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Widespread antibiotic resistance genes (ARGs) have caused critical threats to public health on a global scale. Soil, composed mainly of minerals, acts as a source of resistance determinants, playing a considerable role in the development and dissemination of ARGs. The great abundance of ARGs in the soil environment raises concern about the effect of minerals on the spread of ARGs. Herein, the horizontal transfer of a model plasmid pMP2463 containing ARGs from Escherichia coli S17‐1 to Pseudomonas putida KT2440 was monitored following exposure to four common soil minerals, namely, kaolinite, montmorillonite, goethite and birnessite. Birnessite resulted in concentration‐dependent increases in conjugative transfer of plasmid pMP2463 by 1.3–4.3 fold, compared with that in the control group. However, no obvious laws were found in the change of conjugative transfer rate at different concentrations of kaolinite and montmorillonite. As for goethite, the conjugative transfer rate increased firstly and then decreased as the concentration increased. The possible mechanisms underlying birnessite‐induced conjugative transfer of plasmid were explored; birnessite is capable of initiating intracellular reactive oxygen species (ROS) formation, inducing the oxidative stress response. Additionally, birnessite notably facilitated the mRNA expression of the outer membrane protein genes, which contributed to cellular membrane pore formation and horizontal gene transfer, and altered the mRNA expression of conjugative‐related genes that are responsible for conjugative transfer of mobile genetic elements between bacteria. This study triggers questions regarding the potential role of soil minerals in the global dissemination of antimicrobial resistance and provides insights into the interactions between bacteria and minerals in the natural soil environment. Highlights: The effect of soil minerals on conjugative transfer of ARGs was explored.Birnessite induced the concentration‐dependent increase of conjugative transfer.Mechanisms underlying ROS formation, membrane permeability increase, gene expression alteration were revealed.Our results provide evidence for the effect of birnessite on antibiotic resistance dissemination. [ABSTRACT FROM AUTHOR]

The adsorption of extracellular polymeric substances (EPS) onto soil minerals is an important process for understanding bacterial adhesion to mineral surfaces and environmental cycling of nutrients and contaminants. To clarify the molecular level mechanisms and processes of EPS adsorption, the interaction mechanisms between EPS and goethite was explored using two-dimensional (2D) Fourier transformation infrared (FTIR) correlation spectroscopy (CoS) assisted by C 1s near edge X-ray absorption fine structure spectroscopy (NEXAFS). Results show that the amide functional groups of EPS play an important role in its adsorption on goethite, and the adsorption of EPS-proteins on goethite is a function of electrolyte concentration, with increasing adsorption at a higher electrolyte concentration. Results also show that the order in which the EPS functional groups interact and bind with goethite is dependent on electrolyte concentration, where carboxyl and phosphoryl functional groups are the first to adsorb at low electrolyte concentration, while amide groups are the first to adsorb at higher electrolyte concentration. Deconvolution and curve fitting of the amide I band at the end of the adsorption process (~300 min) shows that the secondary structure of proteins is converted from a random coil conformation to aggregated strands, α-helices and turns. This conversion leads to increased adsorption of EPS-proteins and explains the overall adsorption increase of EPS on goethite surfaces with an increasing concentration of electrolyte. Furthermore, the adsorption of the carboxyl functional groups of EPS decreases with increasing electrolyte concentration, likely due to more effective screening of the goethite surface charge with increasing concentration of electrolyte. The integrated results from ATR-FTIR and 2D-CoS allow us to construct a comprehensive overview of EPS-goethite interaction processes at the molecular level, which can be used to improve our understanding of EPS-mineral interactions in the natural environment. These results also provide fundamental information for a better understanding of bacterial biofilm formation on soil and sediment minerals, and facilitate research on the subsequent interaction of nutrients and contaminants with the reactive constituents of biofilms in natural and contaminated environments. [ABSTRACT FROM AUTHOR]

