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The application of zero-valent iron particles (ZVI) for the treatment of heavily polluted environment and its biological effects have been studied for at least two decades. Still, information on the impact on bacterial metabolic pathways is lacking. This study describes the effect of microscale and nanoscale ZVI (mZVI and nZVI) on the abundance of different metabolic pathways in freshwater bacterial communities. The metabolic pathways were inferred from metabolism modelling based on 16S rRNA gene sequence data using paprica pipeline. The nZVI changed the abundance of numerous metabolic pathways compared to a less influencing mZVI. We identified the 50 most affected pathways, where 31 were related to degradation, 17 to biosynthesis, and 2 to detoxification. The linkage between pathways was two times higher in nZVI samples compared to mZVI, and was specifically higher considering the arsenate detoxification II pathway. Limnohabitans and Roseiflexus were linked to the same pathways in both nZVI and mZVI. The prediction of metabolic pathways increases our knowledge of the impacts of nZVI and mZVI on freshwater bacterioplankton.

Nanomaterials have attracted research attention due to their unique properties, which have also made them increasingly useful for various applications, including remediation technologies. In this work, we tried to explore the aging phenomenon of several newly developed nanoscale zero-valent iron (nZVI) particles containing 0.25, 1, and 5% sulfur and to monitor the possible toxicity changes related to the nZVI particles before and during the aging period. We used several relevant techniques for monitoring nZVI aging, including transmission electron microscopy, X-ray powder diffraction, and particle size analysis. The toxicity of the nZVI particles was monitored using a new oxidative stress assay based on lipid peroxidation, a simple bacterial cultivation test. A test using activated sludge respiration and phospholipid fatty acid analysis of microbial populations was also employed. The results of the material analyses showed that the sulfidated nZVI particles were more stable than bare nZVI particles in terms of Fe0 content and particle diameter. The stability was more pronounced with the increasing content of sulfur in the nanoparticles; the content of α-Fe was only 35.3% in the nZVI particles compared with 78.6% in the 5% sulfur-doped nanoparticles after 60 days of aging. The results of the oxidative stress assay revealed that the toxicity was also lower with increasing sulfur content; nevertheless, the oxidative stress marker increased substantially after 7 days of aging, reaching a similar level to that caused by bare nZVI in some cases. Other results showed that even incubation in media used for the respective tests caused extensive aging; therefore, this information must be considered before the selection of toxicity assays for nanomaterial evaluation.

Decades of antibiotic use and misuse have generated selective pressure toward the rise of antibiotic-resistant bacteria, which now contaminate our environment and pose a major threat to humanity. According to the evolutionary "Red queen theory", developing new antimicrobial technologies is both urgent and mandatory. While new antibiotics and antibacterial technologies have been developed, most fail to penetrate the biofilm that protects bacteria against external antimicrobial attacks. Hence, new antimicrobial formulations should combine toxicity for bacteria, biofilm permeation ability, biofilm deterioration capability, and tolerability by the organism without renouncing compatibility with a sustainable, low-cost, and scalable production route as well as an acceptable ecological impact after the ineluctable release of the antibacterial compound in the environment. Here, we report on the use of silver nanoparticles (NPs) doped with magnetic elements (Co and Fe) that allow standard silver antibacterial agents to perforate bacterial biofilms through magnetophoretic migration upon the application of an external magnetic field. The method has been proved to be effective in opening micrometric channels and reducing the thicknesses of models of biofilms containing bacteria such as

