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Calvanese M, D’Angelo C, Tutino ML, Lauro C. Whole-Cell Biosensor for Iron Monitoring as a Potential Tool for Safeguarding Biodiversity in Polar Marine Environments. Mar Drugs 2024; 22:299. [PMID: 39057408 PMCID: PMC11277574 DOI: 10.3390/md22070299] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2024] [Revised: 06/05/2024] [Accepted: 06/24/2024] [Indexed: 07/28/2024] Open
Abstract
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.
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Affiliation(s)
- Marzia Calvanese
- Department of Chemical Sciences, University of Naples “Federico II”, Complesso Universitario Monte S. Angelo, Via Cintia 4, 80126 Naples, Italy; (M.C.); (C.D.); (M.L.T.)
- Istituto Nazionale Biostrutture e Biosistemi (I.N.B.B), Viale Medaglie D’Oro 305, 00136 Roma, Italy
| | - Caterina D’Angelo
- Department of Chemical Sciences, University of Naples “Federico II”, Complesso Universitario Monte S. Angelo, Via Cintia 4, 80126 Naples, Italy; (M.C.); (C.D.); (M.L.T.)
| | - Maria Luisa Tutino
- Department of Chemical Sciences, University of Naples “Federico II”, Complesso Universitario Monte S. Angelo, Via Cintia 4, 80126 Naples, Italy; (M.C.); (C.D.); (M.L.T.)
- Istituto Nazionale Biostrutture e Biosistemi (I.N.B.B), Viale Medaglie D’Oro 305, 00136 Roma, Italy
| | - Concetta Lauro
- Department of Chemical Sciences, University of Naples “Federico II”, Complesso Universitario Monte S. Angelo, Via Cintia 4, 80126 Naples, Italy; (M.C.); (C.D.); (M.L.T.)
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Wei Y, Shi D, Chen T, Zhou S, Yang Z, Li H, Yang D, Li J, Jin M. CRISPR/Cas9-based engineered Escherichia coli biosensor for sensitive and specific detection of Cd(II) in drinking water. CHEMOSPHERE 2024; 362:142607. [PMID: 38876330 DOI: 10.1016/j.chemosphere.2024.142607] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2024] [Revised: 06/10/2024] [Accepted: 06/12/2024] [Indexed: 06/16/2024]
Abstract
Cadmium (Cd) is a ubiquitous pollutant that poses a potential threat to human health. Monitoring Cd(II) in drinking water has significant implications for preventing potential threats of Cd(II) to human. However, the weak signal output and response to nontarget interference limit the detection of Cd(II) using bacterial biosensors. In this study, to enable sensitive and specific detection of Cd(II) in water, a stable whole-cell biosensor, K12-PMP-luxCDABE-△cysI, was constructed in a dual-promoter mode by fusing the mercury promoter Pmer, regulatory gene merR(m), and luciferase gene luxCDABE into the E.coli chromosome based on CRISPR/Cas9 gene editing technology. By knocking out the cadmium-resistance-gene cysI, the sensitivity of the biosensor to Cd(II) was further enhanced. The constructed E. coli biosensor K12-PMP-luxCDABE-△cysI exhibited good nonlinear responses to 0.005-2 mg/L Cd(II). Notably, among the three constructed E. coli biosensor, it exhibited the strongest fluorescence intensity, with the limit of detection meeting the allowable limit for Cd(II) in drinking water. Simultaneously, it could specifically detect Cd(II). Nontarget metal ions, such as Zn(II), Hg(II), and Pb(II), did not affect its performance. Furthermore, it exhibited superior performance in detecting Cd(II) in real drinking water samples by avoiding background interference, and showed excellent stability with the relative standard deviation under 5%. Thus, K12-PMP-luxCDABE-△cysI holds promise as a potential tool for the detection of Cd(II) in drinking water.
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Affiliation(s)
- Yijun Wei
- Military Medical Sciences Academy, Academy of Military Sciences
| | - Danyang Shi
- Military Medical Sciences Academy, Academy of Military Sciences
| | - Tianjiao Chen
- Military Medical Sciences Academy, Academy of Military Sciences
| | - Shuqing Zhou
- Military Medical Sciences Academy, Academy of Military Sciences
| | - Zhongwei Yang
- Military Medical Sciences Academy, Academy of Military Sciences
| | - Haibei Li
- Military Medical Sciences Academy, Academy of Military Sciences
| | - Dong Yang
- Military Medical Sciences Academy, Academy of Military Sciences
| | - Junwen Li
- Military Medical Sciences Academy, Academy of Military Sciences
| | - Min Jin
- Military Medical Sciences Academy, Academy of Military Sciences.
