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Bacterial metal detoxification mechanisms have been well studied for centuries in pure culture systems. However, profiling metal resistance determinants at the community level is still a challenge due to the lack of comprehensive and reliable quantification tools. Here, a novel high-throughput quantitative polymerase chain reaction (HT-qPCR) chip, termed the metal resistance gene (MRG) chip, has been developed for the quantification of genes involved in the homeostasis of 9 metals. The MRG chip contains 77 newly designed degenerate primer sets and 9 published primer sets covering 56 metal resistance genes. Computational evaluation of the taxonomic coverage indicated that the MRG chip had a broad coverage matching 2 kingdoms, 29 phyla, 64 classes, 130 orders, 226 families, and 382 genera. Temperature gradient PCR and HT-qPCR verified that 57 °C was the optimal annealing temperature, with amplification efficiencies of over 94% primer sets achieving 80-110%, with R 2 > 0.993. Both computational evaluation and the melting curve analysis of HT-qPCR validated a high specificity. The MRG chip has been successfully applied to characterize the distribution of diverse metal resistance determinants in natural and human-related environments, confirming its wide scope of application. Collectively, the MRG chip is a powerful and efficient high-throughput quantification tool for exploring the microbial metal resistome.

Heavy metal pollution is very common in soils. Soils are complex systems including minerals, bacteria, and various other substances. In Cd(II) contaminated soil, the combined effects of clay minerals and heavy metals on bacterial biofilm and Cd(II) adsorption are unappreciated. Our study showed that the combination of clay minerals (goethite, kaolinite, and montmorillonite) and heavy metals promoted Serratia marcescens S14 biofilm development significantly more than clay minerals or Cd(II) alone. The amount of biofilm after binary treatment with clay minerals and Cd(II) was 2.3-7.3 times than that in control. Mineral-induced cell death and the expression of the fimA, bsmA, and eps were key players in biofilm formation. Binary treatment with montmorillonite and Cd(II) significantly enhanced biofilm development and consequently increased the adsorption of Cd(II). Cd(II) removal is the result of co-adsorption of bacteria and minerals. Bacterial biofilm played an important role in Cd(II) adsorption. FTIR spectroscopy showed the components of biofilm were not affected by minerals and revealed the functional groups -OH, -NH, -CH 2 , -SH, -COO participated in Cd(II) immobilization. Our findings are of fundamental significance for understanding how minerals and Cd(II) affect biofilms and thereby enhance Cd(II) adsorption and predicting the mobility and fate of heavy metals in heavy metal-contaminated soil., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Ureolytic microbes play a pivotal role in the maintenance of soil fertility. Soil aggregates are supposed to provide heterogeneous habitats for microorganisms, which may result in distinct metabolic functions. However, limited information is available regarding the distribution patterns, driving factors, and activity of ureolytic microbiota at the aggregate scale. In this study, we characterized the ureolytic microbiota and urease activity of three soil aggregate fractions from an Inceptisol subjected to 5 years of different fertilization regimes. Correlations between soil chemical characteristics and ureolytic microbial communities were analyzed. The results showed that the total abundance as well as the relative abundance of copiotrophic ureolytic microbes generally increased with the increasing soil aggregate size. This trend was in line with the nutrient distribution patterns, including labile carbon, NH 4 + , total carbon, nitrogen, and phosphorus. Soil urease activity also increased significantly with the increasing soil aggregate size and was positively correlated with copiotrophic ureolyric microbes, such as Betaproteobacteria, Alphaproteobacteria, and Gammaproteobacteria. Thus, we speculated that larger size soil aggregates with greater availability of labile carbon support more copiotrophic ureolyric microbes with a high growth rate, leading to a high density of total ureolytic microbes and higher urease activity. Smaller aggregates with less available carbon were associated with more oligotrophs, higher abundances of total ureolytic microbes, and higher urease activity. Our results suggest that larger soil aggregates and associated ureolyric microbes play a more important role in nutrient cycling for crop growth in this Inceptisol ecosystem.