Background Nanoscale zero-valent iron (nZVI) is commonly used for remediation of groundwater contaminated by chlorinated ethenes (CEs); however, its long-term reactivity and subsurface transport are limited. A novel nZVI–AC material, consisting of colloidal activated carbon (AC) with embedded nZVI clusters, was developed with the aim of overcoming the limitations of nZVI alone. Results Application of a limited amount of nZVI–AC to an oxic, nitrate-rich, highly permeable quaternary aquifer triggered time-limited transformation of CEs, with noticeable involvement of reductive dechlorination. Reductive dechlorination of CEs was dominantly abiotic, as an increase in the concentration of vinyl chloride (VC) and ethene did not coincide with an increase in the abundance of reductive biomarkers for complete dechlorination of CEs (Dehalococcoides, Dehalogenimonas, VC reductase genes vcrA and bvcA). Application of nZVI–AC under unfavourable hydrochemical conditions resulted in no dramatic change in the microbial community, the reducing effect resulting in temporal proliferation of nitrate and iron reducers only. At a later stage, generation of reduced iron induced an increase in iron-oxidizing bacteria. High concentrations and a continuous mass influx of competing electron acceptors (nitrate and dissolved oxygen) created unfavourable conditions for sulphate-reducers and organohalide-respiring bacteria, though it allowed the survival of aerobic microorganisms of the genera Pseudomonas, Polaromonas and Rhodoferax, known for their ability to assimilate VC or cis-1,2-dichloroethene. A potential for aerobic oxidative degradation of CE metabolites was also indicated by detection of the ethenotroph functional gene etnE. Conclusions This pilot study, based on the application of nZVI–AC, failed to provide a sustainable effect on CE contamination; however, it provided valuable insights into induced hydrogeochemical and microbial processes that could help in designing full-scale applications.

The application of zero-valent iron particles (ZVI) for the treatment of heavily polluted environment and its biological effects have been studied for at least two decades. Still, information on the impact on bacterial metabolic pathways is lacking. This study describes the effect of microscale and nanoscale ZVI (mZVI and nZVI) on the abundance of different metabolic pathways in freshwater bacterial communities. The metabolic pathways were inferred from metabolism modelling based on 16S rRNA gene sequence data using paprica pipeline. The nZVI changed the abundance of numerous metabolic pathways compared to a less influencing mZVI. We identified the 50 most affected pathways, where 31 were related to degradation, 17 to biosynthesis, and 2 to detoxification. The linkage between pathways was two times higher in nZVI samples compared to mZVI, and was specifically higher considering the arsenate detoxification II pathway. Limnohabitans and Roseiflexus were linked to the same pathways in both nZVI and mZVI. The prediction of metabolic pathways increases our knowledge of the impacts of nZVI and mZVI on freshwater bacterioplankton.

As nanoremediation strategies for in-situ groundwater treatment extend beyond nanoiron-based applications to adsorption and oxidation, ecotoxicological evaluations of newly developed materials are required. The biological effects of four new materials with different iron (Fe) speciations ([i] FerMEG12 - pristine flake-like milled Fe(0) nanoparticles (nZVI), [ii] Carbo-Iron® - Fe(0)-nanoclusters containing activated carbon (AC) composite, [iii] Trap-Ox® Fe-BEA35 (Fe-zeolite) - Fe-doped zeolite, and [iv] Nano-Goethite - ‘pure’ FeOOH) were studied using the unicellular green alga Chlamydomonas sp. as a model test system. Algal growth rate, chlorophyll fluorescence, efficiency of photosystem II, membrane integrity and reactive oxygen species (ROS) generation were assessed following exposure to 10, 50 and 500 mg L−1 of the particles for 2 h and 24 h. The particles had a concentration-, material- and time-dependent effect on Chlamydomonas sp., with increased algal growth rate after 24 h. Conversely, significant intracellular ROS levels were detected after 2 h, with much lower levels after 24 h. All Fe-nanomaterials displayed similar Z-average sizes and zeta-potentials at 2 h and 24 h. Effects on Chlamydomonas sp. decreased in the order FerMEG12 > Carbo-Iron® > Fe-zeolite > Nano-Goethite. Ecotoxicological studies were challenged due to some particle properties, i.e. dark colour, effect of constituents and a tendency to agglomerate, especially at high concentrations. All particles exhibited potential to induce significant toxicity at high concentrations (500 mg L−1), though such concentrations would rapidly decrease to mg or µg L−1 in aquatic environments, levels harmless to Chlamydomonas sp. The presented findings contribute to the practical usage of particle-based nanoremediation in environmental restoration.

