The impacts of different long-term fertilization regimes on the bioavailability of arsenic in soil: integrating chemical approach with Escherichia coli arsRp::luc-based biosensor

Effects of microorganisms on the migration and transformation of typical heavy metal (loid)s in mercury-thallium mining waste slag during the combined application of fish manure and natural minerals

Mercury-thallium mining waste slag has the characteristics of extremely acidic, low fertility and highly toxic polymetallic composite pollution, making it difficult to be treated. We use nitrogen- and phosphorus-rich natural organic matter (fish manure) and calcium- and phosphorus-rich natural minerals (carbonate and phosphate tailings) individually or in combination to amend the slag, analyze their effects on the migration and transformation of potentially toxic elements (Tl and As) in the waste slag. We set up sterile and non-sterile treatments specifically to further investigate the direct or indirect effect of microorganisms attached to added organic matter on Tl and As. The results showed that addition of fish manure and natural minerals to the non-sterile treatments promoted the release of As and Tl, resulting in an increase in As and Tl concentrations in the tailing lixiviums from 0.57 to 2.38-6.37 μg/L and from 69.92 to 107.51-157.21 μg/L, respectively. Sterile treatments promoted the release of As (from 0.28 to 49.88-104.18 μg/L) and inhibited the release of Tl (from 94.53 to 27.60-34.50 μg/L). Use of fish manure and natural minerals alone or in combination significantly reduced the biotoxicity of the mining waste slag, in which the combination was more efficient. XRD analysis showed that microorganisms in the medium promoted the dissolution of jarosite and other minerals, which indicated that the release and migration of As and Tl in Hg-Tl mining waste slag were closely related to microbial activities. Furthermore, metagenomic sequencing revealed that microorganisms such as Prevotella, Bacteroides, Geobacter, and Azospira, which were abundant in the non-sterile treatments, had remarkable resistance to a variety of highly toxic heavy metals and could affect the dissolution of minerals and the release and migration of heavy metals through redox reactions. Our results may aid in the rapid soilless ecological restoration of related large multi-metal waste slag dumps.

Genetic circuits in microbial biosensors for heavy metal detection in soil and water

With the rapid population growth, the world is witnessing an ever-increasing demand for energy and natural resources. Consequently, soil, air, and water are polluted with diverse pollutants, including heavy metals (HM). The detection of heavy metals is necessary to remediate them, which is achieved with biosensors. Initially, these HM were detected using atomic absorption spectroscopy (AAS), emission spectroscopy, mass spectrometry, gas chromatography etc., but these were costly and time consuming which further paved a way for microbe-based biosensors. The development of genetic circuits for microbe-based biosensors has become more popular in recent years for heavy metal detection. In this review, we have especially discussed the various types of genetic circuits such as toggle switches, logic gates, and amplification modules used in these biosensors as they are used to enhance sensitivity and specificity. Genetic circuits also allow for rapid and multiple analyte detection at the same time. The use of microbial biosensors for the detection of HM in the soil as well as the water is also described below. Although with a higher success rate than classical biosensors, these microbial biosensors still have some drawbacks like bioavailability and size of the analyte which are needed to be addressed.

Exploring the abundance and influencing factors of antimicrobial resistance genes in manure plasmidome from swine farms