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Hui CY, Liu MQ, Guo Y. Synthetic bacteria designed using ars operons: a promising solution for arsenic biosensing and bioremediation. World J Microbiol Biotechnol 2024; 40:192. [PMID: 38709285 DOI: 10.1007/s11274-024-04001-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2024] [Accepted: 04/22/2024] [Indexed: 05/07/2024]
Abstract
The global concern over arsenic contamination in water due to its natural occurrence and human activities has led to the development of innovative solutions for its detection and remediation. Microbial metabolism and mobilization play crucial roles in the global cycle of arsenic. Many microbial arsenic-resistance systems, especially the ars operons, prevalent in bacterial plasmids and genomes, play vital roles in arsenic resistance and are utilized as templates for designing synthetic bacteria. This review novelty focuses on the use of these tailored bacteria, engineered with ars operons, for arsenic biosensing and bioremediation. We discuss the advantages and disadvantages of using synthetic bacteria in arsenic pollution treatment. We highlight the importance of genetic circuit design, reporter development, and chassis cell optimization to improve biosensors' performance. Bacterial arsenic resistances involving several processes, such as uptake, transformation, and methylation, engineered in customized bacteria have been summarized for arsenic bioaccumulation, detoxification, and biosorption. In this review, we present recent insights on the use of synthetic bacteria designed with ars operons for developing tailored bacteria for controlling arsenic pollution, offering a promising avenue for future research and application in environmental protection.
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Affiliation(s)
- Chang-Ye Hui
- Shenzhen Prevention and Treatment Center for Occupational Diseases, Shenzhen, China.
| | - Ming-Qi Liu
- Shenzhen Prevention and Treatment Center for Occupational Diseases, Shenzhen, China
- School of Public Health, Guangdong Medical University, Dongguan, China
| | - Yan Guo
- Shenzhen Prevention and Treatment Center for Occupational Diseases, Shenzhen, China
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Hu Q, Wang J, Liu C, Feng Y, Chen H. Determinants of mer Promoter Activity from Pseudomonas aeruginosa. Genes (Basel) 2024; 15:490. [PMID: 38674424 PMCID: PMC11049809 DOI: 10.3390/genes15040490] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2024] [Revised: 04/11/2024] [Accepted: 04/12/2024] [Indexed: 04/28/2024] Open
Abstract
Since the MerR family is known for its special regulatory mechanism, we aimed to explore which factors determine the expression activity of the mer promoter. The Tn501/Tn21 mer promoter contains an abnormally long spacer (19 bp) between the -35 and -10 elements, which is essential for the unique DNA distortion mechanism. To further understand the role of base sequences in the mer promoter spacer, this study systematically engineered a series of mutant derivatives and used luminescent and fluorescent reporter genes to investigate the expression activity of these derivatives. The results reveal that the expression activity of the mer promoter is synergistically modulated by the spacer length (17 bp is optimal) and the region upstream of -10 (especially -13G). The spacing is regulated by MerR transcription factors through symmetrical sequences, and -13G presumably functions through interaction with the RNA polymerase sigma-70 subunit.
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Affiliation(s)
| | | | | | | | - Hao Chen
- State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China; (Q.H.); (J.W.); (C.L.); (Y.F.)
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Hui CY, Ma BC, Hu SY, Wu C. Tailored bacteria tackling with environmental mercury: Inspired by natural mercuric detoxification operons. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2024; 341:123016. [PMID: 38008253 DOI: 10.1016/j.envpol.2023.123016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Revised: 10/30/2023] [Accepted: 11/19/2023] [Indexed: 11/28/2023]
Abstract
Mercury (Hg) and its inorganic and organic compounds significantly threaten the ecosystem and human health. However, the natural and anthropogenic Hg environmental inputs exceed 5000 metric tons annually. Hg is usually discharged in elemental or ionic forms, accumulating in surface water and sediments where Hg-methylating microbes-mediated biotransformation occurs. Microbial genetic factors such as the mer operon play a significant role in the complex Hg biogeochemical cycle. Previous reviews summarize the fate of environmental Hg, its biogeochemistry, and the mechanism of bacterial Hg resistance. This review mainly focuses on the mer operon and its components in detecting, absorbing, bioaccumulating, and detoxifying environmental Hg. Four components of the mer operon, including the MerR regulator, divergent mer promoter, and detoxification factors MerA and MerB, are rare bio-parts for assembling synthetic bacteria, which tackle pollutant Hg. Bacteria are designed to integrate synthetic biology, protein engineering, and metabolic engineering. In summary, this review highlights that designed bacteria based on the mer operon can potentially sense and bioremediate pollutant Hg in a green and low-cost manner.