Substantial interactions of microbes with soil particles present fundamental influences on microbial activities relevant to a series of biogeochemical processes. However, how soil surface-active particles modulate microbial metabolism has received scant attention. The extent to which composition of soil colloids alter the metabolism is not well addressed. This work examined the impacts of soil colloids and minerals on the metabolic activity ofPseudomonas putidausing microcalorimetry and carbon utilization. The results showed that montmorillonite remarkably improved metabolic activity ofP. putida, whereas kaolinite, goethite and soil colloids significantly inhibited the activity. Humus may weaken the inhibition of soil colloids on bacterial metabolism via interfacial interaction rather than nutrient supplements. Soils bearing higher amount of kaolinite and iron oxide may have greater depression on bacterial activity. The thermodynamic method provides different and complementary information to that from other techniques in characterizing microbial activities. The quantity and affinity for the adhesion of bacteria onto soil components together with the detoxification of metabolites were assigned to the modifications of bacterial activities. [ABSTRACT FROM PUBLISHER]

Adhesion ofBacillus subtilison kaolinite, montmorillonite, and goethite was investigated over a wide range of ionic strength (IS) and pH using batch experiment. The related surface properties (size, zeta potential, and hydrophobicity) under varying conditions were systematically determined and the interaction energy between the cell and minerals were calculated using the extended Derjaguin, Landau, Verwey, and Overbeek (ExDLVO) theory. Adhesion on kaolinite and montmorillonite increased with IS at low level (< 0.01 mol L−1MgCl2) but declined at high IS level. An increase in IS generally depressed bacterial adhesion on goethite. Elevated pH resulted in decreasing the adhesions on all three minerals. The IS- and pH-effects on adhesion forphyllosilicatesystems followed the ExDLVO predictions. For goethite systems, this theory predicted the adhesion trend with IS and that under basic pH, but failed to explain the adhesion at low pH. Such deviation from the theory possibly resulted from chemical interactions between extracellular polymeric substances on cell surface and goethite. These results imply that bacterial adhesions onphyllosilicates are primarily governed by the ExDLVO interactions, and those on iron oxides are mediated by the combination of ExDLVO and non-ExDLVO interactions. [ABSTRACT FROM PUBLISHER]

Abstract: Adsorption, desorption and degradation by Pseudomonas putida of methyl parathion (O,O-dimethyl O-p-nitrophenyl phosphorothioate) on montmorillonite, kaolinite and goethite were studied. Metabolic activities of methyl parathion-degrading bacteria P. putida in the presence of minerals were also monitored by microcalorimetry to determine the degradation mechanism of methyl parathion. Montmorillonite presented higher adsorption capacity and affinity for methyl parathion than kaolinite and goethite. The percentage of degradation of methyl parathion adsorbed on minerals by P. putida was in the order of montmorillonite>kaolinite>goethite. The presence of minerals inhibited the exponential growth and the metabolic activity of P. putida. Among the examined minerals, goethite exhibited the greatest inhibitory effect on bacterial activity, while montmorillonite was the least depressing. The biodegradation of adsorbed methyl parathion by P. putida is apparently not controlled by the adsorption affinity of methyl parathion on minerals and may be mainly governed by the activity of the methyl parathion-degrading bacteria. The information obtained in this study is of fundamental significance for the understanding of the behavior of methyl parathion in soil environments. [ABSTRACT FROM AUTHOR]