Plasmids play a critical role in the dissemination of antimicrobial resistance genes (ARGs), however, a systematical understanding of ARGs originated from plasmids in swine production is currently lacking. Herein, quantitative polymerase chain reaction was applied to determine the prevalence of ten ARGs and the class1 integron gene intI1 of plasmid source in swine manure from 44 farms in Sichuan, Hubei and Hebei provinces, China. All assayed ARGs were observed in plasmid DNA samples, and the average absolute abundance of aac(6')-Ib-cr, bla_NDM, bla_CTX-M, optrA, ermB, floR, mcr-1, qnrS, tetM, sul1 and intI1 were 7.09, 2.90, 4.67, 6.62, 7.55, 7.14, 4.08, 4.85, 7.16, 7.11 and 8.07 of 10 log copies/gram, respectively. IntI1 showed a high correlation (r > 0.8, P < 0.01) with the abundance of aac(6')-Ib-cr and sul1 in swine manure. Moreover, the farm scale (i.e., herd population) and geographical location were not found to be critical factors influencing the absolute abundance of ARGs of plasmid DNA in swine farms. However, the concentrations of florfenicol, Cu, Zn, Fe, total phosphorus (TP) and total potassium (TK) demonstrated a significant correlation with the abundance of several ARGs. Particularly, Cu and Zn had high correlations with optrA and bla_CTX-M, respectively. Our results demonstrated that antibiotics, heavy metals and environmental nutrients are likely jointly contributing to the long-term persistence of ARGs in swine production. This study provides insights into the abundance and influencing factors of ARGs from swine manure, which is of significance for assessing and reducing the public health risks in livestock production.

Zero valent iron nanoparticles and organic fertilizer assisted phytoremediation in a mining soil: Arsenic and mercury accumulation and effects on the antioxidative system of Medicago sativa L

Zero valent iron nanoparticles (nZVI) attract interest given their effectiveness in soil remediation. However, little attention has been given to their impacts on plants. Likewise, although fertilizers are commonly used to enhance phytoremediation, their effects on As mobilization, resulting in potential toxic effects, require further study. In this context, we examined the impact of As and Hg accumulation on the antioxidative system of Medicago sativa grown in a soil amended with organic fertilizer and/or nZVI. The experiment consisted of 60 pots. Plants were pre-grown and transferred to pots, which were withdrawn along time for monitoring purposes. As and Hg were monitored in the soil-plant system, and parameters related to oxidative stress, photosynthetic pigments, and non-protein thiol compounds (NPTs) were measured. In general, the application of nZVI immobilized As in soil and increased Hg accumulation in the plant, although it surprisingly decreased oxidative stress. Plants in nZVI-treated soil also showed an increase in NPT content in roots. In contrast, the application of the fertilizer mobilized As, thereby improving bioaccumulation factors. However, when combining fertilizer with nZVI, the As accumulation is mitigated. This observation reveals that simultaneous amendments are a promising approach for soil stabilization and the phytomanagement of As/Hg-polluted soils.

Recent Advances in Chemical Sensors for Soil Analysis: A Review

The continuously rising interest in chemical sensors’ applications in environmental monitoring, for soil analysis in particular, is owed to the sufficient sensitivity and selectivity of these analytical devices, their low costs, their simple measurement setups, and the possibility to perform online and in-field analyses with them. In this review the recent advances in chemical sensors for soil analysis are summarized. The working principles of chemical sensors involved in soil analysis; their benefits and drawbacks; and select applications of both the single selective sensors and multisensor systems for assessments of main plant nutrition components, pollutants, and other important soil parameters (pH, moisture content, salinity, exhaled gases, etc.) of the past two decades with a focus on the last 5 years (from 2017 to 2021) are overviewed.

Development of a whole-cell biosensor based on an ArsR-P ars regulatory circuit from Geobacter sulfurreducens

In this study, an Escherichia coli (E. coli) whole-cell biosensor for the specific detection of bioavailable arsenic was developed by placing a green fluorescent protein (GFP) reporter gene under the control of the ArsR1 (GSU2952) regulatory circuit from Geobacter sulfurreducens. E. coli cells only emitted green fluorescence in the presence of arsenite and were more sensitive to arsenite when they were grown in M9 supplemented medium compared to LB medium. Under optimal test conditions, the Geobacter arsR1 promoter had a detection limit of 0.01 μM arsenite and the GFP expression was linear within a range of 0.03-0.1 μM (2.25-7.5 μg/l). These values were well below World Health Organization's drinking water quality standard, which is 10 μg/l. The feasibility of using this whole-cell biosensor to detect arsenic in water samples, such as arsenic polluted tap water and landfill leachate was verified. The biosensor was determined to be just as sensitive as atomic fluorescence spectrometry. This study examines the potential applications of biosensors constructed with Geobacter ArsR-P _ars regulatory circuits and provides a rapid and cost-effective tool that can be used for arsenic detection in water samples.