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Affiliation(s)
- Chang-Ye Hui
- Shenzhen Prevention and Treatment Center for Occupational Diseases, 2019 Buxin Road, Shenzhen, 518020, China.
| | - Bing-Chan Ma
- Shenzhen Prevention and Treatment Center for Occupational Diseases, 2019 Buxin Road, Shenzhen, 518020, China; School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Road, Wuhan, 430030, China
| | - Shun-Yu Hu
- Shenzhen Prevention and Treatment Center for Occupational Diseases, 2019 Buxin Road, Shenzhen, 518020, China; Department of Toxicology, School of Public Health, Southern Medical University, Guangzhou, 510515, China
| | - Can Wu
- Shenzhen Prevention and Treatment Center for Occupational Diseases, 2019 Buxin Road, Shenzhen, 518020, China; Department of Toxicology, School of Public Health, Southern Medical University, Guangzhou, 510515, China
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Thai TD, Lim W, Na D. Synthetic bacteria for the detection and bioremediation of heavy metals. Front Bioeng Biotechnol 2023; 11:1178680. [PMID: 37122866 PMCID: PMC10133563 DOI: 10.3389/fbioe.2023.1178680] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Accepted: 04/04/2023] [Indexed: 05/02/2023] Open
Abstract
Toxic heavy metal accumulation is one of anthropogenic environmental pollutions, which poses risks to human health and ecological systems. Conventional heavy metal remediation approaches rely on expensive chemical and physical processes leading to the formation and release of other toxic waste products. Instead, microbial bioremediation has gained interest as a promising and cost-effective alternative to conventional methods, but the genetic complexity of microorganisms and the lack of appropriate genetic engineering technologies have impeded the development of bioremediating microorganisms. Recently, the emerging synthetic biology opened a new avenue for microbial bioremediation research and development by addressing the challenges and providing novel tools for constructing bacteria with enhanced capabilities: rapid detection and degradation of heavy metals while enhanced tolerance to toxic heavy metals. Moreover, synthetic biology also offers new technologies to meet biosafety regulations since genetically modified microorganisms may disrupt natural ecosystems. In this review, we introduce the use of microorganisms developed based on synthetic biology technologies for the detection and detoxification of heavy metals. Additionally, this review explores the technical strategies developed to overcome the biosafety requirements associated with the use of genetically modified microorganisms.
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Hui CY, Hu SY, Li LM, Yun JP, Zhang YF, Yi J, Zhang NX, Guo Y. Metabolic engineering of the carotenoid biosynthetic pathway toward a specific and sensitive inorganic mercury biosensor. RSC Adv 2022; 12:36142-36148. [PMID: 36545109 PMCID: PMC9756418 DOI: 10.1039/d2ra06764a] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Accepted: 12/05/2022] [Indexed: 12/23/2022] Open
Abstract
The toxicity of mercury (Hg) mainly depends on its form. Whole-cell biosensors respond selectively to toxic Hg(ii), efficiently transformed by environmental microbes into methylmercury, a highly toxic form that builds up in aquatic animals. Metabolically engineered Escherichia coli (E. coli) have successfully produced rainbow colorants. By de novo reconstruction of the carotenoid synthetic pathway, the Hg(ii)-responsive production of lycopene and β-carotene enabled programmed E. coli to potentially become an optical biosensor for the qualitative and quantitative detection of ecotoxic Hg(ii). The red color of the lycopene-based biosensor cell pellet was visible upon exposure to 49 nM Hg(ii) and above. The orange β-carotene-based biosensor responded to a simple colorimetric assay as low as 12 nM Hg(ii). A linear response was observed at Hg(ii) concentrations ranging from 12 to 195 nM. Importantly, high specificity and good anti-interference capability suggested that metabolic engineering of the carotenoid biosynthesis was an alternative to developing a visual platform for the rapid analysis of the concentration and toxicity of Hg(ii) in environmentally polluted water.
