Visual signal transduction for environmental stewardship: A novel biosensing approach to identify and quantify chlorpyrifos-related residues in aquatic environments.

The pervasive presence of organophosphate pesticides (OPs), such as chlorpyrifos (CPF), in aquatic ecosystems underscores the urgent need for sensitive and reliable detection methods to safeguard environmental and public health. This study addressed the critical need for a novel biosensor capable of detecting CPF and its toxic metabolite, 3,5,6-trichloro-2-pyridinol (TCP), with high sensitivity and selectivity, suitable for field applications in environmental monitoring. The study engineered a whole-cell biosensor based on E. coli strains that utilize the ChpR transcriptional regulator and the vioABCE gene cluster, providing a distinct visual and colorimetric response to CPF and TCP. The biosensor's performance was optimized and evaluated across various water matrices, including freshwater, seawater, and soil leachate. The biosensor demonstrated high sensitivity with a broad linear detection range, achieving limits of detection (LODs) at 0.8 µM for CPF and 7.813 nM for TCP. The linear regression concentration ranges were 1.6-12.5 µM for CPF and 15.6-125 nM for TCP, aligning with environmental standard limits and ensuring the biosensor's effectiveness in real-world scenarios. This innovative biosensing approach offers a robust, user-friendly tool for on-site environmental monitoring, significantly mitigating OPs contamination and advancing current detection technologies to meet environmental protection standards.

[Advances in microbial whole-cell sensors for the detection of aromatic compounds].

The inherent stability and recalcitrance of benzene ring structures render aromatic compounds a major ecological concern and a substantial risk to human health. Hence, developing a facile and efficacious detection technique for aromatic compounds is essential. As our comprehension of aromatic compound characteristics deepens, microbial cell-based biosensors have emerged as increasingly popular tools in the detection of aromatic compounds. This article introduces the operational principles of microbial whole-cell biosensors and elucidates the construction techniques and applications of electroactive biofilm-based microbial whole-cell sensors, transcription factor-based microbial whole-cell sensors, and degradation gene promoter-dependent microbial whole-cell sensors in the detection of aromatic compounds. In addition, we review the methodologies for improving the performance of microbial whole-cell sensors based on surface display, logic gate construction, genetic circuit modification, and quorum sensing signal amplification.

Microbead-Encapsulated Luminescent Bioreporter Screening of P. aeruginosa via Its Secreted Quorum-Sensing Molecules.

Pseudomonas aeruginosa is an opportunistic Gram-negative bacterium that remains a prevalent clinical and environmental challenge. Quorum-sensing (QS) molecules are effective biomarkers in pinpointing the presence of P. aeruginosa. This study aimed to develop a convenient-to-use, whole-cell biosensor using P. aeruginosa reporters individually encapsulated within alginate-poly-L-lysine (alginate-PLL) microbeads to specifically detect the presence of bacterial autoinducers. The PLL-reinforced microbeads were prepared using a two-step method involving ionic cross-linking and subsequent coating with thin layers of PLL. The alginate-PLL beads showed good stability in the presence of a known cation scavenger (sodium citrate), which typically limits the widespread applications of calcium alginate. In media containing synthetic autoinducers-such as N-(3-oxo dodecanoyl) homoserine lactone (3-oxo-C12-HSL) and N-butanoyl-L-homoserine lactone (C4-HSL), or the cell-free supernatants of planktonic or the flow-cell biofilm effluent of wild P. aeruginosa (PAO1)-the encapsulated bacteria enabled a dose-dependent detection of the presence of these QS molecules. The prepared bioreporter beads remained stable during prolonged storage at 4 and -80 °C and were ready for on-the-spot sensing without the need for recovery. The proof-of-concept, optical fiber-based, and whole-cell biosensor developed here demonstrates the practicality of the encapsulated bioreporter for bacterial detection based on specific QS molecules.

Whole-Cell Biosensor for Iron Monitoring as a Potential Tool for Safeguarding Biodiversity in Polar Marine Environments.

