Online detection of metals in environmental samples: comparing two concepts of bioluminescent bacterial biosensors

Recent advances in the development and applications of luminescent bacteria-based biosensors

Luminescent bacteria-based biosensors are widely used for fast and sensitive monitoring of food safety, water quality, and other environmental pollutions. Recent advancements in biomedical engineering technology have led to improved portability, integration, and intelligence of these biotoxicity assays. Moreover, genetic engineering has played a significant role in the development of recombinant luminescent bacterial biosensors, enhancing both detection accuracy and sensitivity. This review provides an overview of recent advances in the development and applications of novel luminescent bacteria-based biosensors, and future perspectives and challenges in the cutting-edge research, market translation, and practical applications of luminescent bacterial biosensing are discussed.

A direct contact bioassay using immobilized microalgal balls to evaluate the toxicity of contaminated field soils

The present study used a bioassay of immobilized microalgae (Chlorella vulgaris) via direct contact to assess the toxicity of eleven uncontaminated (reference) and five field contaminated soils with various physicochemical properties and contamination. Photosynthetic oxygen concentration in the headspace of the test kit by Chlorella vulgaris in the reference soils ranged between 12.93% and 14.80% and only 2.54%-7.14% in the contaminated soils, respectively. Inherent test variability (CV_i) values ranged between 2.90% and 9.04%; variation due to soil natural properties (CV_rs) ranged between 0.33% and 13.0%; and minimal detectable difference (MDD) values ranged from 4.69% to 11.6%. A computed toxicity threshold of 15% was established for microalgae soil toxicity tests based on calculations of the maximal tolerable inhibition (MTI). All contaminated soils were considered toxic to microalgae because their levels of inhibition ranged between 39.5% and 82.9%, exceeding the 15% toxicity threshold. It can be concluded that the elevated concentrations of heavy metals and organic contaminants in the contaminated soils induced the higher inhibitory levels. Overall, direct contact soil toxicity tests using immobilized microalgae provided coherent and repeatable data and can be utilized as a simple and suitable tool for the toxicity testing of contaminated field soils.

A novel gas production bioassay of thiosulfate utilizing denitrifying bacteria (TUDB) for the toxicity assessment of heavy metals contaminated water

This study reports for the first-time the possibility of deploying gas production by thiosulfate utilizing denitrifying bacteria (TUDB) as a proxy to evaluate water toxicity. The test relies on gas production by TUDB due to inhibited metabolic activity in the presence of toxicants. Gas production was measured using a bubble-type respirometer. Optimization studies indicated that 300 mg NO₃^--N/L, 0.5 mL acclimated culture, and 2100 mg S₂O₃^2-/L were the ideal conditions facilitating the necessary volume of gas production for sensitive data generation. Determined EC₅₀ values of the selected heavy metals were: Cr⁶⁺, 0.51 mg/L; Ag⁺, 2.90 mg/L; Cu²⁺, 2.90 mg/L; Ni²⁺, 3.60 mg/L; As³⁺, 4.10 mg/L; Cd²⁺, 5.56 mg/L; Hg²⁺, 8.06 mg/L; and Pb²⁺, 19.3 mg/L. The advantages of this method include operational simplicity through the elimination of cumbersome preprocessing procedures which are used to eliminate interferences caused by turbidity when the toxicity of turbid samples is determined via spectrophotometry.

Construction of a sensitive and specific lead biosensor using a genetically engineered bacterial system with a luciferase gene reporter controlled by pbr and cadA promoters

Background

A bacterial biosensor refers to genetically engineered bacteria that produce an assessable signal in the presence of a physical or chemical agent in the environment.

Methods

We have designed and evaluated a bacterial biosensor expressing a luciferase reporter gene controlled by pbr and cadA promoters in Cupriavidus metallidurans (previously termed Ralstonia metallidurans) containing the CH34 and pI258 plasmids of Staphylococcus aureus, respectively, and that can be used for the detection of heavy metals. In the present study, we have produced and evaluated biosensor plasmids designated pGL3-luc/pbr biosensor and pGL3-luc/cad biosensor, that were based on the expression of luc+ and under the control of the cad promoter and the cadC gene of S. aureus plasmid pI258 and pbr promoter and pbrR gene from plasmid pMOL30 of Cupriavidus metallidurans.