Bacterial adhesion onto mineral surfaces and subsequent biofilm formation play key roles in aggregate stability, mineral weathering, and the fate of contaminants in soils. However, the mechanisms of bacteria-mineral interactions are not fully understood. Atomic force microscopy (AFM) was used to determine the adhesion forces between bacteria and goethite in water and to gain insight into the nanoscale surface morphology of the bacteria-mineral aggregates and biofilms formed on clay-sized minerals. This study yields direct evidence of a range of different association mechanisms between bacteria and minerals. All strains studied adhered predominantly to the edge surfaces of kaolinite rather than to the basal surfaces. Bacteria rarely formed aggregates with montmorillonite, but were more tightly adsorbed onto goethite surfaces. This study reports the first measured interaction force between bacteria and a clay surface, and the approach curves exhibited jump-in events with attractive forces of 97 ± 34 pN between E. coli and goethite. Bond strengthening between them occurred within 4 s to the maximum adhesion forces and energies of −3.0 ± 0.4 nN and −330 ± 43 aJ (10−18 J), respectively. Under the conditions studied, bacteria tended to form more extensive biofilms on minerals under low rather than high nutrient conditions. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption of extracellular polymeric substances (EPS) from Bacillus subtilis on montmorillonite, kaolinite and goethite was investigated as a function of pH and ionic strength using batch studies coupled with Fourier transform infrared (FTIR) spectroscopy. The adsorption isotherms of EPS on minerals conformed to the Langmuir equation. The amount of EPS-C and -N adsorbed followed the sequence of montmorillonite>goethite>kaolinite. However, EPS-P adsorption was in the order of goethite>montmorillonite>kaolinite. A marked decrease in the mass fraction of EPS adsorption on minerals was observed with the increase of final pH from 3.1 to 8.3. Calcium ion was more efficient than sodium ion in promoting EPS adsorption on minerals. At various pH values and ionic strength, the mass fraction of EPS-N was higher than those of EPS-C and -P on montmorillonite and kaolinite, while the mass fraction of EPS-P was the highest on goethite. These results suggest that proteinaceous constituents were adsorbed preferentially on montmorillonite and kaolinite, and phosphorylated macromolecules were absorbed preferentially on goethite. Adsorption of EPS on clay minerals resulted in obvious shifts of infrared absorption bands of adsorbed water molecules, showing the importance of hydrogen bonding in EPS adsorption. The highest K values in equilibrium adsorption and FTIR are consistent with ligand exchange of EPS phosphate groups for goethite surface. The information obtained is of fundamental significance for understanding interfacial reactions between microorganisms and minerals. [Copyright &y& Elsevier]

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]

Extracellular polymeric substances (EPS) play a crucial role in controlling the mobility and bioavailability of heavy metal(loid)s in water, soils, and sediments. The formation of EPS-mineral complex changes the reactivity of the end-member materials. However, little is known about the adsorption and redox mechanisms of arsenate (As(V)) in EPS and EPS-mineral complexes. Here we examined the reaction sites, valence state, thermodynamic parameters and distribution of As in the complexes using potentiometric titration, isothermal titration calorimetry (ITC), FTIR, XPS, and SEM-EDS. The results showed that ∼54% of As(V) was reduced to As(III) by EPS, potentially driven by an enthalpy change (ΔH) of − 24.95 kJ/mol. The EPS coating on minerals clearly affected the reactivity to As(V). The strong masking of functional sites between EPS and goethite inhibited both the adsorption and reduction of As. In contrast, the weak binding of EPS onto montmorillonite retained more reactive sites for the reaction with As. Meanwhile, montmorillonite facilitated the immobilization of As to EPS through the formation of As-organic bounds. Our findings deepen the understanding of EPS-mineral interfacial reactions in controlling the redox and mobility of As, and the knowledge is important for predicting the behavior of As in natural environments. [Display omitted] • Both the functional sites and morphology changed after EPS coating on minerals. • Reactions of As in EPS-mineral complexes were both enthalpy and entropy changes driven. • Strong site masking between EPS and goethite inhibited the reaction. • Weak binding of EPS onto montmorillonite promoted As-organic bounds. [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]

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]

Abstract: The adsorption to goethite of extracellular polymeric substances (EPS) isolated from Pseudomonas putida was investigated using batch adsorption experiments, electrophoretic mobility (EM) measurements, Fourier transform infrared (FTIR) spectroscopy, isothermal titration calorimetry (ITC) and X-ray absorption fine structure (XAFS) spectroscopy. The adsorption of EPS decreased the point of zero charge of goethite from 7.6 to 3.2, suggesting the formation of negatively charged inner-sphere surface complexes. The adsorption isotherms of EPS on goethite conformed to the Langmuir equation. The adsorption energy constant (K) of EPS on goethite was in the sequence of EPS phosphate-containing moieties > nitrogen-containing moieties > carbon-containing moieties, indicating those containing phosphate were the most strongly adsorbed. FTIR showed ligand exchange of phosphate groups of EPS with surface hydroxyls on goethite. Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy results further demonstrated phosphate groups of EPS can form monodentate inner-sphere complexes at lower pH 3.0, while form bidentate inner-sphere complexes at higher pH 9.0. The oxidation state of iron in goethite was not changed after the reaction with EPS at different pH values. The information obtained in this study is of fundamental significance for the understanding of the interaction mechanisms between bacteria and minerals in soil and aquatic environments. [Copyright &y& Elsevier]

