The evolution of the bacterial luciferase gene cassette (lux) as a real-time bioreporter

Mechanisms and applications of bacterial luciferase and its auxiliary enzymes

Bacterial luciferase (LuxAB) catalyzes the conversion of reduced flavin mononucleotide (FMNH⁻), oxygen, and a long-chain aldehyde to oxidized FMN, the corresponding acid and water with concomitant light emission. This bioluminescence reaction requires the reaction of a flavin reductase such as LuxG (in vivo partner of LuxAB) to supply FMNH⁻ for the LuxAB reaction. LuxAB is a well-known self-sufficient luciferase system because both aldehyde and FMNH⁻ substrates can be produced by the associated enzymes encoded by the genes in the lux operon, allowing the system to be auto-luminous. This makes it useful for in vivo applications. Structural and functional studies have long been performed in efforts to gain a better understanding of the LuxAB reaction. Recently, continued exploration of the LuxAB reaction have elucidated the mechanisms of C4a-hydroperoxyflavin formation and identified key catalytic residues such as His44 that facilitates the generation of flavin intermediates important for light generation. Advancements in protein engineering and synthetic biology have improved the bioluminescence properties of LuxAB. Various applications of LuxAB for bioimaging, bioreporters, biosensing in metabolic engineering and real-time monitoring of aldehyde metabolites in biofuel production pathways have been developed during the last decade. Challenging issues such as achieving red-shifted emissions, optimizing the signal intensity and identifying mechanisms related to the generation of light-emitting species remain to be explored. Nevertheless, LuxAB continues to be a promising tool for diverse biotechnological and biomedical applications.

Light-Activated Gene Expression System Using a Caging-Group-Free Photoactivatable Dye

Optical regulation of transcription using chemical compounds is an effective strategy to manipulate gene expression spatiotemporally. Conventional caging approaches with photoremovable protecting groups may require intense UV-light exposure and release potentially toxic byproducts. To address these problems, here we developed a light-mediated transcriptional regulation system by combining a caging-group-free photoactivatable dye PaX560 and a multidrug-binding transcriptional regulator QacR. The cationic dye generated from PaX560 through traceless photoconversion bound QacR and reduced its repressor function, resulting in transcriptional activation. Importantly, this system allowed transcriptional activation with a large dynamic range under mild visible light exposure and simultaneous detection of the state of the photoactivated effector. This module was integrated into the T7 RNA polymerase expression system to demonstrate light-activated transcription in vitro and in living cells.

Phagocytosis by macrophages decreases the radiance of bioluminescent Staphylococcus aureus

BACKGROUND

In vivo evaluations of the antimicrobial efficacy of biomaterials often use bioluminescent imaging modalities based on bioluminescent bacteria to allow follow-up in single animals. Bioluminescence production by bacteria is dependent on their metabolic activity. It is well known that several factors can influence the metabolism of bacteria, such as the use of antimicrobials and changes in bacterial growth phase. However, little is known about the influence of intracellular residence of bacteria on bioluminescence. For example, Staphylococcus aureus can survive in the peri-implant tissue and is known to survive intracellularly in macrophages.

RESULTS

In this study, we evaluated the bioluminescent radiance of S. aureus upon phagocytosis by macrophages. We showed that S. aureus reduced its bioluminescence upon phagocytosis by macrophages compared to S. aureus in a single culture. Simultaneously, bacterial numbers as measured by colony-forming units remained constant over time. S. aureus was released extracellularly as a result of macrophage cell death. Following this release, the bacteria increased their bioluminescence again. Replenishment of fresh macrophages showed an immediate increase in bioluminescence. Moreover, the addition of fresh macrophages showed a diminished decrease in bioluminescence at 24 h of coculture, but this effect did not last.

CONCLUSION

Together, this study demonstrates that phagocytosis by macrophages decreases bioluminescence of S. aureus, which is an important factor to consider when using bioluminescent imaging to study the infection process in an in vivo model.

Development of CadR-based cadmium whole cell biosensor for visual detection of environmental Cd2

BACKGROUND

As a threat to human health and public health, cadmium (Cd) pollution has received widespread social concern. Our previously constructed CadR-based bacterial whole cell biosensor (WCB) epCadR5 showed high sensitivity and specificity in cadmium detection. However, the application of the sensor is still hindered by the need for laboratory equipment to read the fluorescence signal output. In this study, we aimed to optimizing the sensor to make it available for visual detection of environmental cadmium and simplify the detection process to advance practical application of the sensor.

RESULTS

By replacing the constitutive promoter with J110, the fluorescence signal output of the sensor was significantly increased and the fluorescence leakage was decreased. In addition, the fluorescence signal output of green fluorescence protein (GFP) was enhanced by the addition of a 5' untranslated region (5'-UTR) mlcR10. The fluorescence signal output of the WCB is sufficiently robust to be visible and distinguishable to the naked eye, which is of paramount importance for visual detection. The sensor readout can be conveniently recorded by mobile phone camera and quantified. For ease of on-site application, the WCB's visual detection procedures and conditions were further optimized and simplified. The WCB demonstrated good linearity and detection limit (1.81 μg/L) for visual detection of Cd2+ without the assistance of bulky laboratory equipment. For the detection of real environmental samples, the WCB visual detection results were close to those of WCB-flow cytometry (FACS) and graphite furnace atomic absorption spectroscopy (GFAAS).

SIGNIFICANCE

In this work, we developed an easy-to-use, on-site and visual detection biosensor for monitoring environmental Cd2+. It will advance the utilization of cadmium WCBs in practical settings. The optimization and simplification strategy in the study also provide new insights into the visualization of other bacterial biosensors, and will advance the practical application of WCBs.

Bioluminescent Systems for Theranostic Applications

Bioluminescence, the light produced by biochemical reactions involving luciferases in living organisms, has been extensively investigated for various applications. It has attracted particular interest as an internal light source for theranostic applications due to its safe and efficient characteristics that overcome the limited penetration of conventional external light sources. Recent advancements in protein engineering technologies and protein delivery platforms have expanded the application of bioluminescence to a wide range of theranostic areas, including bioimaging, biosensing, photodynamic therapy, and optogenetics. This comprehensive review presents the fundamental concepts of bioluminescence and explores its recent applications across diverse fields. Moreover, it discusses future research directions based on the current status of bioluminescent systems for further expansion of their potential.

