High-throughput visualization mutation screening technology to enhance the specificity of CadR based whole-cell cadmium biosensor.

As a heavy metal pollutant, Cd2+ often enters the human body through the food chain causing great harm to human health. Whole-cell biosensor is an emerging technology for rapid on-site detection of heavy metals with the advantages of inexpensive, fast to mass-produce, and strong in anti-interference resistance, but suffering from insatisfactory specificity. In this study, a strategy of Adjacent Site Saturation Mutation (ASSM) was designed to improve the specificity of transcription factor CadR, which acted as the recognition element and determined the specificity of whole cell Cd2+ biosensors. A specific saturated library was constructed using the strategy of adjacent mutation. After two rounds of high-throughput visual screening, a whole-cell biosensor with good response to Cd2+, and with significant weakened Hg2+ interference was obtained. The optimized whole-cell biosensor showed a linear dynamic concentration range from 500 nM to 100 µM, a detection limit of 0.079 µM, and has satisfactory specificity and anti-interference. The ASSM strategy proposed in this study can provide a new method for the application of synthetic biology in food safety detection, indicating the importance of whole-cell biosensors for the detection of heavy metals.

Research status and hotspots on the mechanisms of liver X receptor in cancer progression: A bibliometric analysis.

BACKGROUND: The mechanism of liver X receptor in cancer has been gradually revealed in recent years. This study is committed to analyzing the current research status of the mechanism of liver × receptor in cancer progression by using bibliometric methods and to explore the development trend of liver × receptor related research in the future, in order to provide some reference for further exploration in this field. METHODS: The Web of Science core collection database was used to carry out the original data retrieval. Excel software was used for data statistics. Vosviewer and CiteSpace software were used to analyze the publication situation, cooperation network, reference co-citation, keyword and term co-occurrence, term bursts, and cluster analysis, and draw visual maps. RESULTS: A total of 631 publications meeting the research criteria were included by December 2022, with an average of 32.5 citations per paper. The main research fields were molecular biology, oncology and cell biology, and the papers were mainly published in journals about molecular, biology and immunology. Cell is the journal with the highest citation. The United States is the most influential country, the University of California, Los Angeles is the main research institution, and Gustafsson, Jan-ake is the author with the highest output. In reference co-citation clustering, cluster#2 "cancer development" is the main cluster, and the period from 2014 to 2018 is an important stage of relevant theoretical progress. "Tumor microenvironment" with high burst and novelty became the most noteworthy term in term burst. CONCLUSION: Using bibliometric methods to reveal the current status of LXR and cancer mechanisms, and making predictions of possible future hotspots based on the analysis of the current situation, the translation of LXR anti-cancer research to clinical applications, the impact on the tumor microenvironment as a whole and more immune pathways, and the formation of a systematic cognition of the effects of more cancer cell lines and oncogenic signaling crosstalk, which is a possible direction for future research.

Replacing manual operation with bio-automation: A high-throughput evolution strategy to construct an integrated whole-cell biosensor for the simultaneous detection of methylmercury and mercury ions without manual sample digestion.

Methylmercury is primarily responsible for most food mercury pollution cases. However, most biosensors developed for mercury pollution analysis can only detect mercury ions. Although oxidative strong-acid digestion or microwave-assisted digestion can convert methylmercury into mercury ions, it is unsuitable for on-site detection. This study designed a bio-digestion gene circuit and integrated it into a mercury ion whole-cell biosensor，creating a novel on-site methylmercury detection method. Five alkyl mercury lyases from different bacterial genomes were screened via bioinformatics analysis, of which goMerB from Gordonia otitis showed the highest catalytic biological digestion efficiency. The goMerB site-specific saturation and random mutation libraries were constructed. After two rounds of high-throughput visualization screening, the catalytic activity of the mutant increased 2.5-fold. The distance between the three crucial amino acid sites and methylmercury changed in the mutant, which likely contributed to the enhanced catalytic efficiency. The optimized whole-cell biosensor showed a linear dynamic concentration range of 100 nM to 100 µM (R2 =0.991), satisfactory specificity, and interference resistance. The detection limit of the goMerBt6-MerR-RFP biosensor was 0.015 µM, while the limit of quantitation was 0.049 µM. This study demonstrated the application of synthetic biology for food safety detection and highlighted the future potential of "Lab in a Cell" for hazard analysis.

