Bacterial bioluminescent emission from recombinant Escherichia coli harboring a recA::luxCDABE fusion

Biocompatibility characterization of vaterite with a bacterial whole-cell biosensor

The growing biomedical challenges impose the continuous development of novel platforms. Ensuring the biocompatibility of drug delivery and implantable biomedical devices is an essential requirement. Calcium carbonate (CaCO3) in the form of vaterite nanoparticles is a promising platform, which has demonstrated distinctive optical and biochemical properties, including high porosity and metastability. In this study, the biocompatibility of differently shaped CaCO₃ vaterite particles (toroids, ellipsoids, and spheroids) are evaluated by bacterial toxicity mode-of-action with a whole-cell biosensor. Different Escherichia coli (E. coli) strains were used in the bioluminescent assay, including cytotoxicity, genotoxicity and quorum-sensing. Firstly, both scanning electron microscopy (SEM) and fluorescence microscopy characterizations were conducted. Bacterial cell death and aggregates were observed only in the highest tested concentration of the vaterite particles, especially in toroids 15-25 µm. After, the bioluminescent bacterial panel was exposed to the vaterite particles, and their bioluminescent signal reflected their toxicity mode-of-action. The vaterite particles resulted in an induction factor (IF > 1) on the bacterial panel, which was higher after exposure to the toroids (1.557 ≤ IF ≤ 2.271) and ellipsoids particles (1.712 ≤ IF ≤ 2.018), as compared to the spheroids particles (1.134 ≤ IF ≤ 1.494), in all the tested bacterial strains. Furthermore, the vaterite particles did not affect the viability of the bacterial cells. The bacterial monitoring demonstrated the biofriendly nature of especially spheroids vaterite nanoparticles.

Whole-cell bacterial biosensor with the capability to detect red palm weevil, Rhynchophorus ferrugineus, in date palm trees, Phoenix dactylifera: a proof of concept study

The red palm weevil (RPW), Rhynchophorus ferrugineus, is considered a severe pest of palms. Usually, the early stages of infection are without visible signs. An attractive early sensing approach of non-visible infections is based on volatile organic compounds (VOCs). In this study, a whole-cell bacterial biosensor was used for the identification of RPW in date palm (Phoenix dactylifera). The cells are genetically modified to produce light in the presence of general stresses. The bioluminescent bacterial panel is based on three genetically engineered Escherichia coli strains that are sensitive to cytotoxicity (TV1061), genotoxicity (DPD2794), or quorum-sensing (K802NR). The bioluminescent bacterial panel detects the presence of VOCs and a change in the light signal is then generated, reflecting the health status of the date palm tree. The bioreporter bacteria cells are immobilized in calcium alginate tablets and placed in a sealed jar without direct contact with the tested sample, thereby exposing them only to the VOCs in the surrounding air. The immobilized bacteria cells were exposed to the air near infected by RPW or uninfected sugar canes, date palm tree pieces, and on date palm trees. Commercial plate reader was used for signal measurement. The findings show that quorum-sensing was induced by all the tested samples of infected sugar canes, date palm tree pieces, and date palm trees. While, cytotoxicity was induced only by infected date palm tree pieces, and genotoxicity was induced only by infected date palm trees. The bacterial monitoring results enable the identification of specific signatures that will allow a quick and accurate diagnosis.

Whole-cell bacterial biosensor for volatile detection from Pectobacterium-infected potatoes enables early identification of potato tuber soft rot disease

Half of the harvested food is lost due to rots caused by microorganisms. Plants emit various volatile organic compounds (VOCs) into their surrounding environment, and the VOC profiles of healthy crops are altered upon infection. In this study, a whole-cell bacterial biosensor was used for the early identification of potato tuber soft rot disease caused by the pectinolytic bacteria Pectobacterium in potato tubers. The detection is based on monitoring the luminescent responses of the bacteria panel to changes in the VOC profile following inoculation. First, gas chromatography-mass spectrometry (GC-MS) was used to specify the differences between the VOC patterns of the inoculated and non-inoculated potato tubers during early infection. Five VOCs were identified, 1-octanol, phenylethyl alcohol, 2-ethyl hexanol, nonanal, and 1-octen-3-ol. Then, the infection was detected by the bioreporter bacterial panel, firstly measured in a 96-well plate in solution, and then also tested in potato plugs and validated in whole tubers. Examination of the bacterial panel responses showed an extensive cytotoxic effect over the testing period, as seen by the elevated induction factor (IF) values in the bacterial strain TV1061 after exposure to both potato plugs and whole tubers. Moreover, quorum sensing influences were also observed by the elevated IF values in the bacterial strain K802NR. The developed whole-cell biosensor system based on bacterial detection will allow more efficient crop management during postharvest, storage, and transport of crops, to reduce food losses.

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.

