Enhanced antimicrobial activity of the food-protecting nisin peptide by bioconjugation with silver nanoparticles

Nisin is an antimicrobial peptide widely used in the food industry. The efficacy of nisin has decreased due to the development of resistant bacteria. For instance, bacteria such as Staphylococcus aureus have resistance by digesting nisin using the nisinase enzyme. The efficacy of nisin could be improved using bioconjugation with metal nanoparticles. Here we synthesized silver nanoparticles using the extract of Cymbopogon citratus; then, we bioconjugated those silver nanoparticles with nisin to form a nanosilver bioconjugate. Silver nanoparticles and silver bioconjugate were characterized by UV–Vis spectroscopy, nanoparticle tracking analysis, zeta potential measurement and transmission electron microscopy. In vitro antimicrobial efficacy of both silver nanoparticles and silver bioconjugate was evaluated against selected food spoilage microorganisms such as Listeria monocytogenes, S. aureus, Pseudomonas fluorescens, Aspergillus niger and Fusarium moniliforme. Results show that the antimicrobial potential of nisin increased after bioconjugation with silver nanoparticles. Further, we developed agar film containing nanosilver bioconjugate and also evaluated its antimicrobial activity against selected food spoilage microorganisms. The agar film demonstrated maximum activity against P. fluorescens, of 19 mm, and the minimum against F. moniliforme, of 12 mm. Overall, agar film containing nisin and silver nanoparticles can be used against food spoilage microorganisms.     

Influence of physico-chemical properties of soil clay fractions on the retention of dissolved organic carbon

This study investigated the effects of surface functional groups, cation exchange capacity (CEC), surface charge, sesquioxides and specific surface area (SSA) of three soil clay fractions (SCFs) (kaolinite–illite, smectite and allophane) on the retention of dissolved organic carbon (DOC) in soils. Physico-chemical properties of the SCFs before and after removing native carbon and/or sesquioxides were characterised, and the DOC adsorption–desorption tests were conducted by a batch method. Native organic carbon (OC)/sesquioxide removal treatments led to a small change in the CEC values of kaolinite–illite, but significant changes in those of smectite and allophane. The net negative surface charge increased in all samples with an increase in pH indicating their variable charge characteristics. The removal of native OC resulted in a slight increase in the net positive charge on soil clay surfaces, while sesquioxide removal increased the negative charge. Changes in the functional groups on the SCF surfaces contributed to the changes in CEC and zeta potential values. There was a strong relationship (R ² = 0.93, p < 0.05) between the Langmuir maximum DOC adsorption capacity (Q _max) and SSA. The Q _max value also showed a moderately strong relationship (R ² = 0.55, p < 0.05) with zeta potential (at pH 7). Q _max was only poorly correlated with CEC and native OC content. Therefore, along with SSA, the surface charge and functional groups of SCFs played the key role in determining the adsorption affinity and hence retention of DOC in soils.     

Properties,synthesis and toxicity of silver nanoparticles

Silver nanoparticles are actually used in several industrial sectors and end up in the environment, thus inducing a possible toxicity for living organisms. This article reviews the properties, synthesis and toxicology of silver nanoparticles, with focus on the toxicity for insects such as Bombyx mori.     

Drag coefficient for rigid vegetation in subcritical open-channel flow

Drag coefficient has been commonly used as a quantifying parameter to represent the vegetative drag, i.e., resistance to the flow by vegetation. In this study, the measured data on the drag coefficient for rigid vegetation in subcritical open-channel flow reported in previous studies are collected and preprocessed for multi-parameter analysis. The effect of Froude number (Fr) on the drag coefficient for rigid vegetation in subcritical flow cannot be ignored, especially when \(Fr < 0.12\). The drag coefficient is observed to exponentially decrease with the stem Reynolds number (R _d ) and logarithmically decreased with the vegetation density (λ) when \(0.012 < \lambda < 0.12\). The relative submergence (h ^* ) has a significant effect on the drag coefficient, and a positive logarithmic relationship is summarized. A simplified three-stage empirical formula is obtained based on the divisions of Fr. Laboratory tests (with \(Fr < 0.02\)) prove that the present empirical model has higher precision compared with existing models.     