Whole-Cell Microbial Bioreporter for Soil Contaminants Detection

Anthropogenic activities have released various contaminants into soil that pose a serious threat to the ecosystem and human well-being. Compared to conventional analytical methodologies, microbial cell-based bioreporters are offering a flexible, rapid, and cost-effective strategy to assess the environmental risks. This review aims to summarize the recent progress in the application of bioreporters in soil contamination detection and provide insight into the challenges and current strategies. The biosensing principles and genetic circuit engineering are introduced. Developments of bioreporters to detect and quantify heavy metal and organic contaminants in soil are reviewed. Moreover, future opportunities of whole-cell bioreporters for soil contamination monitoring are discussed.

Long-Term Manure Application Changes Bacterial Communities in Rice Rhizosphere and Arsenic Speciation in Rice Grains

Bioavailability and speciation of arsenic (As) are impacted by fertilization and bacteria in the rice rhizosphere. In this study, we investigated the effects of long-term manure application on As bioavailability, microbial community structure, and functional genes in a rice paddy field. The results showed that manure application did not affect total As in the soil but increased soluble As forms by 19%, increasing arsenite (As(III)) accumulation in rice grains and roots by 34 and 64% compared to a control. A real-time quantitative polymerase chain reaction (qPCR) and high-throughput sequencing analysis demonstrated that manure application increased the relative abundance of Rhizobium, Burkholderia, Sphingobium, and Sphingomonas containing arsenate reductase genes (arsC) in the rhizosphere soil, consistent with the 529% increase in arsC, which may have promoted arsenate (As(V)) reduction and increased As availability in pore water. In addition, manure application significantly altered the iron (Fe)-plaque microbial community structure and diversity. The microbes, particularly, Bradyrhizobium, Burkholderia, and Ralstonia, were mostly associated with As, Fe, and sulfur (S) cycles. This result was consistent with changes in the functional genes related to As, Fe, and S transformation. Although manure application promoted As(V) reduction (arsC) in Fe-plaque by 682%, it inhibited Fe and S reduction by decreasing Fe^III reduction bacteria (Geobacteraceae) and the sulfate-reducing gene (dsrA) abundance. Further, manure application changed the composition of the microbial community that contained the arsC gene. In short, caution needs to be excised even in the soil with a low As concentration as manure application increased As(III) accumulation in rice grains.

Variation of antibiotic resistome during commercial livestock manure composting

Composting has been widely used to turn livestock manure into organic fertilizer. However, livestock manure contains various contaminants including antibiotics and antibiotic resistance genes (ARGs). Here we investigated the variation of antibiotic resistome and its influencing factors during a commercial livestock manure composting. The results showed that composting could effectively reduce the relative abundance of ARGs and mobile genic elements (MGEs). As the dominant phylum in the composting samples, the key potential bacterial host of ARGs were Actinobacteria such as Leucobacter, Mycobacterium and Thermomonosporaceae unclassified. Meanwhile, Legionella pneumophila, Staphylococcus saprophyticus, Haemophilus ducreyi and Siccibacter turicensis may be the key potential pathogenic host of ARGs because of their co-occurrence with ARG subtypes. Redundancy analysis showed that the dissipation of ARGs during composting was linked to various environmental factors such as moisture. Bacterial succession as well as profile of biocide and metal resistance genes (BMRGs) were the determinants which constructed the antibiotic resistome during manure composting. However, the residues of ARGs and pathogens in compost products may still pose risks to human and crops after fertilization.

