Evaluation of arsenic pollution in field-contaminated soil at the soil's actual pH.

The pollution and ecological risks posed by arsenic (As) entering the soil are the major environmental challenges faced by human beings. Soil phosphatase can serve as a useful indicator for assessing As contamination under specific soil pH conditions. However, the study of phosphatase kinetics in long-term field As-contaminated soil remains unclear, presenting a significant obstacle to the monitoring and evaluation of As pollution and toxicity. The purpose of this study was to determine phosphatase activity and explore enzyme kinetics in soils subjected to long-term field As contamination. Results revealed that the soil phosphatase activity varied among the tested soil samples, depending on the concentrations of As. The relationship between total As, As fractions and phosphatase activity was found to be significant through negative exponential function fitting. Kinetic parameters, including maximum reaction velocity (Vmax), Michaelis constant (Km) and catalytic efficiency (Vmax/Km), ranged from 3.14 × 10-2-53.88 × 10-2 mmol/(L·hr), 0.61-7.92 mmol/L, and 0.46 × 10-2-11.20 × 10-2 hr-1, respectively. Vmax and Vmax/Km of phosphatase decreased with increasing As pollution, while Km was less affected. Interestingly, Vmax/Km showed a significant negative correlation with all As fractions and total As. The ecological doses (ED10) for the complete inhibition and partial inhibition models ranged from 0.22-70.33 mg/kg and 0.001-55.27 mg/kg, respectively, indicating that Vmax/Km can be used as an index for assessing As pollution in field-contaminated soil. This study demonstrated that the phosphatase kinetics parameters in the soil's pH system were better indicators than the optimal pH for evaluating the field ecotoxicity of As.

Soil pH determines arsenic-related functional gene and bacterial diversity in natural forests on the Taibai Mountain.

Arsenic-related functional genes are ubiquitous in microbes, and their distribution and abundance are influenced by edaphic factors. In arsenic-contaminated soils, soil arsenic content and pH determine the distribution of arsenic metabolizing microorganisms. In the uncontaminated natural ecosystems, however, it remains understudied for the key variable factor in determining the variation of bacterial assembly and mediating the arsenic biogeographical cycles. Here, we selected natural forest soils from southern and northern slopes along the altitudinal gradient of Taibai Mountain, China. The arsenic-related functional genes and soil bacterial community was examined using GeoChip 5.0 and high-throughput sequencing of 16S rRNA genes, respectively. It was found that arsenic-related functional genes were ubiquitous in tested forest soils. The gene arsB has the highest relative abundance, followed by arsC, aoxB, arrA, arsM, and arxA. The arsenic-related functional genes distribution on two slopes were decoupled from their corresponding bacterial community. Though there are higher abundance of bacterial communities on the northern slope than that on the southern slope, for arsenic-related functional genes, the abundance has the contrary trend which showing the more arsenic-related functional genes on the southern slope. In the top ten phyla, Proteobacteria and Actinobacteria were dominant phyla which affected the abundance of arsenic-related functional genes. Redundancy analysis and variance partitioning analysis indicated that soil pH, organic matter and altitude jointly determined the arsenic-related functional genes diversity in the two slopes of Taibai Mountain, and soil pH was a key factor. This indicates that the lower pH may shape more microbes with arsenic metabolic capacity. These findings suggested that soil pH plays a significant role in regulating the distribution of arsenic-related functional microorganisms, even for a forest ecosystem with an altitudinal gradient, and remind us the importance of pH in microbe mediated arsenic transformation.

Lactobacillus acidophilus ameliorates obesity in mice through modulation of gut microbiota dysbiosis and intestinal permeability.