Simple model of sludge thickening process in secondary settlers

In wastewater treatment plants (WWTPs), a secondary settler acts as a clarifier, sludge thickener, and sludge storage tank during peak flows and therefore plays an important role in the performance of the activated sludge process. Sludge thickening occurs in the lower portions of secondary clarifiers during their operation. In this study, by detecting the hindered zone from the complete thickening process of activated sludge, a simple model for the sludge thickening velocity, u _s = aX ^b (a = 0.9925SSVI _3.5, b = 3.541ln(SSVI _3.5)+12.973), describing the potential and performance of activated sludge thickening in the hindered zone was developed. However, sludge thickening in the compression zone was not studied because sludge in the compression zone showed limited thickening. This empirical model was developed using batch settling data obtained from four WWTPs and validated using measured data from a fifth WWTP to better study sludge thickening. To explore different sludge settling and thickening mechanisms, the curves of sludge thickening and sludge settling were compared. Finally, it was found that several factors including temperature, stirring, initial depth, and polymer conditioning can lead to highly concentrated return sludge and biomass in a biologic reactor.     

Fungicidal activity of Cu nanoparticles against <Emphasis Type="Italic">Fusarium</Emphasis> causing crop diseases

In India more than 60 % of the population relies on crops for their livelihood. However, crop diseases are one of the major factors limiting productivity. Hence, nanotechnology appears as a new means to control diseases and enhance yield. Here, stable copper nanoparticles were synthesized using cetyl trimethyl ammonium bromide and copper nitrate at room temperature, then characterized by UV–Visible spectrophotometry, X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and zeta potential measurement. The antifungal activity was evaluated against three common crop pathogenic Fusarium spp. We found that stable copper nanoparticles synthesized using 0.030 M cetyl trimethyl ammonium bromide and 0.003 M copper nitrate have the maximum activity against Fusarium equiseti with a 25 mm zone of inhibition, followed by F. oxysporum (20 mm) and F. culmorum (19 mm).     

Heterologous expression of <Emphasis Type="Italic">LamA</Emphasis> gene encoded endo-β-1,3-glucanase and CO<Subscript>2</Subscript> fixation by bioengineered <Emphasis Type="Italic">Synechococcus</Emphasis> sp. PCC 7002

The gene for the catalytic domain of thermostable endo-β-1,3-glucanase (laminarinase) LamA was cloned from Thermotoga maritima MSB8 and heterologously expressed in a bioengineered Synechococcus sp. PCC 7002. The mutant strain was cultured in a photobioreactor to assess biomass yield, recombinant laminarinase activity, and CO₂ uptake. The maximum enzyme activity was observed at a pH of 8.0 and a temperature of 70°C. At a CO₂ concentration of 5%, we obtained a maximum specific growth rate of 0.083 h^–1, a biomass productivity of 0.42 g?L^–1?d^–1, a biomass concentration of 3.697 g?L^–1, and a specific enzyme activity of the mutant strain of 4.325 U?mg^–1 dry mass. All parameters decreased as CO₂ concentration increased from 5% to 10% and further to 15% CO₂, except enzyme activity, which increased from 5% to 10% CO₂. However, the mutant culture still grew at 15% CO₂ concentration, as reflected by the biomass productivity (0.26 g?L^–1?d^–1), biomass concentration (2.416 g?L^–1), and specific enzyme activity (3.247 U?mg^–1 dry mass).

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Effect of chemical amendments on remediation of potentially toxic trace elements (PTEs) and soil quality improvement in paddy fields

