Bacterial Adsorption Research Articles

Development of Antimicrobial and Antifouling Universal Coating via Rapid Deposition of Polydopamine and Zwitterionization.

Biomaterials-associated infections (BAIs) are related to bacterial colonization on medical devices, which lead to a serious medical burden, such as increased healthcare cost, prolonged hospital stays, and high mortality and morbidity. To reduce the risk of infections, in this work, a new approach which makes use of a bioinspired coating with dual antimicrobial and antifouling functions was developed through rapid deposition of functional polydopamine (pDA) and antimicrobial copper ions, and subsequent conjugation of zwitterionic antifouling sulfobetaine (SB) moieties by the aza-Michael addition reaction. pDA permits surface-independent versatile functionalization on a variety of substrates, such as TiO2, SiO2, gold, plastics, and Nitinol alloy. The characterizations for chemical elemental compositions and hydrophilicity by X-ray photoelectron spectroscopy and contact angle goniometer, respectively, indicating the successful grafting of SB moieties and the presence of copper ions in the pDA adlayers. Ellipsometric thicknesses of the thin films were followed to monitor the formation of pDA films and the changes after the post conjugation. UV-vis spectroscopy and inductively coupled plasma-mass spectrometry revealed the coordination structure of catechol-Cu, and release profile of Cu2+ from the constructed functional coatings. The superhydrophilic and charge-balanced SB interface allowed effective resistance of bacterial adsorption. Intriguingly, we scrutinized that the release of bactericidal copper ions enables killing the residual amount of adsorbed bacteria. Moreover, viability tests for fibroblast cells indicate the excellent biocompatibility of the developed medical coatings. For real-world implementation, the antifouling and antimicrobial coatings were applied on commercially available silicone-based urinary catheters, and the existence of bacteria was evaluated by using the plate-counting assay. The results showed an undetectable level of living bacteria. Consequently, the dual functional medical coating offers a promising approach to eliminate BAIs for practical applications.

Functional Biointerfaces Based on Mixed Zwitterionic Self-Assembled Monolayers for Biosensing Applications.

Surface modification for biosensors has focused attention for improvement of their sensitivity and specificity, particularly for the detection in complex medium. In this work, we have synthesized zwitterionic carboxybetaine-thiols (CB-thiols) and sulfobetaine-thiols (SB-thiols) for modification of gold substrates to form a functional self-assembled monolayer (SAM) for the immunoassay in a surface plasmon resonance (SPR) biosensor. X-ray photoelectron spectroscopy (XPS), contact angle goniometer, and cyclic voltammetry were applied for characterizations of elemental composition, surface wettability, and packing density, respectively. The antifouling properties of the SAMs were accessed by quantitative analysis of protein and bacterial adsorption. The results from the SAMs with a single component indicated that the SB-thiol SAM provides better surface hydrophilicity, fouling resistance, and packing density as compared to the CB-thiol SAM, likely due to the ionic association of CB moieties. However, the CB-thiol with the functional carboxylate group plays a critical role in postmodification of biomolecules via commercially available amine coupling chemistry. Thus, the mixed SAMs were prepared to integrate the unique characteristics from CB- and SB-thiols to control compositions and surface properties. The immunoassay was performed in the SPR biosensor, showing that the zwitterionic mixed SAM enables immobilization of biorecognition elements (BREs), and improved sensitivity and specificity. Consequently, the work reveals excellent and attractive versatility, antifouling, and functionalizable properties of zwitterionic mixed SAMs comprising CB- and SB-thiols for biosensing applications. This surface chemistry is expected to be applicable to monitor specific molecular recognition events.

Controlled Silanization Using Functional Silatrane for Thin and Homogeneous Antifouling Coatings.

