Biosynthesis of silver nanoparticles using novel Bacillus sp. SBT8

Biosynthesis of silver nanoparticles (AgNPs) using microorganisms is an important application of nanobiotechnology and green chemistry because of interest by pharmaceutical and food manufacturers. In this study, biosynthesis of AgNPs by a novel Bacillus strain isolated from a soil sample from Sakarya district in Turkey was investigated. Biosynthesis was performed using cell-free supernatant of the bacterium following 24?h growth. Effects of varying AgNO₃ concentration (1–10?mM), pH (5–10), and temperature (30–40°C) on the synthesis of AgNPs were determined. Formation of AgNPs was monitored by UV–VIS spectroscopy. Field emission scanning electron microscopy was used to compare morphologies among the various culture conditions. The peaks created by surface plasmon resonance (SPR) of metals were obtained only at 4 and 6?mM AgNO₃ concentrations and the maximum concentration for the biosynthesis was observed at 6?mM. The highest yield was achieved at pH 10 and larger nanoparticles were obtained at this pH. The optimum temperatures for biosynthesis were 33 and 37°C. Fourier transform infrared spectroscopy analysis and transmission electron microcopy images confirmed that the proteins served as capping. Energy-dispersive spectroscopy analysis validated the formation of AgNPs. AgNPs exhibited antibacterial activity toward Gram-positive and Gram-negative pathogens.     

Extracellular biosynthesis of silver nanoparticles using a novel and non-pathogenic fungus,Neurospora intermedia: controlled synthesis and antibacterial activity

In the present study, the biosynthesis of silver nanoparticles (AgNPs) using Neurospora intermedia, as a new non-pathogenic fungus was investigated. For determination of biomass harvesting time, the effect of fungal incubation period on nanoparticle formation was investigated using UV–visible spectroscopy. Then, AgNPs were synthesized using both culture supernatant and cell-free filtrate of the fungus. Two different volume ratios (1:100 and 1:1) of the culture supernatant to the silver nitrate were employed for AgNP synthesis. In addition, cell-free filtrate and silver nitrate were mixed in presence and absence of light. Smallest average size and highest productivity were obtained when using equal volumes of the culture supernatant and silver nitrate solution as confirmed by UV–visible spectra of colloidal AgNPs. Comparing the UV–visible spectra revealed that using cell-free filtrate for AgNP synthesis resulted in the formation of particles with higher stability and monodispersity than using culture supernatant. The absence of light in cell-free filtrate mediated synthesis led to the formation of nanoparticles with the lowest rate and the highest monodispersity. The presence of elemental silver in all prepared samples was confirmed using EDX, while the crystalline nature of synthesized particles was verified by XRD. FTIR results showed the presence of functional groups which reduce Ag⁺ and stabilize AgNPs. The presence of nitrate reductase was confirmed in the cell-free filtrate of the fungus suggesting the potential role of this enzyme in AgNP synthesis. Synthesized particles showed significant antibacterial activity against E. coli as confirmed by examining the growth curve of bacterial cells exposed to AgNPs.     

Influence of strong bases on the synthesis of silver nanoparticles (AgNPs) using the ligninolytic fungi Trametes trogii

Silver nanoparticles (AgNPs) were biosynthesized using fungal extract of Trametes trogii, a white rot basidiomycete involved in wood decay worldwide, which produces several ligninolytic enzymes. According to previous studies using fungi, enzymes are involved in nanoparticles synthesis, through the so-called green synthesis process, acting as reducing and capping agents. Understanding which factors could modify nanoparticles’ shape, size and production efficiency is relevant. The results showed that under the protocol used in this work, this strain of Trametes trogii is able to synthesize silver nanoparticles with the addition of silver nitrate (AgNO₃) to the fungal extract obtained with an optimal incubation time of 72 h and pH 13, using NaOH to adjust pH. The progress of the reaction was monitored using UV–visible spectroscopy and synthesized AgNPs was characterized by scanning electron microscope (SEM), through in-lens and QBDS detectors, and energy-dispersive X-ray spectroscopy (EDX). Additionally, SPR absorption was modeled using Mie theory and simple nanoparticles and core-shell configurations were studied, to understand the morphology and environment of the nanoparticles. This protocol represents a simple and cheap synthesis in the absence of toxic reagents and under an environmentally friendly condition.     