While nano-scale and micro-scale zero-valent iron (nZVI and mZVI) particles show high potential for remediation of polluted soil aquifers and elimination of cyanobacterial blooms, this has required their release into the environment. This study compares the impact of 100 mg L−1 of nZVI and mZVI on natural planktonic microorganisms from a reservoir, incubated in 1.5 L batches over 21 days. In addition to counting cyanobacterial and algal cell numbers, bacterial community structure was assessed using Ion Torrent sequencing and the number of cultivable bacteria determined using standard cultivation methods. Surprisingly, while mZVI had no significant effect on algal cell number, cyanobacteria numbers increased slightly after 14 days (P < 0.05). Algae were only marginally affected by nZVI after seven days (P < 0.05), while cyanobacteria numbers remained unaffected after 21 days. Total species richness and less common bacteria increased significantly when treated with mZVI (compared to nZVI). The abundance of Limnohabitans (Betaproteobacteria), Roseiflexus (Chloroflexi), hgcl_clade (Actinobacteria) and Comamonadaceae_unclassified (Betaproteobacteria) increased under nZVI treatment, while mZVI enhanced Opitutae_vadinHA64 (Verrucomicrobia) and the OPB35_soil_group (Verrucomicrobia). Interestingly, the number of cultivable bacteria increased significantly after three days in water with nZVI, and further still after seven days. nZVI shaped bacterial community both directly, through release of Fe(II)/Fe(III), and indirectly, through rapid oxygen consumption and establishment of reductive conditions. The strong physico-chemical changes caused by nZVI proved temporary; hence, it can be assumed that, under natural conditions in resilient reservoirs or lakes, microbial plankton would recover within days or weeks.

A facile and eco-friendly approach is developed for the synthesis of a poly(3-hydroxybutyrate)–chitosan (PHB–chit) polymer conjugate, which is an ideal material for the synthesis of safer gold nanoparticles (nAu). The synthesized products are characterized by various electron-based, optical and spectroscopic techniques including the catalytic activity and the stability/toxicity of nAu. In contrast to the conventional synthesis approaches, the use of PHB–chit results in generation of a highly stable and size-controlled nAu material that exhibits important catalytic activity towards the reduction of 4-nitrophenol (4-NP) to 4-aminophenol, and at the same time shows no toxicity against living bacterial systems such as Escherichia coli or Staphylococcus aureus. The synthesis route reported herein would inspire future developments that circumvent toxicity issues of relevance to living systems while performing common catalytic experimentation.

Abiotic and biotic remediation of chlorinated ethenes (CEs) in groundwater from a real contaminated site was studied using biochar-based composites containing nanoscale zero-valent iron (nZVI/BC) and natural resident microbes/specific CE degraders supported by a whey addition. The material represented by the biochar matrix decorated by isolated iron nanoparticles or their aggregates, along with the added whey, was capable of a stepwise dechlorination of CEs. The tested materials (nZVI/BC and BC) were able to decrease the original TCE concentration by 99% in 30 days. Nevertheless, regarding the transformation products, it was clear that biotic as well as abiotic transformation mechanisms were involved in the transformation process when nonchlorinated volatiles (i.e., methane, ethane, ethene, and acetylene) were detected after the application of nZVI/BC and nZVI/BC with whey. The whey addition caused a massive increase in bacterial biomass in the groundwater samples (monitored by 16S rRNA sequencing and qPCR) that corresponded with the transformation of trichloro- and dichloro-CEs, and this process was accompanied by the formation of less chlorinated products. Moreover, the biostimulation step also eliminated the adverse effect caused by nZVI/BC (decrease in microbial biomass after nZVI/BC addition). The nZVI/BC material or its aging products, and probably together with vinyl chloride-respiring bacteria, were able to continue the further reductive dechlorination of dichlorinated CEs into nonhalogenated volatiles. Overall, the results of the present study demonstrate the potential, feasibility, and environmental safety of this nanobioremediation approach.

Bio-based plastics, produced from renewable biomass sources, may contribute to lowering greenhouse gases and the demand for fossil resources. However, their environmental fate is not well understood. Here, we compared the impacts of industrially produced granules (G) and micro-debris (MD) from three pristine bio-based plastics: high-density polyethylene (HDPE), polylactic acid (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) on natural bacterial communities in seawater and freshwater using metagenomics. After one month, we found a dissimilarity between the microbial communities forming a biofilm on the plastics and planktonic bacteria. Further, different bacterial groups became dominant on different bio-based plastics, i.e. Burkholderiaceae, Solimonadaceae, Oleiphilaceae, and Sneathiellaceae on HDPE and Alteromonadaceae on PLA and Rhodobacteraceae on PHBV in seawater, and Beijerinckiaceae and Chitinophagaceae on HDPE, Microtrichaceae on PLA and Caulobacteraceae and Sphingomonadaceae on PHBV in freshwater. Variovorax, Albimonas and Sphingomonas genera were recorded on bio-based plastics in both seawater and freshwater. This study describes how different bio-based plastic materials and granule sizes influence the development of natural bacterial communities.