PAHs reduce DNA synthesis and delay cell division in the widespread primary producer Prochlorococcus

The cyanobacteria Prochlorococcus is the most abundant primary producer in the ocean. In a global study across the Atlantic, Indian and Pacific Oceans, we tested the effect of organic pollutants on the growth and cell division of natural Prochlorococcus populations. Sub-lethal concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) altered Prochlorococcus cell division by reducing DNA synthesis and decreasing the percentage of cells entering mitosis. Cell division time increased with PAHs dosage by 1.2 h per μg L(-1) of mixture added. At PAHs dosages >1 μg L(-1), Prochlorococcus cell division tended to arrest at S-phase (DNA synthesis). As a consequence, population growth was significantly reduced in the presence of PAHs. The presence of PAHs resulted in a predictable alteration of the cell cycle of the widespread cyanobacteria.The dosages tested are above concentrations in the open ocean, but found in the coastal ocean, where Prochlorococcus growth must be inhibited.

Serum complement enhances the responses of genotoxin- and oxidative stress-sensitive Escherichia coli bioreporters

Bacterial bioreporters are limited in their abilities to detect large polar molecules due to their membrane selectivity. In this study, the activity of serum complement was used to bypass this undesired selectivity. Initially, the serum complement activity was assessed using the responses of a bacterial bioreporter harboring a recA::luxCDABE transcriptional fusion when exposed to the chemotherapy drug, mitomycin C (MMC). Using 50 °C-treated serum, the limit of detection for this bacterial sensor was lowered by nearly 450-fold, from 31 μg/L to 0.07 μg/L MMC. Real-time quantitative PCR demonstrated that serum-treated cultures responded more strongly to 100 μg/L MMC, with 3.1-fold higher recA expression levels. Subsequent experiments with other bioreporter strains also found enhanced sensitivities and responses. Finally, combining each of the above findings, tests were performed to demonstrate the potential application of the recA::luxCDABE bioreporter within a lab-on-a-CD platform as a point-of-care diagnostic to measure chemotherapeutic drug concentrations within blood.

Prediction and classification of the modes of genotoxic actions using bacterial biosensors specific for DNA damages

We report on a novel approach to predict the mode of genotoxic action of chemicals using a series of DNA damage specific bioluminescent bacteria. For this, a group of seven different DNA damage sensing recombinant bioluminescent strains were employed. Each of these strains was tested against model DNA damaging agents, such as mitomycin C (MMC), 1-methyl-1-nitroso-N-methylguanidine (MNNG), nalidixic acid (Nal) and 4-nitroquinoline N-oxide (4-NQO). These biosensors were grouped based on their responses to a specific mode of genotoxic action, such as (a) DNA damage cascade response (biosensor with nrdA-, dinI- and sbmC-lux), (b) SOS response or DNA repair (strains carrying recA-, recN- and sulA-lux), and (c) DNA damage potentially by alkylation (biosensor with alkA-lux). The differential response patterns and its strength of these strains to various model genotoxicants allowed classifying the chemical's potential genotoxic mode. Therefore, it is possible to elucidate and classify the mode of genotoxic impacts of an unknown sample and that together they may be utilized in the pre-screening steps of new drugs, newly synthesized chemicals, food and environmental contaminants.

Development of bioluminescent Salmonella strains for use in food safety

BACKGROUND

Salmonella can reside in healthy animals without the manifestation of any adverse effects on the carrier. If raw products of animal origin are not handled properly during processing or cooked to a proper temperature during preparation, salmonellosis can occur. In this research, we developed bioluminescent Salmonella strains that can be used for real-time monitoring of the pathogen's growth on food products. To accomplish this, twelve Salmonella strains from the broiler production continuum were transformed with the broad host range plasmid pAKlux1, and a chicken skin attachment model was developed.

RESULTS

Salmonella strains carrying pAKlux1 constitutively expressed the luxCDABE operon and were therefore detectable using bioluminescence. Strains were characterized in terms of bioluminescence properties and plasmid stability. To assess the usefulness of bioluminescent Salmonella strains in food safety studies, we developed an attachment model using chicken skin. The effect of washing on attachment of Salmonella strains to chicken skin was tested using bioluminescent strains, which revealed the attachment properties of each strain.

CONCLUSION

This study demonstrated that bioluminescence is a sensitive and effective tool to detect Salmonella on food products in real-time. Bioluminescence imaging is a promising technology that can be utilized to evaluate new food safety measures for reducing Salmonella contamination on food products.

