Deciphering the bacterial microbiome in response to long-term mercury contaminated soil.

Hg contaminated soils are of concern due to the toxic effects on soil microbes. Currently, the adaptation of bacterial community to long-term Hg contamination remains largely unknown. Here, we assessed the effects of Hg contaminated soils on the bacterial communities under controlled conditions using 16S rRNA gene amplicon sequencing. The results showed that the bacterial α-diversity and richness were significant positively correlated with total Hg (p < 0.05). Land-use type, pH, EC, TK, and nitrate-N played important roles in shaping the bacterial communities. Long-term Hg-contaminated soils can be divided into three types based on land use types: slag type, farmland type, and mining area type. The dominant phyla include Proteobacteria, Actinobacteriota, Acidobacteriota, Chloroflexi, and Firmicutes. The dominant genera identified were Pseudomonas, Gaiella, Sphingomonas, Bacillus, Arthrobacter, Nocardioides. Network analysis showed that dominant taxa had non-random co-occurrence patterns and module 1 had an important role in responding Hg stress. Keystone genera identified were Bauldia, Phycicoccus, Sphingomonas, Gaiella, Nitrospira. The above results further our understanding of the adaptation of the bacterial community in long-term Hg-contaminated soil. This study has important guiding significance for the use of bacterial consortia to remediate Hg-contaminated soil.

Characterization of cadmium-resistant rhizobacteria and their promotion effects on Brassica napus growth and cadmium uptake.

Excessive cadmium (Cd) accumulation in soil can adversely affect plants, animals, microbes, and humans; therefore, novel and uncharacterized Cd-resistant plant-growth-promoting rhizobacteria (PGPR) are required to address this issue. In the paper, 13 bacteria were screened, their partial 16S rRNA sequences determined, and the isolates, respectively, clustered into Curtobacterium (7), Chryseobacterium (4), Cupriavidus (1), and Sphingomonas (1). Evaluation of PGP traits, including indole-3-acetic acid (IAA) production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, siderophore secretion, and cyanhydric acid production, identified Cupriavidus necator GX_5, Sphingomonas sp. GX_15, and Curtobacterium sp. GX_31 as promising candidates for PGPR based on high IAA or ACC deaminase production. Additionally, root-elongation assays indicated that inoculating GX_5, _15, or _31 increased Brassica napus root length both in the presence and absence of Cd by 19.75-29.96% and 19.15-31.69%, respectively. Pot experiments indicated that inoculating B. napus with GX_5, _15, and _31 significantly increased the dry weight of above-ground tissues and root biomass by 40.97-85.55% and 18.99-103.13%, respectively. Moreover, these isolates significantly increased Cd uptake in the aerial parts and root tissue of B. napus by 7.38-11.98% and 48.09-79.73%, respectively. These results identified GX_5, _15, or _31 as excellent promoters of metal remediation by using microorganism-associated phytoremediation.

Metal-promoted intermolecular electron transfer in tetrathiafulvalene-thiacalix[4]arene conjugates and tetrachlorobenzoquinone.

In this work, two series of tetrathiafulvalene (TTF) and thiacalix[4]arene (TCA) conjugates (TTF-TCA) were designed by CuAAC click reactions. The results obtained from NMR and (1)H NMR NOE indicated that their conformations of thiacalix[4]arene framework may prefer to 1,3-alternate. The cyclic voltammograms of four TTF-TCA compounds containing electroactive TTF units were provided. Meanwhile, their intermolecular electron-transfer (ET) behaviors with tetrachlorobenzoquinone (Q) mediated by different metal ions, Sc(3+), Pb(2+), Ag(+), Cd(2+), and Zn(2+), in CH3CN-CH2Cl2 (V/V = 1:1) solution were studied and analyzed via UV-vis spectroscopy. It was determined that intermolecular ET between each TTF-TCA and Q ensemble was not observed without introduction of the metal ions mentioned above. The added specified metal ions most likely induced the intermolecular ET between TTF-TCA and Q ensemble, and the effects of Sc(3+) functions were the most imperative. The intermolecular ET also proved to be reliant on the structure of TTF-TCA, where TTF-TCA 7a and 7b were more effective than TTF-TCA 6a and 6b. The difference may be credited to TTF-TCA 7a or 7b possessing two independent TTF pendants and providing a more synergic coordination among the TTF radical cation and Q radical anion with a metal ion.