Tree gums are a class of abundantly available carbohydrate polymers that have not been explored thoroughly in film fabrication for food packaging. Films obtained from pristine tree gums are often brittle, hygroscopic, and lack mechanical strength. This study focuses on the chemical modification of gum kondagogu using long-chain alkenyl groups of dodecenyl succinic anhydride (DDSA), an esterifying agent that introduces a 12-carbon hydrophobic chain to the kondagogu structure. The esterification reaction was confirmed by 1H nuclear magnetic resonance and Fourier-transform infrared spectroscopy. The effect of nano-cellulose as an additive on various film properties was investigated. The developed films were characterized for their mechanical, morphological, optical, barrier, antibacterial, and biodegradable properties. The inclusion of long-chain carbon groups acted as internal plasticizers and resulted in an amorphous structure with better film-forming ability, improved hydrophobicity, and higher elongation at break values. The modified films exhibited antibacterial properties and excellent biodegradability under aerobic conditions.

Nanoremediation with iron (Fe) nanomaterials opens new doors for treating contaminated soil and groundwater, but is also accompanied by new potential risks as large quantities of engineered nanomaterials are introduced into the environment. In this study, we have assessed the ecotoxicity of four engineered Fe nanomaterials, specifically, Nano-Goethite, Trap-Ox Fe-zeolites, Carbo-Iron® and FerMEG12, developed within the European FP7 project NanoRem for sub-surface remediation towards a test battery consisting of eight ecotoxicity tests on bacteria (V. fisheri, E. coli), algae (P. subcapitata, Chlamydomonas sp.), crustaceans (D. magna), worms (E. fetida, L. variegatus) and plants (R. sativus, L. multiflorum). The tested materials are commercially available and include Fe oxide and nanoscale zero valent iron (nZVI), but also hybrid products with Fe loaded into a matrix. All but one material, a ball milled nZVI (FerMEG12), showed no toxicity in the test battery when tested in concentrations up to 100 mg/L, which is the cutoff for hazard labeling in chemicals regulation in Europe. However it should be noted that Fe nanomaterials proved challenging to test adequately due to their turbidity, aggregation and sedimentation behavior in aqueous media. This paper provides a number of recommendations concerning future testing of Fe nanomaterials and discusses environmental risk assessment considerations related to these.

The objective of present study was to develop multifunctional and wearable electrically conductive fabrics with acceptable comfort properties by in-situ deposition of silver particles. The effect of silver nitrate concentration and number of dips was investigated for change in electrical conductivity, EMI shielding, and antimicrobial properties of coated fabrics. The dynamic light scattering and SEM analysis were employed to study the morphology of deposited silver particles. The EMI shielding was found to increase with increase in concentration of silver particles. Later, the comfort and mechanical properties were studied. No significant decrease in air permeability and water vapor permeability was observed due to partial coverage of fabric pores by coating of silver particles. Moreover, the coated fabrics also showed promising behavior toward antimicrobial properties. When the durability of coated fabrics was examined against washing, the application of binder provided good retention of silver p...