Nitrite oxidation is recognized as an essential process of biogeochemical nitrogen cycling in agricultural ecosystems. How nitrite-oxidizing bacteria (NOB) respond to land managements (the effect from the long-term straw incorporation and environmental variability caused by the shift from the upland stage to the paddy stage) in a rapeseed-rice rotation field remains unclear. We found the nitrite oxidation (NO) in soils increased from the upland stage to the paddy stage. An inhibitory effect of the long-term straw incorporation on NO was detectable in the upland stage. The abundance of Nitrospira was always greater than Nitrobacter, and it was affected by the rice-growing and straw incorporation while Nitrobacter was not. NO correlated positively with the abundance of Nitrospira and with soluble sulfate (SO 4 2- ), soil moisture, pH and NH 4 + . The high-throughput sequencing analysis of the nitrite oxidoreductase nxrA and nxrB genes for Nitrobacter- and Nitrospira-like NOB was performed respectively. The dominating (relative abundance>1%) operational taxonomic units (OTUs) from Nitrobacter were closely related to Nitrobacter hamburgensis, whereas those from Nitrospira were affiliated with or related to lineage II, lineage V and several unknown groups. Heatmap analysis showed that a few dominant Nitrobacter OTUs were affected by the straw treatment or the rice-growing, and half of the dominant Nitrospira ones were explained by at least one of the variables. Multi-response permutation procedure (MRPP) and redundancy analyses showed that the Nitrospira-like NOB community changes were significantly shaped by the land managements and the soil chemical properties, including pH, moisture and NH 4 + , whereas that of the Nitrobacter-like NOB community was not. These results suggested that Nitrospira are more sensitive than Nitrobacter to land management in acid and fertilized soils of a rapeseed-rice rotation field trial., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Nitrospira are the most widespread and well known nitrite-oxidizing bacteria (NOB) and putatively key nitrite-oxidizers in acidic ecosystems. Nevertheless, their ecology in agriculture soils has not been well studied. To understand the impact of straw incorporation on soil Nitrospira-like bacterial community, a cloned library analysis of the nitrite oxidoreductase gene-nxrB was performed for a long-term rapeseed-rice rotation system. In this study, most members of the Nitrospira-like NOB in the paddy soils from the Wuxue field experiment station were phylogenetically related with Nitrospira lineages II. The Shannon diversity index possessed a decrease trend in the straw applied soils. The relative abundances of 16 OTUs (accounting 72% of the total OTUs, including 11 unique OTUs and 5 shared OTUs) were different between in the straw applied and control soils. These data suggested a selection effect from the long-term straw fertilization. Canonical correspondence analysis data showed that a centralized group of Nitrospira-like NOB OTUs in the community was partly explained by the soil ammonium, nitrate, available phosphorus, and the available potassium. This could suggest that straw fertilization led to the soil Nitrospira-like NOB community shift, which was correlated with the change of available nutrients in the bulk soil., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Soil components (e.g., clays, bacteria and humic substances) are known to produce mineral-organic composites in natural systems. Herein, batch sorption isotherms, isothermal titration calorimetry (ITC), and Cd K-edge EXAFS spectroscopy were applied to investigate the binding characteristics of Cd on montmorillonite(Mont)-humic acid(HA)-bacteria composites. Additive sorption and non-additive Cd(II) sorption behaviour is observed for the binary Mont-bacteria and ternary Mont-HA-bacteria composite, respectively. Specifically, in the ternary composite, the coexistence of HA and bacteria inhibits Cd adsorption, suggesting a "blocking effect" between humic acid and bacterial cells. Large positive entropies (68.1~114.4 J/mol/K), and linear combination fitting of the EXAFS spectra for Cd adsorbed onto Mont-bacteria and Mont-HA-bacteria composites, demonstrate that Cd is mostly bound to bacterial surface functional groups by forming inner-sphere complexes. All our results together support the assertion that there is a degree of site masking in the ternary clay mineral-humic acid-bacteria composite. Because of this, in the ternary composite, Cd preferentially binds to the higher affinity components-i.e., the bacteria.