Advances in the Development of Bacterial Bioluminescence Imaging

Bioluminescence imaging (BLI) is a powerful method for visualizing biological processes and tracking cells. Engineered bioluminescent bacteria that utilize luciferase-catalyzed biochemical reactions to generate luminescence have become useful analytical tools for in vitro and in vivo bacterial imaging. Accordingly, this review initially introduces the development of engineered bioluminescent bacteria that use different luciferase-luciferin pairs as analytical tools and their applications for in vivo BLI, including real-time bacterial tracking of infection, probiotic investigation, tumor-targeted therapy, and drug screening. Applications of engineered bioluminescent bacteria as whole-cell biosensors for sensing biological changes in vitro and in vivo are then discussed. Finally, we review the optimizations and future directions of bioluminescent bacteria for imaging. This review aims to provide fundamental insights into bacterial BLI and highlight the potential development of this technique in the future.

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.

Use of whole-cell bioreporters to assess bioavailability of contaminants in aquatic systems

Water contamination has become increasingly a critical global environmental issue that threatens human and ecosystems’ health. Monitoring and risk assessment of toxic pollutants in water bodies is essential to identifying water pollution treatment needs. Compared with the traditional monitoring approaches, environmental biosensing via whole-cell bioreporters (WCBs) has exhibited excellent capabilities for detecting bioavailability of multiple pollutants by providing a fast, simple, versatile and economical way for environmental risk assessment. The performance of WCBs is determined by its elements of construction, such as host strain, regulatory and reporter genes, as well as experimental conditions. Previously, numerous studies have focused on the design and construction of WCB rather than improving the detection process and commercialization of this technology. For investigators working in the environmental field, WCB can be used to detect pollutants is more important than how they are constructed. This work provides a review of the development of WCBs and a brief introduction to genetic construction strategies and aims to summarize key studies on the application of WCB technology in detection of water contaminants, including organic pollutants and heavy metals. In addition, the current status of commercialization of WCBs is highlighted.

Development of Whole-Cell Biosensors for Screening of Peptidoglycan-Targeting Antibiotics in a Gram-Negative Bacterium

There is an urgent need to develop novel antibiotics since antibiotic resistance is an increasingly serious threat to global public health. Whole-cell biosensors are one of the promising strategies for new antibiotic discovery. The peptidoglycan (PG) of the bacterial cell wall is one of the most important targets for antibiotics. However, the biosensors for the detection of PG-targeting antibiotics in Gram-negative bacteria have not been developed, mainly because of the lack of the regulatory systems that sense and respond to PG stress. Recently, we identified a novel two-component signal transduction system (PghKR) that is responsible for sensing and responding to PG damage in the Gram-negative bacterium Shewanella oneidensis. Based on this system, we developed biosensors for the detection of PG-targeting antibiotics. Using ampicillin as an inducer for PG stress and the bacterial luciferase LuxCDABE as the reporter, we found that the PghKR biosensors are specific to antibiotics targeting PG synthesis, including β-lactams, vancomycin, and d-cycloserine. Deletion of genes encoding PG permease AmpG and β-lactamase BlaA improves the sensitivity of the biosensors substantially. The PghKR biosensor in the background of ΔblaA is also functional on agar plates, providing a simple method for screening bacteria that produce PG-targeting antibiotics. IMPORTANCE The growing problem of antibiotic resistance in Gram-negative bacteria urgently needs new strategies so that researchers can develop novel antibiotics. Microbial whole-cell biosensors are capable of sensing various stimuli with a quantifiable output and show tremendous potential for the discovery of novel antibiotics. As the Achilles' heel of bacteria, the synthesis of the peptidoglycan (PG) is targeted by many antibiotics. However, the regulatory systems that sense and respond to PG-targeting stress in Gram-negative bacteria are reported rarely, restricting the development of biosensors for the detection of PG-targeting antibiotics. In this study, we developed a highly sensitive and specific biosensor based on a novel two-component system in the Gram-negative bacterium Shewanella oneidensis that is responsible for the sensing and responding to PG stress. Our biosensors have great potential for discovering novel antibiotics and determining the mode of action of antibiotics.

Structure-Function Relationships in Temperature Effects on Bacterial Luciferases: Nothing Is Perfect

The evaluation of temperature effects on the structure and function of enzymes is necessary to understand the mechanisms underlying their adaptation to a constantly changing environment. In the current study, we investigated the influence of temperature variation on the activity, structural dynamics, thermal inactivation and denaturation of Photobacterium leiognathi and Vibrio harveyi luciferases belonging to different subfamilies, as well as the role of sucrose in maintaining the enzymes functioning and stability. We used the stopped-flow technique, differential scanning calorimetry and molecular dynamics to study the activity, inactivation rate, denaturation and structural features of the enzymes under various temperatures. It was found that P. leiognathi luciferase resembles the properties of cold-adapted enzymes with high activity in a narrow temperature range and slightly lower thermal stability than V. harveyi luciferase, which is less active, but more thermostable. Differences in activity at the studied temperatures can be associated with the peculiarities of the mobile loop conformational changes. The presence of sucrose does not provide an advantage in activity but increases the stability of the enzymes. Differential scanning calorimetry experiments showed that luciferases probably follow different denaturation schemes.

Cloning and expression of Burkholderia polyyne biosynthetic gene clusters in Paraburkholderia hosts provides a strategy for biopesticide development

Burkholderia have potential as biocontrol agents because they encode diverse biosynthetic gene clusters (BGCs) for a range of antimicrobial metabolites. Given the opportunistic pathogenicity associated with Burkholderia species, heterologous BGC expression within non-pathogenic hosts is a strategy to construct safe biocontrol strains. We constructed a yeast-adapted Burkholderia-Escherichia shuttle vector (pMLBAD_yeast) with a yeast replication origin 2 μ and URA3 selection marker and optimised it for cloning BGCs using the in vivo recombination ability of Saccharomyces cerevisiae. Two Burkholderia polyyne BGCs, cepacin (13 kb) and caryoynencin (11 kb), were PCR-amplified as three overlapping fragments, cloned downstream of the pBAD arabinose promoter in pMLBAD_yeast and mobilised into Burkholderia and Paraburkholderia heterologous hosts. Paraburkholderia phytofirmans carrying the heterologous polyyne constructs displayed in vitro bioactivity against a variety of fungal and bacterial plant pathogens similar to the native polyyne producers. Thirteen Paraburkholderia strains with preferential growth at 30°C compared with 37°C were also identified, and four of these were amenable to genetic manipulation and heterologous expression of the caryoynencin construct. The cloning and successful heterologous expression of Burkholderia biosynthetic gene clusters within Paraburkholderia with restricted growth at 37°C opens avenues for engineering non-pathogenic biocontrol strains.