Organic–inorganic perovskite solar cells (PSCs) are promising candidates as photovoltaic cells. Recently, they have attracted significant attention due to certified power conversion efficiencies exceeding 23%, low–cost engineering, and superior electrical/optical characteristics. These PSCs extensively utilize a perovskite–structured composite with a hybrid of Pb-based nanomaterials. Operation of them may cause the release of Pb-based nanoparticles. However, limited information is available regarding the potential toxicity of Pb-based PSCs on various organisms. This study conducted a battery of in vitro and in vivo toxicity bioassays for three quintessential Pb-based PSCs (CH3NH3PbI3, NHCHNH3PbBr3, and CH3NH3PbBr3) using progressively more complex forms of life. For all species tested, the three different perovskites had comparable toxicities. The viability of Caco–2/TC7 cells was lower than that of A549 cells in response to Pb-based PSC exposure. Concentration–dependent toxicity was observed for the bioluminescent bacterium Vibrio fischeri, for soil bacterial communities, and for the nematode Caenorhabditis elegans. Neither of the tested Pb-based PSCs particles had apparent toxicity to Pseudomonas putida. Among all tested organisms, V. fischeri showed the highest sensitivity with EC50 values (30 min of exposure) ranging from 1.45 to 2.91 mg L-1. Therefore, this study recommends that V. fischeri should be preferably utilized to assess.PSC toxicity due to its increased sensitivity, low costs, and relatively high throughput in a 96–well format, compared with the other tested organisms. These results highlight that the developed assay can easily predict the toxic potency of PSCs. Consequently, this approach has the potential to promote the implementation of the 3Rs (Replacement, Reduction, and Refinement) principle in toxicology and decrease the dependence on animal testing when determining the safety of novel PSCs.

Multifunctional nanoparticles for magnetic hyperthermia which simultaneously display antibacterial properties promise to decrease bacterial infections co-localized with cancers. Current methods synthesize such particles by multi-step procedures, and systematic comparisons of antibacterial properties between coatings, as well as measurements of specific absorption rate (SAR) during magnetic hyperthermia are lacking. Here we report the novel simple method for synthesis of magnetic nanoparticles with shells of oleic acid (OA), polyethyleneimine (PEI) and polyethyleneimine-methyl cellulose (PEI-mC). We compare their antibacterial properties against single gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria as well as biofilms. Magnetite nanoparticles (MNPs) with PEI-methyl cellulose were found to be most effective against both S. aureus and E. coli with concentration for 10% growth inhibition (EC10) of

Despite the ground-breaking potential of nanomaterials, their safe and sustainable incorporation into an array of industrial markets prompts a deep and clear understanding of their potential toxicity for both humans and the environment. Among the many materials with great potential, graphene has shown promise in a variety of applications; however, the impact of graphene based products on living systems remains poorly understood. In this paper, we illustrate that via exploiting the tribological properties of graphene nanosheets, we can successfully improve both the frictional behaviour and the anti-wear capacity of lubricant oil for mechanical transmission. By virtue of reducing friction and enhancing lubricant lifetimes, we can forecast a reduction in friction based energy loss, in addition to a decrease in the carbon footprint of vehicles. The aforementioned positive environmental impact is further strengthened considering the lack of acute toxicity found in our extensive in vitro investigation, in which both eukaryotic and prokaryotic cells were tested. Collectively, our body of work suggests that by the use of safe nanoadditives we could contribute to reducing the environmental impact of transportation and therein take a positive step towards a more sustainable automotive sector. The workflow proposed here for the evaluation of human and environmental toxicity will allow for the study of nanosized bare graphene material and can be broadly applied to the translation of graphene-based nanomaterials into the market.

Recently, the green synthesis of metal nanoparticles has attracted wide attention due to its feasibility and very low environmental impact. This approach was applied in this study to synthesise nanoscale gold (Au), platinum (Pt), palladium (Pd), silver (Ag) and copper oxide (CuO) materials in simple aqueous media using the natural polymer gum karaya as a reducing and stabilising agent. The nanoparticles’ (NPs) zeta-potential, stability and size were characterised by Zetasizer Nano, UV–Vis spectroscopy and by electron microscopy. Moreover, the biological effect of the NPs (concentration range 1.0–20.0 mg/L) on a unicellular green alga (Chlamydomonas reinhardtii) was investigated by assessing algal growth, membrane integrity, oxidative stress, chlorophyll (Chl) fluorescence and photosystem II photosynthetic efficiency. The resulting NPs had a mean size of 42 (Au), 12 (Pt), 1.5 (Pd), 5 (Ag) and 180 (CuO) nm and showed high stability over 6 months. At concentrations of 5 mg/L, Au and Pt NPs only slightly reduced algal growth, while Pd, Ag and CuO NPs completely inhibited growth. Ag, Pd and CuO NPs showed strong biocidal properties and can be used for algae prevention in swimming pools (CuO) or in other antimicrobial applications (Pd, Ag), whereas Au and Pt lack these properties and can be ranked as harmless to green alga. Electronic supplementary material The online version of this article (10.1186/s11671-018-2575-5) contains supplementary material, which is available to authorized users.