Synthetic symbiotic bacteria reduces the toxicity of mercury ingested via contaminated food.

Mercury contamination in food poses a significant threat to human health. In this article, we propose a novel approach to solve this problem by enhancing the function of gut microbiota against mercury using a synthetically engineered bacterial strain. An engineered Escherichia coli biosensor MerR with mercury binding function was introduced into the intestines of mice for colonization, whereafter the mice were challenged with oral mercury. Compared with the control mice and mice colonized with unengineered Escherichia coli, the mice with biosensor MerR cells in their gut showed significantly stronger mercury resistance. Furthermore, mercury distribution analysis revealed that biosensor MerR cells promoted the excretion of oral mercury with feces, thereby blocking the entry of mercury into the mice, decreasing the concentration of mercury in the circulatory system and organs, and, thus, attenuating the toxicity of mercury to the liver, kidneys and intestines. Colonization with the biosensor MerR did not result in significant health problems in the mice, nor were genetic circuit mutations or lateral transfers identified during the experiments, thus demonstrating the safety of this approach. This study elucidates the remarkable promise of synthetic biology for modulating gut microbiota function.

Advances in Synthetic-Biology-Based Whole-Cell Biosensors: Principles, Genetic Modules, and Applications in Food Safety.

A whole-cell biosensor based on synthetic biology provides a promising new method for the on-site detection of food contaminants. The basic components of whole-cell biosensors include the sensing elements, such as transcription factors and riboswitches, and reporting elements, such as fluorescence, gas, etc. The sensing and reporting elements are coupled through gene expression regulation to form a simple gene circuit for the detection of target substances. Additionally, a more complex gene circuit can involve other functional elements or modules such as signal amplification, multiple detection, and delay reporting. With the help of synthetic biology, whole-cell biosensors are becoming more versatile and integrated, that is, integrating pre-detection sample processing, detection processes, and post-detection signal calculation and storage processes into cells. Due to the relative stability of the intracellular environment, whole-cell biosensors are highly resistant to interference without the need of complex sample preprocessing. Due to the reproduction of chassis cells, whole-cell biosensors replicate all elements automatically without the need for purification processing. Therefore, whole-cell biosensors are easy to operate and simple to produce. Based on the above advantages, whole-cell biosensors are more suitable for on-site detection than other rapid detection methods. Whole-cell biosensors have been applied in various forms such as test strips and kits, with the latest reported forms being wearable devices such as masks, hand rings, and clothing. This paper examines the composition, construction methods, and types of the fundamental components of synthetic biological whole-cell biosensors. We also introduce the prospect and development trend of whole-cell biosensors in commercial applications.

Applications of the Whole-Cell System in the Efficient Biosynthesis of Heme.

Heme has a variety of functions, from electronic reactions to binding gases, which makes it useful in medical treatments, dietary supplements, and food processing. In recent years, whole-cell system-based heme biosynthesis methods have been continuously explored and optimized as an alternative to the low-yield, lasting, and adverse ecological environment of chemical synthesis methods. This method relies on two biosynthetic pathways of microbial precursor 5-aminolevulinic acid (C4, C5) and three known downstream biosynthetic pathways of heme. This paper reviews the genetic and metabolic engineering strategies for heme production in recent years by optimizing culture conditions and techniques from different microorganisms. Specifically, we summarized and analyzed the possibility of using biosensors to explore new strategies for the biosynthesis of heme from the perspective of synthetic biology, providing a new direction for future exploration.

Discovery of 2,4-diarylaminopyrimidine derivatives bearing dithiocarbamate moiety as novel ALK inhibitors.