Remediation of potentially toxic trace elements (PTEs) in paddy fields is fundamental for crop safety. In situ application of chemical amendments has been widely adapted because of its cost-effectiveness and environmental safety. The main purpose of this research was to (1) evaluate the reduction in dissolved concentrations of cadmium (Cd) and arsenic (As) with the application of chemical amendments and (2) monitor microbial activity in the soil to determine the remediation efficiency. Three different chemical amendments, lime stone, steel slag, and acid mine drainage sludge, were applied to paddy fields, and rice (Oryza sativa L. Milyang 23) was cultivated. The application of chemical amendments immobilized both Cd and As in soil. Between the two PTEs, As reduction was significant (p < 0.05) with the addition of chemical amendments, whereas no significant reduction was observed for Cd than that for the control. Among six soil-related variables, PTE concentration showed a negative correlation with soil pH (r = ?0.70 for As and r = ?0.54 for Cd) and soil respiration (SR) (r = ?0.88 for As and r = ?0.45 for Cd). This result indicated that immobilization of PTEs in soil is dependent on soil pH and reduces PTE toxicity. Overall, the application of chemical amendments could be utilized for decreasing PTE (As and Cd) bioavailability and increasing microbial activity in the soil.     

Flow and drag force around a free surface piercing cylinder for environmental applications

This paper investigates flows around a free surface piercing cylinder with Froude number F > 0.5 and Reynolds number around Re = 50,000. The aim of this work is to gain a better understanding of the flow behaviour in environmental systems such as fishways. The advances are based upon experimental and numerical results. Several flow discharges and slopes are tested to obtain both subcritical and supercritical flows. The drag force exerted on the cylinder is measured with the help of a torque gauge while the velocity field is obtained using particle velocimetry. For the numerical part, two URANS turbulence models are tested, the k-\(\omega\) SST and the RNG k-\(\varepsilon\) models using the OpenFOAM software suite for subcritical cases, and then compared with the corresponding experimental results. With fishways applications in mind, the changes in drag coefficient \(C_d\) versus Froude number and water depth are studied and experimental correlations proposed. We conclude that the most suitable URANS turbulence model for reproducing this kind of flow is the k-\(\omega\) SST model.     

Geo-accumulation index and contamination factors of heavy metals (Zn and Pb) in urban river sediment

The aim of the present study was to appraise the levels of heavy metal contamination (Zn and Pb) in sediment of the Langat River (Selangor, Malaysia). Samples were collected randomly from 15 sampling stations located along the Langat River. The parameters measured were pH, redox potential, salinity, electrical conductivity, loss of ignition, cation exchanges capacity (Na, Mg, Ca, K), and metal ions (Zn and Pb). The geo-accumulation index (I _geo) and contamination factor (C _f) were applied to determine and classify the magnitude of heavy metal pollution in this urban river sediment. Results revealed that the I _geo of Pb indicated unpolluted to moderately polluted sediment at most of the sampling stations, whereas Zn was considered to be within background concentration. The I _geo results were refined by the C _f values, which showed Pb with very high C _f at 12 stations. Zinc, on the other hand, had low to moderate C _f values. These findings indicated that the sediment of the Langat River is severely polluted with Pb. The Zn concentration at most sampling points was well below most sediment quality guidelines. However, 40% of the sampling points were found to have a Pb concentration higher than the consensus-based probable effect concentration of 128 mg/kg (concentrations above this value are likely to cause harmful effects). This result not only highlights the severity of Pb pollution in the sediment of the Langat River, but also the potential risk it poses to the environment.     

Probing the redox process of <Emphasis Type="Italic">p</Emphasis>-benzoquinone in dimethyl sulphoxide by using fluorescence spectroelectrochemistry

Quinones are common organic compounds frequently used as model dissolved organic matters in water, and their redox properties are usually characterized by either electrochemical or spectroscopic methods separately. In this work, electrochemical methodology was combined with two fluorescence spectroelectrochemical techniques, cyclic volta- fluorescence spectrometry (CVF) and derivative cyclic volta- fluorescence spectrometry (DCVF), to determine the electrochemical properties of p-benzoquinone in dimethyl sulfoxide, an aprotic solution. The CVF results show that the electrochemical reduction of p-benzoquinone resulted in the formation of radical anion and dianion, which exhibited a lower fluorescence intensity and red-shift of the emission spectra compared to that of p-benzoquinone. The fluorescence intensity was found to vary along with the electrochemical oxidation and reduction of p-benzoquinone. The CVF and DCVF results were in good consistence. Thus, the combined method offers a powerful tool to investigate the electrochemical process of p-benzoquinone and other natural organic compounds.

