Acinetobacter bioreporter assessing heavy metals toxicity

Application of magnetic-nanoparticle functionalized whole-cell biosensor array for bioavailability and ecotoxicity estimation at urban contaminated sites

The bioavailability and ecotoxicity of pollutants are important for urban ecological systems and human health, particularly at contaminated urban sites. Therefore, whole-cell bioreporters are used in many studies to assess the risks of priority chemicals; however, their application is restricted by low throughput for specific compounds and complicated operations for field tests. In this study, an assembly technology for manufacturing Acinetobacter-based biosensor arrays using magnetic nanoparticle functionalization was developed to solve this problem. The bioreporter cells maintained high viability, sensitivity, and specificity in sensing 28 priority chemicals, seven heavy metals, and seven inorganic compounds in a high-throughput manner, and their performance remained acceptable for at least 20 d. We also tested the performance by assessing 22 real environmental soil samples from urban areas in China, and our results showed positive correlations between the biosensor estimation and chemical analysis. Our findings prove the feasibility of the magnetic nanoparticle-functionalized biosensor array to recognize the types and toxicities of multiple contaminants for online environmental monitoring at contaminated sites.

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.

Engineered Whole-Cell-Based Biosensors: Sensing Environmental Heavy Metal Pollutants in Water-a Review

The frequent exposure and accumulation of heavy metals in organisms cause serious health issues affecting a range of organs such as the brain, liver, and reproductive organs in adults, infants, and children. Several parts of the world have high levels of heavy metals affecting millions of people, costing millions of dollars for improving the potability of water and medical treatment of the affected. Hence, water quality assessment is required to monitor the degree of heavy metal contamination in potable water. In nature, organisms respond to various environmental pollutants such as heavy metals, allowing their survival in a diverse environmental niche. With the advent of recombinant DNA technology, it is now possible to manipulate these natural bioreporters into controlled systems which either turn on or off gene expression or activity of enzymes in the presence of specific heavy metals (compound-specific biosensors) otherwise termed as whole-cell biosensors (WCBs). WCBs provide an upper hand compared to other immunosensors, enzyme-based sensors, and DNA-based sensors since microbes can be relatively easily manipulated, scaled up with relative ease, and can detect only the bioavailable heavy metals. In this review, we summarize the current knowledge of the various mechanisms of toxicity elicited by various heavy metals, thence emphasizing the need to develop heavy metal sensing platforms. Following this, the biosensor-based platforms including WCBs for detecting heavy metals developed thus far have been briefly elaborated upon, emphasizing the challenges and solutions associated with WCBs.

Strong linkages between dissolved organic matter and the aquatic bacterial community in an urban river

Aquatic bacterial communities play an important role in biogeochemical cycling in river ecosystems; however, knowledge of the linkages between bacterial communities and dissolved organic matter (DOM) in urban rivers is limited. Here, 16S rRNA amplicon sequencing and parallel factor (PARAFAC) modeling of excitation-emission fluorescence spectroscopy were used to analyze the compositions, co-occurrence patterns, and interactions with chromophoric DOM (CDOM) of bacterial communities in urban river water samples influenced by different human activities. The results revealed that two protein-like components accounted for 65.2 ± 9.56% of the total variability in all three fluorescence components, which suggests that CDOM in urban rivers is mainly a microbial source. In addition to pH and DO, CDOM is also an important factor affecting bacterial community structure, and the main classes (Gammaproteobacteria and Clostridia) and genera (Limnohabitans and Alpinimonas) showed strong positive correlations with terrestrial humic-like C1 and tryptophan-like C2, respectively. When autotrophic and heterotrophic bacteria coexist in urban rivers, the production and degradation of CDOM will occur simultaneously. Furthermore, the riverine bacterial co-occurrence network had a nonrandom modular structure, which was mainly driven by classification correlation and bacterial function. The high abundance of genes related to xenobiotic metabolism, carbon metabolism and nitrogen metabolism in the urban river indicated that anthropogenic activity may be the dominant selective force altering the bacterial communities. Overall, our results provide a novel view for the assembly of bacterial communities in urban river ecosystems under the influence of different human activities.