Results

We found that the pGL3-luc/pbr biosensor may be used to measure lead concentrations between 1–100 μM in the presence of other metals, including zinc, cadmium, tin and nickel. The latter metals did not result in any significant signal. The pGL3-luc/cad biosensor could detect lead concentrations between 10 nM to 10 μM.

Conclusions

This biosensor was found to be specific for measuring lead ions in both environmental and biological samples.

Bioluminescence goes portable: recent advances in whole-cell and cell-free bioluminescence biosensors

Recent advancements in synthetic biology, organic chemistry, and computational models have allowed the application of bioluminescence in several fields, ranging from well established methods for detecting microbial contamination to in vivo imaging to track cancer and stem cells, from cell-based assays to optogenetics. Moreover, thanks to recent technological progress in miniaturized and sensitive light detectors, such as photodiodes and imaging sensors, it is possible to implement laboratory-based assays, such as cell-based and enzymatic assays, into portable analytical devices for point-of-care and on-site applications. This review highlights some recent advances in the development of whole-cell and cell-free bioluminescence biosensors with a glance on current challenges and different strategies that have been used to turn bioassays into biosensors with the required analytical performance. Critical issues and unsolved technical problems are also highlighted, to give the reader a taste of this fascinating and challenging field.

A Sensitive Magnetic Arsenite-Specific Biosensor Hosted in Magnetotactic Bacteria

According to the World Health Organization, arsenic is the water contaminant that affects the largest number of people worldwide. To limit its impact on the population, inexpensive, quick, and easy-to-use systems of detection are required. One promising solution could be the use of whole-cell biosensors, which have been extensively studied and could meet all these criteria even though they often lack sensitivity. Here, we investigated the benefit of using magnetotactic bacteria as cellular chassis to design and build sensitive magnetic bacterial biosensors. Promoters potentially inducible by arsenic were first identified in silico within the genomes of two magnetotactic bacteria strains, Magnetospirillum magneticum AMB-1 and Magnetospirillum gryphiswaldense MSR-1. The ArsR-dependent regulation was confirmed by reverse transcription-PCR experiments. Biosensors built by transcriptional fusion between the arsenic-inducible promoters and the bacterial luciferase luxCDABE operon gave an element-specific response in 30 min with an arsenite detection limit of 0.5 μM. After magnetic concentration, we improved the sensitivity of the biosensor by a factor of 50 to reach 10 nM, more than 1 order of magnitude below the recommended guidelines for arsenic in drinking water (0.13 μM). Finally, we demonstrated the successful preservation of the magnetic bacterium biosensors by freeze-drying.IMPORTANCE Whole-cell biosensors based on reporter genes can be designed for heavy metal detection but often require the optimization of their sensitivity and specific adaptations for practical use in the field. Magnetotactic bacteria as cellular hosts for biosensors are interesting models, as their intrinsic magnetism permits them to be easily concentrated and entrapped to increase the arsenic-response signal. This paves the way for the development of sensitive and immobilized whole-cell biosensors tailored for use in the field.

Immobilization of fluorescent bacterial bioreporter for arsenic detection

Whole-cell bacterial biosensors hold great promise as a practical complementary approach for in-field detection of arsenic. Although there are various bacterial bioreporter systems for arsenic detection, fewer studies reported the immobilization of arsenic bioreporters. This study aimed at determining immobilization of specific bacterial bioreporter in agar and alginate biopolymers to measure level of arsenite and/or arsenate. To achieve sensitive detection, immobilization parameters of polymer concentration and cell density were evaluated. Moreover, by changing the culture medium, immobilized bioreporter cells in minimal medium can detect arsenite while they can detect both arsenite and arsenate in phosphate-limited minimal medium. When optimal parameters were applied, agar and alginate immobilized bioreporter systems can detect arsenite and arsenate concentrations of 10 μg/l and 200 μg/l within 5 h and 2 h, respectively. The results showed that the immobilized bacterial bioreporter systems are able to determine the concentrations of the two abundant species of arsenic; arsenite and arsenate, as opposed to other studies which reported only arsenite detection. This is the first study describe agar hydrogel and alginate bead immobilization of fluorescent arsenic bacterial bioreporter that can detect both arsenite and arsenate at the safe drinking water limit. Thus, this study will enable further steps to be taken towards developing sensitive and selective portable devices to assess environmental arsenic contamination and prevent acute arsenic toxicity.