Iron is a key micronutrient essential for various essential biological processes. As a consequence, alteration in iron concentration in seawater can deeply influence marine biodiversity. In polar marine environments, where environmental conditions are characterized by low temperatures, the role of iron becomes particularly significant. While iron limitation can negatively influence primary production and nutrient cycling, excessive iron concentrations can lead to harmful algal blooms and oxygen depletion. Furthermore, the growth of certain phytoplankton species can be increased in high-iron-content environments, resulting in altered balance in the marine food web and reduced biodiversity. Although many chemical/physical methods are established for inorganic iron quantification, the determination of the bio-available iron in seawater samples is more suitably carried out using marine microorganisms as biosensors. Despite existing challenges, whole-cell biosensors offer other advantages, such as real-time detection, cost-effectiveness, and ease of manipulation, making them promising tools for monitoring environmental iron levels in polar marine ecosystems. In this review, we discuss fundamental biosensor designs and assemblies, arranging host features, transcription factors, reporter proteins, and detection methods. The progress in the genetic manipulation of iron-responsive regulatory and reporter modules is also addressed to the optimization of the biosensor performance, focusing on the improvement of sensitivity and specificity.

Detection of Cadmium in Human Biospecimens by a Cadmium-Selective Whole-Cell Biosensor Based on Deoxyviolacein.

Cadmium poses a severe health risk, impacting various bodily systems. Monitoring human exposure is vital. Urine and blood cadmium serve as critical biomarkers. However, current urine and blood cadmium detection methods are expensive and complex. Being cost-effective, user-friendly, and efficient, visual biosensing offers a promising complement to existing techniques. Therefore, we constructed a cadmium whole-cell biosensor using CadR10 and deoxyviolacein pigment in this study. We assessed the sensor for time-dose response, specific response to cadmium, sensitivity response to cadmium, and stability response to cadmium. The results showed that (1) the sensor had a preferred signal-to-noise ratio when the incubation time was 4 h; (2) the sensor showed excellent specificity for cadmium compared to the group 12 metals and lead; (3) the sensor was responsive to cadmium down to 1.53 nM under experimental conditions and had good linearity over a wide range from 1.53 nM to 100 µM with good linearity (R2 = 0.979); and (4) the sensor had good stability. Based on the excellent results of the performance tests, we developed a cost-effective, high-throughput method for detecting urinary and blood cadmium. Specifically, this was realized by adding the blood or urine samples into the culture system in a particular proportion. Then, the whole-cell biosensor was subjected to culture, n-butanol extraction, and microplate reading. The results showed that (1) at 20% urine addition ratio, the sensor had an excellent curvilinear relationship (R2 = 0.986) in the range of 3.05 nM to 100 µM, and the detection limit could reach 3.05 nM. (2) At a 10% blood addition ratio, the sensor had an excellent nonlinear relationship (R2 = 0.978) in the range of 0.097-50 µM, and the detection limit reached 0.195 µM. Overall, we developed a sensitive and wide-range method based on a whole-cell biosensor for the detection of cadmium in blood and urine, which has the advantages of being cost-effective, ease of operation, fast response, and low dependence on instrumentation and has the potential to be applied in the monitoring of cadmium exposure in humans as a complementary to the mainstream detection techniques.

A sensitive, portable, and smartphone-based whole-cell biosensor device for salicylic acid monitoring.

Considerable effort has been invested in developing salicylic acid (SA) biosensors for various application purposes. Here, by engineering the sensing modules and host cell chassis, we have gradually optimized the NahR-Psal/Pr-based SA biosensor, increasing the sensitivity and maximum output by 17.2-fold and 9.4-fold, respectively, and improving the detection limit by 800-fold, from 80 µM to 0.1 µM. A portable SA sensing device was constructed by embedding a gelatin-based hydrogel containing an optimized biosensor into the perforations of tape adhered to glass slide, which allowed good determination of SA in the range of 0.1 µM-10 µM. Then, we developed a customized smartphone App to measure the fluorescence intensity of each perforation and automatically calculate the corresponding SA concentration so that we could detect SA concentrations in real cosmetic samples. We anticipate that this smartphone-based imaging biosensor, with its compact size, higher sensitivity, cost-effectiveness, and easy data transfer, will be useful for long-term monitoring of SA.