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Efficacy of woody biomass and biochar for alleviating heavy metal bioavailability in serpentine soil

Crops grown in metal-rich serpentine soils are vulnerable to phytotoxicity. In this study, Gliricidia sepium (Jacq.) biomass and woody biochar were examined as amendments on heavy metal immobilization in a serpentine soil. Woody biochar was produced by slow pyrolysis of Gliricidia sepium (Jacq.) biomass at 300 and 500 °C. A pot experiment was conducted for 6 weeks with tomato (Lycopersicon esculentum L.) at biochar application rates of 0, 22, 55 and 110 t ha^?1. The CaCl₂ and sequential extractions were adopted to assess metal bioavailability and fractionation. Six weeks after germination, plants cultivated on the control could not survive, while all the plants were grown normally on the soils amended with biochars. The most effective treatment for metal immobilization was BC500-110 as indicated by the immobilization efficiencies for Ni, Mn and Cr that were 68, 92 and 42 %, respectively, compared to the control. Biochar produced at 500 °C and at high application rates immobilized heavy metals significantly. Improvements in plant growth in biochar-amended soil were related to decreasing in metal toxicity as a consequence of metal immobilization through strong sorption due to high surface area and functional groups.     

<Emphasis Type="Italic">Bacillus algicola</Emphasis> decolourises more than 95% of some textile azo dyes

Textile effluents in natural waters pose environmental health problems if not treated to safe limits. Various bacterial species have the potential to degrade dyes. Here we studied the ability of Bacillus algicola to decolourise red, blue and yellow azo dyes. B. algicola was isolated from soil samples taken from a sanitary landfill site. Isolation and screening were performed using mineral salt medium. Dye-decolourising isolates were assessed in their capacity to decolourise dyes. Experiments were conducted at pH 6, 7 and 8, and 25, 35 and 45 °C. Phytotoxicity of the dyes and biodegradation products was assessed by seed germination tests. Results show that B. algicola gave the highest decolourisation at pH 8.0 and 25 °C in the presence of yeast extract as media supplement. B. algicola degraded the red and blue azo dyes by over 95%. The phytotoxicity results indicated that biodegradation products of the red and blue azo dyes were not toxic. Biodegradation products of the yellow dye were, however, toxic and considerably hindered germination. From these results, we infer that B. algicola has good potential for degrading and decolourising the red and blue test azo dyes.     

Selection and characterization of eight freshwater green algae strains for synchronous water purification and lipid production

The objective of this study is to select and characterize the candidate for synchronous water purification and lipid production from eight freshwater microalgae strains (Chlorella sp. HQ, C. emersonii, C. pyrenoidosa, C. vulgaris, Scenedesmus dimorphus, S. quadricauda, S. obiquus, Scenedesmus sp. LX1). The strains Chlorella sp. HQ, C. pyrenoidesa, and S. obliquus showed superiority in biomass accumulation, while the top biomass producers did not correspond to the top lipid producers. S. quadricauda achieved higher lipid content (66.1%), and Chlorella sp. HQ and S. dimorphus ranked down in sequence, with lipid content above 30%. Considering nutrient removal ability (total nitrogen (TN): 52.97%; total phosphorus (TP): 84.81%), the newly isolated microalga Chlorella sp. HQ was the possible candidate for water purification coupled with lipid production. To further investigate the lipid producing and nutrient removal mechanism of candidate microalga, the ultra structural changes especially the lipid droplets under different water qualities (different TN and TP concentrations) were characterized. The results elucidate the nutrient-deficiency (TN: 3.0 mg·L^–1; TP: 0.3 mg·L^–1) condition was in favor of forming lipid bodies in Chlorella sp. HQ at the subcellular level, while the biomass production was inhibited due to the decrease in chloroplast number which could further suppress the nutrient removal effect. Finally, a twophase cultivation process (a nutrient replete phase to produce biomass followed by a nutrient deplete phase to enhance lipid content) was conducted in a photo-bioreactor for Chlorella sp. HQ to serve for algae-based synchronous biodiesel production and wastewater purification.     