To overcome drug resistance caused by ALK kinase mutations especially G1202R, two series of novel 2,4-diarylaminopyrimidine derivatives bearing dithiocarbamate moiety were designed, synthesized and evaluated for their biological activities. Among all the target compounds, B10 efficiently inhibited the proliferation of ALK-positive Karpas299 and H2228 cells both with IC50 values of 0.07 µM. In addition, B10 exhibited remarkable enzymatic inhibitory potency with IC50 values of 4.59 nM, 2.07 nM and 5.95 nM toward ALKWT, ALKL1196M and ALKG1202R, respectively. Furthermore, B10 induced apoptosis in H2228 cell and caused cell cycle arrest in G2/M phase. Ultimately, the binding modes of B10 with ALKWT and ALKG1202R were ideally established, which further confirmed the structural basis in accordance with the SARs analysis. These results indicated that B10 was a potent ALK inhibitor for ALKG1202R mutation treatment and deserved for further investigation.

Pleurotus Ostreatus Ameliorates Obesity by Modulating the Gut Microbiota in Obese Mice Induced by High-Fat Diet.

Pleurotus ostreatus (PO), a common edible mushroom, contains rich nutritional components with medicinal properties. To explore the effect of PO on ameliorating obesity and modulating the gut microbiota, we administered the mice with a low-fat diet or high-fat diet containing different dosages of PO (mass fraction: 0%, 2.5%, 5% and 10%). The body weight, adipose tissue weight, GTT, ITT, blood lipids, serum biomarkers of liver/kidney function, the gut microbiota and function were measured and analyzed after 6 weeks of PO treatment. The results showed PO prevented obesity, maintained glucose homeostasis and beneficially modulated gut microbiota. PO modified the composition and functions of gut microbiota in obese mice and make them similar to those in lean mice, which contributed to weight loss. PO significantly increased the relative abundance of Oscillospira, Lactobacillus group and Bifidobacterium, while decreased the relative abundance of Bacteroides and Roseburia. The prediction of gut microbiota function showed PO upregulated lipid metabolism, carbohydrate metabolism, bile acid biosynthesis, while it downregulated adipocytokine signaling pathway and steroid hormone biosynthesis. Correlation analysis further suggested the potential relationship among obesity, gut microbiota and the function of gut microbiota. In conclusion, all the results indicated that PO ameliorated obesity at least partly by modulating the gut microbiota.

A gas reporting whole-cell microbial biosensor system for rapid on-site detection of mercury contamination in soils.

As optical reporting elements, fluorescent proteins are extensively used in whole-cell microbial biosensors. However, the use of these optical reporters is limited in opaque media such as soil. This study described a method utilizing gas as a reporting signal that could be used for the rapid on-site detection of mercury in soil. In this biosensor, the MerR protein could capture mercury ions and then bind the promoter of the efe gene to initiate the synthesis of the ethylene (C2H4)-forming enzyme that produced the gas. The research showed that the mercury ion concentrations could be converted into C2H4 gas signals, which were quantified using a handheld C2H4 sensor. By optimizing the biosensor to improve its anti-interference ability in the system, it could detect mercury ion concentrations in the soil ranging from 0.2 to 20 mg/kg within 45 min, effectively reflecting whether the mercury pollution in the soil exceeded the limit standard. This study provides a simple, inexpensive, and portable method for the on-site detection of soil pollutants.

Ultrasensitive magnetic DNAzyme-copper nanoclusters fluorescent biosensor with triple amplification for the visual detection of E. coli O157:H7.

A relatively-simple and high-efficient fluorescent magnetic biosensor based on DNAzyme was established for the detection of E. coli O157:H7. In order to solve the problem of weak signal and low sensitivity in the detection of foodborne pathogenic bacteria, we ingeniously designed a fluorescent sensor based on triple signal amplification of magnetic beads, DNAzyme and photoluminescence. In the detection process, the E. coli-specific RNA-cleaving DNAzyme can specifically identify the target protein in crude intracellular mixture (CIM), which caused its conformation changes and induced rolling circle amplification (RCA) to the generation and luminescence of copper nanoclusters (CuNCs). This cascade amplification design can capture weak signals in the sample. The biosensor also indicated a good linear range from 10 CFU mL-1 to 1000 CFU mL-1 and obtained a limit of detection (LOD) of 1.57 CFU mL-1, which showed a relatively high sensitivity compared with other studies. Furthermore, the biosensor displayed high-efficient detection capability in 1.5 h and good reproducibility (relative standard deviations < 2%). It has been proved that this sensor is feasible to the detection of E. coli O157:H7 in drinking water and apple juice. Moreover, we found that the final detection product can effectively wrap the magnetic beads and can be driven by the magnetic field. And this unexpected discovery will provide ideas for the development of biosensing robots.

