Bacterial genotoxicity bioreporters

Anion and Substituents Effect on Spectral-Kinetic and Biological Characteristics of Spiropyran Salts

Spiropyran salts containing a cationic vinyl-3H-indolium moiety are characterized by NIR absorption and fluorescence of their merocyanine forms. This feature makes them promising fluorescent probes and markers for bioimaging. The article focuses on the synthesis and study of the spectral, kinetic and toxic characteristics of such compounds with respect to various substituents in different moieties and the type of anion. A detailed analysis of the acquired data made it possible to draw some important conclusions regarding the influence of structural factors, which will be very useful for the further rational design of such derivatives. In particular, it was shown that the counterion has minimal effect on the spectral and kinetic characteristics of the dyes but dramatically affects the toxicity of the compounds. Following selection of the most appropriate compounds, bioimaging experiments were carried out to visualize planktonic bacteria and bacterial biofilms of E. coli and A. calcoaceticus. The ability to visualize biofilms is critical for the diagnosis of chronic diseases. By the results of molecular docking a theoretical interaction pattern between spiropyran molecules and DNA was proposed.

Glyphosate effect on biofilms formation, mutagenesis and stress response of E. сoli

Glyphosate is the most widely used herbicide in the world. There is still no complete clarity about the degree of its genotoxicity and mutagenicity. In addition, its effect on bacterial biofilms, the main life form of soil microbial communities, has not been adequately studied. Toxicity and mutagenicity, as well as changes in the bacterial biofilm biomass, physiological activity, and the number of living cells in its composition in the presence of glyphosate were assessed using the Escherichia coli model. To assess damage to cellular components under the action of this pesticide, luminescent whole-cell bacterial lux-biosensors were used. Changes in the level of mutagenesis were studied by the method of rifampicin mutants. High integral toxicity of glyphosate, the average level of increased oxidative stress and protein damage were shown with the help of bacterial biosensors. All the studied concentrations of the pesticide completely or partially suppress the matrix and structure of the E. coli CDC F-50 biofilm formation, as well as the bacterial cells metabolic activity in the biofilm. At the concentrations of 6.7 and 0.67 g/L, glyphosate suppresses mutagenesis, probably due to general suppression of metabolism, and at the concentration of 0.0067 g/L, it enhances mutagenesis by six times compared with the spontaneous level. Suppression of bacterial biofilms formation, toxic effects on microorganisms, and mutagenesis enhancement by glyphosate can lead to negative consequences for natural microbiomes.

Bacterial worth in genotoxicity assessment studies

Bacterial-based genotoxicity test systems play a significant role in the detection and evaluation of genotoxicity in vitro and have gained importance due to attributes like wide applicability, speed, high sensitivity, good reproducibility, and simplicity. The Salmonella microsomal mutagenicity assay was created by Ames and colleagues at the beginning of the 1970s, and it was based on the fundamental notion that in auxotrophic bacterial strains with inhibited growth, a mutant gene would revert to its original state on exposure to genotoxicants. This is the most successful and widely used in vitro genotoxicity test. Later, a number of additional test systems that incorporated DNA repair mechanisms including the bacterial SOS response were created. Genetic engineering has further provided significant advancement in these test systems with the development of highly sophisticated bacterial tester strains with significantly increased sensitivity to evaluate the chemical nature of hazardous substances and pollutants. These bacterial bioassays render an opportunity to detect the defined effects of compounds at the molecular level. In this review, all the aspects related to the bacterial system in genotoxicity assessment have been summarized and their role is elaborated concerning real-time requirements and future perspectives.

Molecular design and synthesis of methoxy-substitued spiropyrans with photomodulated NIR-fluorescence

This study focuses on the molecular design and synthesis of salt spiropyrans with near-IR fluorescence. The structure of the obtained compounds was confirmed by NMR, IR and mass spectroscopy. In the course of studying the spectral and photoluminescent characteristics, it was possible to reveal the effect of some substituents in various positions on the properties of spiropyran dyes. Due to the structural similarity of one of the isomers to cyanine dyes, the obtained compounds are of interest as potential fluorescent probes for bioimagimg, in particular, for DNA studies. To reveal their ability of binding to DNA molecules molecular docking was carried out. Toxic effects of compounds demonstrating NIR fluorescence were studied on biofilms, as well as using bacterial lux-biosensors.