Interactions of three berberine mid-chain fatty acid salts with bovine serum albumin (BSA): Spectroscopic analysis and molecular docking.

In this paper, the interaction of three berberine mid-chain fatty acid salts ([BBR][FAs]), viz. berberine caproate ([BBR][CAP]), berberine heptylate ([BBR][HEP]) and berberine octoate ([BBR][OCT]), with bovine serum albumin (BSA) was studied by means of UV-visible absorption spectroscopy, fluorescence spectroscopy, fourier transform infrared spectroscopy (FT-IR) and molecular docking techniques. Fluorescence experiments revealed that three berberine salts quench the fluorescence of BSA by static quenching mechanism resulted from a stable [BBR][FAs]-BSA complex formation. The stoichiometric numbers of [BBR][FAs]-BSA complexes were found to be 1:1. Synchronous and three-dimensional fluorescence spectra as well as FT-IR demonstrated that the binding of [BBR][FAs] altered the microenvironment and conformation of BSA. The binding average distance from [BBR][FAs] to BSA (3.2-3.5 nm) was determined according to Förster energy transfer theory. Site probe investigation showed that [BBR][FAs] bound to BSA active site I (sub-domain IIA). The binding promotes the esterase-like activity of BSA. The molecular docking results confirmed the fluorescence competition findings and provided the type of binding forces. Furthermore, the relationship between the anionic chain length of [BBR][FAs] and the interaction was explored, and the positive correlation was found.

Assembly and Adsorption Properties of Seven Supramolecular Compounds with Heteromacrocycle Imidazolium.

Seven supramolecular compounds comprising multivalent imidazolium macrocycles and metal halides, {[MC-IM][Ag2I4]} n (1), {[PC-IM]2[Ag7I11]} n (2), {[ODC-IM][Ag3I7]} (3), {[ODC-IM][Bi2I10]} (4), {[MDC-IM][Bi2I10]} (5), {[PDC-IM][Bi2I10]} (6), and {[MDC-IM][HgI4]} (7), have been synthesized by solvothermal reactions and structurally characterized by IR spectroscopy, thermogravimetric analysis, and single-crystal X-ray diffraction. Notably, the three tetravalent imidazolium macrocycles were introduced for the first time and the extended anion structures are featured with three-dimensional coordination networks, one-dimensional chains, or zero-dimensional oligomers. This new study attempts to not only fill the gap in this supramolecular hybrid area that has been neglected but also enrich the type of imidazolium cyclophane. It is important that good efforts were devoted to study the adsorption properties of supramolecular compounds. Compound 5 exhibited great adsorption performance for organic dyes methylene blue, methyl orange, and rhodamine B (RhB) and can be evaluated as a potential candidate for industrial wastewater treatment.

Adsorption of cadmium by live and dead biomass of plant growth-promoting rhizobacteria.

Plant growth-promoting rhizobacteria (PGPR) have been extensively investigated in combination remediation with plants in heavy metal contaminated soil. However, being biosorbent, few studies of live and dead cells of PGPR have been undertaken. Meanwhile, the application of live or dead biomass for the removal of heavy metals continues to be debated. Therefore, this study uses living and non-living biosorbents of Cupriavidus necator GX_5, Sphingomonas sp. GX_15, and Curtobacterium sp. GX_31 to compare their Cd(ii) adsorption capacities by SEM-EDX, FTIR, and adsorption experiments. In the present study, whether the cells were living or dead and whatever the initial Cd(ii) concentration was, removal efficiency and adsorption capacity can be arranged as GX_31 > GX_15 > GX_5 (p < 0.05). However, removal efficiency in live and dead biosorbents was quite different and it greatly affected by the initial Cd(ii) concentrations. The dead cells exhibited a higher adsorption capacity than the live cells of GX_31. Nevertheless, for GX_5 and GX_15, the loading capacity of the non-living biomass was stronger than that of the living biomass at 20 mg L-1 of Cd(ii), but the capacity was similar at 100 mg L-1 of Cd(ii). Minor changes of spectra were found after autoclaving and it seemed that more functional groups of the dead biosorbent were involved in Cd(ii) binding by FTIR analysis, which also illustrated that the hydroxyl, amino, amide, and carboxyl groups played an important role in complexation with Cd(ii). Based on these findings, we concluded that the dead cells were more potent for Cd(ii) remediation, especially for GX_31.