Biosynthesis of silver nanoparticles using Bacillus subtilis EWP-46 cell-free extract and evaluation of its antibacterial activity

This study highlights the ability of nitrate-reducing Bacillus subtilis EWP-46 cell-free extract used for preparation of silver nanoparticles (AgNPs) by reduction of silver ions into nano silver. The production of AgNPs was optimized with several parameters such as hydrogen ion concentration, temperature, silver ion (Ag⁺ ion) and time. The maximum AgNPs production was achieved at pH 10.0, temperature 60 °C, 1.0 mM Ag⁺ ion and 720 min. The UV–Vis spectrum showed surface plasmon resonance peak at 420 nm, energy-dispersive X-ray spectroscopy (SEM–EDX) spectra showed the presence of element silver in pure form. Atomic force microscopy (AFM) and transmission electron microscopy images illustrated the nanoparticle size, shape, and average particle size ranging from 10 to 20 nm. Fourier transform infrared spectroscopy provided the evidence for the presence of biomolecules responsible for the reduction of silver ion, and X-ray diffraction analysis confirmed that the obtained nanoparticles were in crystalline form. SDS-PAGE was performed to identify the proteins and its molecular mass in the purified nitrate reductase from the cell-free extract. In addition, the minimum inhibitory concentration and minimum bactericidal concentration of AgNPs were investigated against gram-negative (Pseudomonas fluorescens) and gram-positive (Staphylococcus aureus) bacteria.     

Antibacterial and Cytotoxic Efficacy of Extracellular Silver Nanoparticles Biofabricated from Chromium Reducing Novel OS4 Strain of Stenotrophomonas maltophilia

Biofabricated metal nanoparticles are generally biocompatible, inexpensive, and ecofriendly, therefore, are used preferably in industries, medical and material science research. Considering the importance of biofabricated materials, we isolated, characterized and identified a novel bacterial strain OS4 of Stenotrophomonas maltophilia (GenBank: {"type":"entrez-nucleotide","attrs":{"text":"JN247637.1","term_id":"341941875","term_text":"JN247637.1"}}JN247637.1). At neutral pH, this Gram negative bacterial strain significantly reduced hexavalent chromium, an important heavy metal contaminant found in the tannery effluents and minings. Subsequently, even at room temperature the supernatant of log phase grown culture of strain OS4 also reduced silver nitrate (AgNO₃) to generate nanoparticles (AgNPs). These AgNPs were further characterized by UV–visible, Nanophox particle size analyzer, XRD, SEM and FTIR. As evident from the FTIR data, plausibly the protein components of supernatant caused the reduction of AgNO₃. The cuboid and homogenous AgNPs showed a characteristic UV-visible peak at 428 nm with average size of ∼93 nm. The XRD spectra exhibited the characteristic Bragg peaks of 111, 200, 220 and 311 facets of the face centred cubic symmetry of nanoparticles suggesting that these nanoparticles were crystalline in nature. From the nanoparticle release kinetics data, the rapid release of AgNPs was correlated with the particle size and increasing surface area of the nanoparticles. A highly significant antimicrobial activity against medically important bacteria by the biofabricated AgNPs was also revealed as decline in growth of Staphylococcus aureus (91%), Escherichia coli (69%) and Serratia marcescens (66%) substantially. Additionally, different cytotoxic assays showed no toxicity of AgNPs to liver function, RBCs, splenocytes and HeLa cells, hence these particles were safe to use. Therefore, this novel bacterial strain OS4 is likely to provide broad spectrum benefits for curing chromium polluted sites, for biofabrication of AgNPs and ultimately in the nanoparticle based drug formulation for the treatment of infectious diseases.     

Antifungal potentiality of mycogenic silver nanoparticles capped with chitosan produced by endophytic Amesia atrobrunnea