Application of a bacterial whole cell biosensor for the rapid detection of cytotoxicity in heavy metal contaminated seawater

A toxicity biosensor Acinetobacter baylyi Tox2 was constructed with the host strain A. baylyi ADP1 harboring a new and medium-copy-number plasmid pWH1274_lux, and was applied to detect the cytotoxicity of heavy metal contaminated seawater. The gene cassette luxCDABE was controlled by constitutively expressed promoter P_tet on pWH1274_lux and the bioluminescence intensity of the biosensor reduces in proportional to the concentrations of toxic compounds. A. baylyi Tox2 exhibits tolerance to salinity, hence it is applicable to seawater samples. A. baylyi Tox2 and Mugilogobius chulae were exposed to different concentrations of heavy metals (Hg²⁺, Zn²⁺, Cu²⁺, and Cd²⁺) in artificial seawater for performance comparison and Pearson correlation analysis showed a significant correlation (p < 0.01) between A. baylyi Tox2 toxicity detection and the fish (M. chulae) exposure test. This suggests that the performance of A. baylyi Tox2 is comparable to the conventional fish toxicity test in terms of cytotoxicity detection of heavy metal contaminated seawater. Furthermore, A. baylyi Tox2 was used to evaluate cytotoxicity of field-collected seawater samples. The results indicate that there was a significant correlation between the luminescence inhibition ratio (IR) of A. baylyi Tox2 and heavy metal concentrations detected by ICP-MS in the samples. Two seawater samples, which contained a high concentration of total heavy metals, exhibited stronger cytotoxicity than the samples containing low concentrations of heavy metals. In conclusion, A. baylyi Tox2 can be used as an alternative tool to aquatic animals for the evaluation of the cytotoxicity of heavy metal contamination in the marine environment.

Ecological patterns and adaptability of bacterial communities in alkaline copper mine drainage

Environmental gradient have strong effects on community assembly processes. In order to reveal the effects of alkaline mine drainage (AlkMD) on bacterial and denitrifying bacterial community compositions and diversity in tailings reservoir, here we conducted an experiment to examine all and core bacterial taxa and denitrifying functional genes's (nirS, nirK, nosZ_Ι) abundance along a chemical gradient in tailings water in Shibahe copper tailings in Zhongtiaoshan, China. Differences in bacterial and denitrifying bacterial community compositions in different habitats and their relationships with environmental parameters were analyzed. The results showed that the richness and diversity of bacterial community in downstream seeping water (SDSW) were the largest, while that in upstream tailings water (STW1) were the lowest. The diversity and abundance of bacterial communities tended to increase from STW1 to SDSW. The variation of bacterial community diversity was significantly related to electroconductibility (EC), nitrate (NO₃^-), nitrite (NO₂^-), total carbon (TC), inorganic carbon (IC) and sulfate (SO₄^2-), but was not correlated with geographic distance in local scale. Core taxa from class to genus were all significantly related to NO₃^- and NO₂^-. Core taxa Rhodobacteraceae, Rhodobacter, Acinetobacter and Hydrogenophaga were typical denitrifying bacteria. The variation trends of these groups were consistent with the copy number of nirS, nirK and nosZ_Ι, demonstrating their importance in the process of nitrogen reduction. The copy number of nirK, nosZ_Ι and nirS/16S rDNA, nirK/16Sr DNA correlated strongly with NO₃^-, NO₂^- and IC, but nirS and nosZ_I/16SrDNA had no significant correlation with NO₃^- and NO₂^-. The copy numbers of denitrifying functional genes (nirS, nirK and nosZ_Ι) were negatively correlated with heavy metal plumbum (Pb) and zinc (Zn). It showed that heavy metal contamination was an important factor affecting the structure of denitrifying bacterial community in AlkMD. In this study we have identified the distribution pattern of bacterial community along physiochemical gradients in alkaline tailings reservoir and displayed the driving force of shaping the structure of bacterial community. The influence of NO₃^-, NO₂^-, IC and heavy metal Pb and Zn on bacterial community might via their influence on the functional groups involving nitrogen, carbon and metal metabolisms.

Toxicity assessment using different bioassays and microbial biosensors

Toxicity assessment of water streams, wastewater, and contaminated sediments, is a very important part of environmental pollution monitoring. Evaluation of biological effects using a rapid, sensitive and cost effective method can indicate specific information on ecotoxicity assessment. Recently, different biological assays for toxicity assessment based on higher and lower organisms such as fish, invertebrates, plants and algal cells, and microbial bioassays have been used. This review focuses on microbial biosensors as an analytical device for environmental, food, and biomedical applications. Different techniques which are commonly used in microbial biosensing include amperometry, potentiometry, conductometry, voltammetry, microbial fuel cells, fluorescence, bioluminescence, and colorimetry. Examples of the use of different microbial biosensors in assessing a variety of environments are summarized.