Bacteria–phyllosilicate complexes are commonly found in natural environments and are capable of immobilizing trace metals. However, the molecular binding mechanisms of heavy metals to these complex aggregates still remain poorly understood. This study investigated Cd adsorption on Gram-positive Bacillus subtilis , Gram-negative Pseudomonas putida and their binary mixtures with montmorillonite using surface complexation model, Cd K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and isothermal titration calorimetry (ITC). We have shown that larger amounts of Cd are adsorbed by B. subtilis than by P. putida at pH<∼6, and Cd sorption that binding to phosphate groups plays a more important role in P. putida than in B. subtilis . This remind us that we should consider the microbe species when predict the biochemical behavior of trace metals in microbe-bearing environments. The observed Cd adsorption on the binary bacteria–clay composites was more than that predicted based on the component additivity approach. When taking bacteria–clay (1:1 mass ratio) as a representative example, an approximately 68%:32% metal distribution between the bacterial and mineral fraction was found. Both the EXAFS and ITC fits showed that the binding stoichiometry for Cd-carboxyl/phosphate was smaller in the binary mixtures than that in pure bacteria. We proposed that the significant deviations were possibly due to the physical-chemical interaction between the composite fractions that might reduce the agglomeration of the clay grains, increase the negative surface charges, and provide additional bridging of metals ions between bacterial cells and clays. [ABSTRACT FROM AUTHOR]

Previous studies revealed the thermodynamic properties of DNA adsorption on pure minerals or biomasses; however, there has been little attempt to develop such studies on bacteria–mineral composites. Equilibrium adsorption experiments, attenuated total reflectance Fourier transform infrared spectroscopy, and isothermal titration calorimetry were employed to investigate the adsorption of DNA byBacillus subtilis,Pseudomonas putida, and their composites with minerals. Similar capacity and affinity were observed for DNA adsorption on two bacterial cells. However, different patterns were found in the adsorption of DNA by bacteria–mineral composites. The Gram-positive bacteriumB. subtilisenhanced the adsorption of DNA on its mineral composites compared with their individual components, while the composites of Gram-negative bacterial cells with kaolinite and goethite bound lower amounts of DNA than the predicted values. The thermodynamic parameters and the Fourier transform infrared spectra showed that van der Waals force and hydrogen bonding are responsible for the DNA adsorption onB. subtilis–minerals andP. putida–kaolinite. By contrast, the entropy increases of excluded water rearrangement and dehydration effect play key roles in the interaction between DNA andP. putida–montmorillonite/goethite composites. [ABSTRACT FROM AUTHOR]

Bacterial attachment is a physicochemical interfacial process probably affected by the presence of humic acid (HA) in natural environments. However, the effect of HA coating on bacterial adhesion to soil minerals remains unknown, despite many studies focusing on cell attachment to pure or iron oxide-coated quartz in the presence of HA. The influence of HA on Bacillus subtilis adhesion to kaolinite, montmorillonite, and goethite under neutral pH and 1 mM ionic strength was examined using batch experiments coupled with Fourier-transform infrared spectroscopy (FTIR), isothermal titration calorimetry, and Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. Results showed a reduction in cell adhesion on goethite and montmorillonite with increasing HA content from 0% to 2%, indicating an inhibitory effect of HA coating on the interaction. However, a promotive effect of HA was observed for kaolinite, which disagreed with previous findings based on cell–quartz systems. In addition, the presence of HA reduced the exothermic adhesion enthalpy for kaolinite and goethite, but increased that for montmorillonite. For goethite, the HA coating depressed its positive charge and increased its aggregation, thereby leading to a weaker electrostatic attraction and lesser available surface area, which probably contributed to the observed decreasing adhesion. For montmorillonite, the reduced attachment was likely caused by the increase in electrostatic repulsion that overcompensated for the appeared chemical interactions as suggested by FTIR analysis. The enhanced cell adhesion on kaolinite, which was unexpected from DLVO theory based on its surface charge change, is likely ascribed to the HA-induced decrease in its aggregation. Additionally, the effect of HA vanishes at HA contents higher than 2%, likely due to a saturation effect. Overall, the influence of HA on bacterial attachment is likely a combined result of multiple factors, including not only electrostatic forces and chemical interactions, but also mineral aggregation. [ABSTRACT FROM AUTHOR]