Obesity associated with low-grade chronic inflammation and intestinal dysbiosis is considered as a worldwide public health crisis. In the meanwhile, different probiotics have demonstrated beneficial effects on this condition, thus increasing the interest in the development of probiotic treatments. In this context, the aim of this study is to investigate the anti-obesity effects of potential probiotic Lactobacillus acidophilus isolated from the porcine gut. Then, it is found that L. acidophilus reduces body weight, fat mass, inflammation and insulin resistance in mice fed with a high-fat diet (HFD), accompanied by activation in brown adipose tissue (BAT) as well as improvements of energy, glucose and lipid metabolism. Besides, our data indicate that L. acidophilus not only reverses HFD-induced gut dysbiosis, as indicated by the decreased Firmicutes-to-Bacteroidetes ratios and endotoxin bearing Gram-negative bacteria levels, but also maintains intestinal barrier integrity, reduces metabolic endotoxemia, and inhibits the TLR4 / NF- κB signaling pathway. In addition, the results of microbiome phenotype prediction by BugBase and bacterial functional potential prediction using PICRUSt show that L. acidophilus treatment improves the gut microbiota functions involving metabolism, immune response, and pathopoiesia. Furthermore, the anti-obesity effect is transmissible via horizontal faeces transfer from L. acidophilus-treated mice to HFD-fed mice. According to our data, it is seen that L. acidophilus could be a good candidate for probiotic of ameliorating obesity and associated diseases such as hyperlipidemia, nonalcoholic fatty liver diseases, and insulin resistance through its anti-inflammatory properties and alleviation of endothelial dysfunction and gut dysbiosis.

Time-course transcriptome analysis reveals the mechanisms of Burkholderia sp. adaptation to high phenol concentrations.

Microbial tolerance to phenolic pollutants is the key to their efficient biodegradation. However, the metabolic mechanisms that allow some microorganisms to adapt to high phenol concentrations remain unclear. In this study, to reveal the underlying mechanisms of how Burkholderia sp. adapt to high phenol concentrations, the strain's tolerance ability and time-course transcriptome in combination with cell phenotype were evaluated. Surprisingly, Burkholderia sp. still grew normally after a long adaptation to a relatively high phenol concentration (1500 mg/L) and exhibited some time-dependent changes compared to unstressed cells prior to the phenol addition. Time-course transcriptome analysis results revealed that the mechanism of adaptations to phenol was an evolutionary process that transitioned from tolerance to positive degradation through precise gene regulation at appropriate times. Specifically, basal stress gene expression was upregulated and contributed to phenol tolerance, which involved stress, DNA repair, membrane, efflux pump and antioxidant protein-coding genes, while a phenol degradation gene cluster was specifically induced. Interestingly, both the catechol and protocatechuate branches of the ß-ketoadipate pathway contributed to the early stage of phenol degradation, but only the catechol branch was used in the late stage. In addition, pathways involving flagella, chemotaxis, ATP-binding cassette transporters and two-component systems were positively associated with strain survival under phenolic stress. This study provides the first insights into the specific response of Burkholderia sp. to high phenol stress and shows potential for application in remediation of polluted environments. KEY POINTS: • Shock, DNA repair and antioxidant-related genes contributed to phenol tolerance. • ß-Ketoadipate pathway branches differed at different stages of phenol degradation. • Adaptation mechanisms transitioned from negative tolerance to positive degradation.

Soil enzyme kinetics indicate ecotoxicity of long-term arsenic pollution in the soil at field scale.

Information on the kinetic characteristics of soil enzymes under long-term arsenic (As) pollution in field soils is scarce. We investigated Michaelis-Menten kinetic properties of four soil enzymes including ß-glucosidase (BG), acid phosphatase (ACP), alkaline phosphatase (ALP), and dehydrogenase (DHA) in field soils contaminated by As resulting from long-term realgar mining activity. The kinetic parameters, namely the maximum reaction velocity (Vmax), enzyme-substrate affinity (Km) and catalytic efficiency (Vmax/Km) were calculated. Results revealed that the enzyme kinetic characteristics varied in soils and were significantly influenced by total nitrogen (N) and total As, which explained 31.8% and 30.7% of the variance in enzyme kinetics respectively. Enzyme pools (Vmax) and catalytic efficiency (Vmax/Km) of BG, ACP and DHA decreased with elevated As pollution, while the enzyme affinity for substrate (Km) was less affected. Redundancy analysis and stepwise regression suggested that the adverse influence of As on enzyme kinetics may offset or weakened by soil total N and soil organic matter (SOM). Concentration-response fitting revealed that the specific kinetic parameters expressed as the absolute enzyme kinetic parameters multiplied by normalized soil total N and SOM were more relevant than the absolute ones to soil total As. The arsenic ecological dose values that cause 10% decrease (ED10) in the specific enzyme kinetics were 20-49 mg kg-1, with a mean value of 35 mg kg-1, indicating a practical range of threshold for As contamination at field level. This study concluded that soil enzymes exhibited functional adaptation to long-term As stress mainly through the reduction of enzyme pools (Vmax) or maintenance of enzyme-substrate affinity (Km). Further, this study demonstrates that the specific enzyme kinetics are the better indicators of As ecotoxicity at field-scale compared with the absolute enzyme parameters.