Biosorption and bioaccumulation characteristics of cadmium by plant growth-promoting rhizobacteria.

Plant growth-promoting rhizobacteria (PGPR) not only promote growth and heavy metal uptake by plants but are promising biosorbents for heavy metals remediation. However, there exist arguments over whether extracellular adsorption (biosorption) or intracellular accumulation (bioaccumulation) play dominant roles in Cd(ii) adsorption. Therefore, three cadmium-resistant PGPR, Cupriavidus necator GX_5, Sphingomonas sp. GX_15, and Curtobacterium sp. GX_31 were used to study bioaccumulation and biosorption mechanisms under different initial Cd(ii) concentrations, using batch adsorption experiments, desorption experiments, scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX) spectroscopy, transmission electron microscopy (TEM), and Fourier-transform infrared (FTIR) spectroscopy. In this study, with the increase of the initial Cd(ii) concentrations, the removal efficiency of strains decreased and the adsorption capacity improved. The highest Cd(ii) removal efficiency values were 25.05%, 53.88%, and 86.06% for GX_5, GX_15, and GX_31 with 20 mg l-1 of Cd(ii), while the maximum adsorption capacity values were 7.97, 17.13, and 26.43 mg g-1 of GX_5, GX_15, and GX_31 with 100 mg l-1 of Cd(ii). Meanwhile, the removal efficiency and adsorption capacity could be ordered as GX_31 > GX_15 > GX_5. The dominant adsorption mechanism for GX_5 was bioaccumulation (50.66-60.38%), while the dominant mechanisms for GX_15 and GX_31 were biosorptions (60.29-64.89% and 75.93-79.45%, respectively). The bioaccumulation and biosorption mechanisms were verified by SEM-EDX, TEM and FTIR spectroscopy. These investigations could provide a more comprehensive understanding of metal-bacteria sorption reactions as well as practical application in remediation of heavy metals.

An improved procedure for determination of the mean aggregation number of micelles.

In this paper, a theory of fluorescence quenching in micelles which enables a dynamic approach to the evaluation of the aggregation numbers of micelles is presented. This method is based on a detailed kinetic model of quenching of fluorescent probe developed by Tachiya (1975, 1982) and takes into account that a part of quenchers are associated with micelles but the remaining quenchers are in the aqueous phase. The approach presented is an improvement on a previous fluorescence quenching method (Turro and Yekta, 1978) and is applied to determine the aggregation number of sodium dodecyl sulfonate (SAS) in aqueous dipeptide solution using cetylpyridinium chloride as quencher. The values of aggregation number and association constant for quencher-micelle association are presented.

Viscosity behavior of some alpha-amino acids and their groups in water-sodium acetate mixtures.

Viscosities of glycine, DL-alpha-alanine, DL-alpha-amino-n-butyric acid, DL-valine and DL-leucine have been determined in water-sodium acetate mixtures at 298.15 and 308.15 K. The viscosity B-coefficients have been calculated. The corresponding activation free energies (Deltamu(2)(0 not equal )) for viscous flow have been evaluated with the help of the Feakins equation. The contributions of the charged end group (NH(3)(+),COO(-)) and CH(2) groups of the amino acids to B-coefficient and Deltamu(2)(0 not equal) have been also determined using the linear correlation between B-coefficient or Deltamu(2)(0 not equal) and the number of carbon atoms in alkyl chains of the amino acids. The results have been interpreted in the light of the solute-solvent interactions in aqueous media.

Selective electrodes for [PF6](-) and [BF4](-) anions based on the associates formed by ionic liquid and cationic dyes.