Abstract: Equilibrium adsorption along with scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and isothermal titration calorimetry (ITC) techniques were employed to investigate the adhesion of Pseudomonas putida on goethite. The adhesion isotherm revealed the high affinity of P. putida for goethite. The SEM analysis also showed a tight association between bacteria and mineral particles. Larger amounts of adhesion of bacteria on goethite were observed at pH lower than the isoelectric point (IEP) of goethite. The bacterial adhesion increased with increasing concentration of K+. The calorimetric results demonstrated that the P. putida–goethite adhesion was an exothermic process. The adhesion enthalpy increased with increasing pH and concentrations of electrolyte. The increase of the negative enthalpy with increment of temperature indicated that the bacteria–goethite adhesion was an enthalpy-driven process. Electrostatic interactions and hydrogen bonding were considered to contribute mainly to the adhesion of bacterial adhesion on goethite. The data obtained in this study would provide valuable information for a better understanding of the mechanisms of mineral–microorganism interactions in soil and associated environments. [Copyright &y& Elsevier]

Abstract: Bioavailability of pesticides adsorbed on mineral surfaces is an important determinant of their environmental fate. Carbaryl (1-naphthyl-N-methylcarbamate) was used as a model compound to illustrate the impact of adsorption characteristics and microbial activity on the bioavailability of organic compound adsorbed on clay minerals and goethite. Batch experiments were applied to determine the sorption isotherms and biodegradation kinetics. Metabolic activity of Pseudomonas putida in the absence and presence of montmorillonite, kaolinite or goethite was monitored by microcalorimetry. Adsorption mechanisms of carbaryl were studied by Fourier Transform Infrared Spectroscopy (FTIR). Montmorillonite presented a higher adsorption capacity for carbaryl than goethite and kaolinite. Degradation of adsorbed carbaryl by P. putida followed the sequence montmorillonite>kaolinite>goethite, which is in accordance with the binding strength of carbaryl on the minerals. The presence of montmorillonite enhanced the activity of P. putida and ultimately stimulated the bioavailability of carbaryl. Goethite displayed an inhibitory effect on bacterial activity and reduced carbaryl degradation. The biodegradation of mineral-adsorbed carbaryl was mainly controlled by the activity of the degrading microorganisms. [Copyright &y& Elsevier]

[Display omitted] • Distribution of minerals in microaggregates revealed by SEM-EDS. • Coaction of EPS and mineral size on forming the complexes of microaggregates. • EPS is a dispersant in the mineral mixture containing nano-sized goethite. • EPS is an agglomerant in the system containing micro-sized goethite. • No effect in the goethite size on the complexes forming without EPS. Soil microaggregates composed of mineral–mineral and organo-mineral complexes are crucial for controlling many soil ecosystem functions such as soil stability and persistence of organic matter. However, mechanisms of how microbial-derived organic matter (e.g., extracellular polymeric substances, EPS) and particle size of the mineral shape mineral–mineral and organo-mineral complexes in multiphase system are unclear. Here, batch experiments (i.e., mineral mixtures of quartz, kaolinite, and three different sizes of goethite) were used to determine the effect of goethite size and EPS on the formation of mineral–mineral and organo-mineral complexes. Our results revealed that the multiphase system containing micro-sized goethite had a higher proportion of 50–250 μm aggregates than these containing nano-sized goethite in the presence of EPS. When EPS was absent, the particle distribution was not related to goethite size, and the mineral suspension was homogeneous. The mechanisms of mineral–mineral and organo-mineral complexes formation were further investigated by measuring zeta potential. Negatively charged EPS adsorbed onto positively charged goethite surface through electrostatic interactions, resulting in stable organo-mineral complexes and inhibition of mineral–mineral complexes. EPS-goethite interaction resulted in a marked decrease of phosphorus in the suspension, suggesting preferred adsorption of EPS-P compounds to goethite. This interaction led to EPS fractionation which was affected by goethite size due to the particle size-dependent surface interactions. The information obtained in this study is of fundamental significance for understanding the initial formation of microaggregates in the edaphic microenvironment. [ABSTRACT FROM AUTHOR]