Transcriptional analysis of the laccase-like gene from Burkholderia cepacia BNS and expression in Escherichia coli.

Bacterial laccases have received considerable attention because of several advantages associated with the higher environmental stability of these enzymes compared with fungal laccases. In this study, a laccase-like gene from Burkholderia cepacia BNS was successfully cloned. This gene was found to encode a mature protein of 279 amino acids that exhibited laccase activity in dimer form. The mature protein was found to contain approximately 4 mol of copper per monomer, and the metal ion-binding sites were predicted. BC_lacL gene transcription levels were analyzed by qRT-PCR to study expression patterns in the presence of different putative inducers (copper ions, guaiacol, veratryl alcohol, vanillin, coniferaldehyde, p-coumaric acid, sinapic acid, and ferulic acid). Copper ions had a positive effect on both transcription levels and intracellular laccase activity. Interestingly, upon induction with sinapic acid, BC_lacL gene transcription was lower than in the presence of copper ions, but laccase activity was highest under these conditions. The BC_lacL protein expressed in Escherichia coli exhibited a specific activity of 7.81 U/mg with 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as the substrate and 12.3 U/mg with 2,6-dimethoxyphenol (2,6-DMP) as the substrate after purification through Ni-affinity chromatography. The optimal activity and kinetic parameters of the recombinant BC_lacL protein were observed (kcat/Km = 3.96 s-1 µM-1) at a pH of 4.0 at 55 °C for ABTS oxidization and (kcat/Km = 11.6 s-1 µM-1) at a pH of 10.0 at 75 °C for 2,6-DMP oxidization. The protein exhibited high stability in an alkaline environment, with a half-life of more than 12 h. The same results were obtained via decolorization of eight dyes. Hence, this laccase-like enzyme may have potential industrial applications.

Catalytic efficiency is a better predictor of arsenic toxicity to soil alkaline phosphatase.

Arsenic (As) is an inhibitor of phosphatase, however, in the complex soil system, the substrate concentration effect and the mechanism of As inhibition of soil alkaline phosphatase (ALP) and its kinetics has not been adequately studied. In this work, we investigated soil ALP activity in response to As pollution at different substrate concentrations in various types of soils and explored the inhibition mechanism using the enzyme kinetics. The results showed that As inhibition of soil ALP activity was substrate concentration-dependent. Increasing substrate concentration decreased inhibition rate, suggesting reduced toxicity. This dependency was due to the competitive inhibition mechanism of As to soil ALP. The kinetic parameters, maximum reaction velocity (Vmax) and Michaelis constant (Km) in unpolluted soils were 0.012-0.267mMh-1 and 1.34-3.79mM respectively. The competitive inhibition constant (Kic) was 0.17-0.70mM, which was lower than Km, suggesting higher enzyme affinity for As than for substrate. The ecological doses, ED10 and ED50 (concentration of As that results in 10% and 50% inhibition on enzyme parameter) for inhibition of catalytic efficiency (Vmax/Km) were lower than those for inhibition of enzyme activity at different substrate concentrations. This suggests that the integrated kinetic parameter, catalytic efficiency is substrate concentration independent and more sensitive to As than ALP activity. Thus, catalytic efficiency was proposed as a more reliable indicator than ALP activity for risk assessment of As pollution.

Using Qmsax* to evaluate the reasonable As(V) adsorption on soils with different pH.