A panel of visual bacterial biosensors for the rapid detection of genotoxic and oxidative damage: A proof of concept study

The emergence of new compounds during the past decade requires a high-throughput screening method for toxicity assay. The stress-responsive whole-cell biosensor is a powerful tool to evaluate direct or indirect damages of biological macromolecules induced by toxic chemicals. In this proof-of-concept study, nine well-characterized stress-responsive promoters were first selected to assemble a set of blue indigoidine-based biosensors. The PuspA-based, PfabA-based, and PgrpE-based biosensors were eliminated due to their high background. A dose-dependent increase of visible blue signal was observed in PrecA-, PkatG-, and PuvrA-based biosensors, responsive to potent mutagens, including mitomycin and nalidixic acid, but not to genotoxic lead and cadmium. The PrecA, PkatG, and Ppgi gene promoters were further fused to a purple deoxyviolacein synthetic enzyme cluster. Although high basal production of deoxyviolacein is unavoidable, an enhanced visible purple signal in response to mitomycin and nalidixic acid was observed as dose-dependent, especially in PkatG-based biosensors. The study shows that a set of stress-responsive biosensors employing visible pigment as a reporter is pre-validating in detecting extensive DNA damage and intense oxidative stress. Unlike widely-used fluorescent and bioluminescent biosensors, the visual pigment-based biosensor can become a novel, low-cost, mini-equipment, and high-throughput colorimetric device for the toxicity assessment of chemicals. However, combining multiple improvements can further improve the biosensing performance in future studies.

Bioaccessible PAH influence on distribution of antibiotic resistance genes and soil toxicity of different types of land use

For a better understanding of the dissemination of antibiotic resistance genes (ARGs) in natural microbial communities, it is necessary to study the factors influencing it. There are not enough studies showing the connection of some pollutants with the dissemination of ARGs and especially few works on the effect of polycyclic aromatic compounds (PAHs) on the spread of resistance in microbiocenosis. In this respect, the aim of the study was to determine the effect of bioaccessible PAHs on soil resistome. The toxicity and the content of bioaccessible PAHs and ARGs were studied in 64 samples of soils of different types of land use in the Rostov Region of Russia. In most soils, a close positive correlation was demonstrated between different ARGs and bioaccessible PAHs with different content of rings in the structure. Six of the seven studied ARGs correlated with the content of 2-, 3-, 4-, 5- or 6-ring PAHs. The greatest number of close correlations was found between the content of PAHs and ARGs in the soils of protected areas, for agricultural purposes, and in soils of hospitals. The diverse composition of microbial communities in these soils might greatly facilitate this process. A close correlation between various toxic effects identified with a battery of whole-cell bacterial biosensors and bioaccessible PAHs of various compositions was established. This correlation showed possible mechanisms of PAHs' influence on microorganisms (DNA damage, oxidative stress, etc.), which led to a significant increase in horizontal gene transfer and spread of some ARGs in soil microbial communities. All this information, taken together, suggests that bioaccessible PAHs can enhance the spread of antibiotic resistance genes.

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.

Live-Cell Systems in Real-Time Biomonitoring of Water Pollution: Practical Considerations and Future Perspectives

Continuous monitoring and early warning of potential water contamination with toxic chemicals is of paramount importance for human health and sustainable food production. During the last few decades there have been noteworthy advances in technologies for the automated sensing of physicochemical parameters of water. These do not translate well into online monitoring of chemical pollutants since most of them are either incapable of real-time detection or unable to detect impacts on biological organisms. As a result, biological early warning systems have been proposed to supplement conventional water quality test strategies. Such systems can continuously evaluate physiological parameters of suitable aquatic species and alert the user to the presence of toxicants. In this regard, single cellular organisms, such as bacteria, cyanobacteria, micro-algae and vertebrate cell lines, offer promising avenues for development of water biosensors. Historically, only a handful of systems utilising single-cell organisms have been deployed as established online water biomonitoring tools. Recent advances in recombinant microorganisms, cell immobilisation techniques, live-cell microarrays and microfluidic Lab-on-a-Chip technologies open new avenues to develop miniaturised systems capable of detecting a broad range of water contaminants. In experimental settings, they have been shown as sensitive and rapid biosensors with capabilities to detect traces of contaminants. In this work, we critically review the recent advances and practical prospects of biological early warning systems based on live-cell biosensors. We demonstrate historical deployment successes, technological innovations, as well as current challenges for the broader deployment of live-cell biosensors in the monitoring of water quality.