Prêt-à-porter nanoYESα and nanoYESβ bioluminescent cell biosensors for ultrarapid and sensitive screening of endocrine-disrupting chemicals

Cell-based assays utilizing reporter gene technology have been widely exploited for biosensing, as they provide useful information about the bioavailability and cell toxicity of target analytes. The long assay time due to gene transcription and translation is one of the main drawbacks of cell biosensors. We report the development of two yeast biosensors stably expressing human estrogen receptors α and β and employing NanoLuc as the reporter protein to upgrade the widely used yeast estrogen screening (YES) assays. A viability control strain was also developed based on a chimeric green-emitting luciferase, PLG2, expressed for the first time in Saccharomycescerevisiae. Thanks to their brightness, NanoLuc and PLG2 provided excellent sensitivity, enabling the implementation of these biosensors into low-cost smartphone-based devices. The developed biosensors had a rapid (1 h) response and reported on (anti)estrogenic activity via human estrogen receptors α and β as well as general sample toxicity. Under optimized conditions, we obtained LODs of 7.1 ± 0.4 nM and 0.38 ± 0.08 nM for E2 with nanoYESα and nanoYESβ, respectively. As a proof of concept, we analyzed real samples from plants showing significant estrogenic activity or known to contain significant amounts of phytoestrogens. Graphical abstract.

Dual detection of bioaccumulated Hg2+ based on luminescent bacteria and aggregation-induced emission

We develop a dual detection strategy for bioaccumulated Hg²⁺ based on turn-off of the bioluminescence of P. phosphoreum bacteria by disrupting the quorum sensing system and turn-on of the photoluminescence of an aggregation-induced emission (AIE) probe by forming aggregates with Hg²⁺ inside the bacteria.

Luciferase Genes as Reporter Reactions: How to Use Them in Molecular Biology?

: The latest advances in molecular biology have made available several biotechnological tools that take advantage of the high detectability and quantum efficiency of bioluminescence (BL), with an ever-increasing number of novel applications in environmental, pharmaceutical, food, and forensic fields. Indeed, BL proteins are being used to develop ultrasensitive binding assays and cell-based assays, thanks to their high detectability and to the availability of highly sensitive BL instruments. The appealing aspect of molecular biology tools relying on BL reactions is their general applicability in both in vitro assays, such as cell cultures or purified proteins, and in vivo settings, such as in whole-animal BL imaging. The aim of this chapter is to provide the reader with an overview of state-of-the-art bioluminescent tools based on luciferase genes, highlighting molecular biology strategies that have been applied so far, together with some selected examples.

Biosensors for wastewater monitoring: A review

Water pollution and habitat degradation are the cause of increasing water scarcity and decline in aquatic biodiversity. While the freshwater availability has been declining through past decades, water demand has continued to increase particularly in areas with arid and semi-arid climate. Monitoring of pollutants in wastewater effluents are critical to identifying water pollution area for treatment. Conventional detection methods are not effective in tracing multiple harmful components in wastewater due to their variability along different times and sources. Currently, the development of biosensing instruments attracted significant attention because of their high sensitivity, selectivity, reliability, simplicity, low-cost and real-time response. This paper provides a general overview on reported biosensors, which have been applied for the recognition of important organic chemicals, heavy metals, and microorganisms in dark waters. The significance and successes of nanotechnology in the field of biomolecular detection are also reviewed. The commercially available biosensors and their main challenges in wastewater monitoring are finally discussed.

Current status of water environment and their microbial biosensor techniques - Part II: Recent trends in microbial biosensor development

In Part I of the present review series, I presented the current state of the water environment by focusing on Japanese cases and discussed the need to further develop microbial biosensor technologies for the actual water environment. I comprehensively present trends after approximately 2010 in microbial biosensor development for the water environment. In the first section, after briefly summarizing historical studies, recent studies on microbial biosensor principles are introduced. In the second section, recent application studies for the water environment are also introduced. Finally, I conclude the present review series by describing the need to further develop microbial biosensor technologies. Graphical abstract Current water pollution indirectly occurs by anthropogenic eutrophication (Part I). Recent trends in microbial biosensor development for water environment are described in part II of the present review series.