Bacterial adhesion to minerals in soils and sediments is of fundamental importance in mineral weathering and formation, soil aggregate stability, organic matter degradation and the fate of pollutants. Bacterial surface properties are considered to govern adhesion, and these properties likely change as a function of bacterial growth phase. However, the effect of growth stage on bacterial adhesion to clay minerals remains unclear. This work examined the influence of growth phase on the adhesion of Pseudomonas putida to kaolinite-coated coverslips. Fluorescence microscopy, together with a bacterial viability stain, was used to directly quantify surface cell density and viability of adhered P. putida . In situ attenuated total reflectance Fourier transform infrared spectroscopy was applied to yield molecular information about the characteristics of the bacteria, and the adsorption and desorption kinetics. Stationary-phase cells exhibited a higher adsorption density on kaolinite surfaces than mid-exponential-phase cells under static deposition conditions. Compared with the mid-exponential-phase cells, the stationary-phase cells displayed higher saturation coverage, and we fitted the results using a pseudo-first-order kinetics equation. The greater extent of adhesion of the stationary-phase cells was probably due to their smaller cell size and less negative surface charges compared with the cells from other growth stages, which resulted in deeper secondary energy minima and lower energy barriers for adhesion. The results from this study suggest that growth phase may strongly influence cell mobility and biofilm formation in aqueous geochemical environments. [ABSTRACT FROM AUTHOR]

Bacteria and their secreted extracellular polymeric substances (EPS) are widely distributed in ecosystems and have high capacity for heavy metal immobilization. The knowledge about the molecular-level interactions with heavy metal ions is essential for predicting the behavior of heavy metals in natural and engineering systems. This comprehensive study using potentiometric titration, Fourier-transform infrared (FTIR) spectroscopy, isothermal titration calorimetry (ITC) and X-ray absorption fine structure (XAFS) was able to reveal the functional diversity and adsorption mechanisms for Pb onto bacteira and the EPS in greater detail than ever before. We identified mono-carboxylic, multi-carboxylic, phosphodiester, phosphonic and sulfhydryl sites and found the partitioning of Pb to these functional groups varied between gram-negative and gram-positive bacterial strains, the soluble and cell-bound EPS and Pb concentrations. The sulfhydryl and phosphodiester groups preferentially complexed with Pb in P. putida cells, while multifunctional carboxylic groups promoted Pb adsorption in B. subtilis cells and the protein fractions in EPS. Though the functional site diversity, the adsorption of Pb to organic ligands occurred spontaneously through a universal entropy increase and inner-sphere complexation mechanism. The functional group scale knowledge have implications for the modeling of heavy metal behavior in the environment and application of these biological resources. [Display omitted] • Mono-/multi-carboxylic, phosphodiester, phosphonic and sulfhydryl sites were identified. • EXAFS and ITC noticed concentration, strain and EPS type dependent Pb coordination. • P. putida cells were richer in sulfhydryl and phosphodiester groups than B. subtilis. • Pb adsorption follow universal entropy increase and inner-sphere complexation mechanism. [ABSTRACT FROM AUTHOR]