Cigarette smoke toxicity modes of action estimated by a bioluminescent bioreporter bacterial panel

Cigarette smoking is considered to be a risk factor for several chronic diseases and even premature death. However, despite the importance of this detrimental habit, little seems known in terms of the overall toxicity potential of its ingredients in humans. In this study, a panel of genetically modified bioluminescent bioreporter bacteria was used to evaluate its usefulness in estimating the cigarette smoke's complex molecular mixture on a bacterial toxicity-bioreporter panel, both filtered or unfiltered. This work enabled to confirm the usefulness of cigarette filters, with better protection found in higher priced brands despite both having genotoxic and cytotoxic attributes. Quorum sensing interference was also shown, which may explain why cigarette smokers are at greater risk for pulmonary infections. Moreover, the findings of this study support the fact that the filter is a dominating contributor to reducing the harm caused by cigarette smoke. Increased efforts should be conducted to reduce the harmful effects of cigarette smoke, via increasingly effective filters. To conclude, the panel of bioreporter bacteria was found to be useful in the evaluation of the general effect of the toxic mixture found in cigarette smoke and therefore has the potential to be used in cigarette research, helping researchers pinpoint the reduction of toxicity when working with filter improvement.

Microbial bioassays in environmental toxicity testing

Accidental spills and the misuse of chemicals may lead to current and legacy environmental contamination and pose concerns over possible (eco)toxicological secondary effects and risks toward non-target microbes and higher eukaryotes, including humans, in ecosystems. In the last decades, scientists and regulators have faced requests to thoroughly screen, prioritize and predict the possible deleterious effects of the huge numbers of existing and emerging xenobiotics, wastewaters and environmental samples on biological systems. In this context, it has become necessary to develop and validate (eco)toxicity bioassays based on microorganisms (e.g., bacteria, microalga, yeast, filamentous fungi, protozoa) as test-organisms whose data should be meaningful for environmental (micro)organisms that may be exposed to contaminated environments. These generally simple, fast and cost-effective bioassays may be preliminary and complementary to the more complex and long-term whole-organism animal-based traditional ecotoxicity tests. With the goal of highlighting the potential offered by microbial-based bioassays as non-animal alternatives in (eco)toxicity testing, the present chapter provides an overview of the current state-of-the art in the development and use of microbial toxicity bioassays through the examination of relatively recent examples with a diverse range of toxicity endpoints. It goes into the (eco)toxicological relevance of these bioassays, ranging from the more traditional microalga- and bacterial-based assays already accepted at regulatory level and commercially available to the more innovative microbial transcriptional profiling and gene expression bioassays, including some examples of biosensors.

Polycyclic aromatic hydrocarbons, antibiotic resistance genes, toxicity in the exposed to anthropogenic pressure soils of the Southern Russia

The influence of anthropogenic pollution, particularly with polycyclic aromatic hydrocarbons (PAHs) on soil toxicity and spread of antibiotic resistance genes (ARGs) is extremely important nowadays. We studied 20 soil samples from a technogenically polluted site, municipal solid wastes (MSW) landfills, and rural settlements in the southwestern part of the Rostov Region of Russia. A close correlation was established between the results of biosensor testing for integral toxicity, the content of genes for the biodegradation of hydrocarbons, and the concentration of PAHs in soils. The relation between the quantitative content of ARGs and the qualitative and quantitative composition of PAHs has not been registered. Soils subjected to different types of the anthropogenic pressure differed in PAHs composition. The technogenic soils are the most polluted ones. These soils are enriched with 5 ring PAHs and carry the maximum variety of assayed ARGs, despite the fact that they do not receive household or medical waste.