Sensitive and Specific Whole-Cell Biosensor for Arsenic Detection

Whole-cell biosensors (WCBs) have been designed to detect As(III), but most suffer from poor sensitivity and specificity. In this paper, we developed an arsenic WCB with a positive feedback amplifier in Escherichia coli DH5α. The output signal from the reporter mCherry was significantly enhanced by the positive feedback amplifier. The sensitivity of the WCB with positive feedback is about 1 order of magnitude higher than that without positive feedback when evaluated using a half-saturation As(III) concentration. The minimum detection limit for As(III) was reduced by 1 order of magnitude to 0.1 µM, lower than the World Health Organization standard for the arsenic level in drinking water, 0.01 mg/liter or 0.13 µM. Due to the amplification of the output signal, the WCB was able to give detectable signals within a shorter period, and a fast response is essential for in situ operations. Moreover, the WCB with the positive feedback amplifier showed exceptionally high specificity toward As(III) when compared with other metal ions. Collectively, the designed positive feedback amplifier WCB meets the requirements for As(III) detection with high sensitivity and specificity. This work also demonstrates the importance of genetic circuit engineering in designing WCBs, and the use of genetic positive feedback amplifiers is a good strategy to improve the performance of WCBs.IMPORTANCE Arsenic poisoning is a severe public health issue. Rapid and simple methods for the sensitive and specific monitoring of arsenic concentration in drinking water are needed. In this study, we designed an arsenic WCB with a positive feedback amplifier. It is highly sensitive and able to detect arsenic below the WHO limit level. In addition, it also significantly improves the specificity of the biosensor toward arsenic, giving a signal that is about 10 to 20 times stronger in response to As(III) than to other metals. This work not only provides simple but effective arsenic biosensors but also demonstrates the importance of genetic engineering, particularly the use of positive feedback amplifiers, in designing WCBs.

Metals in Soil and Runoff from a Piedmont Hay Field Amended with Broiler Litter and Flue Gas Desulfurization Gypsum

Flue gas desulfurization gypsum (FGDG) from coal-fired power plants is readily available for agricultural use in many US regions. Broiler litter (BL) provides plant available N, P, and K but can be a source of unwanted As, Cu, and Zn. As a source of Ca and S, FGDG can reduce losses of P and other elements in runoff from BL-amended areas. Rainfall simulation plots (2.0 m) were established on a Piedmont Cecil soil growing 'Coastal' bermudagrass ( L.) for hay. Accumulation and transport of As, Cu, Cd, Cr, Hg, Pb, and Zn were evaluated after annual BL applications (13.5 Mg ha) with four FGDG rates (0, 2.2, 4.5, 9.0 Mg ha) and two FGDG treatments (0 and 9 Mg ha) without BL. Runoff As concentrations were sixfold greater with BL than without ( ≤ 0.01) and were similar to BL with FGDG at 2.2, 4.5 or 9.0 Mg ha ( ≤ 0.10). Runoff concentrations of target elements did not increase where FGDG was applied alone. After three annual applications of FGDG and BL, soil concentrations of As, Cr, Pb, Hg, and Cu were well below levels of environmental concern. Our findings indicate that runoff losses of As from BL application are not reduced with FGDG but support other research indicating no identifiable environmental risks from FGDG beneficial use in agricultural systems.

The behavior of antibiotic resistance genes and arsenic influenced by biochar during different manure composting

The effect of two different biochar types, rice straw biochar (RSB) and mushroom biochar (MB), on chicken manure composting was previously examined by monitoring the fate of antibiotic resistance genes (ARGs) and arsenic. The behavior of ARGs and arsenic in other kinds of manure composting with the same biochar types had not been examined. In this study, we added either RSB or MB to pig and duck manure composts to study the behavior of ARGs (tet genes, sul genes, and chloramphenicol resistance genes) and arsenic under the same experimental condition. The results showed that the average removal values of selected ARGs were respectively 2.56 and 2.09 log units in duck and pig manure compost without the addition of biochar. The effect of biochar addition on the average removal value of ARGs depended on the type of biochar and manure. For instance, in pig manure compost, MB addition increased the average removal value of ARGs, while RSB addition decreased. And both biochar additions had a negative influence on the average removal value of ARGs in duck manure compost. Analytical results also demonstrated that MB addition reduced total arsenic and the percentage of bioavailable arsenic more than RSB.