Preparation and Assay of Simple Light off Biosensor Based on Immobilized Bioluminescent Bacteria for General Toxicity Assays

We describe a simple light off bioluminescent biosensor for general environmental toxicity assays based on immobilized bioluminescent bacteria engineered with beetle luciferases.

Novel application of pH-sensitive firefly luciferases as dual reporter genes for simultaneous ratiometric analysis of intracellular pH and gene expression/location

Firefly luciferases are widely used as bioluminescent reporter genes for bioimaging and biosensors. Aiming at simultaneous analyses of different gene expression and cellular events, luciferases and GFPs that exhibit distinct bioluminescence and fluorescence colors have been coupled with each promoter, making dual and multicolor reporter systems. Despite their wide use, firefly luciferase bioluminescence spectra are pH-sensitive, resulting in a typical large red shift at acidic pH, a side-effect that may affect some bioanalytical purposes. Although some intracellular pH-indicators employ dual color and fluorescent dyes, none has been considered to benefit from the characteristic spectral pH-sensitivity of firefly luciferases to monitor intracellular pH-associated stress, an important indicator of cell homeostasis. Here we demonstrate a linear relationship between the ratio of intensities in the green and red regions of the bioluminescence spectra and pH using firefly luciferases cloned in our laboratory (Macrolampis sp2 and Cratomorphus distinctus), allowing estimation of E. coli intracellular pH, thus providing a new analytical method for ratiometric intracellular pH-sensing. This is the first dual reporter system that employs a single luciferase gene to simultaneously monitor intracellular pH using spectral changes, and gene expression and/or ATP concentration using the bioluminescence intensity, showing great potential for real time bioanalysis of intracellular processes associated with metabolic changes such as apoptosis, cell death, inflammation and tissue acidification, among the other physiological changes.

Evaluation of the ecotoxicity of pollutants with bioluminescent microorganisms

This chapter deals with the use of bioluminescent microorganisms in environmental monitoring, particularly in the assessment of the ecotoxicity of pollutants. Toxicity bioassays based on bioluminescent microorganisms are an interesting complement to classical toxicity assays, providing easiness of use, rapid response, mass production, and cost effectiveness. A description of the characteristics and main environmental applications in ecotoxicity testing of naturally bioluminescent microorganisms, covering bacteria and eukaryotes such as fungi and dinoglagellates, is reported in this chapter. The main features and applications of a wide variety of recombinant bioluminescent microorganisms, both prokaryotic and eukaryotic, are also summarized and critically considered. Quantitative structure-activity relationship models and hormesis are two important concepts in ecotoxicology; bioluminescent microorganisms have played a pivotal role in their development. As pollutants usually occur in complex mixtures in the environment, the use of both natural and recombinant bioluminescent microorganisms to assess mixture toxicity has been discussed. The main information has been summarized in tables, allowing quick consultation of the variety of luminescent organisms, bioluminescence gene systems, commercially available bioluminescent tests, environmental applications, and relevant references.

Genetically modified whole-cell bioreporters for environmental assessment

Living whole-cell bioreporters serve as environmental biosentinels that survey their ecosystems for harmful pollutants and chemical toxicants, and in the process act as human and other higher animal proxies to pre-alert for unfavorable, damaging, or toxic conditions. Endowed with bioluminescent, fluorescent, or colorimetric signaling elements, bioreporters can provide a fast, easily measured link to chemical contaminant presence, bioavailability, and toxicity relative to a living system. Though well tested in the confines of the laboratory, real-world applications of bioreporters are limited. In this review, we will consider bioreporter technologies that have evolved from the laboratory towards true environmental applications, and discuss their merits as well as crucial advancements that still require adoption for more widespread utilization. Although the vast majority of environmental monitoring strategies rely upon bioreporters constructed from bacteria, we will also examine environmental biosensing through the use of less conventional eukaryotic-based bioreporters, whose chemical signaling capacity facilitates a more human-relevant link to toxicity and health-related consequences.

Electrochemical cell-based sensors

One of the recently developed monitoring technologies involves the use of whole cell biosensors. Such biosensors can be constructed to detect expression of genes of interest and the effect of the environment on this expression. These biosensors are essential for monitoring environmental stress, such as general toxicity or specific toxicity caused by pollutants. Currently, a large spectrum of microbial biosensors have been developed that enable the monitoring of gene expression by measuring light, fluorescence, color, or electric current. The electrochemical monitoring is of special interest for in situ measurements as it can be performed using simple, compact, and mobile equipment and is easily adaptable for online measurements. Here we survey the potential application of electrochemical biosensors with special focus on monitoring environmental pollution.