Studies on survival and growth rate of transplanted Acroporidae in Gulf of Kachchh Marine National Park,India

Fragments of live colonies of scleractinian coral Acropora sp. and Montipora sp. under the family Acroporiidae were collected from Gulf of Mannar and transplanted in Pirotan, Narara and Mithapur reefs of Gulf of Kachchh Marine National Park. All the transplanted corals survived one complete season and it was observed that 87 nubbins out of the total 110 samples survived in Narara reef and 70 nubbins out of 102 samples stayed alive in Pirotan Island. Growth rate was measured for four months period, and it was found maximum in Narara reef, while minimum in Pirotan Island. The rate of sedimentation was higher during monsoon and low in winter season. Present study showed that species of Acropora and Montipora are suitable for transplantation in Gulf of Kachchh Marine National Park, Gujarat, India.     

Direct measurements of the drag force over aligned arrays of cubes exposed to boundary-layer flows

Wind tunnel measurements of the total drag force for aligned arrays of cubes exposed to two different boundary-layer flows at three flow velocities are discussed. The drag force for eight different building packing densities λ _p (from 0.028 to 1) is measured with a standard load cell generating a novel dataset. Different λ _p are reproduced by increasing the number of buildings on the same lot area; this represents a real situation that an urban planner is faced with when a lot area of a given (fixed) size is allocated to the development of new built areas. It is assumed that the surrounding terrain is uniform and there is a transition from a given roughness (smooth) to a new roughness (rough). The approaching flow will adjust itself over the new surface within a distance that in general may be larger than the horizontal length covered by the array. We investigate the region where the flow adjustment occurs. The wide range of packing densities allowed us to analyse in detail the evolution of the drag force. The drag force increases with increasing packing densities until it reaches a maximum at an intermediate packing density (λ _p  = 0.25 in our case) followed by a slight decrease at larger packing densities. The value of the drag force depends on the flow adjustment along the array which is evaluated by introducing the parameter “drag area” to retrieve information about the drag distribution at different λ _p . Results clearly suggest a change of the distribution of the drag force, which is found to be relatively uniform at low packing densities, while most of the force acts on first rows of the arrays at large packing densities. The drag area constitutes the basis for the formulation of a new adjustment length scale defined as the ratio between the volume of the air within the array and the drag area. The proposed adjustment length scale automatically takes into account the change in drag distribution along the array for a better parameterization of urban effects in dispersion models.     

Copper sulphate use in South African traditional medicine

Copper (Cu) is an essential element to humans; however, exposure to elevated concentrations through occupational hazard and/or environmental means may be detrimental. This paper provides results of a cross-sectional study aimed to determine the prevalence of copper sulphate (CuSO₄) use in South African traditional medicine by traditional health practitioners (THPs) and details the use thereof. A total of 201 THPs were enrolled from two main municipal areas of KwaZulu-Natal (South Africa). Information on demographic characteristics of THPs, reasons for using or not using CuSO₄ as well as administration methods and age groups of recipients were collected. Of the 201 THPs interviewed, 145 (72 %) use CuSO₄ for healing purposes. The use of CuSO₄ was strongly associated with gender (p = 0.009) where the proportion of CuSO₄ users was higher for female than male THPs. CuSO₄ was reportedly administered to individuals of all ages, including infants and children. The main routes of administration were enema (n = 110; 76 %), oral (n = 40; 28 %) and use in bath (n = 40; 28 %). The reasons cited for use are diverse and included skin rashes (n = 43; 30 %), aches, pains and swelling (n = 38; 28 %) as well as sexually transmitted diseases (n = 28; 19 %). This study identified a high prevalence of THPs using CuSO₄ for healing purposes. These findings support the need to regulate South African traditional medicine to safeguard the user.     