As a toxic metalloid element, arsenic (As) derived from human activities can pose hazardous risks to soil and water. The bioavailability of arsenic is influenced by its behavior, in particular its adsorption-desorption in the soil environment. The maximum adsorption amount (Qmax) calculated from Langmuir equation is an important parameter to estimate the adsorption capacity of adsorbents. However, the soil is a more complicated system compared with specific adsorbents. Thus, in this study, we tried to find a more reasonable parameter (Qmax*) to evaluate the adsorption capacity of soils. Eighteen Chinese soil samples with different pH were used for adsorption-desorption experiments. The maximum As(V) adsorption capacity calculated through Langmuir fitting for 18 samples were ranged from 50.25 (S13) to 312.50 (S4) mg kg-1. Besides, Qmax was highly related with soil pH. Using the difference value of adsorption amount and desorption amount to indicate the amount of non-electrostatic adsorption of As(V) onto soils, calculated the maximum adsorption amount of non-electrostatic adsorption (Qmax*). The average Qmax* of acidic and neutral soils was 162.18 mg kg-1 whereas that for alkaline soils it was only 79.52 mg kg-1. The result from multiple linear regression analysis showed Qmax* was strongly influenced by Feox and clay contents. Furthermore, hysteresis index (HI) in the As(V) desorption varied from 0.83 (S13) to 1.82 (S6). The results further indicated the risk of secondary pollution originating from the desorption process cannot be ignored.

Soil mineral alters the effect of Cd on the alkaline phosphatase activity.

The toxicity of heavy metals (HMs) to soil enzymes is directly influenced by the status of the enzyme (free vs. immobilized on minerals) and the duration of exposure. However, little information is available on the interaction effect of HMs, mineral, and exposure time on soil enzyme activities. We investigated the interaction mechanism of alkaline phosphatase (ALP) with minerals (montmorillonite and goethite) and the response of free and immobilized ALP to cadmium (Cd) toxicity under different exposure times. The adsorption isotherms of ALP on both minerals were L-type. The maximum adsorption capacity of goethite for ALP was 3.96 times than montmorillonite, although both had similar adsorption constant (K). Goethite showed a greater inhibitory effect on ALP activity than montmorillonite. The toxicity of Cd to free- and goethite-ALP was enhanced with increasing exposure time, indicating a time-dependent inhibition. However, Cd toxicity to montmorillonite-ALP was not affected by the exposure time. The inhibition of Cd to soil enzyme activity is influenced by the properties of mineral complexes and the duration of exposure. A further understanding of the time pattern of HMs toxicity is helpful for accurately assessing the hazards of HMs to soil enzyme activity.

Arsenic biotransformation in solid waste residue: comparison of contributions from bacteria with arsenate and iron reducing pathways.

Arsenic- and iron-reducing bacteria play an important role in regulating As redox transformation and mobility. The motivation of this study was to compare the contributions of different As- and Fe-reducing bacteria to As biotransformation. In this work, three bacteria strains with different functional genes were employed including Pantoea sp. IMH with the arsC gene, Alkaliphilus oremlandii OhILAs possessing the arrA gene, and Shewanella oneidensis MR-1, an iron reducer. The incubation results showed that Pantoea sp. IMH aerobically reduced 100% of As(V) released from waste residues, though total As release was not enhanced. Similarly, strain OhILAs anaerobically reduced dissolved As(V) but could not enhance As release. In contrast, strain MR-1 substantially enhanced As mobilization because of iron reduction, but without changing the As speciation. The formation of the secondary iron mineral pyrite in the MR-1 incubation experiments, as evidenced by the X-ray absorption near-edge spectroscopy (XANES) analysis, contributed little to the uptake of the freed As. Our results suggest that the arsC gene carriers mainly control the As speciation in the aqueous phase in aerobic environments, whereas in anaerobic conditions, the As speciation should be regulated by arrA gene carriers, and As mobility is greatly enhanced by iron reduction.

Prognostic implications of combining EGFR-TKIs and radiotherapy in Stage IV lung adenocarcinoma with 19-Del or 21-L858R mutations: A real-world study.