Organosilicons for surface modification are gaining prominence because of their easy and rapid preparation, high availability, and effective modification for varying interfacial properties. However, their implementation has been humbled by poor control of the packing density, thickness, and molecular structures due to the uncontrollable hydrolysis and condensation. This study reports for the first time new functional silatrane chemistry for the precision deposition of a thin and homogeneous zwitterionic coating. Sulfobetaine silatrane (SBSiT) has a tricyclic caged structure and a transannular N → Si dative bond, which shows excellent chemical stability in the presence of water and an acid-modulated hydrolysis characteristic. Results from X-ray photoelectron spectroscopy indicate the progressive deposition of SBSiT on a silicon surface. Characterization using atomic force microscopy and ellipsometry shows the uniform and thin SBSiT films on silicon surfaces. The superior antifouling properties of SBSiT coatings were demonstrated by resisting bacterial and protein adsorption. More importantly, the stable and complete formation of the SBSiT coatings allows an accurate interpretation of the interfacial phenomena for sensing and nanomaterial applications.

Contact Behavior between Cells and Particles in Bioleaching of Precious Metals from Waste Printed Circuit Boards

Bioleaching of precious metals from waste printed circuit boards such as using cyanogenic cultures for extraction of gold and silver has gained considerable attention. It has the advantages of low cost and environmental friendliness. However, low efficiency hindered its industrialization. In this study, a novel strategy has been proposed to improve bioleaching efficiency. We applied optical microscopy to investigate the surface interactions between bacteria and silver particles in two-step bioleaching. Results showed that bacterial adsorption and extracellular polymeric substances (EPS) binding were the primary negative behavior that hindered the leaching reaction. Functional group analysis by Fourier-transform infrared spectroscopy indicated that carboxyl, hydroxyl, and amine groups were the main chemical structures responsible for the negative influences. Bacteria–metal interactions were reduced in the presence of polyvinylpyrrolidone (PVP), and the silver recovery increased 1.8 times. Imaging analysis ...

Polyurethane–polyvinylpyrrolidone iodine blends as potential urological biomaterials

Biomaterial-centred infections are major complications of implanted and indwelling medical devices like urological and venous catheters with significant economic consequences and increased patient morbidity. In the present study, polyurethane (PU) blends comprising the polymeric complex of polyvinylpyrrolidone iodine (PVPI) were developed. The developed PU/PVPI blends were extensively characterized for both surface and thermal properties using contact angle, ATR-FTIR, SEM-EDAX, TGA and DSC analyses. The suitability of the developed blends as urinary tract biomaterial was evaluated using bacterial adhesion (both qualitative and quantitative), protein adsorption and salt encrustation studies. The PU blends with PVPI exhibited reduced protein adsorption and excellent antimicrobial efficacy against the three clinically relevant bacteria, viz. Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa. A progressive increase in the antiadhesive and antimicrobial efficacy was observed with the increase in PVPI concentration from 0.5 to 1.5% w/w in the PU/PVPI blends. The developed blends showed a strong resistance towards salt encrustation process as the deposition of the salts, namely struvite and hydroxyapatite, which usually forms the major components of urinary tract encrustation, was significantly reduced on PU/PVPI blends. Due to the combined antiadhesive, antimicrobial and encrustation-resistant properties, along with good stability these PU/PVPI blends can offer a promising strategy to reduce medical device-associated infections.

Efficient water disinfection using hybrid polyaniline/graphene/carbon nanotube nanocomposites

ABSTRACTPathogens, such as Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), contaminate water resources and are the main causes of diseases, not just waterborne diseases. The present study aims to fabricate hybrid materials composed of polyaniline (PANI), graphene nanosheets (GNs), and carbon nanotubes (CNTs) and utilize the materials for water disinfection. Thus, a new class of hybrid nanocomposites (PANI/GN/CNTsa–e) was fabricated under ultrasonic conditions following a well-known in situ oxidative polymerization technique in an aqueous acidic solution. A homogeneous mixture of GNs and CNTs (40/60 weight %) prepared at 2, 5, 10, 20 and 30% fixed ratios of GNs/CNTs was utilized in the fabrication of the nanocomposites. The structure of this new hybrid class of materials was confirmed by various characterization techniques that were utilized to corroborate their assembly. Column removal studies with bacteria indicated that the removal percentages of S. aureus and E. coli were 99.5 and 99.2%, respectively, using PANI/GN/CNTse. The bacterial count is an indication of bacterial removal after and before adsorption. Additionally, the data indicated clear synergic effects among the nanocomposites. Reuse studies revealed that the same percentage of adsorption was obtained for four cycles, which shows the PANI/GN/CNTse nanocomposites can be reused and recycled for a number of cycles with almost the same bacterial adsorption capability.