Preclinical confirmation of UVC efficacy in treating infectious keratitis

PURPOSE

Preclinical evaluation of the therapeutic potential of antimicrobial 265 nm UVC for infectious keratitis.

METHODS

Four experiments explored UVC: 1) impact on bacterial and fungal lawns on agar, in individual or mixed culture, 2) bacterial inactivation dose in an in vitro deep corneal infection model, 3) dose validation in an ex vivo porcine keratitis model and 4) efficacy in a masked, randomised, controlled murine keratitis trial using bioluminescent Pseudomonas aeruginosa.

RESULTS

Minimum effective UVC exposures ranged between 2 s and 5 s for lawn bacteria and fungi in individual or mixed culture. Significant P. aeruginosa growth inhibition in the in vitro infection model was achieved with 15 s UVC, that resulted in a >3.5 log10 reduction of bacteria in a subsequent ex vivo keratitis model (p < 0.05). Bioluminescence fell below baseline levels in all treated animals, within 8 h of treatment (p < 0.05), in the in vivo study. Re-epithelialisation with corneal clarity occurred within 24 h in 75% of UVC-treated cases, with no relapse at 48 h. On plating, bacteria were recovered only from untreated controls.

CONCLUSIONS

UVC inhibited all tested bacteria and fungi, including mixed culture and strains linked to antibiotic resistance, in vitro, with exposures of ≤ 5 s. In vitro and ex vivo testing confirmed therapeutic potential of 15 s UVC. In vivo, 15 s UVC administered in two doses, 4 h apart, proved effective in treating murine bacterial keratitis.

Highly Sensitive Whole-Cell Biosensor for Cadmium Detection Based on a Negative Feedback Circuit

Although many whole-cell biosensors (WCBs) for the detection of Cd2+ have been developed over the years, most lack sensitivity and specificity. In this paper, we developed a Cd2+ WCB with a negative feedback amplifier in P. putida KT2440. Based on the slope of the linear detection curve as a measure of sensitivity, WCB with negative feedback amplifier greatly increased the output signal of the reporter mCherry, resulting in 33% greater sensitivity than in an equivalent WCB without the negative feedback circuit. Moreover, WCB with negative feedback amplifier exhibited increased Cd2+ tolerance and a lower detection limit of 0.1 nM, a remarkable 400-fold improvement compared to the WCB without the negative feedback circuit, which is significantly below the World Health Organization standard of 27 nM (0.003 mg/L) for cadmium in drinking water. Due to the superior amplification of the output signal, WCB with negative feedback amplifier can provide a detectable signal in a much shorter time, and a fast response is highly preferable for real field applications. In addition, the WCB with negative feedback amplifier showed an unusually high specificity for Cd2+ compared to other metal ions, giving signals with other metals that were between 17.6 and 41.4 times weaker than with Cd2+. In summary, the negative feedback amplifier WCB designed in this work meets the requirements of Cd2+ detection with very high sensitivity and specificity, which also demonstrates that genetic negative feedback amplifiers are excellent tools for improving the performance of WCBs.

Bacterial bioluminescence assay for bioanalysis and bioimaging

Bioluminescence occurs through a chemical reaction in organisms that spontaneously produce light. Luminescent bacteria are unique among bioluminescent organisms. Their bioluminescence intensity is an indicator of their metabolic activity, which can directly reflect the influence of environmental factors on cell viability. Moreover, the whole bioluminescence process is totally gene encoded without the addition of extra substrates. As a result, bacterial bioluminescence has been a powerful tool for whole-cell biosensors and bio-reporters in bioanalysis and bioimaging. This review aims to cover the applications of wild-type and recombinant luminescent bacteria to detect the toxicity of environmental pollutants and biological molecules. The bacterial bioluminescence analytical assay has characteristics such as high sensitivity, short-term detection, and easy operation. Meanwhile, due to the development of gene engineering and optical technology, bacterial luciferase as a reporter protein has been successfully expressed in prokaryotic and eukaryotic cells, tissues, and organs of animals. The major applications for bacterial luciferase-based bioluminescence imaging, such as infectious diseases, cancer therapy, and stem cell tracing, are discussed in this review.

Relationships between community composition, productivity and invasion resistance in semi-natural bacterial microcosms

Common garden experiments that inoculate a standardised growth medium with synthetic microbial communities (i.e. constructed from individual isolates or using dilution cultures) suggest that the ability of the community to resist invasions by additional microbial taxa can be predicted by the overall community productivity (broadly defined as cumulative cell density and/or growth rate). However, to the best of our knowledge, no common garden study has yet investigated the relationship between microbial community composition and invasion resistance in microcosms whose compositional differences reflect natural, rather than laboratory-designed, variation. We conducted experimental invasions of two bacterial strains (Pseudomonas fluorescens and Pseudomonas putida) into laboratory microcosms inoculated with 680 different mixtures of bacteria derived from naturally occurring microbial communities collected in the field. Using 16S rRNA gene amplicon sequencing to characterise microcosm starting composition, and high-throughput assays of community phenotypes including productivity and invader survival, we determined that productivity is a key predictor of invasion resistance in natural microbial communities, substantially mediating the effect of composition on invasion resistance. The results suggest that similar general principles govern invasion in artificial and natural communities, and that factors affecting resident community productivity should be a focal point for future microbial invasion experiments.

Applications of bacteriophages against intracellular bacteria

Infectious diseases pose a significant threat to both human and animal populations. Intracellular bacteria are a group of pathogens that invade and survive within the interior of eukaryotic cells, which in turn protect them from antibacterial drugs and the host immune system. Limited penetration of antibacterials into host cells results in insufficient bacterial clearance and treatment failure. Bacteriophages have, over the decades, been proved to play an important role in combating bacterial infections (phage therapy), making them an important alternative to classical antibiotic strategies today. Phages have been found to be effective at killing various species of extracellular bacteria, but little is still known about how phages control intracellular infections. With advances in phage genomics and mechanisms of delivery and cell uptake, the development of phage-based antibacterial strategies to address the treatment of intracellular bacteria has general potential. In this review, we present the current state of knowledge regarding the application of bacteriophages against intracellular bacteria. We cover phage deployment against the most common intracellular pathogens with special attention to therapeutic and preventive strategies.