This research reports the fabrication of silver nanoparticles (AgNPs) from endophytic fungus, Amesia atrobrunnea isolated from Ziziphus spina-christi (L.). Influencing factors for instance, thermal degree of incubation, media, pH, and silver nitrate (AgNO₃) molarity were optimized. Then, the AgNPs were encapsulated with chitosan (Ch-AgNPs) under microwave heating at 650 W for 90 s. Characterization of nanoparticles was performed via UV–visible (UV–vis) spectrophotometer, Fourier-transform infrared spectrophotometer (FTIR), zeta potential using dynamic-light scattering (DLS), and field-emission-scanning electron microscope (FE-SEM). Anti-fungal activity of Ch-AgNPs at (50, 25, 12.5, 6.25 mg/L) was tested against Fusarium oxysporum, Curvularia lunata, and Aspergillus niger using the mycelial growth inhibition method (MGI). Results indicated that Czapek-dox broth (CDB) with 1 mM AgNO₃, an acidic pH, and a temperature of 25–30 °C were the optimum for AgNPs synthesis. (UV–vis) showed the highest peak at 435 nm, whereas Ch-AgNPs showed one peak for AgNPs at 405 nm and another peak for chitosan at 230 nm. FTIR analysis confirmed that the capping agent chitosan was successfully incorporated and interacted with the AgNPs through amide functionalities. Z-potential was −19.7 mV for AgNPs and 38.9 mV for Ch-AgNPs, which confirmed the significant stability enhancement after capping. FES-SEM showed spherical AgNPs and a reduction in the nanoparticle size to 44.65 nm after capping with chitosan. The highest mycelial growth reduction using fabricated Ch-AgNPs was 93% for C. lunata followed by 77% for A. niger and 66% F. oxysporum at (50 mg/L). Biosynthesis of AgNPs using A. atrobrunnea cell-free extract was successful. Capping with chitosan exhibited antifungal activity against fungal pathogens.     

Comparison of Antimicrobial Properties of Silver Nanoparticles Synthesized from Selected Bacteria

Green silver nanoparticle (AgNP) biosynthesis is facilitated by the enzyme mediated reduction of Ag ions by plants, fungi and bacteria. The antimicrobial activity of green AgNPs is useful to overcome the challenge of antimicrobial resistance. Antimicrobial properties of biosynthesized AgNPs depend on multiple factors including culture conditions and the microbial source. The antimicrobial activity of AgNPs biosynthesized by Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923 and Acinetobacter baumannii (confirmed clinical isolate) were investigated in this study. Biosynthesis conditions (AgNO₃ concentration, pH, incubation temperature and incubation time) were optimized to obtain the maximum AgNP yield. Presence of AgNPs was confirmed by observing a characteristic UV–Visible absorbance peak in 420–435 nm range. AgNP biosynthesis was optimal at 0.4 g/L AgNO₃ concentration under alkaline conditions at 60–70 °C. The biosynthesized AgNPs showed higher stability compared to chemogenized AgNPs in the presence of electrolytes. AgNPs synthesized by P. aeruginosa were the most stable while NPs of S. aureus were the least stable. AgNPs synthesized by P. aeruginosa and S. aureus showed good antimicrobial potential against E. coli, P. aeruginosa, S. aureus, MRSA and Candida albicans. AgNPs synthesized by S. aureus had greater antimicrobial activity. The antimicrobial activity of NPs may vary depending on the size and the morphology of NPs.     

利用Mariannaea sp.HJ菌株胞内提取物合成纳米银及其抗菌特性研究

【目的】近年来,纳米银由于其自身独特的抗菌活性而受到越来越多的关注,有研究表明纳米银是一种广谱的抗菌剂,其对数十种致病微生物都有强烈的抑制和杀灭作用。相较于传统的合成方法而言,具有反应条件温和、环境友好等优势的生物合成法是目前的研究热点。【方法】本研究利用真菌Mariannaea sp. HJ的胞内提取物合成纳米银,并对其合成条件进行优化调控,还进一步考察了合成的纳米银颗粒的抗菌性能。【结果】胞内提取物浓度350 mg/L、AgNO_3浓度5 mmol/L、pH 7.0为菌株HJ胞内提取物合成纳米银的最优条件;TEM图像表明合成的纳米银颗粒主要为球形和伪球形,分散性良好,无明显的团聚现象;XRD表明合成的纳米银晶体结构为面心立方体结构;通过FTIR分析结果推测提取物中的羟基、羧基等官能团可能参与了纳米银的还原和稳定过程。此外,在本实验条件下合成的纳米银颗粒对革兰氏阴性菌Escherichia coli BL21和革兰氏阳性菌Arthrobacter sp. W1都有较好的抗菌活性。【结论】真菌Mariannaea sp. HJ胞内提取物能合成尺寸均一且分散性良好的球形纳米银颗粒,合成的纳米银颗粒在抗菌方面具有潜在的研究价值。     