Streptomyces-based whole-cell biosensors for detecting diverse cell envelope-targeting antibiotics.

Cell envelope-targeting antibiotics are potent therapeutic agents against various bacterial infections. The emergence of multiple antibiotic-resistant strains underscores the significance of identifying potent antimicrobials specifically targeting the cell envelope. However, current drug screening approaches are tedious and lack sufficient specificity and sensitivity, warranting the development of more efficient methods. Genetic circuit-based whole-cell biosensors hold great promise for targeted drug discovery from natural products. Here, we performed comparative transcriptomic analysis of Streptomyces coelicolor M1146 exposed to diverse cell envelope-targeting antibiotics, aiming to identify regulatory elements involved in perceiving and responding to these compounds. Differential gene expression analysis revealed significant activation of VanS/R two-component system in response to the glycopeptide class of cell envelope-acting antibiotics. Therefore, we engineered a pair of VanS/R-based biosensors that exhibit functional complementarity and possess exceptional sensitivity and specificity for glycopeptides detection. Additionally, through promoter screening and characterization, we expanded the biosensor's detection range to include various cell envelope-acting antibiotics beyond glycopeptides. Our genetically engineered biosensor exhibits superior performance, including a dynamic range of up to 887-fold for detecting subtle antibiotic concentration changes in a rapid 2-h response time, enabling high-throughput screening of natural product libraries for antimicrobial agents targeting the bacterial cell envelope.

A Portable, Encapsulated Microbial Whole-Cell Biosensing System for the Detection of Bioavailable Copper (II) in Soil.

A portable, field deployable whole-cell biosensor was developed that can withstand the complex matrices of soil and requires minimal to no sample preparation to monitor bioavailable concentrations of the essential micronutrient copper (II). Conventional measurement of micronutrients is often complex, laboratory-based, and not suitable for monitoring their bioavailable concentration. To address this need, we developed a fluorescence based microbial whole-cell biosensing (MWCB) system encoding for a Cu2+-responsive protein capable of generating a signal upon binding to Cu2+. The sensing-reporting protein was designed by performing circular permutation on the green fluorescent protein (GFP) followed by insertion of a Cu2+ binding motif into the structure of GFP. The design included insertion of several binding motifs and creating plasmids that encoded the corresponding sensing proteins. The signal generated by the sensing-reporting protein is directly proportional to the concentration of Cu2+ in the sample. Evaluation of the resulting biosensing systems carrying these plasmids was performed prior to selection of the optimal fluorescence emitting Cu2+-binding protein. The resulting optimized biosensing system was encapsulated in polyacrylate-alginate beads and embedded in soil for detection of the analyte. Once exposed to the soil, the beads were interrogated to measure the fluorescence signal emitted by the sensing-reporting protein using a portable imaging device. The biosensor was optimized for detection of Cu2+ in terms of selectivity, sensitivity, matrix effects, detection limits, and reproducibility in both liquid and soil matrices. The limit of detection (LoD) of the optimized encapsulated biosensor was calculated as 0.27 mg/L and 1.26 mg/kg of Cu2+ for Cu2+ in solution and soil, respectively. Validation of the portable imaging tools as a potential biosensing device in the field was performed.

Engineered live bacteria as disease detection and diagnosis tools.