Water toxicity evaluations: Comparing genetically modified bioluminescent bacteria and CHO cells as biomonitoring tools

The use of water for drinking and agriculture requires knowledge of its toxicity. In this study, we compared the use of genetically modified bioluminescent (GMB) bacteria whose luminescence increases in the presence of toxicants and Chinese Hamster Ovary (CHO) cells for the characterization of the toxicity of water samples collected from a lake and streams, hydroponic and aquaponic farms, and a wastewater treatment plant. GMB bacteria were used to probe genotoxicity, cytotoxicity and reactive oxygen species-induced effects in the whole water samples. Unlike GMB bacteria, the use of CHO cells requires XAD resin-based pre-concentration of toxic material present in water samples for the subsequent cytotoxicity assay. In addition to the examination of the toxicity of the water from the different sources, the GMB bacteria were also used to test the XAD extracts diluted to the concentrations causing 50% growth inhibition of the CHO cells. The two biomonitoring tools provided different results when they were used to test the above-mentioned diluted XAD extracts. A pre-concentration procedure based on adsorption by XAD resins with subsequent elution was not sufficient to represent the material responsible for the toxicity of the whole water samples toward the GMB bacteria. Therefore, the use of XAD resin extracts may lead to major underestimates of the toxicity of water samples. Although the toxicity findings obtained using the GMB bacteria and CHO cells may not correlate with each another, the GMB bacteria assay did provide a mechanism-specific biomonitoring tool to probe the toxicity of water samples without a need for the pre-concentration step.

Coupling High-Performance Thin-Layer Chromatography with Bacterial Genotoxicity Bioreporters

We present an innovative technological platform for monitoring the direct genotoxicity of individual components in complex environmental samples, based on bioluminescent Escherichia coli genotoxicity bioreporters, sprayed onto the surface of a high-performance thin-layer chromatography (HPTLC) plate. These sensor strains harbor plasmid-borne fusions of selected gene promoters of the E. coli SOS DNA repair system to the Photorhabdus luminescens luxABCDE gene cassette, and mark by increased luminescence the presence of potentially DNA-damaging sample components separated on the plate. We demonstrate an "on plate" quantifiable dose-dependent response to several model genotoxicants (without metabolic activation). We further demonstrate the applicability of the system by identifying as genotoxic specific components of HPTLC-separated influent and effluent samples of wastewater treatment plants, thereby alleviating the need for a comprehensive chemical analysis of the sample.

Vibrio fischeri bioluminescence inhibition assay for ecotoxicity assessment: A review

Vibrio fischeri bioluminescence inhibition bioassay (VFBIA) has been widely applied for the monitoring of toxicity on account of multiple advantages encompassing shorter test duration, sensitive, cost-effective and ease of operation. Moreover, this bioassay found to be equally applicable to all types of matrices (organic & inorganic compounds, metals, wastewater, river water, sewage sludge, landfill leachate, herbicides, treated wastewater etc.) for toxicity monitoring. This review highlights the apparent significance of Vibrio fischeri bioluminescence inhibition assay for ecotoxicological screening and evaluation of diverse chemical substances toxicity profile. The biochemical and genetic basis of the bioluminescence assay and its regulatory mechanism have been concisely discussed. The basic test protocol with ongoing improvements, widespread applications, typical advantages and probable limitations of the assay have been overviewed. The sensitivity of VFBIA and toxicity bioassays has also been compared.

A whole-cell bioreporter assay for quantitative genotoxicity evaluation of environmental samples

Whole-cell bioreporters have emerged as promising tools for genotoxicity evaluation, due to their rapidity, cost-effectiveness, sensitivity and selectivity. In this study, a method for detecting genotoxicity in environmental samples was developed using the bioluminescent whole-cell bioreporter Escherichia coli recA::luxCDABE. To further test its performance in a real world scenario, the E. coli bioreporter was applied in two cases: i) soil samples collected from chromium(VI) contaminated sites; ii) crude oil contaminated seawater collected after the Jiaozhou Bay oil spill which occurred in 2013. The chromium(VI) contaminated soils were pretreated by water extraction, and directly exposed to the bioreporter in two phases: aqueous soil extraction (water phase) and soil supernatant (solid phase). The results indicated that both extractable and soil particle fixed chromium(VI) were bioavailable to the bioreporter, and the solid-phase contact bioreporter assay provided a more precise evaluation of soil genotoxicity. For crude oil contaminated seawater, the response of the bioreporter clearly illustrated the spatial and time change in genotoxicity surrounding the spill site, suggesting that the crude oil degradation process decreased the genotoxic risk to ecosystem. In addition, the performance of the bioreporter was simulated by a modified cross-regulation gene expression model, which quantitatively described the DNA damage response of the E. coli bioreporter. Accordingly, the bioluminescent response of the bioreporter was calculated as the mitomycin C equivalent, enabling quantitative comparison of genotoxicities between different environmental samples. This bioreporter assay provides a rapid and sensitive screening tool for direct genotoxicity assessment of environmental samples.