Protonation status and control mechanism of flavin-oxygen intermediates in the reaction of bacterial luciferase

Bacterial luciferase catalyzes a bioluminescent reaction by oxidizing long-chain aldehydes to acids using reduced FMN and oxygen as co-substrates. Although a flavin C4a-peroxide anion is postulated to be the intermediate reacting with aldehyde prior to light liberation, no clear identification of the protonation status of this intermediate has been reported. Here, transient kinetics, pH variation, and site-directed mutagenesis were employed to probe the protonation state of the flavin C4a-hydroperoxide in bacterial luciferase. The first observed intermediate, with a λ_max of 385 nm, transformed to an intermediate with a λ_max of 375 nm. Spectra of the first observed intermediate were pH-dependent, with a λ_max of 385 nm at pH < 8.5 and 375 at pH > 9, correlating with a pK_a of 7.7-8.1. These data are consistent with the first observed flavin C4a intermediate at pH < 8.5 being the protonated flavin C4a-hydroperoxide, which loses a proton to become an active flavin C4a-peroxide. Stopped-flow studies of His44Ala, His44Asp, and His44Asn variants showed only a single intermediate with a λ_max of 385 nm at all pH values, and none of these variants generate light. These data indicate that His44 variants only form a flavin C4a-hydroperoxide, but not an active flavin C4a-peroxide, indicating an essential role for His44 in deprotonating the flavin C4a-hydroperoxide and initiating chemical catalysis. We also investigated the function of the adjacent His45; stopped-flow data and molecular dynamics simulations identify the role of this residue in binding reduced FMN.

Imaging of bioluminescent Klebsiella pneumoniae induced pulmonary infection in an immunosuppressed mouse model

Objective

To establish a mouse model of bioluminescent Klebsiella pneumoniae-induced lung infection, under different infection states after pretreatment with various dosages of cyclophosphamide (CTX).

Methods

A K. pneumoniae strain carrying the luxCDABE operon was used to infect immunocompetent mice (intraperitoneal injection of saline at 4 days and 1 day prior to experimental lung infection) and immunodeficient mice (50 mg/kg CTX at 4 days and 50 mg/kg CTX at 1 day prior to lung infection; or 150 mg/kg CTX at 4 days and 100 mg/kg CTX at 1 day prior to lung infection). Disease progression was monitored in living mice using a bioluminescence imaging system. The bioluminescent images, bacterial loads in lungs, blood cytological changes and histopathology of lungs were analysed.

Results

K. pneumoniae-induced lung infection models were established in mice pretreated with CTX. Different doses of CTX led to different severities of lung infection. Mice pretreated with 150/100 mg/kg CTX were more suitable for real-time monitoring as they had more typical bioluminescent images of lung infection, more obvious changes in the bioluminescent intensity values, more bacterial colonies in the lungs and more distinct pulmonary pathological changes.

Conclusions

A stable bioluminescent K. pneumonia-induced lung infection model was successfully established in mice pretreated with CTX, which can be semi-quantitatively monitored in real-time.

Bacterial luciferase: Molecular mechanisms and applications

Bacterial luciferase is a flavin-dependent monooxygenase which is remarkable for its distinctive feature in transforming chemical energy to photons of visible light. The bacterial luciferase catalyzes bioluminescent reaction using reduced flavin mononucleotide, long-chain aldehyde and oxygen to yield oxidized flavin, corresponding acid, water and light at λ_max around 490nm. The enzyme comprises of two non-identical α and β subunits, where α subunit is a catalytic center and β subunit is crucially required for maintaining catalytic function of the α subunit. The crystal structure with FMN bound and mutagenesis studies have assigned a number of amino acid residues that are important in coordinating critical reactions and stabilizing intermediates to attain optimum reaction efficiency. The enzyme achieves monooxygenation by generating C4a-hydroperoxyflavin intermediate that later changes its protonation status to become C4a-peroxyflavin, which is necessary for the nucleophilic attacking with aldehyde substrate. The decomposing of C4a-peroxyhemiacetal produces excited C4a-hydroxyflavin and acid product. The chemical basis regrading bioluminophore generation in Lux reaction remains an inconclusive issue. However, current data can, at least, demonstrate the involvement of electron transfer to create radical molecules which is the key step in this mechanism. Lux is a self-sufficient bioluminescent system in which all substrates can be recycled and produced by a group of enzymes from the lux operon. This makes Lux distinctively advantageous over other luciferases for reporter enzyme application. The progression of understanding of Lux catalysis is beneficial to improve light emitting efficiency in order to expand the robustness of Lux application.

Bioluminescence-Triggered Photoswitchable Bacterial Adhesions Enable Higher Sensitivity and Dual-Readout Bacterial Biosensors for Mercury

We present a new concept for whole-cell biosensors that couples the response to Hg²⁺ with bioluminescence and bacterial aggregation. This allows us to use the bacterial aggregation to preconcentrate the bioluminescent bacteria at the substrate surface and increase the sensitivity of Hg²⁺ detection. This whole-cell biosensor combines a Hg²⁺-sensitive bioluminescence reporter and light-responsive bacterial cell-cell adhesions. We demonstrate that the blue luminescence in response to Hg²⁺ is able to photoactivate bacterial aggregation, which provides a second readout for Hg²⁺ detection. In return, the Hg²⁺-triggered bacterial aggregation leads to faster sedimentation and more efficient formation of biofilms. At low Hg²⁺ concentrations, the enrichment of the bacteria in biofilms leads to an up to 10-fold increase in the signal. The activation of photoswitchable proteins with biological light is a new concept in optogenetics, and the presented bacterial biosensor design is transferable to other bioluminescent reporters with particular interest for environmental monitoring.

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

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.

Current issues confounding the rapid toxicological assessment of oil spills

Oil spills of varying magnitude occur every year, each presenting a unique challenge to the local ecosystem. The complex, changeable nature of oil makes standardised risk assessment difficult. Our review of the state of science regarding oil's unique complexity; biological impact of oil spills and use of rapid assessment tools, including commercial toxicity kits and bioassays, allows us to explore the current issues preventing effective, rapid risk assessment of oils. We found that despite the advantages to monitoring programmes of using well validated standardised tests, which investigate impacts across trophic levels at environmentally relevant concentrations, only a small percentage of the available tests are specialised for use within the marine environment, or validated for the assessment of crude oil toxicity. We discuss the use of rapid tests at low trophic levels in addition to relevant sublethal toxicity assays to allow the characterisation of oil, dispersant and oil and dispersant mixture toxicity. We identify novel, passive dosing techniques as a practical and reproducible means of improving the accuracy and maintenance of nominal concentrations. Future work should explore the possibility of linking this tiered testing system with ecosystem models to allow the prediction and risk assessment of the entire ecosystem.