Sensitive and minimally invasive medical diagnostics are essential to the early detection of diseases, monitoring their progression and response to treatment. Engineered bacteria as live sensors are being developed as a new class of biosensors for sensitive, robust, noninvasive, and in situ detection of disease onset at low cost. Akin to microrobotic systems, a combination of simple genetic rules, basic logic gates, and complex synthetic bioengineering principles are used to program bacterial vectors as living machines for detecting biomarkers of diseases, some of which cannot be detected with other sensing technologies. Bacterial whole-cell biosensors (BWCBs) can have wide-ranging functions from detection only, to detection and recording, to closed-loop detection-regulated treatment. In this review article, we first summarize the unique benefits of bacteria as living sensors. We then describe the different bacteria-based diagnosis approaches and provide examples of diagnosing various diseases and disorders. We also discuss the use of bacteria as imaging vectors for disease detection and image-guided surgery. We conclude by highlighting current challenges and opportunities for further exploration toward clinical translation of these bacteria-based systems.

Application of whole-cell biosensors for analysis and improvement of L- and D-lactic acid fermentation by Lactobacillus spp. from the waste of glucose syrup production.

BACKGROUND: Lactic acid is one of the most important organic acids, with various applications in the food, beverage, pharmaceutical, cosmetic, and chemical industries. Optically pure forms of L- and D-lactic acid produced via microbial fermentation play an important role in the synthesis of biodegradable polylactic acid. Alternative substrates, including by-products and residues from the agro-food industry, provide a cost-effective solution for lactic acid production and are a promising avenue for the circular economy. RESULTS: In this study, the transcription factor (TF)-based whole-cell biosensor strategy was developed for the L- and D-lactic acid determination. It was cross validated with commonly used high-performance liquid chromatography and enzymatic methods. The utility of biosensors as an efficient analytical tool was demonstrated by their application for the lactic acid determination and fermentation improvement. We explored the ability of Lacticaseibacillus paracasei subsp. paracasei, Lactobacillus delbrueckii subsp. lactis, and Lactobacillus amylovorus to biosynthesize optically pure L-lactic acid, D-lactic acid or mixture of both from organic-rich residual fraction (ORRF), a waste of glucose syrup production from wheat starch. The fermentation of this complex industrial waste allowed the production of lactic acid without additional pretreatment obtaining yields from 0.5 to 0.9 Cmol/Cmol glucose. CONCLUSIONS: This study highlights the utility of whole cell biosensors for the determination of L- and D-forms of lactic acid. The fermentation of L-lactic acid, D-lactic acid and mixture of both by L. paracasei, L. lactis, and L. amylovorus, respectively, was demonstrated using waste of glucose syrup production, the ORRF.

Performance upgrade of a microbial explosives' sensor strain by screening a high throughput saturation library of a transcriptional regulator.

We present a methodology for a high-throughput screening (HTS) of transcription factor libraries, based on bacterial cells and GFP fluorescence. The method is demonstrated on the Escherichia coli LysR-type transcriptional regulator YhaJ, a key element in 2,4-dinitrotuluene (DNT) detection by bacterial explosives' sensor strains. Enhancing the performance characteristics of the YhaJ transcription factor is essential for future standoff detection of buried landmines. However, conventional directed evolution methods for modifying YhaJ are limited in scope, due to the vast sequence space and the absence of efficient screening methods to select optimal transcription factor mutants. To overcome this limitation, we have constructed a focused saturation library of ca. 6.4 × 107 yhaJ variants, and have screened over 70 % of its sequence space using fluorescence-activated cell sorting (FACS). Through this screening process, we have identified YhaJ mutants exhibiting superior fluorescence responses to DNT, which were then effectively transformed into a bioluminescence-based DNT detection system. The best modified DNT reporter strain demonstrated a 7-fold lower DNT detection threshold, a 45-fold increased signal intensity, and a 40 % shorter response time compared to the parental bioreporter. The FACS-based HTS approach presented here may hold a potential for future molecular enhancement of other sensing and catalytic bioreactions.

[Development of a whole-cell biosensor for detecting organophosphorus pesticide methyl parathion in the farmland soil].