Third Generation Whole-Cell Sensing Systems: Synthetic Biology Inside, Nanomaterial Outside.

Whole-cell sensing systems (WCSSs) are highly anticipated in the field of on-site detection. However, due to their low specificity, poor stability, and potential environmental problems, their commercial application is unrealistic. Recently, synthetic biology and nanomaterials have provided potential solutions to these problems, propelling WCSSs into a new generation. Synthetic biology provides a complete solution for the intelligent design and assembly of elements, modules, and genetic circuits. Nanomaterials covering the exterior of the cells provide stable protection, remote control capability, and catalytic ability for the WCSSs, and they can limit the horizontal transfer of genetic elements. These advancements enable personalized customization, intelligent control, and self-destruction in the next generation of cell sensors, promoting their industrialization.

A test strip platform based on a whole-cell microbial biosensor for simultaneous on-site detection of total inorganic mercury pollutants in cosmetics without the need for predigestion.

Mercury pollutants such as mercuric chloride (HgCl2), mercurous chloride (Hg2Cl2) and mercuric ammonium chloride (Hg(NH2)Cl) are often found in cosmetics. Previous attempts at the on-site detection of mercury were hindered by the complicated and dangerous pretreatment procedure of converting various forms of mercury to Hg (II) ions. In this study, a test strip platform was developed based on a whole-cell microbial biosensor for the simultaneous detection of soluble and insoluble inorganic mercury pollutants in cosmetics without the need for predigestion. The genetic circuits with constitutively expressed MerR as sensor proteins and inducible red fluorescent protein (RFP) as the reporter were introduced into Escherichia coli to construct the mercury detection biosensor. The RFP fluorescence intensity of this biosensor showed a excellent linear relationship (R2 = 0.9848) with the Hg (II) concentration ranging from 50 nM to 10 µM in Luria-Bertani (LB) broth. Further research indicated that this biosensor could respond not only to Hg (II) ions but also to insoluble Hg2Cl2 and Hg2Cl2. The transcriptomic results confirmed the mercury conversion ability of the whole-cell biosensor from a gene expression perspective. This biosensor was embedded on filter paper to form a test strip, which could be used to determine whether the total inorganic mercury pollutants in cosmetics exceeded 1 mg/kg. Therefore, this strip provided a low cost, easy-to-use, and instrument-independent method for the detection of mercury pollution in cosmetics, while this study revealed the unique advantages of microbial biosensors in the automatic bioconversion of targets.

Feedback regulation mode of gene circuits directly affects the detection range and sensitivity of lead and mercury microbial biosensors.

Whole cell biosensors offer high potential for the detection of heavy metals in a manner that is simple, rapid and low-cost. However, previous researchers have paid little attention to the impacts of construction models on the performance of these biosensors, thereby limiting the achievement of rational design and the optimization of detection characteristics. Herein, for the first time, three basic models of lead and mercury detection circuits, namely feedback coupled, uncoupled and semi-coupled models, have been constructed and compared to explore the effects of uncoupling the topology of sensing circuits on the reporter signals. The results demonstrated that the uncoupled model had better sensitivity for both lead (50 nM) and mercury (1 nM), while the feedback coupled circuits had a wider detection range for mercury (10 nM - 7.5 µM). Introducing the semi-coupled model into the comparison revealed that both the type and location of promoters for regulatory protein genes were key factors for sensitivity. Moreover, the detection characteristics of the uncoupled biosensors were robust, as conditions such as induction time, the concentration of microbial cells, and the concentration of antibiotics had little interference on the performance of the microbial biosensors. This study also established a novel and simple pre-treatment method for sample detection by biosensors. When the uncoupled microbial biosensor was put into practice, the concentration levels of mercury in milk and lead in sewage were determined quickly and accurately. Our study, therefore, provides a strategy for the rational design of whole cell heavy metal biosensors and has developed the potential of their application.