OBJECTIVE: To elucidate the potential benefits of combining radiotherapy and epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) for individuals with Stage IV lung adenocarcinoma (LUAD) harboring either exon 19 deletion (19-Del) or exon 21 L858R mutation (21-L858R). METHODS: In this real-world retrospective study, 177 individuals with Stage IV LUAD who underwent EGFR-TKIs and radiotherapy at Shandong Cancer Hospital from June 2012 to August 2017 were included. The main focus of this real-world study was overall survival (OS). RESULTS: The clinical characteristics of patients with Stage IV LUAD harboring 19-Del were similar to those harboring 21-L858R (p > 0.05). Overall, the patients had a median OS (mOS) of 32.0 months (95% confidence interval [CI]: 28.6-35.5). Subsequently, multivariate analysis indicated that both EGFR mutations and thoracic radiotherapy were independent predictors of OS (p = 0.001 and 0.013). Furthermore, subgroup analysis highlighted a longer OS for the 19-Del group compared to the 21-L858R group, especially when EGFR-TKIs were combined with bone metastasis or thoracic radiotherapy (mOS: 34.7 vs. 25.1 months and 51.0 vs. 29.6 months; p = 0.0056 and 0.0013, respectively). However, no significant differences were found in OS when considering patients who underwent brain metastasis radiotherapy (mOS: 34.7 vs. 25.1 months; p = 0.088). CONCLUSIONS: Patients with Stage IV LUAD harboring 19-Del experience a notably prolonged OS following combined therapy with EGFR-TKIs and radiotherapy, while this OS benefit is observed despite the absence of substantial differences in the clinical characteristics between the 19-Del and 21-L858R groups.

Arsenic stress on soil microbial nutrient metabolism interpreted by microbial utilization of dissolved organic carbon.

In a 120-day microcosm incubation experiment, we investigated the impact of arsenic contamination on soil microbial nutrient metabolism, focusing on carbon cycling processes. Our study encompassed soil basal respiration, key enzyme activities (particularly, ß-1,4-N-acetylglucosaminidase and phosphatases), microbial biomass, and community structure. Results revealed a substantial increase (1.21-2.81 times) in ß-1,4-N-acetylglucosaminidase activities under arsenic stress, accompanied by a significant decrease (9.86%-45.20%) in phosphatase activities (sum of acid and alkaline phosphatases). Enzymatic stoichiometry analysis demonstrated the mitigation of microbial C and P requirements in response to arsenic stress. The addition of C-sources alleviated microbial C requirements but exacerbated P requirements, with the interference amplitude increasing with the complexity of the C-source. Network analysis unveiled altered microbial nutrient requirements and an increased resistance process of microbes under arsenic stress. Microbial carbon use efficiency (CUE) and basal respiration significantly increased (1.17-1.59 and 1.18-3.56 times, respectively) under heavy arsenic stress (500 mg kg-1). Arsenic stress influenced the relative abundances of microbial taxa, with Gemmatimonadota increasing (5.5-50.5%) and Bacteroidota/ Nitrospirota decreasing (31.4-47.9% and 31.2-63.7%). Application of C-sources enhanced microbial resistance to arsenic, promoting cohesion among microorganisms. These findings deepen our understanding of microbial nutrient dynamics in arsenic-contaminated areas, which is crucial for developing enzyme-based toxicity assessment systems for soil arsenic contamination.

Characteristics of bacterial community and extracellular enzymes in response to atrazine application in black soil.

The ecological functioning of black soil largely depends on the activities of various groups of microorganisms. However, little is known about how atrazine, a widely used herbicide with known harmful effects on the environment, influences the microbial ecology of black soil, and the extracellular enzymes related to the carbon, nitrogen and phosphorus cycles. Here, we evaluated the change in extracellular enzymes and bacterial community characteristics in black soil after exposure to various concentrations of atrazine. Low concentrations of applied atrazine (10 - 20 mg kg-1) were almost completely degraded after 120 days. At high concentrations (80 - 100 mg kg-1), about 95% of the applied atrazine was degraded over the same period. Additionally, linear fitting of data indicated that the total enzymatic activity index (TEI) and bacterial α-diversity index were negatively correlated with atrazine applied concentration. The atrazine had a greater effect on bacterial beta diversity after 120 days, which differentiated species clusters treated with low and high atrazine concentrations. Soil bacterial community structure and function were affected by atrazine, especially at high atrazine concentrations (80 - 100 mg kg-1). Key microorganisms such as Sphingomonas and Nocardioides were identified as biomarkers for atrazine dissipation. Functional prediction indicated that most metabolic pathways might be involved in atrazine dissipation. Overall, the findings enhance our understanding of the factors driving atrazine degradation in black soil and supports the use of biomarkers as indicators of atrazine dissipation.