Influence of phenolics on the sensitivity of free and immobilized bioluminescent Acinetobacter bacterium

In this work, the constructed bioluminescent Acinetobacter strain DF4/PUTK2 was employed to assess the toxicity of phenolic compounds and the 5 min EC50 values were calculated. The results of the DF4/PUTK2 assay were further evaluated by comparing with the results of the Vibrio fischeri luminescence inhibition assay. To develop a bioassay system appropriate to be used in continuous toxicity testing, strain DF4/PUTK2 was subjected for immobilization in microtiter plates into the matrices Ca-alginate, polyacrylamide, agar and agarose. After a choice of materials was tried, Ca-alginate was selected as the most suitable candidate material. Because, it could be stored at least 8 weeks at 4 degrees C, during which the ability of the bioreporter DF4/PUTK2 to detect the toxicity of phenolics was maintained. However, the stability of the bioluminescence for DF4/PUTK2 cells immobilized into agarose and agar was significantly less than that of cells stored in alginate suspensions. This study recommended that luxCDABE-marked Acinetobacter strain DF4/PUTK2 could be employed to assay the ecotoxicity of environmental samples contaminated with phenols. The host strain of the bioreporter DF4/PUTK2 is Acinetobacter strain DF4. It is known that members of the genus Acinetobacter are widespread in nature and also involved in biodegradation, leaching and removal of several organic and inorganic man-made hazardous wastes.

Monitoring of environmental pollutants by bioluminescent bacteria

This review deals with the applications of bioluminescent bacteria to the environmental analyses, published during the years 2000-2007. The ecotoxicological assessment, by bioassays, of the environmental risks and the luminescent approaches are reported. The review includes a brief introduction to the characteristics and applications of bioassays, a description of the characteristics and applications of natural bioluminescent bacteria (BLB), and a collection of the main applications to organic and inorganic pollutants. The light-emitting genetically modified bacteria applications, as well as the bioluminescent immobilized systems and biosensors are outlined. Considerations about commercially available BLB and BLB catalogues are also reported. Most of the environmental applications, here mentioned, of luminescent organisms are on wastewater, seawater, surface and ground water, tap water, soil and sediments, air. Comparison to other bioindicators and bioassay has been also made. Various tables have been inserted, to make easier to take a rapid glance at all possible references concerning the topic of specific interest.

[(3)H]Adenine is a suitable radioligand for the labeling of G protein-coupled adenine receptors but shows high affinity to bacterial contaminations in buffer solutions

[³H]Adenine has previously been used to label the newly discovered G protein-coupled murine adenine receptors. Recent reports have questioned the suitability of [³H]adenine for adenine receptor binding studies because of curious results, e.g. high specific binding even in the absence of mammalian protein. In this study, we showed that specific [³H]adenine binding to various mammalian membrane preparations increased linearly with protein concentration. Furthermore, we found that Tris-buffer solutions typically used for radioligand binding studies (50 mM, pH 7.4) that have not been freshly prepared but stored at 4°C for some time may contain bacterial contaminations that exhibit high affinity binding for [³H]adenine. Specific binding is abolished by heating the contaminated buffer or filtering it through 0.2-μm filters. Three different, aerobic, gram-negative bacteria were isolated from a contaminated buffer solution and identified as Achromobacter xylosoxidans, A. denitrificans, and Acinetobacter lwoffii. A. xylosoxidans, a common bacterium that can cause nosocomial infections, showed a particularly high affinity for [³H]adenine in the low nanomolar range. Structure–activity relationships revealed that hypoxanthine also bound with high affinity to A. xylosoxidans, whereas other nucleobases (uracil, xanthine) and nucleosides (adenosine, uridine) did not. The nature of the labeled site in bacteria is not known, but preliminary results indicate that it may be a high-affinity purine transporter. We conclude that [³H]adenine is a well-suitable radioligand for adenine receptor binding studies but that bacterial contamination of the employed buffer solutions must be avoided.

Biosensing environmental pollution

Whole-cell biosensors are finding increasing use for the detection of environmental pollution and toxicity. These biosensors are constructed through the fusion of promoters, responsive to the relevant environmental conditions, to easily monitored reporter genes. Depending on the choice of reporter gene, expression can be monitored by the production of colour, light, fluorescence or electrochemical reactions. Recent advances in this area have included the development of biosensors of compact size that enable the on-line and in situ monitoring of a large number of environmental parameters.