Reporter Gene Assays in Ecotoxicology

The need for simple and rapid means for evaluating the potential toxic effects of environmental samples has prompted the development of reporter gene assays, based on tester cells (bioreporters) genetically engineered to report on sample toxicity by producing a readily quantifiable signal. Bacteria are especially suitable to serve as bioreporters owing to their fast responses, low cost, convenient preservation, ease of handling, and amenability to genetic manipulations. Various bacterial bioreporters have been introduced for general toxicity and genotoxicity assessment, and the monitoring of endocrine disrupting and dioxin-like compounds has been mostly covered by similarly engineered eukaryotic cells. Some reporter gene assays have been validated, standardized, and accredited, and many others are under constant development. Efforts are aimed at broadening detection spectra, lowering detection thresholds, and combining toxicity identification capabilities with characterization of the toxic effects. Taking advantage of bacterial robustness, attempts are also being made to incorporate bacterial bioreporters into field instrumentation for online continuous monitoring or on-site spot checks. However, key hurdles concerning test validation, cell preservation, and regulatory issues related to the use of genetically modified organisms still remain to be overcome.

UV/H2O2 advanced oxidation for abatement of organophosphorous pesticides and the effects on various toxicity screening assays

Advanced oxidation processes (AOPs) are utilized due to their ability to treat emerging contaminants with the fast reacting and non-selective hydroxyl radical (OH). Organophosphorous insecticides are common drinking water contaminants, with 12 different compounds of this class being found on the US EPA's most recent Candidate Contaminant List (CCL4). The use of the AOP UV/H₂O₂ for the treatment of organophosphorous insecticides was explored in this study, by coupling biological and analytical tools to follow the abatement of the target compounds. Four insecticides were explored for advanced oxidation treatment: acephate, dicrotophos, fenamiphos, and methamidophos. All four compounds were fast reacting with OH, all reacting with second order rate constants ≥5.5 × 10⁹ M^-1s^-1. Three major endpoints of toxicity were studied: estrogenicity, genotoxicity (mutagenicity) and neurotoxicity. None of the target compounds showed any estrogenic activity, while all compounds showed an active genotoxic (mutagenic) response (AMES II assay) and most compounds had some level of neurotoxic activity. AOP treatment did not induce any estrogenic activity, and reduced the compounds' neurotoxicity and genotoxicity in all but one case. Methamidophos degradation by UV/H₂O₂ resulted in an increase in genotoxicity, likely due to the formation of toxic transformation products. The increase in toxicity gradually decreased with time, possibly due to hydrolysis of the transformation products formed. This study provides insights into parent compound abatement and the changes in toxicity due to transformation products.

Microbially derived biosensors for diagnosis, monitoring and epidemiology

Living cells have evolved to detect and process various signals and can self-replicate, presenting an attractive platform for engineering scalable and affordable biosensing devices. Microbes are perfect candidates: they are inexpensive and easy to manipulate and store. Recent advances in synthetic biology promise to streamline the engineering of microbial biosensors with unprecedented capabilities. Here we review the applications of microbially-derived biosensors with a focus on environmental monitoring and healthcare applications. We also identify critical challenges that need to be addressed in order to translate the potential of synthetic microbial biosensors into large-scale, real-world applications.

Fluorescence-Based Reporters for Detection of Mutagenesis in E. coli

Mutagenesis in model organisms following exposure to chemicals is used as an indicator of genotoxicity. Mutagenesis assays are also used to study mechanisms of DNA homeostasis. This chapter focuses on detection of mutagenesis in prokaryotes, which boils down to two approaches: reporter inactivation (forward mutation assay) and reversion of an inactivating mutation (reversion mutation assay). Both methods are labor intensive, involving visual screening, quantification of colonies on solid media, or determining a Poisson distribution in liquid culture. Here, we present two reversion reporters for in vivo mutagenesis that produce a quantitative output, and thus have the potential to greatly reduce the amount of test chemical and labor involved in these assays. This output is obtained by coupling a TEM β lactamase-based reversion assay with GFP fluorescence, either by placing the two genes on the same plasmid or by fusing them translationally and interrupting the N-terminus of the chimeric ORF with a stop codon. We also describe a reporter aimed at facilitating the monitoring of continuous mutagenesis in mutator strains. This reporter couples two reversion markers, allowing the temporal separation of mutation events in time, thus providing information about the dynamics of mutagenesis in mutator strains. Here, we describe these reporter systems, provide protocols for use, and demonstrate their key functional features using error-prone Pol I mutagenesis as a source of mutations.