Berberine alleviates concanavalin A-induced autoimmune hepatitis in mice by modulating the gut microbiota.

BACKGROUND: Autoimmune hepatitis (AIH) is an immune-mediated liver disease of unknown etiology accompanied by intestinal dysbiosis and a damaged intestinal barrier. Berberine (BBR) is a traditional antibacterial medicine that has a variety of pharmacological properties. It has been reported that BBR alleviates AIH, but relevant mechanisms remain to be fully explored. METHODS: BBR was orally administered at doses of 100 mg⋅kg-1⋅d-1 for 7 days to mice before concanavalin A-induced AIH model establishment. Histopathological, immunohistochemical, immunofluorescence, western blotting, ELISA, 16S rRNA analysis, flow cytometry, real-time quantitative PCR, and fecal microbiota transplantation studies were performed to ascertain BBR effects and mechanisms in AIH mice. RESULTS: We found that liver necrosis and apoptosis were decreased upon BBR administration; the levels of serum transaminase, serum lipopolysaccharide, liver proinflammatory factors TNF-α, interferon-γ, IL-1ß, and IL-17A, and the proportion of Th17 cells in spleen cells were all reduced, while the anti-inflammatory factor IL-10 and regulatory T cell proportions were increased. Moreover, BBR treatment increased beneficial and reduced harmful bacteria in the gut. BBR also strengthened ileal barrier function by increasing the expression of the tight junction proteins zonula occludens-1 and occludin, thereby blocking lipopolysaccharide translocation, preventing lipopolysaccharide/toll-like receptor 4 (TLR4)/ NF-κB pathway activation, and inhibiting inflammatory factor production in the liver. Fecal microbiota transplantation from BBR to model mice also showed that BBR potentially alleviated AIH by altering the gut microbiota. CONCLUSIONS: BBR alleviated concanavalin A-induced AIH by modulating the gut microbiota and related immune regulation. These results shed more light on potential BBR therapeutic strategies for AIH.

Fate of Arsenate adsorbed on Nano-TiO2 in the presence of sulfate reducing bacteria.

Arsenic removal using nanomaterials has attracted increasing attention worldwide, whereas the potential release of As from spent nanomaterials to groundwater in reducing environments is presently underappreciated. This research investigated the fate of As(V) adsorbed on nano-TiO2 in the presence of sulfate reducing bacteria (SRB) Desulfovibrio vulgaris strains DP4 and ATCC 7757. The incubation results demonstrated that As(V) was desorbed from nano TiO2, and subsequently reduced to As(III) in aqueous solution. The release of adsorbed As(V) was two to three times higher in biotic samples than that in abiotic controls. Reduction of As(V) to As(III) in biotic samples was coupled with the conversion of sulfate to sulfide, while no As(III) was observed in abiotic controls. STXM results provided the direct evidence of appreciable As(III) and As(V) on TiO2. XANES analysis indicated that As(V) was the predominant species for three As loads of 150, 300, and 5700 mg/g, whereas 15-28% As precipitated as orpiment for a high As load of 5700 mg/g. In spite of orpiment formation, As mobilized in higher amounts in the SRB presence than in abiotic controls, highlighting the key role of SRB in the fate of As in the presence of nanomaterials.

Arsenic mobilization in nZVI residue by Alkaliphilus sp. IMB: Comparison between static and flowing incubation.