Continuous and Real-Time In Vivo Autobioluminescent Imaging in a Mouse Model

In vivo small animal bioluminescent imaging has become an indispensable technique for interrogating the localization, health, and functionality of implanted cells within the complex environment of a living organism. However, this task can be daunting for even the most experienced researchers because it requires multiple animal handling steps and produces differential output signal characteristics in response to a number of experimental design variables. The recent emergence of autobioluminescent cells, which autonomously and continuously produce bioluminescent output signals without external stimulation, has the potential to simplify this process, reduce variability by removing human-induced error, and improve animal welfare by reducing the number of required needlesticks per procedure. This protocol details the implantation and imaging of autobioluminescent cells within a mouse model to demonstrate how cells implanted from a single injection can be imaged repeatedly across any post-implantation timescale without the need for further human-animal interaction or signal activation steps. This approach provides a facile means to continuously monitor implanted cellular output signals in real-time for extended time periods.

A novel universal nano-luciferase-involved reporter system for long-term probing food-borne probiotics and pathogenic bacteria in mice by in situ bioluminescence imaging

Food-borne bacteria have received increasing attention due to their great impact on human health. Bioimaging makes it possible to monitor bacteria inside the living body in real time and in situ. Nano-luciferase (NLuc) as a new member of the luciferase family exhibits superior properties than the commonly used luciferases, including small size, high stability and improved luminescence. Herein, NLuc, CBRLuc and FLuc were well expressed in varied food-borne bacteria. Results showed that the signal intensity of E. coli-NLuc was about 41 times higher than E. coli-CBRLuc, L. plantarum-NLuc was nearly 227 times that of L. plantarum-FLuc in vitro. Moreover, NLuc was applied to trace L. plantarum and E. coli in vivo through the whole body and separated digestive tract imaging, as well as the feces bacterium counting and probing. The persistence of bioluminescent strains was predominantly localized in colon and cecum of mice after oral administration. The NLuc system showed its incomparable superiority, especially in the application of intestinal imaging and the universality for food-borne bacteria. We demonstrated that the NLuc system was a brilliant alternative for specific application of food-borne bacteria in vivo, aiming to collect more accurate and real-time information of food-borne bacteria from the living body for further investigation of their damage mechanism and nutrition effect.

Schematic illustration of the preparation of bioluminescent bacteria and the experimental design of tracing of the foodborne bacteria in vivo.

Deconvolution of Luminescence Cross-Talk in High-Throughput Gene Expression Profiling

Luciferase reporters have become standard genetic tools to monitor gene expression in real time and in high-throughput using microplate readers. Compared to reporter gene assays based on fluorescence proteins, luciferase reporters have a superior signal-to-noise ratio, since they do not suffer from the high autofluorescence background of the bacterial cell. However, at the same time luciferase reporters have the drawback of constant light emission, which leads to undesired cross-talk between neighboring wells on a microplate. To overcome this limitation, we developed a computational method to correct for luminescence bleed-through and to estimate the "true" luminescence activity for each well of a microplate. As the sole input our algorithm uses the signals measured from a calibration plate, in which the light emitted from a single luminescent well serves as an estimate for the "light-spread function". We show that this light-spread function can be used to deconvolve any other measurement obtained under the same technical conditions. Our analysis demonstrates that the correction preserves low-level signals close to the background and shows that it is universally applicable to different kinds of microplate readers and plate types.

Sensitive and Specific Whole-Cell Biosensor for Arsenic Detection

Whole-cell biosensors (WCBs) have been designed to detect As(III), but most suffer from poor sensitivity and specificity. In this paper, we developed an arsenic WCB with a positive feedback amplifier in Escherichia coli DH5α. The output signal from the reporter mCherry was significantly enhanced by the positive feedback amplifier. The sensitivity of the WCB with positive feedback is about 1 order of magnitude higher than that without positive feedback when evaluated using a half-saturation As(III) concentration. The minimum detection limit for As(III) was reduced by 1 order of magnitude to 0.1 µM, lower than the World Health Organization standard for the arsenic level in drinking water, 0.01 mg/liter or 0.13 µM. Due to the amplification of the output signal, the WCB was able to give detectable signals within a shorter period, and a fast response is essential for in situ operations. Moreover, the WCB with the positive feedback amplifier showed exceptionally high specificity toward As(III) when compared with other metal ions. Collectively, the designed positive feedback amplifier WCB meets the requirements for As(III) detection with high sensitivity and specificity. This work also demonstrates the importance of genetic circuit engineering in designing WCBs, and the use of genetic positive feedback amplifiers is a good strategy to improve the performance of WCBs.IMPORTANCE Arsenic poisoning is a severe public health issue. Rapid and simple methods for the sensitive and specific monitoring of arsenic concentration in drinking water are needed. In this study, we designed an arsenic WCB with a positive feedback amplifier. It is highly sensitive and able to detect arsenic below the WHO limit level. In addition, it also significantly improves the specificity of the biosensor toward arsenic, giving a signal that is about 10 to 20 times stronger in response to As(III) than to other metals. This work not only provides simple but effective arsenic biosensors but also demonstrates the importance of genetic engineering, particularly the use of positive feedback amplifiers, in designing WCBs.

An ingestible bacterial-electronic system to monitor gastrointestinal health

Biomolecular monitoring in the gastrointestinal tract could offer rapid, precise disease detection and management but is impeded by access to the remote and complex environment. Here, we present an ingestible micro-bio-electronic device (IMBED) for in situ biomolecular detection based on environmentally resilient biosensor bacteria and miniaturized luminescence readout electronics that wirelessly communicate with an external device. As a proof of concept, we engineer heme-sensitive probiotic biosensors and demonstrate accurate diagnosis of gastrointestinal bleeding in swine. Additionally, we integrate alternative biosensors to demonstrate modularity and extensibility of the detection platform. IMBEDs enable new opportunities for gastrointestinal biomarker discovery and could transform the management and diagnosis of gastrointestinal disease.

1001 lights: luciferins, luciferases, their mechanisms of action and applications in chemical analysis, biology and medicine

Bioluminescence (BL) is a spectacular phenomenon involving light emission by live organisms. It is caused by the oxidation of a small organic molecule, luciferin, with molecular oxygen, which is catalysed by the enzyme luciferase. In nature, there are approximately 30 different BL systems, of which only 9 have been studied to various degrees in terms of their reaction mechanisms. A vast range of in vitro and in vivo analytical techniques have been developed based on BL, including tests for different analytes, immunoassays, gene expression assays, drug screening, bioimaging of live organisms, cancer studies, the investigation of infectious diseases and environmental monitoring. This review aims to cover the major existing applications for bioluminescence in the context of the diversity of luciferases and their substrates, luciferins. Particularly, the properties and applications of d-luciferin, coelenterazine, bacterial, Cypridina and dinoflagellate luciferins and their analogues along with their corresponding luciferases are described. Finally, four other rarely studied bioluminescent systems (those of limpet Latia, earthworms Diplocardia and Fridericia and higher fungi), which are promising for future use, are also discussed.