Biodetection of potential genotoxic pollutants entering the human food chain through ashes used in livestock diets

Ash derived from energy generation is used as a source of minerals in livestock feeds. The microbial biosensor recApr-Luc2 was built to detect genotoxic hazard in recycled ash. Escherichia coli SOS gene (recA, lexA, dinI and umuC) expression in response to cisplatin-induced DNA damage led to the selection of the recA promoter. The biosensor required functional RecA expression to respond to genotoxic heavy metals (Cr>Cd≈Pb), and polluted ash induced a strong recApr-Luc2 response. In human liver and intestinal cells, heavy metals induced acute toxicity (Cr>Cd>Pb) at concentrations sufficient to activate recApr-Luc2. Cytostatic effects, including genotoxicity, were cell- and metal-dependent, apart from Cr. In agreement with the recApr-Luc2 bioassay, Cr had the strongest effect in all cells. In conclusion, recApr-Luc2 could be useful for evaluating the genotoxic risk of pollutants present in ash that might be concentrated in animal products and, thus, entering the human food chain.

Construction of a bioreporter by heterogeneously expressing a Vibrio natriegens recA::luxCDABE fusion in Escherichia coli, and genotoxicity assessments of petrochemical-contaminated groundwater in northern China

Here, we constructed an Escherichia coli recA::luxCDABE bioreporter for genotoxicity assessments. The recA promoter was cloned from the marine bacterium Vibrio natriegens. This bioreporter showed a dose-response relationship following induction by mitomycin C, and other pollutants or environmental samples could be calculated as mitomycin C equivalents, which provided a way to quantitatively compare the genotoxicities of different environmental samples. This bioreporter was used to evaluate the genotoxicity under a wide range of external environmental conditions, like temperatures ranging from 15 °C to 42 °C, pH between 4.0 and 9.0, and salinity ranging from 0% to 3%. This successfully extended its application from the laboratory to the field, and allowed the bioreporter to assess the genotoxicity and bioavailability of genotoxins in various environmental media, including surface water, groundwater, seawater, and soil matrix. Expression of V. natriegens recA in E. coli indicated a LexA-like regulator in V. natriegens, and the putative SOS box of V. natriegens recA was similar to that of E. coli. The genotoxicities of groundwater samples from a petrochemical-contaminated site in northern China were evaluated by this bioreporter assay, and the genotoxic levels were in accordance with contamination levels obtained by chemical analyses.

Genetically engineered microorganisms for the detection of explosives' residues

The manufacture and use of explosives throughout the past century has resulted in the extensive pollution of soils and groundwater, and the widespread interment of landmines imposes a major humanitarian risk and prevents civil development of large areas. As most current landmine detection technologies require actual presence at the surveyed areas, thus posing a significant risk to personnel, diverse research efforts are aimed at the development of remote detection solutions. One possible means proposed to fulfill this objective is the use of microbial bioreporters: genetically engineered microorganisms “tailored” to generate an optical signal in the presence of explosives’ vapors. The use of such sensor bacteria will allow to pinpoint the locations of explosive devices in a minefield. While no study has yet resulted in a commercially operational system, significant progress has been made in the design and construction of explosives-sensing bacterial strains. In this article we review the attempts to construct microbial bioreporters for the detection of explosives, and analyze the steps that need to be undertaken for this strategy to be applicable for landmine detection.

Discovery and preclinical development of new antibiotics

Antibiotics are the medical wonder of our age, but an increasing frequency of resistance among key pathogens is rendering them less effective. If this trend continues the consequences for cancer patients, organ transplant patients, and indeed the general community could be disastrous. The problem is complex, involving abuse and overuse of antibiotics (selecting for an increasing frequency of resistant bacteria), together with a lack of investment in discovery and development (resulting in an almost dry drug development pipeline). Remedial approaches to the problem should include taking measures to reduce the selective pressures for resistance development, and taking measures to incentivize renewed investment in antibiotic discovery and development. Bringing new antibiotics to the clinic is critical because this is currently the only realistic therapy that can ensure the level of infection control required for many medical procedures. Here we outline the complex process involved in taking a potential novel antibiotic from the initial discovery of a hit molecule, through lead and candidate drug development, up to its entry into phase I clinical trials. The stringent criteria that a successful drug must meet, balancing high efficacy in vivo against a broad spectrum of pathogens, with minimal liabilities against human targets, explain why even with sufficient investment this process is prone to a high failure rate. This emphasizes the need to create a well-funded antibiotic discovery and development pipeline that can sustain the continuous delivery of novel candidate drugs into clinical trials, to ensure the maintenance of the advanced medical procedures we currently take for granted.