Transformation of aromatic dyes using green synthesized silver nanoparticles

Nowadays, increasing use of nanoproducts in area of human and environmental applications raises concern about safety aspects of nanoparticles synthesized using traditional physicochemical methods. Silver nanoparticles (AgNPs) synthesis at ambient parameters using latex of medicinally important plant Jatropha gossypifolia (J. gossypifolia) is reported in the present study. Potential of AgNPs in degradation of methylene blue and eosin B was also evaluated. Rapid formation of stable AgNPs was analyzed by visual color change from colorless to yellow-red after addition of latex in AgNO₃ solution and by characteristic surface plasmon resonance (SPR) peak at 430 nm in UV–Vis spectroscopy. FT-IR analysis, protein coagulation test showed capping of proteins, flavonoids, terpenoids and polyphenols of latex on surface of AgNPs. FE-SEM, HR-TEM analysis revealed spherical shape of AgNPs. Narrow size range of AgNPs (5–40 nm) observed in HR-TEM analysis. EDS analysis confirms the presence of elemental silver while XRD revealed crystalline nature of AgNPs. Zeta potential of ?21.4 mV indicates high stability of AgNPs. Effects of different parameters (pH, temperature, incubation time) on nanosynthesis were studied in the present study. Dye reduction studies were performed using UV–Vis spectroscopy, TLC, FT-IR and HPLC analysis showing decreased absorbance maxima of both dyes with respect to time, change in R _f values, changes in wave number, transmittance, and retention time of dyes after AgNPs addition. The rate constant for methylene blue and eosin B reduction by AgNPs was found to be 0.062 and 0.022 min^?1.     

Toxicity of biosynthetic silver nanoparticles on the growth,cell ultrastructure and physiological activities of barley plant

Silver nanoparticles (AgNPs) were biosynthesized using the cell-free filtrate of bacterium Proteus mirabilis, reacted with 1 mM of AgNO₃ solutions at 37 °C. The synthesis of AgNPs was monitored by UV–Vis spectroscopy and transmission electron microscopy (TEM) equipped with selected area electron diffraction (SAED). The results point to formation of spherical to cubical particles of AgNPs ranging in size from 5 to 35 nm with an average of 25 nm in diameter. The toxicity of Ag on barley (Hordeum vulgare L. cv. Gustoe) that was subjected to Ag⁺ as AgNO₃ and AgNPs was explored. The grain germination and seedling growth of barley decreased in the presence of 0.1 mM Ag⁺ and was inhibited at 1 mM Ag⁺. In contrast, our results indicated that the AgNPs at low concentration (0.1 mM) could be useful for barley grain germination and seedling growth. However, the higher concentrations of AgNPs (0.5 and 1 mM) reduced grain germination and exhibited a stronger reduction in the root length. A decline in the photosynthetic pigments and disorganization of chloroplast grana thylakoids in Ag⁺ and AgNPs-treated plants confirmed the leaf chlorosis. An increase of plastoglobuli within chloroplasts was observed in Ag⁺ and AgNPs-treated leaves. Ag⁺ caused dense aggregation of nuclear chromatin materials and degeneration of mitochondria. Ag⁺ and AgNPs increased contents of malondialdehyde, soluble proteins, total phenolic compounds and activity of guaiacol peroxidase in barley leaves; these results point to activation of plant defence mechanisms against oxidative stress in barley.     

Synthesis of silver nanoparticles by solar irradiation of cell-free Bacillus amyloliquefaciens extracts and AgNO3

Silver nanoparticles (AgNPs) were obtained by solar irradiation of cell-free extracts of Bacillus amyloliquefaciens and AgNO₃. Light intensity, extract concentration, and NaCl addition influenced the synthesis of AgNPs. Under optimized conditions (solar intensity 70,000 lx, extract concentration 3 mg/mL, and NaCl content 2 mM), 98.23 ± 0.06% of the Ag⁺ (1 mM) was reduced to AgNPs within 80 min, and the ζ-potential of AgNPs reached −70.84 ± 0.66 mV. TEM (Transmission electron microscopy) and XRD (X-ray diffraction) analysis confirmed that circular and triangular crystalline AgNPs with mean diameter of 14.6 nm were synthesized. Since heat-inactivated extracts also mediated the formation of AgNPs, enzymatic reactions are likely not involved in AgNPs formation. A high absolute ζ-potential value of the AgNPs, possibly caused by interaction with proteins likely explains the high stability of AgNPs suspensions. AgNPs showed antimicrobial activity against Bacillus subtilis and Escherichia coli in liquid and solid medium.     