The present study explores the synthesis of dodecenyl succinic anhydride (DDSA) modified deacetylated gum Kondagogu (DGK) in an aqueous phase and its characterization. The fabrication of nanofibre membranes (NFM) was provided using a mixture of polyvinyl alcohol (PVA, 10 wt.%) and DDSA/DGK (10 wt.%) by the electrospinning method. The electrospun PVA/DDSA/DGK nanofibre membrane was cross-linked by heating at 130 °C and later by oxygen plasma treatment. The morphology and characterization of the cross-linked untreated nanofibre (U-NFM) and plasma treated (P-NFM) membranes were investigated by water contact angle measurements; scanning electron microscopy and Fourier transform infrared (FTIR) spectroscopy. The plasma treatment resulted in reduced fibre diameter, increased surface roughness, and enhanced hydrophilicity and created additional oxygen rich functionalities such as carbonyl, carboxyl and hydroxyl groups. The anti-microbial activities of the P-NFM and U-NFM were then investigated against Gram-negative Escherichia coli and Pseudomonas aeruginosa, and Gram-positive Staphylococcus aureus. It was found that plasma modification enhances the antibacterial properties of the membrane in comparison to the unmodified sample. The inhibition of different bacteria on P-NFM was found to be higher compared to U-NFM and decreases as follows: S. aureus > E. coli > P. aeruginosa. This study suggests that plasma modified electrospun membranes could be used as antimicrobial membranes in food, water and environmental applications.

The most challenging task in the preparation of magnetic poly(N-isopropylacrylamide) (Fe3O4-PNIPAAm) nanocomposites for bio-applications is to maximise their reactivity and stability. Emulsion polymerisation, in situ precipitation and physical addition were used to produce Fe3O4-PNIPAAm-1, Fe3O4-PNIPAAm-2 and Fe3O4-PNIPAAm-3, respectively. Their properties were characterised using scanning electron microscopy (morphology), zeta-potential (surface charge), thermogravimetric analysis (stability), vibrating sample magnetometry (magnetisation) and dynamic light scattering. Moreover, we investigated the antibacterial effect of each nanocomposite against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Both Fe3O4-PNIPAAm-1 and Fe3O4-PNIPAAm-2 nanocomposites displayed high thermal stability, zeta potential and magnetisation values, suggesting stable colloidal systems. Overall, the presence of Fe3O4-PNIPAAm nanocomposites, even at lower concentrations, caused significant damage to both E. coli and S. aureus DNA and led to a decrease in cell viability. Fe3O4-PNIPAAm-1 displayed a stronger antimicrobial effect against both bacterial strains than Fe3O4-PNIPAAm-2 and Fe3O4-PNIPAAm-3. Staphylococcus aureus was more sensitive than E. coli to all three magnetic PNIPAAm nanocomposites.

Elementary mode analysis (EMA) identifies all possible metabolic states of the cell metabolic network. Investigation of these states can provide a detailed insight into the underlying metabolism in the cell. In this study, the flux states of Scheffersomyces (Pichia) stipitis metabolism were examined. It was shown that increasing oxygen levels led to a decrease of ethanol synthesis. This trend was confirmed by experimental evaluation of S. stipitis in glucose-xylose fermentation. The oxygen transfer rate for an optimal ethanol production was 1.8 mmol/l/h, which gave the ethanol yield of 0.40 g/g and the ethanol productivity of 0.25 g/l/h. For a better understanding of the cell's regulatory mechanism in response to oxygenation levels, EMA was used to examine metabolic flux patterns under different oxygen levels. Up- and downregulation of enzymes in the network during the change of culturing condition from oxygen limitation to oxygen sufficiency were identified. The results indicated the flexibility of S. stipitis metabolism to cope with oxygen availability. In addition, relevant genetic targets towards improved ethanol-producing strains under all oxygenation levels were identified. These targeted genes limited the metabolic functionality of the cell to function according to the most efficient ethanol synthesis pathways. The presented approach is promising and can contribute to the development of culture optimization and strain engineers for improved lignocellulosic ethanol production by S. stipitis.