Genetic screens in mice for genome integrity maintenance and cancer predisposition

Genome instability is a feature of nearly all cancers and can be exploited for therapy. In addition, a growing number of genome maintenance genes have been associated with developmental disorders. Efforts to understand the role of genome instability in these processes will be greatly facilitated by a more comprehensive understanding of their genetic network. We highlight recent genetic screens in model organisms that have assisted in the discovery of novel regulators of genome stability and focus on the contribution of mice as a model organism to understanding the role of genome instability during embryonic development, tumour formation and cancer therapy.

Microbial genotoxicity bioreporters based on sulA activation

A bacterial genotoxicity reporter strain was constructed in which the tightly controlled strong promoter of the Escherichia coli SOS response gene sulA was fused to the alkaline phosphatase-coding phoA reporter gene. The bioreporter responded in a dose-dependent manner to three model DNA-damaging agents-hydrogen peroxide, nalidixic acid (NA), and mitomycin C (MMC)-detected 30-60 min after exposure. Detection thresholds were 0.15 μM for MMC, 7.5 μM for nalidixic acid, and approximately 50 μM for hydrogen peroxide. A similar response to NA was observed when the bioreporter was integrated into a specially designed, portable electrochemical detection platform. Reporter sensitivity was further enhanced by single and double knockout mutations that enhanced cell membrane permeability (rfaE) and inhibited DNA damage repair mechanisms (umuD, uvrA). The rfaE mutants displayed a five- and tenfold increase in sensitivity to MMC and NA, respectively, while the uvrA mutation was advantageous in the detection of hydrogen peroxide. A similar sensitivity was displayed by the double rfaE/uvrA mutant when challenged with the pre-genotoxic agents 2-amino-3-methylimidazo[4,5-f]quinoline and 2-aminoanthracene following metabolic activation with an S9 mammalian liver fraction.

A printed nanolitre-scale bacterial sensor array

The last decade has witnessed a significant increase in interest in whole-cell biosensors for diverse applications, as well as a rapid and continuous expansion of array technologies. The combination of these two disciplines has yielded the notion of whole-cell array biosensors. We present a potential manifestation of this idea by describing the printing of a whole-cell bacterial bioreporters array. Exploiting natural bacterial tendency to adhere to positively charged abiotic surfaces, we describe immobilization and patterning of bacterial "spots" in the nanolitre volume range by a non-contact robotic printer. We show that the printed Escherichia coli-based sensor bacteria are immobilized on the surface, and retain their viability and biosensing activity for at least 2 months when kept at 4 °C. Immobilization efficiency was improved by manipulating the bacterial genetics (overproducing curli protein), the growth and the printing media (osmotic stress and osmoprotectants) and by a chemical modification of the inanimate surface (self-assembled layers of 3-aminopropyl-triethoxysilane). We suggest that the methodology presented herein may be applicable to the manufacturing of whole-cell sensor arrays for diverse high throughput applications.

Whole-cell biochips for bio-sensing: integration of live cells and inanimate surfaces

Recent advances in the convergence of the biological, chemical, physical, and engineering sciences have opened new avenues of research into the interfacing of diverse biological moieties with inanimate platforms. A main aspect of this field, the integration of live cells with micro-machined platforms for high throughput and bio-sensing applications, is the subject of the present review. These unique hybrid systems are configured in a manner that ensures positioning of the cells in designated patterns, and enables cellular viability maintenance, and monitoring of cellular functionality. Here we review both animate and inanimate surface properties and how they affect cellular attachment, describe relevant modifications of both types of surfaces, list technologies for platform engineering and for cell deposition in the desired configurations, and discuss the influence of various deposition and immobilization methods on the viability and performance of the immobilized cells.