Determination of Bacterial Endotoxins in Drugs: False-Negative Results

One of the possible causes of false-negatives in bacterial endotoxin determinations, endotoxin aggregation and adsorption, was examined in a model experiment (positive control). A solution for eliminating the interfering actor using kinetic methods and a dispersing solvent was proposed based with the drug caspofungin as an example.

Remediation potential of immobilized bacterial consortium with biochar as carrier in pyrene-Cr(VI) co-contaminated soil

ABSTRACTPolycyclic aromatic hydrocarbons (PAHs) and potentially toxic trace elements (PTEs) soil contamination have become areas of concern. Bioaugmentation is regarded as an effective bioremediation method, however it is difficult to simultaneously degrade organic compounds and remove PTEs with individual microbial strains. Therefore, the objective of this study was to evaluate the feasibility of using immobilized microbial consortia, including two PAH-degrading bacterial strains (W1 and W2) and a Cr(VI)-reducing bacterium (Y2), for the remediation of pyrene-Cr(VI) co-contaminated soil. Three immobilization methods were investigated: (1) bacterial consortium adsorption onto biochar (BC), (2) bacterial consortium entrapment in alginate beads (AC), (3) bacterial consortium adsorption on biochar and sequential entrapment in alginate beads (BAC). In addition, a free bacterial consortium (FC) was also used for comparison. Ten treatments were designed to illustrate the bioremediation efficiency of the free and immobilized consortia. The results show that treatments AC and BAC resulted in more efficient Cr(VI) removal compared with BC and FC. Pyrene levels in AC and BAC microcosms were reduced from 42.33 ± 3.82 to 11.56 ± 1.37 and 7.48 ± 0.39 mg kg−1, respectively. Bioavailable Cr (VI) in AC and BAC was significantly lower than that in other microcosms after 28 days’ incubation. Both AC and BAC microcosms exhibited a higher level of dehydrogenase and fluorescein diacetate hydrolysis activity. Furthermore, soil microbial diversity was higher in AC and BAC microcosms compared with the others. Thus, the entrapped consortia may be useful for bioremediation of pyrene and Cr (VI) without compromising soil ecology.

Extracellular DNA enhances the adsorption of Sulfobacillus thermosulfidooxidans strain ST on chalcopyrite surface

Extracellular polymeric substances (EPS) and their key components play an important role in bioleaching. Herein, the amount of extracellular DNA (eDNA) secreted by Sulfobacillus thermosulfidooxidans strain ST during bioleaching of chalcopyrite concentrate was investigated through traditional extraction method and confocal laser scanning microscope (CLSM) analysis. DNase I was added into the bioleaching system to degrade eDNA, and then the effects of eDNA deficiency on bacterial adsorption, copper extraction and the synthesis of other key components of EPS were evaluated. The results of adsorption experiment indicated that the adsorption time was prolonged and the equilibrium adsorption quantity was decreased when the eDNA was absent. The bioleaching experiment showed that eDNA in the EPS was favorable to the copper extraction, which increased by 18.5% compared with that of the eDNA-deficient group. Furthermore, it was found that the removal of eDNA decreased the formation of other key EPS components like polysaccharides and proteins. In situ observation and monitoring of eDNA on the chalcopyrite surface by CLSM were carried out. The results showed that the loss of eDNA attenuated the fluorescence intensity of each component of EPS, which was consistent with the above results. These studies suggested that eDNA in the EPS could enhance the adsorption of bacteria on the surface of chalcopyrite and further increase the copper extraction.

