminescence in biotechnology and beyond

“…293 As discussed earlier, whole cell bioluminescent bacterial biosensors are widely used to detect heavy metal concentrations such as mercury, zinc and chromium in ecotoxicology studies. [294][295][296] For more details on this please refer to Section 4.3.…”

Whole-Cell Microbial Bioreporter for Soil Contaminants Detection

“…The proteins from MerR family recognize specific target metal ions, such as the mercury-sensing regulatory protein MerR and lead-sensing regulatory protein PbrR ( Brown et al, 2003 ). For example, mercury-specific bioreporters are constructed via fusing reporter genes such as luxAB and gfp to the downstream of the merR promoter ( Branyikova et al, 2020 ).…”

“…The metal-sensing repressors like ArsR and MerR function as sensing apparatuses to control the transcription of downstream operons ( Kaur et al, 2015 ; Guo et al, 2019 ). Selective mercury-sensing system was incorporated in E. coli via using regulator protein MerR and promoter mer ( Branyikova et al, 2020 ). The detection limit of the mercury-selective bioreporter is 0.035 mg/kg, which is not interfered by other toxic heavy metal ions ( Branyikova et al, 2020 ).…”

“…Selective mercury-sensing system was incorporated in E. coli via using regulator protein MerR and promoter mer ( Branyikova et al, 2020 ). The detection limit of the mercury-selective bioreporter is 0.035 mg/kg, which is not interfered by other toxic heavy metal ions ( Branyikova et al, 2020 ). The arsenic-specific bioreporter with regulators NikR and ArsR exhibits good sensitivity with a detection limit of 22 μg/kg ( Yoon et al, 2016a ; Frick et al, 2019 ).…”

“…The conventional techniques for soil contaminant analysis include gas chromatography–mass spectrometry (GC-MS), high-performance liquid chromatography (HPLC), atomic absorption spectroscopy (AAS), atomic fluorescence spectroscopy (AFS), inductively coupled plasma mass spectrometry (ICP-MS), and X-ray absorption spectroscopy ( Branyikova et al, 2020 ; Wang et al, 2020 ). These instrumental-based analyses enable soil contamination measurements with high sensitivity and accuracy.…”