Detection of bioavailable cadmium, lead, and arsenic in polluted soil by tailored multiple Escherichia coli whole-cell sensor set

Microbial whole-cell sensor has been widely used to assess bioavailability and risk of toxic elements, but their environmental use is still limited due to the presence of other interfering pollutants and the nonspecific binding in cells, which leads to inaccurate results. Here, we proposed a strategy combining Escherichia coli sensor set with binary regression models for the specific detection of bioavailable cadmium (Cd), lead (Pb), and arsenic (As) in a co-polluted environment. Initial tests suggested that the sensor set respectively termed pcadCluc, pzntRluc, and parsRluc could be classified into two groups according to their specific response to Cd, Pb, and As: group 1 (pcadCluc and pzntRluc) induced by a Cd-Pb mix and group 2 (parsRluc) induced by a Cd-As mix. Based on the variance in responses of each sensor to mixtures of target elements, three binary linear equations for two sensor groups were set up to calculate the individual concentrations in the mixture solutions. This method was then used to quantify the bioavailable Cd, Pb, and As in soils from a co-polluted mining region and to compare the results with other methods. Results showed that the conventional single target sensor method overestimated the bioavailability of each element, while sensor set was credible for accurate bioavailable Cd, Pb, and As quantification and comparable with the results from inductively coupled plasma mass spectrometry (ICP-MS) analysis. Our method can potentially be extended to cover the specific detection of other bioavailable toxic elements in different environmental settings.

Thin and ordered hydrogel films deposited through electrospinning technique; a simple and efficient support for organic bilayers

Thermal behavior of Dipalmitoylphosphatidylcholine (DPPC) bilayers deposited over hydrogel fibers was examined. Thus, membrane stability, water absorption-release, phase transitions and phase transition temperatures were studied through different methods during heating cycles. Hydrogel films were realized using an oligomer mixture (HEMA-PEGDA575/photo-initiator) with adequate viscosity. Then, the fibers were deposited over silicon wafers (hydrophilic substrate) through electrospinning technique using four different voltages: 15, 20, 25 and 30 kV. The films were then exposed to UV light, favoring polymer chain crosslinking and interactions between hydrogel and substrate. For samples deposited at 20 and 25 kV, hierarchical wrinkle folds were observed at surface level, their arrangement distribution depends directly on thickness and associated point defects. DPPC bilayers were then placed over hydrogel scaffold using Langmuir-Blodgett technique. Field emission scanning electron microscopy (FE-SEM) analysis were used to investigate sample surface, micrographies show homogeneous layer formation with chain polymer order/disorder related to applied voltage during hydrogel deposition process, among other parameters. According to the results obtained, it is possible to conclude that the oligomer deposited at 20 kV produce thin homogenous films (~40 nm) with enhanced ability to absorb water and release it in a controlled way during heating cycles. These scaffold properties confer to DPPC membrane thermal stability, which allow an easy detection of phase(s) and phase transitions. Thermal behavior was also studied via Atomic Force Microscopy (roughness analysis). Contact angle measurements corroborate system wettability, supporting the theory that hydrogel thin films act as DPPC membrane enhancers for thermal stability against external stimuli.

Advances in arsenic biosensor development--a comprehensive review

Biosensors are analytical devices having high sensitivity, portability, small sample requirement and ease of use for qualitative and quantitative monitoring of various analytes of human importance. Arsenic (As), owing to its widespread presence in nature and high toxicity to living creatures, requires frequent determination in water, soil, agricultural and food samples. The present review is an effort to highlight the various advancements made so far in the development of arsenic biosensors based either on recombinant whole cells or on certain arsenic-binding oligonucleotides or proteins. The role of futuristic approaches like surface plasmon resonance (SPR) and aptamer technology has also been discussed. The biomethods employed and their general mechanisms, advantages and limitations in relevance to arsenic biosensors developed so far are intended to be discussed in this review.