Anaerobic microbial activity affects earliest diagenetic pathways of bivalve shells

AbstractThe earliest diagenetic post‐mortem exposure of biogenic carbonates at the sea floor and in the uppermost sediment column results in the colonization of hard‐part surfaces by bacterial communities. Some of the metabolic redox processes related to these communities have the potential to alter carbonate shell properties, and hence affect earliest diagenetic pathways with significant consequences for archive data. During a three‐month in vitro study, shell subsamples of the ocean quahog Arctica islandica (Linnaeus, 1767) were incubated in natural anoxic sediment slurries and bacterial culture medium of the heterotrophic Shewanella sediminisHAW‐EB3. Bulk analyses of the liquid media from the Shewanella sediminis incubation revealed an over ten‐fold increase in total alkalinity, dissolved inorganic carbon and ΩAragonite, and the alteration of the Mg/Ca, Mg/Sr and Sr/Ca ratios relative to control incubations without cultures. Ion ratios were most affected in the incubation with anoxic sediment, depicting a 25% decrease in Mg/Ca relative to the control. Shell sample surfaces that were exposed to both incubations displayed visible surface dissolution features, and an 8 wt% loss in calcium content. No such alteration features were detected in control shells. Apparently, alteration of shell carbonate properties was induced by microbially driven decomposition of shell intercrystalline organic constituents and subsequent opening of pathways for pore fluid–crystal exchange. This study illustrates the potential influence of benthic bacterial metabolism on biogenic carbonate archives during the initial stages of diagenetic alteration within a relatively short experimental duration of only three months. These results suggest that foremost the biological effect of bacterial cation adsorption on divalent cation ratios has the potential to complicate proxy interpretation. Results shown here highlight the necessity to consider bacterial metabolic activities in marine sediments for the interpretation of palaeo‐environmental proxies from shell carbonate archives.

Sulfadiazine/ciprofloxacin promote opportunistic pathogens occurrence in bulk water of drinking water distribution systems.

Effects of sulfadiazine and ciprofloxacin on the occurrence of free-living and particle-associated opportunistic pathogens in bulk water of simulated drinking water distribution systems (DWDSs) were investigated. It was found that sulfadiazine and ciprofloxacin greatly promoted the occurrence of opportunistic pathogens including Pseudomonas aeruginosa, Legionella pneumophila, Mycobacterium avium and its broader genus Mycobacterium spp., as well as the amoebae Acanthamoeba spp. and Hartmanella vermiformis, in bulk water of DWDSs. Moreover, sulfadiazine and ciprofloxacin exhibited much stronger combined effects on the increase of these opportunistic pathogens. Based on the analysis of the antibiotic resistance genes (ARGs) and extracellular polymeric substances (EPS), it was verified that EPS production was increased by the antibiotic resistant bacteria arising from the effects of sulfadiazine/ciprofloxacin. The combined effects of sulfadiazine and ciprofloxacin induced the greatest increase of EPS production in DWDSs. Furthermore, the increased EPS with higher contents of proteins and secondary structure β-sheet led to greater bacterial aggregation and adsorption. Meanwhile, large numbers of suspended particles were formed, increasing the chlorine-resistance capability, which was responsible for the enhancement of the particle-associated opportunistic pathogens in bulk water of DWDSs with sulfadiazine/ciprofloxacin. Therefore, sulfadiazine and ciprofloxacin promoted the occurrence of particle-associated opportunistic pathogens in bulk water of DWDSs due to the role of EPS produced by the bacteria with ARGs.

Streptavidin-coated surfaces suppress bacterial colonization by inhibiting non-specific protein adsorption.