Gene expression analysis and classification of mode of toxicity of polycyclic aromatic hydrocarbons (PAHs) in Escherichia coli

Escherichia coli is known to respond to certain toxic chemicals through an increased expression of various stress genes. In this study, therefore, the expression of recA, katG, fabA and grpE genes was used as a representative for DNA, oxidative, membrane and protein damage, respectively, after E. coli was exposed to different polycyclic aromatic hydrocarbons (PAHs), i.e., phenanthrene, naphthalene and benzo[a]pyrene. To accomplish this, the expression levels of these four genes were quantified using a real-time RT-PCR analysis when E. coli cultures were under stressful conditions, such as those caused by an exposure to mitomycin C, hydrogen peroxide and phenol. It was found that the primary toxic effect of each chemical is clearly seen when the expression levels of the different genes are compared. Tests with the PAHs showed naphthalene and benzo[a]pyrene to be genotoxic, while phenanthrene had no clear effect on the expression of any of these genes. Based on these results, the effects due to these toxic chemicals and the extent of each stress can be evaluated with ease using the expression levels of different stress responsive genes.

Intracellular redox equilibrium and growth phase affect the performance of luciferase-based biosensors

Light emission from the bacterial luciferase operon has been variously exploited during last two decades. The use of convenient inducible promoters has granted significant degrees of specificity to whole cell-based assays for high-throughput screening and environmental monitoring. Nevertheless, unexplained unspecific responses have been repeatedly reported. Here, we show that the impairment of the intracellular biochemical equilibrium interferes with the luminescence produced by Escherichia coli and Staphylococcus aureus strains carrying the lux operon under constitutive or inducible control. Compounds as trimethoprim and methotrexate, by indirectly inducing NADPH accumulation, enhance light emission. Conversely, molecules driving the cell toward an oxidized state, as dimethyl sulfoxide, inhibit luminescence. These findings fit into the accepted biochemical pathway for bioluminescence, where NADPH and reducing equivalents are necessary for the production of luciferase substrates, although they do not directly take part into the light-emitting reaction. Moreover, we investigated the influence of induction timing upon the bioluminescence response from inducible reporter systems and demonstrated a correlation between the emitted light and the growth phase at which induction is performed. Our results provide explanations for some unspecific responses recorded so far in whole cell-based luminescent biosensors and emphasize the intrinsic limitations of this kind of reporting system.

Construction of a ColD cda promoter-based SOS-green fluorescent protein whole-cell biosensor with higher sensitivity toward genotoxic compounds than constructs based on recA, umuDC, or sulA promoters

Four different green fluorescent protein (GFP)-based whole-cell biosensors were created based on the DNA damage inducible SOS response of Escherichia coli in order to evaluate the sensitivity of individual SOS promoters toward genotoxic substances. Treatment with the known carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) revealed that the promoter for the ColD plasmid-borne cda gene had responses 12, 5, and 3 times greater than the recA, sulA, and umuDC promoters, respectively, and also considerably higher sensitivity. Furthermore, we showed that when the SOS-GFP construct was introduced into an E. coli host deficient in the tolC gene, the minimal detection limits toward mitomycin C, MNNG, nalidixic acid, and formaldehyde were lowered to 9.1 nM, 0.16 microM, 1.1 microM, and 141 microM, respectively, which were two to six times lower than those in the wild-type strain. This study thus presents a new SOS-GFP whole-cell biosensor which is not only able to detect minute levels of genotoxins but, due to its use of the green fluorescent protein, also a reporter system which should be applicable in high-throughput screening assays as well as a wide variety of in situ detection studies.

Acclimation and repair of DNA damage in recombinant bioluminescent Escherichia coli

AIMS

The aim of this study is to understand different adaptive responses in bacteria caused by three different mutagens, namely, an intercalating agent, an alkylating agent and a hydroxylating agent, and the repair systems according to the type of DNA damage, that is, DNA cross-linking and delayed DNA synthesis, alkylation and hydroxylation of DNA. A recombinant bioluminescent Escherichia coli, DPD2794 with the recA promoter fused to luxCDABE originating from Vibrio fischeri, was used in this study.

METHODS AND RESULTS

The recombinant bioluminescent E. coli strain DPD2794, containing a recA promoter fused to luxCDABE from V. fischeri, was used to detect adaptive and repair responses to DNA damage caused by mitomycin C (MMC), and these responses were compared with those when the cells were induced with N-methyl-N-nitro-N-nitrosoguanidine (MNNG) and hydrogen peroxide (H2O2). The response ratio between the induced samples and that of the controls decreased suddenly when the induced culture was used in further inductions, indicating a possible adaptive response to DNA damage. DNA damage, or the proteins produced, because of MMC addition does not appear to be completely resolved until the seventh sub-culture after the initial induction, whereas simple damage, such as the base modification caused by MNNG and H2O2, appears to be repaired rapidly as evidenced by the quick recovery of sensitivity.

CONCLUSIONS

These results suggest that it takes more time to completely repair DNA damage caused by MMC, as compared with a simple repair such as that required for the damage caused by MNNG and H2O2. Therefore, repair of the damage caused by these three mutagens is controlled by different regulons, even though they all induced the recA promoter.

SIGNIFICANCE AND IMPACT OF THE STUDY

Using a bioluminescent E. coli harbouring a recA promoter-lux fusion, it was found that different adaptive responses and repair systems for DNA damage caused by several mutagens exists in E. coli.