Using the promoters of MerR family proteins as "rheostats" to engineer whole-cell heavy metal biosensors with adjustable sensitivity.

BACKGROUND: Whole cell biosensors provide a simple method for the detection of heavy metals. However, previous designs of them rely primarily on simulation of heavy metal resistance systems of bacteria. RESULTS: This study proposes a strategy for the rational design of metal detection circuits based on sensor proteins of the MerR family. Our results indicate the expression level of sensor protein can be used as a "rheostat" for tuning detection sensitivity with parabola curves to represent the relationships between the detection slopes and the sensor protein levels. This circuits design strategy (named as "Parabola Principle"), is used as a guide for the discovery of optimum metal detection circuits, and the design of biosensors with specific metal detection characteristics. For example, visible qualitative Hg (II) biosensors with a threshold of 0.05 mg/L are successfully constructed. CONCLUSIONS: These results indicate the feasibility of developing a sensor that is much more tunable than what is presented.

Diagnosing and tracing the pathogens of infantile infectious diarrhea by amplicon sequencing.

BACKGROUND: Metagenomic methods have been widely applied to study the relationship between gut microbiota and human health. To test whether metagenomic amplicon sequencing could be an effective method to diagnose and trace the pathogens of infantile infectious diarrhea, the fecal samples of 20 diarrheic and 13 healthy infants were collected. After 16S rDNA amplicon sequencing, diversity analyses were carried out. The relationship between the pathogens of the gut microbiota and geography of patients was analyzed. RESULTS: The diversity of the gut microbiota in diarrheic infants was significantly lower than that of the gut microbiota in healthy ones and that, the composition of gut microbiota in the diarrheic group was significantly different than that of the gut microbiota in the healthy group. The results also indicated that in some of the patients, the amounts of Escherichia coli were significantly increased in the diarrheic infants, which was in agreement with the result of the qPCR analysis. Using a geographical map, we found some patterns between pathogen source and geographical location. This is helpful for an early warning of the disease. CONCLUSIONS: The method of using high-throughput DNA sequencing and a comprehensive and deep data analysis can be a new strategy to detect and trace pathogens in infantile infectious diarrhea.Trial registration Diagnosing and tracing the pathogens of infantile infectious diarrhea by amplicon sequencing, ChiCTR-DDD-1701088, Registered 16 March 2017-Retrospectively registered, http://www.chictr.org.cn/showproj.aspx?proj=18477.

A 90-day subchronic toxicology screen of genetically modified rice Lac-3 and its effects on the gut microbiota in Sprague-Dawley rats.

A 90-day subchronic toxicology screen of genetically modified (GM) rice Lac-3 expressing human lactoferrin (hLF) and its effects on the gut microbiota were studied in comparison to non-GM rice fed to Sprague-Dawley (SD) rats. Three different dietary concentrations (17.5%, 35% and 70%, w/w) of the GM rice or its corresponding non-GM rice were used. Additionally, the phylotypes of gut microbiota in the control group, the 70% GM rice diet group and the 70% non-GM rice diet group on day 90 were determined by 16S rRNA sequencing. The results of the 90-day subchronic feeding study demonstrated that the GM rice Lac-3 containing human lactoferrin (LF) gene is considered as safe as the non-GM rice. The results of bacterial 16S rRNA sequencing showed that the structure of gut microbiota in the 70% GM group slightly changed when compared with the control group and the 70% non-GM group. There were no significant differences in the microbiota diversity among the three groups.

Safety assessment of transgenic canola RF3 with bar and barstar gene on Sprague-Dawley (SD) rats by 90-day feeding test.

Canola is one of the most important plant oilseed crops. To avoid the threat of herbicides, the RF3 line with bar gene and barstar gene was developed, which can act as glufosinate resistance resources and restore fertility in hybrid lines. To assess the food safety of transgenic canola RF3, 2.5%, 5% and 10% GM canola RF3 and its non-GM isogenic line Drakkar were formulated into diet to feed Spragure-Dawley (SD) rats for 90 days. The effects on the general growth and toxicological parameters, as well as gut microbiota of rats, were evaluated. Several significant differences on body weight, feed consumption, relative organ weight, hematology and serum biochemistry were observed among rats in the 90-day feeding test. However, these statistical differences were randomly observed among different groups and were not dose-related, which were not considered to be biologically significant. Furthermore, the results of bacterial 16S rRNA sequencing of fecal samples showed that the diets containing GM canola did not disturb the balance of gut microbiota. In conclusion, the canola RF3 is considered as safe and wholesome as the non-GM canola based on this 90-day feeding test and gut microbiota analysis.