Arsenate reducing bacteria (AsRB) enhance arsenic (As) release via reducing As(V) to As(III), and As mobility is usually controlled by As(III) re-uptake on in-situ formed secondary iron minerals. The re-uptake of As(III) under groundwater flow conditions significantly impacts the fate and transport of As. Herein, a novel As(V)-reducing bacterium Alkaliphilus IMB was isolated in an As-contaminated soil. Scanning transmission X-ray microscopy showed that dissolved As(V) was mainly bound to the cell walls whereas dissolved As(III) was homogeneously distributed around IMB, indicating that As(V) reduction occurs outside the cell membrane. To explore the effect of IMB on As mobility, IMB was incubated with As-loaded nanoscale zero-valent iron (nZVI) residues under static and flowing conditions. IMB reduced 100% dissolved As(V) to As(III) even in a short contact time (∼1 h) during flowing incubation. The formation of As(III) did not influence As mobility under static condition as evidenced by the comparable concentrations of released As in the presence of IMB (8.5% to total As) and the abiotic control (10% to total As). Biogenic As(III) was re-adsorbed on the solids as shown by the higher ratio of solid-bound As(III) to total As in the presence of IMB (54%) than that in the abiotic control (12%). By contrast, the degree of As(III) re-adsorption was inhibited in the flowing environment, as suggested by the lower As(III) ratio in the solid (31%). This inhibition can be ascribed to the relatively slow adsorption of As(III) compared with the quick reduction of As(V) (∼1 h). Thus, IMB significantly enhanced As release during flowing incubation as shown that 9.8% As was released in the presence of IMB while 2.1% As in the abiotic control. This study found the contrary effect of AsRB on As mobility in static and flowing environments, highlighting the importance of re-adsorption rate of As(III).

Using soil enzyme Vmax as an indicator to evaluate the ecotoxicity of lower-ring polycyclic aromatic hydrocarbons in soil: Evidence from fluorescein diacetate hydrolase kinetics.

Fluorescein diacetate hydrolase (FDA hydrolase) is a reliable biochemical biomarker of changes in soil microbial activity and quality. However, the effect and mechanism of lower-ring polycyclic aromatic hydrocarbons (PAHs) on soil FDA hydrolase are still unclear. In this work, we investigated the effects of two typical lower-ring PAHs, naphthalene (Nap) and anthracene (Ant), on the activity and kinetic characteristics of FDA hydrolases in six soils differing in their properties. Results demonstrated that the two PAHs severely inhibited the activities of the FDA hydrolase. The values of Vmax and Km dropped by 28.72-81.24 % and 35.84-74.47 % at the highest dose of Nap, respectively, indicating an uncompetitive inhibitory mechanism. Under Ant stress, the values of Vmax decreased by 38.25-84.99 %, and the Km exhibited two forms, unchanged and decreased (74.00-91.61 %), indicating uncompetitive and noncompetitive inhibition. The inhibition constant (Ki) of the Nap and Ant ranged from 0.192 to 1.051 and 0.018 to 0.087 mM, respectively. The lower Ki of Ant compared to Nap indicated a higher affinity for enzyme-substrate complex, resulting in higher toxicity of Ant than Nap to soil FDA hydrolase. The inhibitory effect of Nap and Ant on soil FDA hydrolase was mainly affected by soil organic matter (SOM). SOM influenced the affinity of PAHs with enzyme-substrate complex, which resulted in a difference in PAHs toxicity to soil FDA hydrolase. The enzyme kinetic Vmax was a more sensitive indicator than enzyme activity to evaluate the ecological risk of PAHs. This research offers a strong theoretical foundation for quality control and risk evaluation of PAH-contaminated soils through a soil enzyme-based approach.

Respecting catalytic efficiency of soil arylsulfatase as soil Sb contamination bio-indicator by enzyme kinetic strategy.

Antimony (Sb), a toxic metalloid, is ubiquitous in the environment and threatens human and ecological health. Soil arylsulfatase (ARS) activity indicates heavy metal pollution. However, the enzyme's substrate concentration can affect the toxicity evaluation of heavy metals using enzyme activity. Enzyme kinetic parameters directly reflect the potency of heavy metals, and the magnitude of these parameters does not change with the substrate concentration of soil enzyme. In this work, seventeen soils were exposed to Sb contamination to investigate the change of kinetic parameters of soil arylsulfatase under Sb stress. Results showed that Sb inhibited soil arylsulfatase activity. The maximum reaction rate (Vmax) of soil arylsulfatase was reduced by 11.58-46.72% in 16 tested soils and unchanged in S15 when exposed to Sb. The Michaelis constant (Km) presented three trends: unchanged, increased by 28.46-41.27%, and decreased by 19.71-29.91% under Sb stress. The catalytic efficiency (Ka as the ratio of Vmax to Km) decreased by 12.56-55.17% in all soils except for S12 and S16. Antimony acted as a non-competitive and linear mixed inhibitor by decreasing ARS activity in S1-S12, S14, and S17-S18 soils, as an uncompetitive inhibitor in S13 and S16 soils and as a competitive inhibitor in S15. The competitive and uncompetitive inhibition constants (Kic and Kiu) were 0.058-0.142 mM and 0.075-0.503 mM. The ecological dose values of Sb to catalytic efficiency (Ka) of ARS (ED10-Ka) ranged from 50 to 1315 mg kg-1. Soil pH and total phosphorus (TP) contents were the dominant factors responsible for Sb toxicity on Ka by affecting the interaction of inhibitor (Sb) with enzyme-substrate (ES) complex. The findings of this study advance the current knowledge on Sb toxicity to soil enzymes and have significant implications for the risk assessment of Sb in soils.