The evaluation of the bioavailability of pollutants in soil is crucial to accurately assess the pollution risk, and whole-cell biosensor is one of the important tools for such evaluation. This study aimed to develop a novel whole-cell biosensor for the detection of methyl parathion in soil using. First, a whole-cell biosensor was constructed by the screened methyl parathion hydrolase mpd gene, the existing specific induction element pobR, and the pUC19 plasmid skeleton. Then, the detection method of methyl parathion in soil extracts was established using 96-well microtiter plate as carrier and five whole-cell biosensors as indicator. The method was applied in the detection of methyl parathion in tested and field soil extracts. Taking E. coli DH5α/pMP-AmilCP with the best detection performance as an example, this biosensor had a detection limit of 6.21-6.66 µg/L and a linear range of 10-10 000 µg/L for methyl parathion in four soil extracts. E. coli DH5α/pMP-RFP and E. coli DH5α/pMP-AmilCP methods have good detection performance for the analysis of methyl parathion in soil extract samples. This biosensor method can help to quickly assess the bioavailability of methyl parathion in soil, and thus help to understand the risk of soil pollution caused by organophosphorus pesticide methyl parathion.

Pb(II)-inducible proviolacein biosynthesis enables a dual-color biosensor toward environmental lead.

With the rapid development of synthetic biology, various whole-cell biosensors have been designed as valuable biological devices for the selective and sensitive detection of toxic heavy metals in environmental water. However, most proposed biosensors are based on fluorescent and bioluminescent signals invisible to the naked eye. The development of visible pigment-based biosensors can address this issue. The pbr operon from Klebsiella pneumoniae is selectively induced by bioavailable Pb(II). In the present study, the proviolacein biosynthetic gene cluster was transcriptionally fused to the pbr Pb(II) responsive element and introduced into Escherichia coli. The resultant biosensor responded to Pb(II) in a time- and dose-dependent manner. After a 5-h incubation with Pb(II), the brown pigment was produced, which could be extracted into n-butanol. Extra hydrogen peroxide treatment during n-butanol extract resulted in the generation of a stable green pigment. An increased brown signal was observed upon exposure to lead concentrations above 2.93 nM, and a linear regression was fitted from 2.93 to 3,000 nM. Extra oxidation significantly decreased the difference between parallel groups. The green signal responded to as low as 0.183 nM Pb(II), and a non-linear regression was fitted in a wide concentration range from 0.183 to 3,000 nM. The specific response toward Pb(II) was not interfered with by various metals except for Cd(II) and Hg(II). The PV-based biosensor was validated in monitoring bioaccessible Pb(II) spiked into environmental water. The complex matrices did not influence the regression relationship between spiked Pb(II) and the dual-color signals. Direct reading with the naked eye and colorimetric quantification enable the PV-based biosensor to be a dual-color and low-cost bioindicator for pollutant heavy metal.

Directed evolution of TetR for constructing sensitive and broad-spectrum tetracycline antibiotics whole-cell biosensor.

Antibiotic abuse is the main reason for the drug resistance of pathogenic bacteria, posing a potential health risk. Antibiotic surveillance is critical for preventing antibiotic contamination. This study aimed to develop a sensitive and broad-spectrum whole-cell biosensor for tetracycline antibiotics (TCs) detection. Wild-type TCs-responsive biosensor was constructed by introducing a tetracycline operon into a sfGFP reporter plasmid. Using error-prone PCR, mutation libraries containing approximately 107 variants of the tetracycline repressor (TetR) gene were generated. The tigecycline-senstive mutants were isolated using high-throughput flow cytometric sorting. After 2 rounds of directed evolution, a mutant epS2-22 of TerR was isolated and assembled as a TCs biosensor. The epS2-22 biosensor was more sensitive and broad-spectrum than the wild-type biosensors. The detection limits of the epS2-22 biosensor for seven TCs were 4- to 62-fold lower than the wild-type biosensor (no response to tigecycline). Meanwhile, the epS2-22 biosensor had a shorter detection time and a stronger signal output than the wild type. In addition, the evolved epS2-22 biosensor showed excellent performance in detecting low traces of TCs in environmental water. These results suggest that directed evolution is a powerful tool for developing high-performance whole-cell biosensors, and the evolved epS2-22 biosensors have the potential for wider applications in real-world TCs detection.