Abstract: The functions of extracellular polymeric substances (EPS) during the adhesion of Bacillus subtilis to kaolinite, montmorillonite, and goethite were examined by a direct comparison of the adhesion behaviors of native and EPS-free cells via cation exchange resin (CER) treatment using batch experiments, attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy, and potentiometric titration. The EPS removal had no apparent influence on bacterial adhesion when the wet bacteria/mineral mass ratio was low (<0.4 for the clay mineral systems and <1.8 for the goethite system). With higher mass ratios, the absence of EPS reduced adhesion to clay minerals but enhanced adhesion to goethite. The ATR-FTIR spectra suggested that protein conformational changes were involved in the adhesion of bacteria to clay minerals, whereas additional chemical interactions such as P OFe bonds were important for adhesion to goethite. In addition to electrostatic forces (repulsion for clays and attraction for goethite), absence of chemical interactions may also cause the relatively much weaker bacterial adhesion to clay minerals than to goethite. The absence of EPS did not change the interaction mode of the adhesion to clay minerals but enhanced the chemical interactions via carboxyl groups for bacteria–goethite adhesion. The potentiometric titration results coupled with the ATR-FTIR spectra showed a significant increase in site concentrations of the CER-treated bacteria as compared to the native cells. Changes in surface site concentrations and chemical interactions that were accompanied by the EPS removal may reasonably explain the influences of EPS on bacterial adhesion to different minerals. [Copyright &y& Elsevier]

Remediation of toxic metals by bacteria offers a relatively inexpensive and efficient way for the decontamination of soil and associated environments. The present study was carried out to investigate the surface characteristics, adsorption, and remobilization of Cd and Cu on bacteria and their composites with soil colloidal components, which are the most active constituents in soils. The bacterial strain NTG-01 ( Enterobacter aerogenes ), which was both Cd- and Cu-resistant, was isolated from a heavily Cu-contaminated soil of the mining area in Daye suburb of Hubei Province, China. Batch laboratory experiments with NTG-01 and soil colloids were performed to quantify adsorption of Cu and Cd. The surface area of kaolinite and the soil colloids from an Alfisol and Ultisol increased by 3.0–8.8% after the introduction of the bacteria. In the presence of bacterial cells, the negative charges of soil colloid systems increased and the positive charges decreased, shifting pH from 4.0 to 6.5. Our results demonstrate that bacteria promote the adsorption of Cd and Cu by kaolinite and soil colloid systems. However, the heavy metals bound by the bacterial composites could also be easily released by NH 4 NO 3 and EDTA. Caution should be taken when using such bacterial strains in bioremediation of heavy metal-contaminated soils. [ABSTRACT FROM AUTHOR]

The accurate modeling of heavy metal adsorption in complex systems is fundamental for risk assessments in soils and associated environments. Bacteria-iron (hydr)oxide associations in soils and sediments play a critical role in heavy metal immobilization. The reduced adsorption of heavy metals on these composites have been widely reported using the component additivity (CA) method. However, there is a lack of a mechanism model to account for these deviations. In this study, we established models for Cd adsorption on goethite- Pseudomonas putida composites at 1:1 and 5:1 mass ratios. Cadmium adsorption on the 5:1 composite was consistent with the additivity method. However, the CA method over predicted Cd adsorption by approximately 8% on the 1:1 composite at high Cd concentration. The deviation was corrected by adding the site blockage reactions between P. putida and goethite. Both CA and “CA-site masking” models for Cd adsorption onto the composites were in line with the ITC data. These results indicate that CA method in simulating Cd adsorption on bacteria-iron oxides composites is limited to low bacterial and Cd concentrations. Therefore the interfacial complexation reactions that occur between iron (hydr)oxides and bacteria should be taken into account when high concentrations of bacteria and heavy metals are present. [ABSTRACT FROM AUTHOR]

Abstract: In this study, Fourier transform infrared spectroscopy, potentiometric titration, along with sorption experiments using chemically modified bacteria were conducted to compare the behavior of Gram-positive Bacillus thuringiensis and Gram-negative Escherichia coli as sorbents for Cu2+ and Cd2+ ions. The IR spectra showed that there were obvious changes connected with the–COOH groups for Cu(II)- and Cd(II)-loaded B. thuringiensis. A three site non-electrostatic model provides an excellent fit to the titration curves of both E. coli and B. thuringiensis with the first corresponding pK a values of 4.16±0.18 and 3.30±0.24, respectively, implying that B. thuringiensis contains more carboxyl groups than E. coli. Chemical modification and metal sorption experiments further confirmed that carboxyl groups may play a more important role in the binding Cd(II) and Cu(II) for B. thuringiensis than for E. coli, which could be attributed to the higher concentration of carboxyl sites of B. thuringiensis than E. coli. These results show that the main chemical functional group responsible for the binding of metal ions on B. thuringiensis and E. coli is obviously different because of the different composition and structure of bacterial cell walls. The concentrations of the chemical functional groups on bacterial cell walls are regarded to govern their role in the binding of metal ions and affect the affinity between the bacterial cells and metal ions. [Copyright &y& Elsevier]