Streptavidin is a 58 kDa tetrameric protein with the highest known affinity to biotin with a wide range of applications in bionanotechnology and molecular biology. Dissolved streptavidin is stable at a broad range of temperature, pH, proteolytic enzymes and exhibits low non-specific binding. In this study, a streptavidin monolayer was assembled directly on a biotinylated TiO2 -surface to investigate its stability against proteolytic digestion and its suppression of initial bacterial adsorption of Escherichia coli, Bacillus subtilis, and Streptococcus intermedius. In contrast to nonmodified TiO2 surfaces, streptavidin-coated substrates showed only a negligible non-specific protein adsorption at physiological protein concentrations as well as a significantly reduced bacterial adhesion. The antiadhesive properties were demonstrated to be the main reason for the suppression of bacterial adhesion, which makes this approach a promising option for future surface biofunctionalization applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 758-768, 2018.

Bacterial adsorption with graphene family materials compared to nano-alumina

The present study investigates the bio-activity and bio-adsorption properties of graphene family materials (GFMs) in comparison to nano-Al2O3 (12 nm, gamma phase). This is the first study that determines the type of solid adsorbent (GFMs or nano-Al2O3) preferred by living bacteria cells. The invest igated GFMs were: graphene, graphene oxide (GO) and reduced graphene oxide (RGO). The SEM images indicated that bacterial preferences depended on the particular strain, the type of GFM and the composition of the suspension. Generally, bacteria preferred to colonize the GFMs surfaces in the presence of nano-Al2O3 which resulted in no changes of zeta potential (ζ) measured for bacteria cells due to the fact that carbon is known as a good nourishment for microorganisms. There were however few exceptions from that rule i.e. the Sarcina bacteria preferred to adsorb on the surface of nano-Al2O3 when suspended with RGO flakes, and the E. coli preferred to colonize the surface of nano-Al2O3 when suspended with graphene sheets. For this suspension, ζ of bacteria cells decreased suggesting their starving state on the surface of nano-Al2O3. We also found disruptions in morphology of almost all E. coli cells, when attached to all investigated adsorbents.

The impact of adsorption on the exposure assessment of Bacillus thuringiensis in the water-sediment system: a mathematical model approach

A model to assess the environmental fate of bacteria to be used as plant protection products or biocides is presented. The model, based on a black-box approach, takes into account the bacterial cell adsorption on the sediment phase and the degradation kinetics and allows the calculation of the expected environmental density of bacterial cells and the predicted environmental concentration of bacterial toxins in the water-sediment system. An example of calculation results is reported for the study cases of Bacillus thuringiensis subsp. aizawai strain GC-91, B. thuringiensis subsp. kurstaki strain ABTS-351, and B. thuringiensis subsp. tenebrionis strain NB 176, used as plant protection products, and B. thuringiensis subsp. israelensis strains AM 65–52 and SA3A, used as biocides. The calculation of expected environmental density and predicted environmental concentration for bacteria in soil-water systems allows to achieve an appropriate risk assessment of the environmental fate and of the impact of bacterial pest control agents or bacterial biocides on non-target organisms.

Carbon nanotubes/carbon fiber hybrid material: a super support material for sludge biofilms

ABSTRACTCarbon fiber (CF) is widely used as a sludge biofilm support material for wastewater treatment. Carbon nanotubes/carbon fiber (CNTs/CF) hybrid material was prepared by ultrasonically assisted electrophoretic deposition (EPD). CF supports (CF without handling, CF oxidized by nitric acid, CNTs/CF hybrid material) were evaluated by sludge immobilization tests, bacterial cell adsorption tests and Derjaguin −Landau −Verwey −Overbeek (DLVO) theory. We found that the CNTs/CF hybrid material has a high capacity for adsorbing activated sludge, nitrifying bacterial sludge and pure strains (Escherichia coli and Staphylococcus aureus). CNTs deposited on CF surface easily wound around the curved surface of bacterial cell which resulted in capturing more bacterial cells. DLVO theory indicated the lowest total interaction energy of CNTs/CF hybrid material, which resulted in the highest bacteria cell adsorption velocity. Experiments and DLVO theory results proved that CNTs/CF hybrid material is a super support material for sludge biofilms.