Development and Validation of an On-Line Water Toxicity Sensor with Immobilized Luminescent Bacteria for On-Line Surface Water Monitoring

Surface water used for drinking water production is frequently monitored in The Netherlands using whole organism biomonitors, with for example Daphnia magna or Dreissena mussels, which respond to changes in the water quality. However, not all human-relevant toxic compounds can be detected by these biomonitors. Therefore, a new on-line biosensor has been developed, containing immobilized genetically modified bacteria, which respond to genotoxicity in the water by emitting luminescence. The performance of this sensor was tested under laboratory conditions, as well as under field conditions at a monitoring station along the river Meuse in The Netherlands. The sensor was robust and easy to clean, with inert materials, temperature control and nutrient feed for the reporter organisms. The bacteria were immobilized in sol-gel on either an optical fiber or a glass slide and then continuously exposed to water. Since the glass slide was more sensitive and robust, only this setup was used in the field. The sensor responded to spikes of genotoxic compounds in the water with a minimal detectable concentration of 0.01 mg/L mitomycin C in the laboratory and 0.1 mg/L mitomycin C in the field. With further optimization, which should include a reduction in daily maintenance, the sensor has the potential to become a useful addition to the currently available biomonitors.

Chemically individual armoured bioreporter bacteria used for the in vivo sensing of ultra-trace toxic metal ions

A chemically engineered mesoporous silica armour is developed for simultaneously improving bioreporter bacterial vitality and shielding infectivity.

Main Technological Advancements in Bacterial Bioluminescent Biosensors Over the Last Two Decades

Environmental quality assessment is an extensive field of research due to the permanent increase of the stringency imposed by the legislative framework. To complete the wide panel of measurement methods, essentially based on physicochemical tools, some scientists focused on the development of alternative biological methods such as those based on the use of bioluminescent bacteria biosensors. The first report dedicated to the development of such biosensors dates back to 1967 and describes an analytical system designed to address the problem of air toxicity assessment. Nevertheless the available technologies in the photosensitive sensors field were not mature enough and, as a result, limited biosensor development possibilities. For about 20 years, the wide democratisation of photosensors coupled with advances in the genetic engineering field have allowed the expansion of the scope of possibilities of bioluminescent bacterial biosensors, allowing a significant emergence of these biotechnologies. This chapter retraces the history of the main technological evolutions that bacterial bioluminescent biosensors have known over the last two decades. Graphical Abstract.

Measurement of Bacterial Bioluminescence Intensity and Spectrum: Current Physical Techniques and Principles

: Bioluminescence is light production by living organisms, which can be observed in numerous marine creatures and some terrestrial invertebrates. More specifically, bacterial bioluminescence is the "cold light" produced and emitted by bacterial cells, including both wild-type luminescent and genetically engineered bacteria. Because of the lively interplay of synthetic biology, microbiology, toxicology, and biophysics, different configurations of whole-cell biosensors based on bacterial bioluminescence have been designed and are widely used in different fields, such as ecotoxicology, food toxicity, and environmental pollution. This chapter first discusses the background of the bioluminescence phenomenon in terms of optical spectrum. Platforms for bacterial bioluminescence detection using various techniques are then introduced, such as a photomultiplier tube, charge-coupled device (CCD) camera, micro-electro-mechanical systems (MEMS), and complementary metal-oxide-semiconductor (CMOS) based integrated circuit. Furthermore, some typical biochemical methods to optimize the analytical performances of bacterial bioluminescent biosensors/assays are reviewed, followed by a presentation of author's recent work concerning the improved sensitivity of a bioluminescent assay for pesticides. Finally, bacterial bioluminescence as implemented in eukaryotic cells, bioluminescent imaging, and cancer cell therapies is discussed.