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Affiliation(s)
- Chang-ye Hui
- Department of Pathology & Toxicology, Shenzhen Prevention and Treatment Center for Occupational DiseasesShenzhen 518020China
| | - Shun-yu Hu
- Department of Toxicology, School of Public Health, Southern Medical UniversityGuangzhou 510515China
| | - Li-mei Li
- Department of Pathology & Toxicology, Shenzhen Prevention and Treatment Center for Occupational DiseasesShenzhen 518020China
| | - Jian-pei Yun
- Physical & Chemical Testing Laboratory, Shenzhen Prevention and Treatment Center for Occupational DiseasesShenzhen 518020China
| | - Yan-fang Zhang
- Physical & Chemical Testing Laboratory, Shenzhen Prevention and Treatment Center for Occupational DiseasesShenzhen 518020China
| | - Juan Yi
- Department of Pathology & Toxicology, Shenzhen Prevention and Treatment Center for Occupational DiseasesShenzhen 518020China
| | - Nai-xing Zhang
- National Key Clinical Specialty of Occupational Diseases, Shenzhen Prevention and Treatment Center for Occupational DiseasesShenzhen 518020China
| | - Yan Guo
- Department of Toxicology, School of Public Health, Southern Medical UniversityGuangzhou 510515China,National Key Clinical Specialty of Occupational Diseases, Shenzhen Prevention and Treatment Center for Occupational DiseasesShenzhen 518020China
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Guo Y, Huang ZL, Zhu DL, Hu SY, Li H, Hui CY. Anthocyanin biosynthetic pathway switched by metalloregulator PbrR to enable a biosensor for the detection of lead toxicity. Front Microbiol 2022; 13:975421. [PMID: 36267188 PMCID: PMC9577363 DOI: 10.3389/fmicb.2022.975421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Accepted: 09/21/2022] [Indexed: 11/26/2022] Open
Abstract
Environmental lead pollution mainly caused by previous anthropogenic activities continuously threatens human health. The determination of bioavailable lead is of great significance to predict its ecological risk. Bacterial biosensors using visual pigments as output signals have been demonstrated to have great potential in developing minimal-equipment biosensors for environmental pollutant detection. In this study, the biosynthesis pathway of anthocyanin was heterogeneously reconstructed under the control of the PbrR-based Pb(II) sensory element in Escherichia coli. The resultant metabolic engineered biosensor with colored anthocyanin derivatives as the visual signal selectively responded to concentrations as low as 0.012 μM Pb(II), which is lower than the detection limit of traditional fluorescent protein-based biosensors. A good linear dose–response pattern in a wide Pb(II) concentration range (0.012–3.125 μM) was observed. The color deepening of culture was recognized to the naked eye in Pb(II) concentrations ranging from 0 to 200 μM. Importantly, the response of metabolic engineered biosensors toward Pb(II) was not significantly interfered with by organic and inorganic ingredients in environmental water samples. Our findings show that the metabolic engineering of natural colorants has great potential in developing visual, sensitive, and low-cost bacterial biosensors for the detection and determination of pollutant heavy metals.