Effect of ultraviolet treatment on bacterial attachment and osteogenic activity to alkali-treated titanium with nanonetwork structures.

PurposeAlkali-treated titanium with nanonetwork structures (TNS) possesses good osteogenic activity; however, the resistance of this material to bacterial contamination remains inadequate. As such, TNS implants are prone to postoperative infection. In this work, we attempted to alter the biological properties of TNS by treatment with short-duration high-intensity ultraviolet (UV) irradiation.MethodsTNS discs were treated with UV light (wavelength =254 nm, strength =100 mW/cm2) for 15 minutes using a UV-irradiation machine. We carried out a surface characterization and evaluated the discs for bacterial film formation, protein adsorption, and osteogenic features.ResultsThe superhydrophilicity and surface hydrocarbon elimination exhibited by the treated material (UV-treated titanium with a nanonetwork structure [UV-TNS]) revealed that this treatment effectively changed the surface characteristics of TNS. Notably, UV-TNS also showed reduced colonization by Actinomyces oris during an initial attachment period and inhibition of biofilm formation for up to 6 hours. Moreover, compared to conventional TNS, UV-TNS showed superior osteogenic activity as indicated by increased levels of adhesion, proliferation, alkaline phosphatase activity, osteogenic factor production, and osteogenesis-related gene expression by rat bone marrow mesenchymal stem cells (rBMMSCs). This inverse relationship between bacterial attachment and cell adhesion could be due to the presence of electron–hole pairs induced by high-intensity UV treatment.ConclusionWe suggest that simple UV treatment has great clinical potential for TNS implants, as it promotes the osseointegration of the TNS while reducing bacterial contamination, and can be conducted chair-side immediately prior to implantation.

Zearalenone adsorption capacity of lactic acid bacteria isolated from pigs.

The ability to adsorb zearalenone by five strain of lactic acid bacteria was evaluated: four strains of Lactobacillus spp. isolated from pig rectal swabs and one commercial strain (Lactobacillus rhamnosus). Several factors affecting the adsorption capacity were evaluated in order to improve the adsorption of the mycotoxin by bacteria. The stability of the zearalenone–bacteria complex was analyzed. In every case, bacterial adsorption capacity was higher than 40.0%. The strain showing the highest adsorption (68.2%) was selected for the following steps of this research. The adsorption percentages obtained after processing 6.5 and 7.5 mL MRS broth were 57.40% + 3.53 and 64.46% + 0.76, respectively. The stability of zearalenone–bacteria complex was evaluated by successively rinsing. In the first rinsing step 42.26% + 0.414 was still bound. In the second rinsing step 25.12% + 0.664 was still bound, whereas 15.82% + 0.675 remained in the pellet after the third rinse. Results obtained demonstrated that Lactic Acid Bacteria has capacity to adsorb zearalenone. Finally adsorption was increased using a higher volume of initial broth. These results could be used to design a new lyophilized powder for detoxification, using lactic acid bacteria as potential zearalenone adsorbents.

Identification of bacterial contaminants from calcium carbonate filler production lines and an evaluation of biocide based decontamination procedures

The aim of this study was to analyze the bacterial community in the production line of a calcium carbonate filler production company and to investigate possible causes for bacterial presence. Throughout 2012, 24 carbonate slurry and six groundwater samples were analyzed. Pseudomonas and Microbacterium were the most frequent contaminants in the slurry, whereas Pseudomonas and Brevundimonas dominated the groundwater samples. Of the 43 different bacterial strains isolated, only five were found both in the slurry and the groundwater, indicating that the latter was not a major source of contamination. The efficacy of 54 commercial biocidal formulations was tested against an artificial bacterial consortium composed of selected slurry isolates. A formulation containing 7.5–15% (v v–1) bronopol and 1.0–2.5% (v v–1) [chloroisothiazolinone (CIT) + methylisothiazolinone (MIT)] exhibited the highest efficacy. Of the possible causes for bacterial presence, sporogenesis and biocide adsorption to carbonate particles were found to be less probable compared to bacterial adsorption to particles, and the acquisition of resistance to biocides.