Co-Cultured Continuously Bioluminescent Human Cells as Bioreporters for the Detection of Prodrug Therapeutic Impact Pre- and Post-Metabolism

Modern drug discovery workflows require assay systems capable of replicating the complex interactions of multiple tissue types, but that can still function under high throughput conditions. In this work, we evaluate the use of substrate-free autobioluminescence in human cell lines to support the performance of these assays with reduced economical and logistical restrictions relative to substrate-requiring bioluminescent reporter systems. The use of autobioluminescence was found to support assay functionality similar to existing luciferase reporter targets. The autobioluminescent assay format was observed to correlate strongly with general metabolic activity markers such as ATP content and the presence of reactive oxygen species, but not with secondary markers such as glutathione depletion. At the transcriptional level, autobioluminescent dynamics were most closely associated with expression of the CYP1A1 phase I detoxification pathway. These results suggest constitutively autobioluminescent cells can function as general metabolic activity bioreporters, while pairing expression of the autobioluminescent phenotype to detoxification pathway specific promoters could create more specific sensor systems.

A Versatile Toolbox for the Control of Protein Levels Using Nε-Acetyl-l-lysine Dependent Amber Suppression

The analysis of the function of essential genes in vivo depends on the ability to experimentally modulate levels of their protein products. Current methods to address this are based on transcriptional or post-transcriptional regulation of mRNAs, but approaches based on the exploitation of translation regulation have so far been neglected. Here we describe a toolbox, based on amber suppression in the presence of N^ε-acetyl-l-lysine (AcK), for translational tuning of protein output. We chose the highly sensitive luminescence system LuxCDABE as a reporter and incorporated a UAG stop codon into the gene for the reductase subunit LuxC. The system was used to measure and compare the effects of AcK- and N^ε-(tert-butoxycarbonyl)-l-lysine (BocK) dependent amber suppression in Escherichia coli. We also demonstrate here that, in combination with transcriptional regulation, the system allows protein production to be either totally repressed or gradually adjusted. To identify sequence motifs that provide improved translational regulation, we varied the sequence context of the amber codon and found that insertion of two preceding prolines drastically decreases luminescence. In addition, using LacZ as a reporter, we demonstrated that a strain encoding a variant with a Pro-Pro amber motif can only grow on lactose when AcK is supplied, thus confirming the tight translational regulation of protein output. In parallel, we constructed an E. coli strain that carries an isopropyl β-d-1-thiogalactopyranoside (IPTG)-inducible version of the AcK-tRNA synthetase (AcKRS) gene on the chromosome, thus preventing mischarging of noncognate substrates. Subsequently, a diaminopimelic acid auxotrophic mutant (ΔdapA) was generated demonstrating the potential of this strain in regulating essential gene products. Furthermore, we assembled a set of vectors based on the broad-host-range pBBR ori that enable the AcK-dependent amber suppression system to control protein output not only in E. coli, but also in Salmonella enterica and Vibrio cholerae.

Bioluminescence Imaging of Colonization and Clearance Dynamics of Brucella Suis Vaccine Strain S2 in Mice and Guinea Pigs

PURPOSE

The goal of this study was to develop a plasmid-based lux bio-reporter for use to obtain in vivo images of Brucella suis vaccine strain 2 (B.suis S2) infection with high resolution and good definition.

PROCEDURES

The pBBR-lux (pBBR1MCS-2-lxCDABE) plasmid that carries the luxCDABE operon was introduced into B. suis S2 by electroporation yielding B. suis S2-lux. The spatial and temporal transit of B. suis S2 in mice and guinea pigs was monitored by bioluminescence imaging.

RESULTS

The plasmid pBBR-lux is stable in vivo and does not appear to impact the virulence or growth of bacteria. This sensitive luciferase reporter could represent B. suis S2 survival in real time. B. suis S2 mainly colonized the lungs, liver, spleen, and uterus in mice and guinea pigs as demonstrated by bioluminescence imaging.

CONCLUSION

The plasmid-based lux bioreporter strategy can be used to obtain high resolution in vivo images of B. suis S2 infection in mice and guinea pigs.

Reconstructing promoter activity from Lux bioluminescent reporters

The bacterial Lux system is used as a gene expression reporter. It is fast, sensitive and non-destructive, enabling high frequency measurements. Originally developed for bacterial cells, it has also been adapted for eukaryotic cells, and can be used for whole cell biosensors, or in real time with live animals without the need for euthanasia. However, correct interpretation of bioluminescent data is limited: the bioluminescence is different from gene expression because of nonlinear molecular and enzyme dynamics of the Lux system. We have developed a computational approach that, for the first time, allows users of Lux assays to infer gene transcription levels from the light output. This approach is based upon a new mathematical model for Lux activity, that includes the actions of LuxAB, LuxEC and Fre, with improved mechanisms for all reactions, as well as synthesis and turn-over of Lux proteins. The model is calibrated with new experimental data for the LuxAB and Fre reactions from Photorhabdus luminescens—the source of modern Lux reporters—while literature data has been used for LuxEC. Importantly, the data show clear evidence for previously unreported product inhibition for the LuxAB reaction. Model simulations show that predicted bioluminescent profiles can be very different from changes in gene expression, with transient peaks of light output, very similar to light output seen in some experimental data sets. By incorporating the calibrated model into a Bayesian inference scheme, we can reverse engineer promoter activity from the bioluminescence. We show examples where a decrease in bioluminescence would be better interpreted as a switching off of the promoter, or where an increase in bioluminescence would be better interpreted as a longer period of gene expression. This approach could benefit all users of Lux technology.

Bioluminescent reporters are used in many areas of biology as fast, sensitive and non-destructive measures of gene expression. They have been developed for bacteria, adapted now for other kinds of organisms, and recently been used for whole cell biosensors, and for real-time live animal models for infection without the need for euthanasia. However, users of Lux technologies rely on the light output being similar to the gene expression they wish to measure. We show that this is not the case. Rather, there is a nonlinear relationship between the two: light output can be misleading and so limits the way that such data can be interpreted. We have developed a new computational method that, for the first time, allows users of Lux reporters to infer accurate gene transcription levels from bioluminescent data. We show examples where a small decrease in light would be better interpreted as promoter being switched off, or where an increase in light would be better interpreted as promoter activity for a longer time.