The feasibility of the newly synthesized ionic associates L1 and L2 formed by ionic liquid [C4mim][PF6] and cationic dyes (malachite green and methylene blue) has been tested as a novel ionophore for the preparation of anion-selective polymeric membrane electrodes. The electrode exhibits Nernstian response and enhanced potentiometric selectivity towards [PF6](-) compared to many other anions. The influence of some experimental parameters such as membrane composition, nature of plasticizer and amount of additive on the potential response of the [PF6](-) sensor are investigated. Under the optimized conditions, the response slopes of the membrane electrodes towards [PF6](-) are 59.7±0.5 and 58.1±0.5 mV/decade based on ionophore L1 and L2, respectively, in 1.0×10(-5)-1.0×10(-1) or 1.0×10(-6)-1.0×10(-1) mol/L concentration range. Interestingly, the optimized electrodes based on ionophores L1 and L2 also exhibit Nernstian response characteristics (60.3±0.5 and 56.0±0.5 mV/decade) for tetrafluoroborate anion [BF4](-) in a wide concentration range. Thus, the proposed sensor has been used for the determination of [PF6](-) and [BF4](-) in aqueous ionic liquids samples and the solubility of the [PF6](-) and [BF4](-) based ionic liquids in water. The satisfactory results are obtained.

Bismuth (III) PVC membrane ion selective electrodes based on two compounds: acylhydrazone and thiosemicarbazone with 1,3,4-thiadiazole.

Two Bi(3+) selective electrodes based on L1 and L2 incorporated into a polyvinylchloride (PVC) membrane have been developed. The ionophores L1 and L2 are 2-(5-amino-1,3,4-thiadiazol-2-ylthio)-N'-benzylidene acetohydrazone and 1-(2-(5-amino-1,3,4-thiadiazol-2-ylthio) acetyl)-4-benzoylthiosemicarbazone, respectively. These electrodes are composed of dioctylphtalate (DOP) as a plasticizer and sodium tetraphenylborate (NaTPB) as the lipophilic additive. The best performance was obtained with the membrane compositions of L1 (0.30): PVC (33.22): DOP (66.36): NaTPB (0.12) (%, w/w) and L2 (1.00): PVC (33.00): DOP (65.91): NaTPB (0.09) (%, w/w). Two membrane electrodes show Nernstian response slopes towards Bi(3+) (20.2 and 19.7 mV/decade, respectively) over the concentration range of 10(-7)-10(-3) and 10(-7)-10(-2) M, respectively. The effects of the pH and the possible interfering cations were investigated. Both electrodes have a response time of about 10 s, and they can work in a certain concentration aqueous ethanol solution. The prepared electrodes were used as an indicator electrode in potentiometric titration of Bi(3+) ions with EDTA. The membrane sensors were also applied to the determination of Bi(3+) content in compound bismuth aluminate tablets.

Tripodal compound 1,1,1-tris(N-ethyl-N-phenylamino-carboxylmethoxymethyl) propane as an ionophore for alkali and alkaline earth metal cations-selective electrode.

A new tripodal compound, 1,1,1-tris(N-ethyl-N-phenylamino-carboxylmethoxymethyl) propane, has been synthesized and evaluated as an ionophore in PVC membrane electrode for the analysis of alkali and alkaline earth metal cations. The influence of the nature of the plasticizers (o-NPOE, DBP and DOP) and of the amount of incorporated ionophore on the characteristics of the electrode was discussed. Selectivity coefficients against alkali and alkaline earth metal cations were calculated. The electrodes based on the tripodal compound with o-NPOE and DBP as plasticizer gave good performance (slope, limits of detection) to lithium and sodium ions. The electrode plasticized with o-NPOE also exhibited near-Nernstian response to divalent ions: Ca(2+), Sr(2+) and Ba(2+). The electrode prepared with 3.9 mg ionophore, 185 mg o-NPOE, 92 mg PVC and 0.46 mg KTpClPB can be used as a Ca(2+) electrode. The influence of pH has also been studied. The electrodes exhibited better potential stability and operational lifetime of more than 3 months.