Escherichia coli removal from model substrates: Underlying mechanism based on nanofluid structural forces.

Understanding the interactions between bacteria and solid surfaces that result in bacterial adhesion and removal is of immense importance for reducing foodborne illness outbreaks. A nanofluid formulation comprised of a sodium dodecyl sulfate (SDS) micellar aqueous solution in the presence of an organic acid (as a pH controller) was used to test the E. coli K12 removal from two substrates, polyvinylchloride (PVC) and partially hydrophobic glass. We investigated the bacterial removal efficacy based on the combined effect of the nanofluid's structural forces and bacterial isoelectric point. To quantify the bacteria-PVC coverage, we used fluorescence microscope. The Langmuir isotherm at the low volume fraction was applied to estimate the adsorption energy of E. coli K12. We obtained a value of about 2.5±0.2kT. This value compared favorably with the value of 2.1kT reported previously for E. coli NCTC 9002 (Vanloosdrecht et al., 1989). We applied the dynamic light scattering method to estimate the radius of the gyration of E. coli K12. The radius of the gyration was used to estimate the limit of surface area covered by the bacterium and compared it to the surface area measured from the image taken with fluorescence microscope. We found that they are in good agreement with each other. We modeled the nanofluid oscillatory structural energy against the E. coli K12 adsorption energy by applying the statistical mechanics approach. Based on the model prediction, the oscillatory interaction energy was estimated at the vertex between a bacterium and the substrate (i.e., the wedge film's interaction energy at one particle layer). The evaluated film's repulsive energy due to the oscillatory structural forces (OSF) was about 15.6±4.4kT of the 0.02M SMNF (the SDS micellar nanofluid formulation) and several times higher than the bacterial adsorption energy, 2.5±0.2kT. The OSF of the 0.06M SMNF was measured by AFM (the oscillatory decay force curve). The period and number of oscillations versus distance was annualized and used to obtain information for the effective size of the nanoparticles and nanofluid's effective volume fraction. These findings suggest that the OSF is capable of bacteria/microorganism removal from contaminated substrates.

Parameters influencing adsorption of Paraburkholderia phytofirmans PsJN onto bentonite, silica and talc for microbial inoculants

The aim of this study was to evaluate the mineral carriers bentonite, silica and talc as potential supports for immobilization of the plant growth promoting bacterium Paraburkholderia phytofirmans PsJN, and determine the factors influencing bacterial adsorption to provide stable and efficient microbial inoculants for use in the field. Results reveal that adsorption of PsJN depends on pH, the number of immobilized cells decreasing from pH5.5 to 9. Zeta potential measurements indicated that the surface charge of the carrier had certain, but not major influence on bacteria immobilization. The amount of Mg2+ contained in the carrier was a key feature, determining the extent of immobilization of PsJN in buffer (talc>bentonite>silica). Moreover, we evaluated the hydrophobicity and its influence on adsorption of PsJN by measuring the contact angle and the number of adsorbed bacterial cells. Highest number of bacterial cells was found on talc, the most hydrophobic material of the three tested ones (bentonite: 3.8×109CFUg−1; silica: 3.0×109CFUg−1; talc: 1.4×1010CFUg−1). By contrast, similar immobilization capacity was observed on the three materials, when bacteria culturing and bacteria adsorption were performed in a single step. This might be related to the fact that during culturing biofilm is formed as a result of clonal growth of initially attached bacteria, rather than the recruitment of planktonic cells.Altogether, the important factors for adsorption in buffer (pH5.5) appeared to be mainly the electrostatic and hydrophobic interactions.