Influence of Antibiotic Pressure on Five Plasmid-based Bioluminescent Gram-negative Bacterial Strains

PURPOSE

The present study aims to develop five Gram-negative bacteria expressing bacterial luciferase for use to evaluate the influence of different antibiotics on bacterial bioluminescence.

PROCEDURES

The pBBR-lux plasmid was introduced into five Gram-negative bacteria; the bioluminescent signals and colony-forming unit (CFU)/ml of all the bioluminescent strains were monitored with six antibiotics at various concentrations.

RESULTS

Dose-dependent bioluminescence signals can be used for rapid bacterial antibiotic susceptibility test (AST). All five bioluminescent bacterial strains have similar bioluminescence and CFU enhancement at sub-minimum inhibitory concentration (MIC) of six different antibiotics.

CONCLUSION

The bioluminescent signals and CFU enhancement at sub-MIC antibiotic concentrations should be of value in the research of new antibiotic drugs and bioluminescent imaging.

Bacterial Biosensors for in Vivo Spatiotemporal Mapping of Root Secretion

Plants engineer the rhizosphere to their advantage by secreting various nutrients and secondary metabolites. Coupling transcriptomic and metabolomic analyses of the pea (Pisum sativum) rhizosphere, a suite of bioreporters has been developed in Rhizobium leguminosarum bv viciae strain 3841, and these detect metabolites secreted by roots in space and time. Fourteen bacterial lux fusion bioreporters, specific for sugars, polyols, amino acids, organic acids, or flavonoids, have been validated in vitro and in vivo. Using different bacterial mutants (nodC and nifH), the process of colonization and symbiosis has been analyzed, revealing compounds important in the different steps of the rhizobium-legume association. Dicarboxylates and sucrose are the main carbon sources within the nodules; in ineffective (nifH) nodules, particularly low levels of sucrose were observed, suggesting that plant sanctions affect carbon supply to nodules. In contrast, high myo-inositol levels were observed prior to nodule formation and also in nifH senescent nodules. Amino acid biosensors showed different patterns: a γ-aminobutyrate biosensor was active only inside nodules, whereas the phenylalanine bioreporter showed a high signal also in the rhizosphere. The bioreporters were further validated in vetch (Vicia hirsuta), producing similar results. In addition, vetch exhibited a local increase of nod gene-inducing flavonoids at sites where nodules developed subsequently. These bioreporters will be particularly helpful in understanding the dynamics of root exudation and the role of different molecules secreted into the rhizosphere.

Insightful directed evolution of Escherichia coli quorum sensing promoter region of the lsrACDBFG operon: a tool for synthetic biology systems and protein expression

Quorum sensing (QS) regulates many natural phenotypes (e.q. virulence, biofilm formation, antibiotic resistance), and its components, when incorporated into synthetic genetic circuits, enable user-directed phenotypes. We created a library of Escherichia coli lsr operon promoters using error-prone PCR (ePCR) and selected for promoters that provided E. coli with higher tetracycline resistance over the native promoter when placed upstream of the tet(C) gene. Among the fourteen clones identified, we found several mutations in the binding sites of QS repressor, LsrR. Using site-directed mutagenesis we restored all p-lsrR-box sites to the native sequence in order to maintain LsrR repression of the promoter, preserving the other mutations for analysis. Two promoter variants, EP01rec and EP14rec, were discovered exhibiting enhanced protein expression. In turn, these variants retained their ability to exhibit the LsrR-mediated QS switching activity. Their sequences suggest regulatory linkage between CytR (CRP repressor) and LsrR. These promoters improve upon the native system and exhibit advantages over synthetic QS promoters previously reported. Incorporation of these promoters will facilitate future applications of QS-regulation in synthetic biology and metabolic engineering.

In Vivo Analysis of Protein-Protein Interactions with Bioluminescence Resonance Energy Transfer (BRET): Progress and Prospects

Proteins are the elementary machinery of life, and their functions are carried out mostly by molecular interactions. Among those interactions, protein-protein interactions (PPIs) are the most important as they participate in or mediate all essential biological processes. However, many common methods for PPI investigations are slightly unreliable and suffer from various limitations, especially in the studies of dynamic PPIs. To solve this problem, a method called Bioluminescence Resonance Energy Transfer (BRET) was developed about seventeen years ago. Since then, BRET has evolved into a whole class of methods that can be used to survey virtually any kinds of PPIs. Compared to many traditional methods, BRET is highly sensitive, reliable, easy to perform, and relatively inexpensive. However, most importantly, it can be done in vivo and allows the real-time monitoring of dynamic PPIs with the easily detectable light signal, which is extremely valuable for the PPI functional research. This review will take a comprehensive look at this powerful technique, including its principles, comparisons with other methods, experimental approaches, classifications, applications, early developments, recent progress, and prospects.

Fast plasmid based protein expression analysis in insect cells using an automated SplitGFP screen

Recombinant protein expression often presents a bottleneck for the production of proteins for use in many areas of animal‐cell biotechnology. Difficult‐to‐express proteins require the generation of numerous expression constructs, where popular prokaryotic screening systems often fail to identify expression of multi domain or full‐length protein constructs. Post‐translational modified mammalian proteins require an alternative host system such as insect cells using the Baculovirus Expression Vector System (BEVS). Unfortunately this is time‐, labor‐, and cost‐intensive. It is clearly desirable to find an automated and miniaturized fast multi‐sample screening method for protein expression in such systems. With this in mind, in this paper a high‐throughput initial expression screening method is described using an automated Microcultivation system in conjunction with fast plasmid based transient transfection in insect cells for the efficient generation of protein constructs. The applicability of the system is demonstrated for the difficult to express Nucleotide‐binding Oligomerization Domain‐containing protein 2 (NOD2). To enable detection of proper protein expression the rather weak plasmid based expression has been improved by a sensitive inline detection system. Here we present the functionality and application of the sensitive SplitGFP (split green fluorescent protein) detection system in insect cells. The successful expression of constructs is monitored by direct measurement of the fluorescence in the BioLector Microcultivation system. Additionally, we show that the results obtained with our plasmid‐based SplitGFP protein expression screen correlate directly to the level of soluble protein produced in BEVS. In conclusion our automated SplitGFP screen outlines a sensitive, fast and reliable method reducing the time and costs required for identifying the optimal expression construct prior to large scale protein production in baculovirus infected insect cells. Biotechnol. Bioeng. 2016;113: 1975–1983. © 2016 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.