Ecotoxicity of soil Pb pollution reflected by soil ß-glucosidase: Comparison of extracellular and intracellular enzyme pool.

Lead (Pb) is a major environmental pollutant that threatens the soil environment and human health. Monitoring and assessing Pb toxicity on soil health are of paramount importance to the public. To use soil enzymes as biological indicators of Pb contamination, herein, the responses of soil ß-glucosidase (BG) in different pools of soil (total, intracellular and extracellular enzyme) to Pb contamination were investigated. The results indicated that the intra-BG (intracellular BG) and extra-BG (extracellular BG) responded differently to Pb contamination. While the addition of Pb caused a significant inhibition of the intra-BG activities, the extra-BG activities were only slightly inhibited. Pb showed a non-competitive inhibition to extra-BG, while both non-competitive and uncompetitive inhibition were observed for intra-BG in the tested soils. The dose-response modeling was used to calculate ecological dose ED10, which represents the concentration of Pb pollutant that causes a 10 % reduction in Vmax, to express the ecological consequences of Pb contamination. A positive correlation was found between ecological dose ED10 values of intra-BG and soil total nitrogen (p < 0.05), which suggests soil properties may influence Pb toxicity to soil BG. Based on the differences in ED10 and inhibition rate among different enzyme pools, this study suggests that the intra-BG is more sensitive for Pb contamination assessment. From this, we propose that intra-BG should be considered when evaluating Pb contamination using soil enzymes as indicators.

Soil phosphatase assay to evaluate arsenic toxicity should be performed at the soil's actual pH.

Soil phosphatase is considered an indicator to assess soil arsenic (As) pollution. In the phosphatase activity determination, a fixed buffer value (pH 5-10) is commonly used for all soils, ignoring the soil's actual pH. Here, we determined the soil phosphatase activity of 20 soils under As stress at the soils' pH, and the As inhibition mechanism was also explored by the enzyme kinetics. Our results show that soil phosphatase activity was significantly inhibited under As stress. The inhibition rate in acid soils (39.2 %) was considerably higher than in alkaline soils (25.4 %) when As concentration was 600 mg kg-1. For alkaline soils, As inhibited phosphatase by competitive inhibition or linear mixed inhibition, while for acid soils, it was more complex, including linear mixed inhibition, non-competitive inhibition, and anti-competitive inhibition. Simultaneously, our results showed that the ecological dose (ED10) described by the partial inhibition model was far below than the complete inhibition model. According to the partial inhibition model, the ED10 of As ranged from 2.66 to 164.07 mg kg-1 for alkaline soils and 0.11 to 89.95 mg kg-1 for acid soils. Moreover, Vmax/Km of phosphatase is a more sensitive index for evaluating As contamination than Vmax in partial inhibition models. The ED10 obtained based on the relationship between Vmax/Km and As concentration was 0.64-34.75 mg kg-1 for acid soils and 8.48 to 20.16 mg kg-1 for alkaline soils. This also confirms Vmax/Km as a sensitive and ideal index for assessing As pollution under soils' actual pH. Furthermore, soil pH and cation exchange capacity are dominant factors affecting As inhibition on soil phosphatase. The above kinetic studies indicate that performing the assay by adjusting the buffer pH to the soil pH is essential for more accurately evaluating arsenic toxicity.