Synthesis of silver nanoparticles employing Polyalthia longifolia leaf extract and their in vitro antifungal activity against phytopathogen

The P. longifolia mediated silver (PL-AgNPs) nanoparticles are very stable and efficient. UV–Vis spectroscopy, dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDX) were used to characterize the produced AgNPs. UV–Vis analysis showed a characteristic peak at 435 nm corresponding to surface plasmon resonance. The synthesis process was spectrophotometrically optimized for various parameters. After optimization, highly stable AgNPs were prepared using 3.0 ml of P. longifolia leaf extract, pH 7.0, 1.0 mM AgNO₃, and 60 °C. The zeta potential was measured by DLS, which showed ?20.8 mV and the PDI value was 5.42. TEM and SEM analysis shows a spherical shape of the synthesized nanoparticles, and the size was measured between 10 and 40 nm. EDX analysis showed intense peaks from silver and oxygen and small peaks from various metal atoms such as Na, P, S and Al indicating their presence in trace amounts. The average size of the PL-AgNPs was 14 nm. The phytochemical analysis shows that the presence of alkaloids, essential oils and saponins seems to be responsible for the synthesis of nanoparticles. PL-AgNPs were further investigated for their antifungal activity against Alternaria alternata. The minimum inhibitory concentration (MIC), minimum fungicidal concentration (MFC) and effect of nanoparticles on cytomorphology of A. alternata have also been reported. Biosynthesized nanoparticles have proven to be inexpensive, environmentally friendly, stable, easily reproducible, and highly effective against plant-pathogenic fungi.     

Synthesis of silver nanoparticles using haloarchaeal isolate Halococcus salifodinae BK3

Numerous bacteria, fungi, yeasts and viruses have been exploited for biosynthesis of highly structured metal sulfide and metallic nanoparticles. Haloarchaea (salt-loving archaea) of the third domain of life Archaea, on the other hand have not yet been explored for nanoparticle synthesis. In this study, we report the intracellular synthesis of stable, mostly spherical silver nanoparticles (AgNPs) by the haloarchaeal isolate Halococcus salifodinae BK₃. The culture on adaptation to silver nitrate exhibited growth kinetics similar to that of the control. NADH-dependent nitrate reductase was involved in silver tolerance, reduction, synthesis of AgNPs, and exhibited metal-dependent increase in enzyme activity. The AgNPs preparation was characterized using UV–visible spectroscopy, XRD, TEM and EDAX. The XRD analysis of the nanoparticles showed the characteristic Bragg peaks of face-centered cubic silver with crystallite domain size of 22 and 12 nm for AgNPs synthesized in NTYE and halophilic nitrate broth (HNB), respectively. The average particle size obtained from TEM analysis was 50.3 and 12 nm for AgNPs synthesized in NTYE and HNB, respectively. This is the first report on the synthesis of silver nanoparticles by haloarchaea.     

Morphological and Proteomic Responses of Eruca sativa Exposed to Silver Nanoparticles or Silver Nitrate

Silver nanoparticles (AgNPs) are widely used in commercial products, and there are growing concerns about their impact on the environment. Information about the molecular interaction of AgNPs with plants is lacking. To increase our understanding of the mechanisms involved in plant responses to AgNPs and to differentiate between particle specific and ionic silver effects we determined the morphological and proteomic changes induced in Eruca sativa (commonly called rocket) in response to AgNPs or AgNO₃. Seedlings were treated for 5 days with different concentrations of AgNPs or AgNO₃. A similar increase in root elongation was observed when seedlings were exposed to 10 mg Ag L¹ of either PVP-AgNPs or AgNO₃. At this concentration we performed electron microscopy investigations and 2-dimensional electrophoresis (2DE) proteomic profiling. The low level of overlap of differentially expressed proteins indicates that AgNPs and AgNO₃ cause different plant responses. Both Ag treatments cause changes in proteins involved in the redox regulation and in the sulfur metabolism. These responses could play an important role to maintain cellular homeostasis. Only the AgNP exposure cause the alteration of some proteins related to the endoplasmic reticulum and vacuole indicating these two organelles as targets of the AgNPs action. These data add further evidences that the effects of AgNPs are not simply due to the release of Ag ions.     