A Luciferase-Based Assay to Test Whether Gene Expression Responses to Environmental Inputs Are Temporally Restricted by the Circadian Clock

Gating is the mechanism by which the influence of an environmental signal on a particular output is temporally restricted by the circadian clock, so that the maximum response of the output to the signal occurs at a specific time. Gated regulation mechanisms have been described for several genes whose expression is strongly induced by light or temperature at certain times but repressed by the circadian clock at others. To reveal a gated pattern of expression in response to light, light pulses are applied in the dark at different times of the 24 h cycle and the transcriptional response of the gene of interest is then monitored with an appropriate technique. Luciferase (LUC) reporters have been the method of choice to study circadian rhythms in the past decades, but this methodology also provides an ideal platform for performing a gating assay. In this chapter, we describe a LUC imaging based protocol designed to test whether the influence of light on the expression of a gene of interest is gated by the circadian clock.

Fiber-Optic Chemical Sensors and Fiber-Optic Bio-Sensors

This review summarizes principles and current stage of development of fiber-optic chemical sensors (FOCS) and biosensors (FOBS). Fiber optic sensor (FOS) systems use the ability of optical fibers (OF) to guide the light in the spectral range from ultraviolet (UV) (180 nm) up to middle infrared (IR) (10 μm) and modulation of guided light by the parameters of the surrounding environment of the OF core. The introduction of OF in the sensor systems has brought advantages such as measurement in flammable and explosive environments, immunity to electrical noises, miniaturization, geometrical flexibility, measurement of small sample volumes, remote sensing in inaccessible sites or harsh environments and multi-sensing. The review comprises briefly the theory of OF elaborated for sensors, techniques of fabrications and analytical results reached with fiber-optic chemical and biological sensors.

Application of internal standard method in recombinant luminescent bacteria test

Mercury and its organic compounds have been of severe concern worldwide due to their damage to the ecosystem and human health. The development of effective and affordable technology to monitor and signal the presence of bioavailable mercury is an urgent need. The Mer gene is a mercury-responsive resistant gene, and a mercury-sensing recombinant luminescent bacterium using the Mer gene was constructed in this study. The mer operon from marine Pseudomonas putida strain SP1 was amplified and fused with prompterless luxCDABE in the pUCD615 plasmid within Escherichia coli cells, resulting in pTHE30-E. coli. The recombinant strain showed high sensitivity and specificity. The detection limit of Hg(2+) was 5nmol/L, and distinct luminescence could be detected in 30min. Cd(2+), Cu(2+), Zn(2+), Ca(2+), Pb(2+), Mg(2+), Mn(2+), and Al(3+) did not interfere with the detection over a range of 10(-5)-1mM. Application of recombinant luminescent bacteria testing in environmental samples has been a controversial issue: especially for metal-sensing recombinant strains, false negatives caused by high cytotoxicity are one of the most important issues when applying recombinant luminescent bacteria in biomonitoring of heavy metals. In this study, by establishing an internal standard approach, the false negative problem was overcome; furthermore, the method can also help to estimate the suspected mercury concentration, which ensures high detection sensitivity of bioavailable Hg(2+).

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.

Development of Bioluminescent Cronobacter sakazakii ATCC 29544 in a Mouse Model

Cronobacter sakazakii is an emerging pathogen that causes severe and life-threatening conditions including meningitis, bacteremia, and necrotizing enterocolitis. An animal model study for extrapolation of C. sakazakii infection can provide a better understanding of pathogenesis. However, methods for real-time monitoring of the course of C. sakazakii infection in living animals have been lacking. We developed a bioluminescent C. sakazakii strain (ATCC 29544) that can be used for real-time monitoring of C. sakazakii infection in BALB/c mice. C. sakazakii ATCC 29544 mainly colonized brain, liver, spleen, kidney, and gastrointestinal tract, as indicated by bioluminescence imaging. This work provides a novel approach for studying the progression of C. sakazakii infection and evaluating therapeutics in a living mouse model.

High-throughput viability assay using an autonomously bioluminescent cell line with a bacterial Lux reporter

Cell viability assays are extensively used to determine cell health, evaluate growth conditions, and assess compound cytotoxicity. Most existing assays are endpoint assays, in which data are collected at one time point after termination of the experiment. The time point at which toxicity of a compound is evident, however, depends on the mechanism of that compound. An ideal cell viability assay allows the determination of compound toxicity kinetically without having to terminate the assay prematurely. We optimized and validated a reagent-addition-free cell viability assay using an autoluminescent HEK293 cell line that stably expresses bacterial luciferase and all substrates necessary for bioluminescence. This cell viability assay can be used for real-time, long-term measurement of compound cytotoxicity in live cells with a signal-to-basal ratio of 20- to 200-fold and Z-factors of ~0.6 after 24-, 48- 72-, or 96-h incubation with compound. We also found that the potencies of nine cytotoxic compounds correlated well with those measured by four other commonly used cell viability assays. The results demonstrated that this kinetic cell viability assay using the HEK293(lux) autoluminescent cell line is useful for high-throughput evaluation of compound cytotoxicity.

Engineering an enhanced, thermostable, monomeric bacterial luciferase gene as a reporter in plant protoplasts

The application of the luxCDABE operon of the bioluminescent bacterium Photorhabdus luminescens as a reporter has been published for bacteria, yeast and mammalian cells. We report here the optimization of fused luxAB (the bacterial luciferase heterodimeric enzyme) expression, quantum yield and its application as a reporter gene in plant protoplasts. The fused luxAB gene was mutated by error prone PCR or chemical mutagenesis and screened for enhanced luciferase activity utilizing decanal as substrate. Positive luxAB mutants with superior quantum yield were subsequently shuffled by DNase I digestion and PCR assembly for generation of recombinants with additional increases in luciferase activity in bacteria. The coding sequence of the best recombinant, called eluxAB, was then optimized further to conform to Arabidopsis (Arabidopsis thaliana) codon usage. A plant expression vector of the final, optimized eluxAB gene (opt-eluxAB) was constructed and transformed into protoplasts of Arabidopsis and maize (Zea mays). Luciferase activity was dramatically increased for opt-eluxAB compared to the original luxAB in Arabidopsis and maize cells. The opt-eluxAB driven by two copies of the 35S promoter expresses significantly higher than that driven by a single copy. These results indicate that the eluxAB gene can be used as a reporter in plant protoplasts. To our knowledge, this is the first report to engineer the bacterium Photorhabdus luminescens luciferase luxAB as a reporter by directed evolution which paved the way for further improving the luxAB reporter in the future.