Biosensing environmental pollution

https://doi.org/10.1016/j.copbio.2007.05.005Get rights and content

Whole-cell biosensors are finding increasing use for the detection of environmental pollution and toxicity. These biosensors are constructed through the fusion of promoters, responsive to the relevant environmental conditions, to easily monitored reporter genes. Depending on the choice of reporter gene, expression can be monitored by the production of colour, light, fluorescence or electrochemical reactions. Recent advances in this area have included the development of biosensors of compact size that enable the on-line and in situ monitoring of a large number of environmental parameters.

Introduction

Bioremediation (i.e. the use of plants or microorganisms to clean up environmental pollution) has seen a surge of interest in recent years. Traditionally, the efficacy of bioremediation has been determined chemically, by measuring changes in total pollutant concentrations, usually complemented by chromatographic results (gas chromatography or gas chromatography-mass spectrometry). Recently, however, attempts have been made to use biosensors, especially microbial whole-cell biosensors, to monitor the rate of pollutant elimination [1, 2, 3, 4, 5, 6, 7].

Biosensors are defined as monitoring systems based on the use of biological organisms or biologically derived reactions. For example, whole organisms, such as Daphnia or small fish, are being used to monitor water toxicity and enzymes can be used as biosensors of oxygen or glucose. The main drawback of biosensors is that, because they depend on biological systems, they are less reproducible than chemical methods and the values obtained are usually relative and not absolute. However, they can be considerably more time-effective and cost-effective and constitute a good tool for monitoring changes or on-line processes. Another important advantage of biosensors is that they detect only the biologically active pollutants, and the response is proportional to the level of toxicity.

This review focuses on whole-cell, ‘man-made’ biosensors based on recombinant DNA technology. These biosensors are constructed by fusing a pollutant-responsive gene promoter to a gene coding for a protein that can be easily quantified. In one such example, an Escherichia coli K-12 strain has been adapted for the detection of aromatic hydrocarbons. The E. coli cells carry the promoter of the xylS gene (induced by aromatic hydrocarbons) from Pseudomonas putida fused to a promoterless luciferase operon (from Vibrio harveyi or firefly). The expression of luciferase is induced by the presence of aromatic compounds and can be measured by light emission. Similar biosensors were constructed that can monitor the level of additional environmental pollutants, such as octane [3, 4].

Recently, new whole-cell biosensors have been reported in which gene expression is monitored by electrochemical means. These promoter-based, whole-cell biosensors are suitable for on-line and in situ monitoring of pollutants [8, 10, 11, 12]. An example is depicted in Figure 1, which shows a recombinant gene construct effective in biosensing heavy metals [8, 9]. In this construct, the promoter and N-terminal region of the zntA gene, involved in the efflux of heavy metals, is fused to a promoterless lacZ gene, which codes for the enzyme β-galactosidase. Bacteria carrying this gene fusion respond to the presence of heavy metals by inducing the production of β-galactosidase, an enzyme that can easily be monitored by colorimetric and electrochemical reactions.

Here, I review the major types of reporters and promoters used for the construction of biosensors and discuss the advantages and disadvantages of these different systems. I go on to look at possible future directions in biosensor research in relation to monitoring environmental pollution.

Section snippets

The construction of biosensors

As mentioned above, whole-cell, man-made biosensors typically consist of a promoter, responsive to one or more pollutants or toxicants, genetically fused to a promoterless reporter gene. The recombinant genes can be located on plasmids or on the chromosome. An effective biosensor depends on the correct choice of its two constituents: the promoter and the reporter gene.

In situ and on-line measurements

An important aspect of biosensing environmental pollutants is the ability to monitor in situ and preferably on-line. Having biosensors that can be used in the field dispenses with the need to bring samples to the laboratory, and enables real-time assessment of the level of pollution. On-line and in situ monitoring of gene expression can be performed by employing reporter enzymes whose activity can be monitored electrochemically [8]. The electrochemical measurements are highly sensitive,

Monitoring with biological systems – when and where

Biosensors are fast, cost-effective and indicate the level of ‘relevant’ toxic materials. Their main disadvantage is that they do not give absolute chemical values. Moreover, because they depend on biological systems, they can only indicate relative levels, never absolute levels. For authorities such as the Environmental Protection Agency, with the present set of regulations, the inability to determine absolute concentrations is a drawback. However, because there is no way to determine absolute

Future directions for biosensor development

There are several obvious directions for developing biosensors. One of the main problems with the use of biological material is the difficulty of maintaining constant activity for a long time. For environmental biosensors it is also important to enable long storage at room temperature. To meet these demands, various conservation techniques have been reported, including freeze drying, vacuum drying, continuous cultivation, and immobilization in biocompatible polymers of organic or inorganic

Conclusions

In conclusion, cell-based biosensors provide effective tools for detecting environmental pollution and toxicity. In the future, biosensors are likely to become smaller and more flexible and will enable the on-line and in situ monitoring of a large number of environmental parameters. Clearly, we are a long way from the times of the ‘classic’ biosensor — the canary down the mine shaft or the dog of the wine maker!