The persistence of Escherichia coli O157:H7 in soil is one of the most common causes of the food-borne outbreaks. Nano-sized iron oxide minerals in soil, especially goethite, have been found to reduce bacterial viability, which helps to control the spread of human pathogens. However, little is known about the antibacterial effects of iron oxides with different particle sizes. Our result revealed that the micro-sized goethite exhibited a more effective antibacterial activity against E. coli O157:H7 than the nano-sized goethite. The underlying antibacterial mechanisms were further investigated via single-cell Raman microspectroscopy. The exposure to nano-sized goethite increased the levels of ribonucleoside-related substances, phenylalanine and adenosine 5′-triphosphate, while decreased those of glycogen, protein and lipopolysaccharide & outer membrane porins (LPS & OMPs). Meanwhile, micro-sized goethite triggered less variation in ribonucleoside-related substances and induced more reduction in LPS & OMPs. Therefore, the antibacterial effects of nano-sized goethite were mediated by both ROS-dependent RNA damage and cell membrane destruction, whereas micro-sized goethite induced severer membrane damage and less ROS-dependent oxidative stress. This work demonstrates the role of particle sizes in antibacterial effects of iron oxides and provides implications for the pathogen control in soil. ga1 • Micro-sized goethite exhibited a more effective antibacterial activity than the nano-sized counterparts. • Goethite caused RNA and membrane damages which inhibited protein synthesis and affected energy metabolism. • Antibacterial mechanisms of nano-sized goethite were mediated by both ROS-dependent damage and cell membrane destruction. • Micro-sized goethite induced more severe membrane damage and less ROS-dependent oxidative stress. [ABSTRACT FROM AUTHOR]

Mineral-organic interfacial reactions strongly influence the adsorption, distribution and bioavailability of metal cations in soil systems. The molecular binding mechanisms and distribution of Cd onto goethite, humic acid, Pseudomonas putida cells, and their composites at different mass ratios were studied through the combination of bulk adsorption coupled with EXAFS, ITC and SCM. In binary and ternary composites, the energetics of the overall adsorption of Cd was dominated by the entropy of Cd adsorption onto the organic fraction. The formation of a type-B HA bridging complex >FeOH−HACOOCdOH enhanced Cd adsorption by 10−30% at low Cd concentrations, and more than 93.5% of the adsorbed Cd was bound onto HA fraction. In ternary systems, the component additivity over-estimated Cd adsorption onto bacteria by ~21.8%, likely due to site blocking effects. Models involving the masking of phosphoryl sites and HA bridging reactions can simulate the distribution of Cd in the composites. Our modelling suggests that HA is the main scavenger of Cd under a range of environmental conditions, and that bacteria become important in affecting the distribution of Cd under lower pH settings. This study demonstrates the impact of iron oxide−HA−bacteria interactions on the fate and distribution of Cd in soils and associated environments. ga1 • Adsorption of Cd was driven by entropy increment on organic fraction in composites. • Composite SCMs for Cd adsorption were established based on EXAFS and ITC. • Formation of type-B HA bridging complex enhanced Cd adsorption. • Masking of phosphoryl and HA bridging reduced allocation of Cd onto bacteria. • HA is the main scavenger of Cd under a range of environmental conditions. [ABSTRACT FROM AUTHOR]