Soil aggregates provide spatially heterogeneous microhabitats for microorganisms and their activities. In metal contaminated soil, the microbial community is shaped by both metal stress and aggregate sizes. However, it remains unclear whether and how aggregate sizes affect the legacy effect of metal pollution on microbial communities. Here, we investigated the legacy effect of long-term copper (Cu) pollution on the distribution patterns of the bacterial and protistan communities in soil aggregates. Our results showed that soil aggregates of different sizes possessed distinct bacterial and protistan communities under Cu-polluted and unpolluted conditions (aggregate effects), as reflected by distinct α-diversity and community compositions. The bacterial and protistan communities in micro- and macro-aggregates were more responsive to Cu pollution than those in mega-aggregates, primarily because micro- and macro-aggregates contained a greater number of Cu susceptible bacterial and protistan species. Ciliophora and Chlorophyta displayed great sensitivity to Cu, especially in small aggregate-size fractions, and could serve as a bio-indicator of Cu pollution. Furthermore, the magnitude of aggregate effects on microbial communities was weakened in Cu-polluted soils compared to unpolluted soils. With decreasing aggregate sizes, the co-occurrence networks between bacteria and protists became more complex, connected and compact. Robustness analysis showed that phagotrophic protists played essential roles in sustaining the network stability, especially in mega-aggregates. Our findings highlight the asymmetrical changes in microorganisms in aggregates under long-term Cu pollution, providing a novel insight into the legacy effects of metal pollution on soil microbiomes at the micro-level. • The distribution of bacteria and protists in Cu-polluted and unpolluted soil aggregates was distinct. • The Cu legacy effect on the bacterial and protist communities was strong in aggregates of small size. • Cu pollution lessened aggregate size-induced effects on the bacterial and protistan communities. • Phagotrophs were crucial in sustaining the network stability in large aggregates. [ABSTRACT FROM AUTHOR]

Though abundant studies have targeted the characterization of heavy metal adsorption by either clay minerals or bacteria, to date, minimal literature exists which specifically assesses bacteria-clay mineral interactions in the context of metal immobilization. The adsorption of Pb onto montmorillonite, Pseudomonas putida , and their 1:1, 2:1, 6:1 and 12:1 mass ratio composites were investigated by using a combination of atomic force microscope (AFM), X-ray diffraction (XRD), surface complexation modeling (SCM), Pb-L III edge extended X-ray absorption fine structure (EXAFS) spectroscopy and isothermal titration calorimetry (ITC). The SCM and EXAFS demonstrated that Pb ions coordinate with phosphoryl and carboxyl functional groups on bacteria at low and high concentrations, respectively. The ITC analysis found adverse enthalpy values for Pb adsorption to permanent (−2.91 kJ/mol) and variable charge sites (6.93 kJ/mol) on montmorillonite. The ternary bridging model, EXAFS and ITC provide molecular and thermodynamic evidences for the formation of enthalpy driven (−4.74 kJ/mol) ternary complex (>AlO-Pb-PO 4 ) in the composites. The proportion for the bridging structures increased at pH > 5 and high bacterial mass ratios. The formation of ternary complex did not result in the enhanced adsorption of Pb on the composites, but promoted the allocation of Pb on the mineral fraction. The results obtained from SCM, EXAFS and ITC may provide an essential assumption for predicting the speciation and fate of Pb in soils and associated environments. [ABSTRACT FROM AUTHOR]