Effect of electrokinetic property of charged polyether sulfone membrane on bovine serum albumin fouling behavior

Negatively charged carboxymethylated polyethersulfone (CMPES) and positively charged quaternized polyethersulfone (QAPES) ultrafiltration (UF) membranes were prepared by bulk chemical modification and non-solvent induced phase separation method. The effects of PES membrane interfacial electrokinetic property on the bovine serum albumin (BSA) membrane fouling behavior were studied with the aid of the membrane-modified colloidal atomic force microscopy (AFM) probe. Electrokinetic test results indicated that the streaming potential (ΔE) of QAPES membrane was not consistent with its expected IEC value, however, within the pH range of 3–10, the ζ potentials of two charged-modified PES membranes were more stable than the unmodified membrane. When pH value was 3, 4.7 or 9, the interaction behavior between charged PES membrane and BSA showed that there was significant linear correlation between the jump distance r ₀ of membrane-BSA adhesion force (F/R) and the ζ potential absolute value. Charged modification significantly reduced the adhesion of PES membrane-BSA, and the adhesion data was good linear correlated with the flux decline rate in BSA filtration process, especially reflected in the CMPES membrane. The above experimental facts proved that the charged membrane interfacial electric double layer structure and its electrokinetic property had strong ties with the protein membrane fouling behavior.

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Impact of salt-marsh management on fish nursery function in the bay of Aiguillon (French Atlantic coast), with a focus on European sea bass diet

The Bay of Aiguillon is a national French Nature Reserve of great importance for birds. Recently, the managers of the Reserve (ONCFS-LPO) paid attention to the influence of saltmarshes management on the nursery function for fish feeding in creeks at high tide. A study carried out from March to July 2012 aimed to evaluate the use of saltmarshes by fish juvenile fraction according to the mowing intensity in salt marshes surrounding creeks: ceased, irregular or annual mowing. This community approach was completed by a focus on the European sea bass Dicentrarchus labrax individual diet, vacuity index and growth, and the biomass of a main potential prey (the amphipod Orchestia gammarella). Whatever the mowing intensity, the juvenile fraction was very high for the main species, which were the grey mullet Liza ramada, the European sea bass, undetermined clupeid and the European flounder Platichthys flesus. Adult and subadult for these species were anecdotic or totally absent. Despite very different biomasses of amphipods between mown and natural sites, vacuity index, prey composition and their relative abundance in the diet of European sea bass juveniles were little different, contrary to their hypothetical growth (i.e. when assuming site fidelity), which appeared higher in non-mown site. The low distance between sampling sites could allow fish exchange over time between optimal and suboptimal creeks to feed on, as a hypothesis to explain such results. Because mowing was subsidized by European Union (EU) to favour open habitats for geese and maintain an economic activity, indirect impacts on nursery for fish called into question the appropriateness of such agro-environmental measure on natural habitats, and related fish nursery function.     

Bacterial community structure and microorganism inactivation following water treatment with ferrate(VI) or chlorine

Drinking water disinfection plays a critical role in protecting humans from waterborne pathogens. Ferrate(VI) (Fe^VIO₄ ^2?) has also been proposed as a disinfectant. This is the first study investigating the bacterial microbiomes of ferrate(VI)-treated water compared to chlorinated water. Tested water was collected after sand filtration and before disinfection from a drinking water treatment plant at Jiaxing, Zhejiang Province, China. A culture-independent method utilizing propidium monoazide was used with quantitative polymerase chain reaction and pyrosequencing of 16S rRNA genes to distinguish between the viable and nonviable bacterial populations. The operational taxonomic units and α-diversity indexes of the live bacterial phylotypes in the samples were determined. Viable bacteria remained in all samples following chlorination or ferrate treatment. However, the genera Vibrio, Salmonella, Shigella, Escherichia, Campylobacter, Yersinia, Plesiomonas, Legionella, and Helicobacter, which contain important human pathogens, were not present among the 25 dominant genera seen in these samples. The profiles of the bacteria remaining after treatment with either chlorine or ferrate differed. The ferrate-treated samples showed a reduced percent relative abundance of operational taxonomic units of the class Alphaproteobacteria within the total remaining viable bacteria. The genera Flavobacterium and Duganella were relatively resistant to treatment by either chlorine or ferrate(VI). At the highest doses of chlorine and ferrate(VI), the genus Sphingobium represented a greater percentage of live bacteria in the chlorinated sample than in the ferrate(VI)-treated sample. The results suggest that ferrate(VI) and chlorine could inactivate slightly different sets of bacteria and could have different mechanisms of bacterial inactivation.