Construction of a self-luminescent cyanobacterial bioreporter that detects a broad range of bioavailable heavy metals in aquatic environments

A self-luminescent bioreporter strain of the unicellular cyanobacterium Synechococcus sp. PCC 7942 was constructed by fusing the promoter region of the smt locus (encoding the transcriptional repressor SmtB and the metallothionein SmtA) to luxCDABE from Photorhabdus luminescens; the sensor smtB gene controlling the expression of smtA was cloned in the same vector. The bioreporter performance was tested with a range of heavy metals and was shown to respond linearly to divalent Zn, Cd, Cu, Co, Hg, and monovalent Ag. Chemical modeling was used to link bioreporter response with metal speciation and bioavailability. Limits of Detection (LODs), Maximum Permissive Concentrations (MPCs) and dynamic ranges for each metal were calculated in terms of free ion concentrations. The ranges of detection varied from 11 to 72 pM for Hg²⁺ (the ion to which the bioreporter was most sensitive) to 1.54–5.35 μM for Cd²⁺ with an order of decreasing sensitivity as follows: Hg²⁺ >> Cu²⁺ >> Ag⁺ > Co²⁺ ≥ Zn²⁺ > Cd²⁺. However, the maximum induction factor reached 75-fold in the case of Zn²⁺ and 56-fold in the case of Cd²⁺, implying that Zn²⁺ is the preferred metal in vivo for the SmtB sensor, followed by Cd²⁺, Ag⁺ and Cu²⁺ (around 45–50-fold induction), Hg²⁺ (30-fold) and finally Co²⁺ (20-fold). The bioreporter performance was tested in real environmental samples with different water matrix complexity artificially contaminated with increasing concentrations of Zn, Cd, Ag, and Cu, confirming its validity as a sensor of free heavy metal cations bioavailability in aquatic environments.

Therapeutic and analytical applications of arsenic binding to proteins

Knowledge of arsenic binding to proteins advances the development of bioanalytical techniques and therapeutic drugs.

Advances in arsenic biosensor development--a comprehensive review

Biosensors are analytical devices having high sensitivity, portability, small sample requirement and ease of use for qualitative and quantitative monitoring of various analytes of human importance. Arsenic (As), owing to its widespread presence in nature and high toxicity to living creatures, requires frequent determination in water, soil, agricultural and food samples. The present review is an effort to highlight the various advancements made so far in the development of arsenic biosensors based either on recombinant whole cells or on certain arsenic-binding oligonucleotides or proteins. The role of futuristic approaches like surface plasmon resonance (SPR) and aptamer technology has also been discussed. The biomethods employed and their general mechanisms, advantages and limitations in relevance to arsenic biosensors developed so far are intended to be discussed in this review.

Methods for assessing biochemical oxygen demand (BOD): a review

The Biochemical Oxygen Demand (BOD) is one of the most widely used criteria for water quality assessment. It provides information about the ready biodegradable fraction of the organic load in water. However, this analytical method is time-consuming (generally 5 days, BOD5), and the results may vary according to the laboratory (20%), primarily due to fluctuations in the microbial diversity of the inoculum used. Work performed during the two last decades has resulted in several technologies that are less time-consuming and more reliable. This review is devoted to the analysis of the technical features of the principal methods described in the literature in order to compare their performances (measuring window, reliability, robustness) and to identify the pros and the cons of each method.

Improved detection of antibiotic compounds by bacterial reporter strains achieved by manipulations of membrane permeability and efflux capacity

The occurrence of pharmaceuticals, including antibacterial compounds, in the environment has been acknowledged as an emerging and troubling issue in environmental safety; their usage is constantly on the rise, and their effects on the environment are only partially understood. Such compounds can accumulate, contaminate the ecosystem, and contribute to the spreading of antibiotic resistance among bacteria, hindering human health. Bioluminescent Escherichia coli reporter strains, engineered to detect antibiotic compounds by fusing the promoter of the global regulator soxS to the Photorhabdus luminescens luxCDABE cassette, were further modified by altering their membrane permeability and efflux capabilities. This was accomplished by introducing several mutations in the efflux system (ΔemrE, ΔacrB, and ΔtolC) and by overexpressing OmpF, a porin located in the outer membrane that allows passive diffusion of molecules. Combinations of these alterations had a cumulative effect in lowering the detection threshold of several antibiotics, in some of the cases to concentrations reported from pharmaceutical-polluted environments.