Harnessing split fluorescent proteins in modular protein logic for advanced whole-cell detection.

Whole-cell biosensors have demonstrated promising capabilities in detecting target molecules. However, their limited selectivity and precision can be attributed to the broad substrate tolerance of natural proteins. In this study, we aim to enhance the performance of whole-cell biosensors by incorporating of logic AND gates. Specifically, we utilize the HrpR/S system, a widely employed hetero-regulation module from Pseudomonas syringae in synthetic biology, to construct an orthogonal AND gate in Escherichia coli. To accomplish this, we compare the HrpR/S system with self-associating split fluorescent proteins using the Spy Tag/Spy Catcher system. Our objective is to selectively activate a reporter gene in the presence of both IPTG and Hg(II) ions. Through systematic genetic engineering and evaluation of various biological parts under diverse working conditions, our research demonstrates the utility of self-associating split fluorescent proteins in developing high-performance whole-cell biosensors. This approach offers advantages such as engineering simplicity, reduced basal activity, and improved selectivity. Furthermore, the comparison with the HrpR/S system serves as a valuable control model, providing insights into the relative advantages and limitations of each approach. These findings present a systematic and adaptable strategy to overcome the substrate tolerance challenge faced by whole-cell biosensors.

Directly Evolved AlkS-Based Biosensor Platform for Monitoring and High-Throughput Screening of Alkane Production.

Biosynthetic alkane using acyl-ACP aldehyde reductase (AAR) and aldehyde-deformylating oxygenase (ADO) from cyanobacteria is considered a promising alternative for the production of biofuels and chemical feedstocks. However, the lack of suitable screening methods to improve the catalytic efficiency of AAR and ADO has hindered further improvements in alkane production. Herein, a novel alkane biosensor was developed based on transcriptional factor AlkS by directed evolution, which shows sensitive dynamic response curves for exogenous long-chain alkanes as well as in situ monitoring of endogenously produced alkanes. The evolved biosensor enables high-throughput screening of alkane-producing strains from the AAR and ADO mutant library, which led to a 13-fold increase in the production of long-chain alkanes, including a 22-fold increase of C15. This study is the first to improve the alkane production through biosensors, which provides a good reference for the establishment of microbial cell factories for alkane production.

Oral Metal-Organic Gel Protected Whole-Cell Biosensor for in Situ Monitoring Nitrosamines in the Gastrointestinal Tract.

Nitrite, a type of food additive, has been proved convertible to genotoxic nitrosamines in the gastrointestinal tract by intestinal flora. There is no appropriate method for in situ detection of nitrosamines. Herein, plasmid-introduced Saccharomyces cerevisiae, which can respond to nitrosamine-induced DNA damage and activate pMAG1-based DNA damage repair (DDR), was designed as whole-cell biosensors (WCBs) for monitoring the in situ generated nitrosamines by a reporter gene expressing enhanced green fluorescent protein (EGFP). In order to protect the validity of WCBs (pMAG1 yeast) from the gastric acid environment, a type of metal-organic gel (MOG), coordinated by Fe3+ and 2,2'-thiodiacetic acid (TDA), was prepared to embed the WCBs. The MOG(Fe-TDA) is gastric acid resistant and can deliver the pMAG1 yeast to the gut without compromising the performance of pMAG1 yeast to detect in situ generated nitrosamines. The genotoxicity of nitrosamines converted from nitrite was successfully detected in the gastrointestinal tract of mice.

Permeability-Engineered Compartmentalization Enables In Vitro Reconstitution of Sustained Synthetic Biology Systems.