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Affiliation(s)
- Yan Guo
- National Key Clinical Specialty of Occupational Diseases, Shenzhen Prevention and Treatment Center for Occupational Diseases, Shenzhen, China
| | - Zhen-lie Huang
- Department of Toxicology, School of Public Health, Southern Medical University, Guangzhou, China
| | - De-long Zhu
- School of Public Health, Guangdong Medical University, Dongguan, China
- Department of Pathology and Toxicology, Shenzhen Prevention and Treatment Center for Occupational Diseases, Shenzhen, China
| | - Shun-yu Hu
- National Key Clinical Specialty of Occupational Diseases, Shenzhen Prevention and Treatment Center for Occupational Diseases, Shenzhen, China
- Department of Toxicology, School of Public Health, Southern Medical University, Guangzhou, China
| | - Han Li
- Department of Pathology and Toxicology, Shenzhen Prevention and Treatment Center for Occupational Diseases, Shenzhen, China
- College of Lab Medicine, Hebei North University, Zhangjiakou, China
| | - Chang-ye Hui
- Department of Pathology and Toxicology, Shenzhen Prevention and Treatment Center for Occupational Diseases, Shenzhen, China
- *Correspondence: Chang-ye Hui,
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Liu C, Yu H, Zhang B, Liu S, Liu CG, Li F, Song H. Engineering whole-cell microbial biosensors: Design principles and applications in monitoring and treatment of heavy metals and organic pollutants. Biotechnol Adv 2022; 60:108019. [PMID: 35853551 DOI: 10.1016/j.biotechadv.2022.108019] [Citation(s) in RCA: 28] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Revised: 07/13/2022] [Accepted: 07/13/2022] [Indexed: 01/18/2023]
Abstract
Biosensors have been widely used as cost-effective, rapid, in situ, and real-time analytical tools for monitoring environments. The development of synthetic biology has enabled emergence of genetically engineered whole-cell microbial biosensors. This review updates the design and optimization principles for a diverse array of whole-cell biosensors based on transcription factors (TF) including activators or repressors derived from heavy metal resistance systems, alkanes, and aromatics metabolic pathways of bacteria. By designing genetic circuits, the whole-cell biosensors could be engineered to intelligently sense heavy metals (Hg2+, Zn2+, Pb2+, Au3+, Cd2+, As3+, Ni2+, Cu2+, and UO22+) or organic compounds (alcohols, alkanes, phenols, and benzenes) through one-component or two-component system-based TFs, transduce signals through genetic amplifiers, and response as various outputs such as cell fluorescence and bioelectricity for monitoring heavy metals and organic pollutants in real conditions, synthetic curli and surface metal-binding peptides for in situ bio-sorption of heavy metals. We further review strategies that have been implemented to optimize the selectivity and correlation between ligand concentration and output signal of the TF-based biosensors, so as to meet requirements of practical applications. The optimization strategies include protein engineering to change specificities, promoter engineering to improve sensitivities, and genetic circuit-based amplification to enhance dynamic ranges via designing transcriptional amplifiers, logic gates, and feedback loops. At last, we outlook future trends in developing novel forms of biosensors.
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Affiliation(s)
- Changjiang Liu
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Key Laboratory of Systems Bioengineering, Tianjin University, Tianjin 300072, China; Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Huan Yu
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Key Laboratory of Systems Bioengineering, Tianjin University, Tianjin 300072, China; Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Baocai Zhang
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Key Laboratory of Systems Bioengineering, Tianjin University, Tianjin 300072, China; Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Shilin Liu
- Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Chen-Guang Liu
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences of Ministry of Education, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Feng Li
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Key Laboratory of Systems Bioengineering, Tianjin University, Tianjin 300072, China; Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China.
| | - Hao Song
- Frontiers Science Center for Synthetic Biology (Ministry of Education), Key Laboratory of Systems Bioengineering, Tianjin University, Tianjin 300072, China; Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China.
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Detection of environmental pollutant cadmium in water using a visual bacterial biosensor. Sci Rep 2022; 12:6898. [PMID: 35477977 PMCID: PMC9046199 DOI: 10.1038/s41598-022-11051-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Accepted: 04/18/2022] [Indexed: 11/10/2022] Open
Abstract
Cadmium (Cd) contamination in water and soil is considered an environmental pollutant. Food crops can absorb and accumulate bioavailable Cd. Continuous monitoring of Cd levels in the environment can minimize exposure and harm to humans. Visual pigments have been demonstrated to have great potential in the development of minimal-equipment biosensors. In the present study, a metabolically engineered bacterium was employed to produce blue-purple pigment violacein responsive to toxic Cd(II). The high stability of the bisindole pigment contributed to determining the violacein at wavelengths of 578 nm. Visual and quantifiable signals could be captured after a 1.5-h Cd(II) exposure. This novel biosensor showed significantly stronger responses to Cd(II) than to other heavy metals including Pb(II), Zn(II), and Hg(II). A significant increase in pigment signal was found to respond to as low as 0.049 μM Cd(II). The naked eye can detect the color change when violacein-based biosensor is exposed to 25 μM Cd(II). A high-throughput method for rapid determination of soluble Cd(II) in environmental water was developed using a colorimetric microplate.
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