Abstract: In order to have a better understanding of the interactions of heavy metals with bacteria and minerals in soil and associated environments, isothermal titration calorimetry (ITC), potentiometric titration and equilibrium sorption experiments were conducted to investigate the adsorption behavior of Cu(II) by Bacillus thuringiensis, Pseudomonas putida and their composites with minerals. The interaction of montmorillonite with bacteria increased the reactive sites and resulted in greater adsorption for Cu(II) on their composites, while decreased adsorption sites and capacities for Cu(II) were observed on goethite–bacteria composites. A gram-positive bacterium B. thuringiensis played a more important role than a gram-negative bacterium P. putida in determining the properties of the bacteria–minerals interfaces. The enthalpy changes (ΔH ads) from endothermic (6.14kJmol−1) to slightly exothermic (−0.78kJmol−1) suggested that Cu(II) is complexed with the anionic oxygen ligands on the surface of bacteria–mineral composites. Large entropies (32.96–58.89Jmol−1 K−1) of Cu(II) adsorption onto bacteria–mineral composites demonstrated the formation of inner-sphere complexes in the presence of bacteria. The thermodynamic data implied that Cu(II) mainly bound to the carboxyl and phosphoryl groups as inner-sphere complexes on bacteria and mineral–bacteria composites. [Copyright &y& Elsevier]

Abstract: Adsorption and desorption of salmon sperm DNA on bacteria (Bacillus thuringiensis, Pseudomonas putida), two different colloidal fractions (organic and inorganic clay) from an Alfisol, minerals (montmorillonite, kaolinite and goethite) and colloid–bacteria composites were studied. Similar adsorption capacity and affinity of DNA were observed on two bacterial cells. However, the two bacterial strains played different roles in affecting the adsorption of DNA on the composites of soil colloidal particles with bacteria. The introduction of B. thuringiensis in soil colloids and minerals systems dramatically promoted DNA adsorption on colloidal particles especially organic clay, while P. putida decreased the adsorption of DNA on kaolinite and goethite. Electrostatic force and ligand exchange are regarded to be the major driving forces involved in the adsorption of DNA on bacterial cells, montmorillonite, soil colloids and goethite. Presence of bacteria enhanced the proportion of DNA adsorption on soil colloidal particles by electrostatic force and depressed that by ligand exchange process. Information obtained in this study is of fundamental significance for the understanding of the ultimate fate of extracellular DNA in soil systems. [Copyright &y& Elsevier]

E. coli @UiO-67 composites were obtained using an effective and simple self-assembly method. The composites showed unique properties as a remarkable and recyclable adsorbent for the efficient removal of bisphenol A (BPA) from water with a high adsorption capacity (402.930 mg g−1). The increase in pore size is a key factor why E. coli @UiO-67 composites maintained high capacity. The reason might be due to that the composites with large pore sizes and defects could effectively improve mass transport and active molecular metal sites. The adsorption of BPA is a chemisorption process due to the Zr–OH groups in UiO-67 exhibit affinity toward BPA molecules, π–π interaction, and electrostatic attraction. The adsorption efficiency remained at 82.5% after 15 cycles without any remarkable changes in the PXRD patterns of E. coli @UiO-67. Moreover, the use of microorganism-loading MOFs could reduce the cost to at least 50% and minimize secondary pollution through nanoscale MOFs usage reduction. The developed composites have advantages, including low-cost, high adsorption capacity, easy to be separated and regenerated from aqueous solution, a large number of cycles, short adsorption equilibrium time, and stability, showing excellent application prospects. The presented strategy would be a potentially promising way to produce novel MOFs-based adsorbents with high-performance to control environmental pollution from wastewater. Image 1 • E. coli @UiO-67 composites were obtained using self-assembly approach. • E. coli @UiO-67 composites exhibit high adsorption capacity and reusability for BPA. • Microorganism loaded MOF could reduce cost of BPA removal and minimize secondary pollution. • E. coli @UiO-67 composites exhibit good application prospects for water purification. [ABSTRACT FROM AUTHOR]