Mutation of environmental mycobacteria to resist silver nanoparticles also confers resistance to a common antibiotic

Non-tuberculous mycobacteria are a threat to human health, gaining entry to the body through contaminated water systems, where they form persistent biofilms despite extensive attempts at disinfection. Silver is a natural antibacterial agent and in nanoparticle form activity is increased by a high surface area. Silver nanoparticles (AgNPs) have been used as alternative disinfectants in circulating water systems, washing machines and even clothing. However, nanoparticles, like any other antibiotic that has a pervasive durable presence, carry the risk of creating a resistant population. In this study Mycobacterium smegmatis strain mc²155 was cultured in AgNP enriched agar such that only a small population survived. Surviving cultures were isolated and re-exposed to AgNPs and AgNO₃ and resistance to silver was compared to a negative control. After only a single exposure, mutant M. smegmatis populations were resistant to AgNPs and AgNO₃. Further, the silver resistant mutants were exposed to antibiotics to determine if general resistance had been conferred. The minimum inhibitory concentration of isoniazid was four times higher for silver resistant mutants than for strain mc²155. However, core resistance was not conferred to other toxic metal ions. The mutants had lower resistance to CuSO₄ and ZnSO₄ than the mc²155 strain.     

Biosynthesis of silver nanoparticles using Penicillium verrucosum and analysis of their antifungal activity

The present study describes the biosynthesis of silver nanoparticles, using the fungus Penicillium verrucosum. The silver nanoparticles were synthesised by reacting silver nitrate (AgNO₃) with the cell free filtrates of the fungal culture, and were then characterized by UV–visible spectroscopy, transmission electron microscopy, scanning electron microscopy, energy-dispersive, and X-ray diffraction analysis to further evaluate their successful biosynthesis, optical and morphological features (size and shape), and crystallinity. The bioactivity of the synthesized nanoparticles against two phytopathogenic fungi i.e: Fusarium chlamydosporum and Aspergillus flavus was evaluated using nanomaterial seeding media. These biogenic silver nanoparticles were polydisperse in nature, with a size of 10–12 nm. With regard to the antifungal activity, 150 ppm of the nanoparticles suppressed the growth of F. chlamydosporum and A. flavus by about 50%. To the best of our knowledge, this is the first report on the use of P. verrucosum to synthesise silver nanoparticles. The present study demonstrates a novel, simple, and eco-friendly process for the generation of biofunctionally useful biogenic nanoparticles.     

Comparative study of antifungal activity of two preparations of green silver nanoparticles from Portulaca oleracea extract

The green silver nanoparticles (green AgNPs) exhibit an exceptional antimicrobial property against different microbes, including bacteria and fungi. The current study aimed to compare the antifungal activities of both the crude aqueous extract of Portulaca oleracea or different preparations of green AgNPs biosynthesized by mixing that aqueous extract with silver nitrate (AgNO₃). Two preparations of the green AgNPs were synthesized either by mixing the aqueous extract of P. oleracea with silver nitrate (AgNO₃) (normal AgNPs) or either irradiation of the AgNPs, previously prepared, under ⁶⁰Co γ-ray using chitosan (gamma-irradiated AgNPs). Characterization of different AgNPs were tested by Zeta potential analyzer, Ultraviolet (UV) Visible Spectroscopy, and Fourier-Transform Infrared (FTIR) spectrometry. Three different plant pathogenic fungi were tested, Curvularia spicifera, Macrophomina phaseolina, and Bipolaris sp. The antifungal activities were evaluated by Transmission Electron Microscope (TEM) for either the crude aqueous extract of P. oleracea at three doses (25%, 50%, and 100%) or the newly biosynthesized AgNPs, normal or gamma-irradiated. With a few exceptions, the comparative analysis revealed that the irradiated green AgNPs at all three concentrations showed a relatively stronger antifungal effect than the normal AgNPs against all the three selected fungal strains. UV–visible spectroscopy of both preparations showed surface plasmon resonance at 421 nm. TEM results showed that both AgNPs were aggregated and characterized by a unique spherical shape, however, the gamma-irradiated AgNPs were smaller than the non-irradiated AgNPs (0.007–0.026 µM vs. 0.009–0.086 µM). TEM photographs of the fungal strains treated with the two AgNPs preparations showed flaccid structures, condensed hyphae, and shrunken surface compared with control cells. The data suggested that the biosynthesized P. oleracea AgNPs have antifungal properties against C. spicifera, M. phaseolina, and Bipolaris sp. These AgNPs may be considered a fungicide to protect different plants against phytopathogenic fungi.     