In nature, biological compartments such as cells rely on dynamically controlled permeability for matter exchange and complex cellular activities. Likewise, the ability to engineer compartment permeability is crucial for in vitro systems to gain sustainability, robustness, and complexity. However, rendering in vitro compartments such a capability is challenging. Here, a facile strategy is presented to build permeability-configurable compartments, and marked advantages of such compartmentalization are shown in reconstituting sustained synthetic biology systems in vitro. Through microfluidics, the strategy produces micrometer-sized layered microgels whose shell layer serves as a sieving structure for biomolecules and particles. In this configuration, the transport of DNAs, proteins, and bacteriophages across the compartments can be controlled an guided by a physical model. Through permeability engineering, a compartmentalized cell-free protein synthesis system sustains multicycle protein production; ≈100 000 compartments are repeatedly used in a five-cycle synthesis, featuring a yield of 2.2 mg mL-1 . Further, the engineered bacteria-enclosing compartments possess near-perfect phage resistance and enhanced environmental fitness. In a complex river silt environment, compartmentalized whole-cell biosensors show maintained activity throughout the 32 h pollutant monitoring. It is anticipated that permeability-engineered compartmentalization should pave the way for practical synthetic biology applications such as green bioproduction, environmental sensing, and bacteria-based therapeutics.

A Luciferase Mutant with Improved Brightness and Stability for Whole-Cell Bioluminescent Biosensors and In Vitro Biosensing.

The availability of new bioluminescent proteins with tuned properties, both in terms of emission wavelength, kinetics and protein stability, is highly valuable in the bioanalytical field, with the potential to improve the sensitivity and analytical performance of the currently used methods for ATP detection, whole-cell biosensors, and viability assays among others. We present a new luciferase mutant, called BgLuc, suitable for developing whole-cell biosensors and in vitro biosensors characterized by a bioluminescence maximum of 548 nm, narrow emission bandwidth, favorable kinetic properties, and excellent pH- and thermo-stabilities at 37 and 45 °C and pH from 5.0 to 8.0. We assessed the suitability of this new luciferase for whole-cell biosensing with a cell-based bioreporter assay for Nuclear Factor-kappa B (NF-kB) signal transduction pathway using 2D and 3D human embryonic kidney (HEK293T) cells, and for ATP detection with the purified enzyme. In both cases the luciferase showed suitable for sensitive detection of the target analytes, with better or similar performance than the commercial counterparts.

Comparative Analysis of Cell Metabolic Activity Sensing by Escherichia coli rrnB P1-lux and Cd Responsive-Lux Biosensors: Time-Resolved Experiments and Mechanistic Modelling

Whole-cell bacterial sensors are used in medical/environmental applications to detect chemicals, and to assess medium toxicity or stress. Non-specific constitutive biosensors generally serve the latter purpose, whereas chemical detection is performed with biosensors involving a specific chemical-inducible promoter. Herein, we show that functioning principles of specific and non-specific whole-cell biosensors are not exclusive as both can probe modulations of cell metabolic activity under stressing conditions. The demonstration is based on (i) time-resolved measurements of bioluminescence produced by constitutive rrnB P1-luxCDABE Escherichia coli biosensor in media differing with respect to carbon source, (ii) theoretical reconstruction of the measured signals using a here-reported theory for bioluminescence generated by constitutive cells, (iii) comparison between time-dependent cell photoactivity (reflecting metabolic activity) retrieved by theory with that we reported recently for cadmium-inducible PzntA-luxCDABE E. coli in media of similar compositions. Whereas signals of constitutive and non-constitutive biosensors differ in terms of shape, amplitude and peak number depending on nutritional medium conditions, analysis highlights the features shared by their respective cell photoactivity patterns mediated by the interplay between stringent response and catabolite repressions. The work advocates for the benefits of a theoretical interpretation for the time-dependent response of biosensors to unravel metabolic and physicochemical contributions to the bioluminescence signal.