References and recommended reading

Papers of particular interest, published within the period of review, have been highlighted as:

  • • of special interest

  • •• of outstanding interest

Acknowledgements

This work was supported, in part, by the Manja and Morris Leigh Chair for Biophysics and Biotechnology.

References (48)

  • A. Norman et al.

    A flow cytometry-optimized assay using an SOS-green fluorescent protein (SOS-GFP) whole-cell biosensor for the detection of genotoxins in complex environments

    Mutat Res

    (2006)
  • S.J. Sorensen et al.

    Making bio-sense of toxicity: new developments in whole-cell biosensors

    Curr Opin Biotechnol

    (2006)
  • J.W. Choi et al.

    Cell immobilization using self-assembled synthetic oligopeptide and its application to biological toxicity detection using surface plasmon resonance

    Biosens Bioelectron

    (2005)
  • S. Belkin

    Microbial whole-cell sensing systems of environmental pollutants

    Curr Opin Microbiol

    (2003)
  • J. Bjerketorp et al.

    Advances in preservation methods: keeping biosensor microorganisms alive and active

    Curr Opin Biotechnol

    (2006)
  • S. Marques et al.

    Controlling bacterial physiology for optimal expression of gene reporter constructs

    Curr Opin Biotechnol

    (2006)
  • J.H. Lee et al.

    A cell array biosensor for environmental toxicity analysis

    Biosens Bioelectron

    (2005)
  • J.H. Lee et al.

    An integrated mini biosensor system for continuous water toxicity monitoring

    Biosens Bioelectron

    (2005)
  • I. Biran et al.

    Optical imaging fiber-based live bacterial cell array biosensor

    Anal Biochem

    (2003)
  • R.S. Burlage et al.

    Living biosensors for the management and manipulation of microbial consortia

    Annu Rev Microbiol

    (1994)
  • S. Kohler et al.

    Reporter gene bioassays in environmental analysis

    Fresenius J Anal Chem

    (2000)
  • P. Sticher et al.

    Development and characterization of a whole-cell bioluminescent sensor for bioavailable middle-chain alkanes in contaminated groundwater samples

    Appl Environ Microbiol

    (1997)
  • S. Daunert et al.

    Genetically engineered whole-cell sensing systems: coupling biological recognition with reporter genes

    Chem Rev

    (2001)
  • I. Biran et al.

    Online and in situ monitoring of environmental pollutants: electrochemical biosensing of cadmium

    Environ Microbiol

    (2000)
  • Cited by (80)

    • The state-of-the-art in bioluminescent whole-cell biosensor technology for detecting various organic compounds in oil and grease content in wastewater: From the lab to the field

      2022, Talanta
      Citation Excerpt :

      Second, the whole-cell biosensor consists of a living bacterium that has its specific requirements for environmental conditions during the metabolic process towards the target analyte. According to Ron, it was reported that a whole-cell biosensor can't function in an anaerobic condition [38]. Furthermore, the optimal induction temperature for whole-cell biosensors has been reported to be between 20 and 37 °C [22,23,27].

    • Microbial-derived biosensors for monitoring environmental contaminants: Recent advances and future outlook

      2019, Process Safety and Environmental Protection
      Citation Excerpt :

      Owing to the concerted efforts of scientific community and researchers, around the globe, mutant GFPs with improved signal strength, augmented stability, and altered spectral intensity have recently been commercialized and might display high perspective for biosensor applications in the coming years (Johnson et al., 2017). A recombinant DNA technology has been applied to tailor numerous microorganisms, often by integrating natural regulatory genes that encode a transcriptional regulator and along with a promoter with a bio-recognition gene (Vollmer and Van Dyk, 2004; Ron, 2007). The lux/luc (encoding firefly/bacterial luciferase enzyme), lacZ (encoding β-galactosidase), and gfp (encoding green fluorescent protein) genes are the most widely exploited reporter genes.

    View all citing articles on Scopus
    View full text