Rice- or pork-based diets with similar calorie and content result in different rat gut microbiota.

Rice is the most important food crop, and pork is the most widely eaten meat in the world. In this study, we compared the gut microbiota of the rats fed with rice or pork mixed diets, which have similar caloric contents. The physiological indices (body weights, hematology, serum chemistry, organ weights and histopathology) of two groups were all within the normal range. Two diets did not induce difference in the diversity of gut bacteria. However, Firmicutes were significantly higher in rice diet group, while Bacteroidetes were enriched in pork diet group. Butyrate and the bacteria enzymes ß-glucuronidase, ß-glucosidase and nitroreductase in the feces were all drastically higher in pork diet group. This study indicates that different diets with similar calorie and nutritional composition could change the community structure but not the diversity of rat fecal microbiota.

Insoluble Dietary Fiber from Pear Pomace Can Prevent High-Fat Diet-Induced Obesity in Rats Mainly by Improving the Structure of the Gut Microbiota.

Supplement of dietary fibers (DF) is regarded as one of the most effective way to prevent and relieve chronic diseases caused by long-term intake of a high-fat diet in the current society. The health benefits of soluble dietary fibers (SDF) have been widely researched and applied, whereas the insoluble dietary fibers (IDF), which represent a higher proportion in plant food, were mistakenly thought to have effects only in fecal bulking. In this article, we proved the anti-obesity and glucose homeostasis improvement effects of IDF from pear pomace at first, and then the mechanisms responsible for these effects were analyzed. The preliminary study by real-time PCR and ELISA showed that this kind of IDF caused more changes in the gut microbiota compared with in satiety hormone or in hepatic metabolism. Further analysis of the gut microbiota by high-throughput amplicon sequencing showed IDF from pear pomace obviously improved the structure of the gut microbiota. Specifically, it promoted the growth of Bacteroidetes and inhibited the growth of Firmicutes. These results are coincident with previous hypothesis that the ratio of Bacteroidetes/Firmicutes is negatively related with obesity. In conclusion, our results demonstrated IDF from pear pomace could prevent high-fat diet-induced obesity in rats mainly by improving the structure of the gut microbiota.

In Vivo Effects of Pichia Pastoris-Expressed Antimicrobial Peptide Hepcidin on the Community Composition and Metabolism Gut Microbiota of Rats.

Hepcidin, one kind of antimicrobial peptides, is one of the promising alternatives to antibiotics with broad spectrum of antimicrobial activity. Hepcidins cloned from different kinds of fishes have been produced using exogenous expression systems, and their in vitro antimicrobial effects have been verified. However their in vivo effects on gut microbiota and gut health of hosts remain unclear. Here we performed a safety study of hepcidin so that it can be used to reduce microbial contaminations in the food and feed. In this study, Pichia pastoris-expressed Pseudosciaena crocea hepcidin (PC-hepc) was first assessed by simulated digestion tests and then administered to male and female Sprague-Dawley (SD) rats in different concentrations. Subchronic toxicity testing, high throughput 16S rRNA sequencing of gut microbiota, and examinations on gut metabolism and permeability were conducted. The results showed PC-hepc could be digested in simulated intestinal fluid but not in simulated gastric fluid. PC-hepc had no adverse effects on general health, except causing increase of blood glucose (still in the normal value range of this index) in all trial groups of female rats and intestinal inflammation in HD group of female rats. Community composition of gut microbiota of female MD and HD groups shifted compared with control group, of which the decrease of genus Akkermansia might be related to the increase of blood glucose and intestinal inflammation. Significant increase of fecal nitroreductase activity was also observed in female MD and HD groups. Our results suggest the uses of exogenous PC-hepc in normal dosage are safe, however excess dosage of it may cause intestinal disorder of animals.