Gum karaya (GK), a natural hydrocolloid, was mixed with polyvinyl alcohol (PVA) at different weight ratios and electrospun to produce PVA/GK nanofibers. An 80 : 20 PVA/GK ratio produced the most suitable nanofiber for further testing. Silver nanoparticles (Ag-NPs) were synthesised through chemical reduction of AgNO3(at different concentrations) in the PVA/GK solution, the GK hydroxyl groups being oxidised to carbonyl groups, and Ag+cations reduced to metallic Ag-NPs. These PVA/GK/Ag solutions were then electrospun to produce nanofiber membranes containing Ag-NPs (Ag-MEMs). Membrane morphology and other characteristics were analysed using scanning electron microscopy coupled with energy dispersive X-ray analysis, transmission electron microscopy, and UV-Vis and ATR-FTIR spectroscopy. The antibacterial activity of the Ag-NP solution and Ag-MEM was then investigated against Gram-negativeEscherichia coliandPseudomonas aeruginosaand Gram-positiveStaphylococcus aureus. Our results show that electrospun nanofiber membranes based on natural hydrocolloid, synthetic polymer, and Ag-NPs have many potential uses in medical applications, food packaging, and water treatment.

Magnetite (Fe3O4) nanoparticles were prepared using coprecipitation and subsequently surface-functionalized with 3-aminopropyltriethoxysilane (APTS), polyethylene glycol (PEG), and tetraethoxysilane (TEOS). Nanoparticle morphology was characterized using scanning electron microscopy, while structure and stability were assessed through infrared spectroscopy and zeta potential, respectively. Average size of the nanoparticles analysed by dynamic light scattering was 89 nm, 123 nm, 109 nm, and 130 nm for unmodified magnetite and APTS-, PEG-, and TEOS-modified magnetite nanoparticles, respectively. Biological effect was studied on two bacterial strains: Gram-negativeEscherichia coliCCM 3954 and Gram-positiveStaphylococcus aureusCCM 3953. Most of modified magnetite nanoparticles had a significant effect onS. aureusand not onE. coli, whereas PEG-magnetite nanoparticles displayed no significant effect on the growth rate of either bacteria.

Scheffersomyces stipitis was cultivated in an optimized, controlled fed-batch fermentation for production of ethanol from glucose-xylose mixture. Effect of feed medium composition was investigated on sugar utilization and ethanol production. Studying influence of specific cell growth rate on ethanol fermentation performance showed the carbon flow towards ethanol synthesis decreased with increasing cell growth rate. The optimum specific growth rate to achieve efficient ethanol production performance from a glucose-xylose mixture existed at 0.1 h(-1). With these optimized feed medium and cell growth rate, a kinetic model has been utilized to avoid overflow metabolism as well as to ensure a balanced feeding of nutrient substrate in fed-batch system. Fed-batch culture with feeding profile designed based on the model resulted in high titer, yield, and productivity of ethanol compared with batch cultures. The maximal ethanol concentration was 40.7 g/L. The yield and productivity of ethanol production in the optimized fed-batch culture was 1.3 and 2 times higher than those in batch culture. Thus, higher efficiency ethanol production was achieved in this study through fed-batch process optimization. This strategy may contribute to an improvement of ethanol fermentation from lignocellulosic biomass by S. stipitis on the industrial scale.

Optimization of culture parameters for achieving the most efficient ethanol fermentation is challenging due to multiple variables involved. Here we presented a rationalized methodology for multi-variables optimization through the design of experiments DoE approach. Three critical parameters, pH, temperature, and agitation speed, affecting ethanol fermentation in S. stipitis was investigated. A predictive model showed that agitation speed significantly affected ethanol synthesis. Reducing pH and temperature also improved ethanol production. The model identified the optimum culture conditions for the most efficient ethanol production with the yield and productivity of 0.46 g/g and 0.28 g/l h, respectively, which is consistent with experimental observation. The results also indicated the scalability of the model from shake flask to bioreactor. Thus, DoE is a promising tool permitting the rapid establishment of culture conditions for the most efficient ethanol fermentation in S. stipitis. The approach could be useful to reduce process development time in lignocellulosic ethanol industry. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012