Extracellular biosynthesis,characterization, optimization of silver nanoparticles (AgNPs) using Bacillus mojavensis BTCB15 and its antimicrobial activity against multidrug resistant pathogens

Abstract

Biosynthesis of metal nanoparticles is an area of interest among researchers because of its eco-friendly approach. Current study focuses at biosynthesis of silver nanoparticles (AgNPs) and optimization of physico-chemical conditions to obtain mono-dispersed and stable AgNPs having antimicrobial activity. Initially Bacillus mojavensis BTCB15 produced silver nanoparticles (AgNPs) of 105?nm. Silver nanoparticles (AgNPs) were characterized by particle size analyzer, UV-Vis Spectroscopy, Fourier transforms infrared spectroscopy (FTIR), Atomic force microscopy (AFM), and X-ray diffraction (XRD). Whereas, under optimal conditions of temperature 55?°C, pH 8, addition of surfactant Tween 20, and metal ion K₂SO₄, about 104% size reduction was achieved with average size of 2.3nm. Molecular characterization revealed 98% sequence homology with Bacillus mojavensis. AgNPs exhibited antibacterial activity at concentrations ranging from 0.5 to 2.5?µg/µl against Escherichia coli BTCB03, Klebsiella pneumonia BTCB04, Acinetobacter sp. BTCB05, and Pseudomonas aeruginosa BTCB01 but none against Staphylococcus aureus BTCB02. Highest antibacterial activity was observed at 0.27?µg/µl and lowest at 0.05?µg/µl of AgNPs indicated by zone of inhibition. Conclusively, under optimum conditions, Bacillus mojavensis BTCB15 was able to produce AgNPs of 2.3?nm size and had antibacterial activity against multi drug resistant pathogens.     

Hybrid nanofibrous yarns based on N-carboxyethylchitosan and silver nanoparticles with antibacterial activity prepared by self-bundling electrospinning

Hybrid nanofibrous materials with antibacterial activity consisting of yarns from N-carboxyethylchitosan (CECh) and poly(ethylene oxide) (PEO) that contain 5 wt % or 10 wt % silver nanoparticles (AgNPs) were prepared. This was achieved by electrospinning using formic acid as a solvent and as a reducing agent for silver ions. AgNO₃ was used as an Ag⁺-containing salt. Its concentration was selected to be 0.02 mol/L or 0.04 mol/L in order the content of the AgNPs in the electrospun nanofibers to be 5 wt % or 10 wt %, respectively. The self-bundling of the fibers into yarns with a mean diameter of ca. 35 μm was enabled only by using a grounded needle electrode. The reduction of the silver ions to an elemental silver was evidenced by UV-vis spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The transmission electron microscopy (TEM) analyses revealed that AgNPs formed at AgNO₃ concentration of 0.02 mol/L were with a mean diameter of 4 ± 0.5 nm and were distributed uniformly within the fiber. The increase of AgNO₃ concentration to 0.04 mol/L led to the preparation of AgNPs with a higher mean diameter and a broader diameter distribution as well as to aggregate formation. The performed studies on the antibacterial activity of CECh/PEO/AgNPs fibrous materials against Staphylococcus aureus showed that at AgNPs content of 5 wt % the mats had bacteriostatic, and at AgNPs content of 10 wt %—bactericidal activity.     

Development and evaluation of different strategies for the clean synthesis of silver nanoparticles using Yarrowia lipolytica and their antibacterial activity

An environment-friendly, cheap method, biogenic synthesis of silver nanoparticles (AgNPs) is interesting as compared to physical and chemical synthesis methods. The aim of the present study was to utilize the inherent capability of Yarrowia lipolytica as a novel biocatalyst for green production of AgNPs using different strategies, including growing cells, resting cells, and cell-free extracts (CFE) under optimized reaction conditions. The produced AgNPs were evaluated with UV–vis spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, and Fourier transform infrared spectrometry. In the growing cells strategy, Y. lipolytica produced spherical AgNPs under the optimized conditions, 2.5 mM of silver ions, 7.5 g/l of yeast biomass, a temperature of 30 °C, a pH of 6, and a shaking rate of 50 rpm after 48 h. The sizes and monodispersity of the AgNPs in the resting cells strategy were better than those in the other two. However, the AgNPs were produced faster in the CFE strategy. The antibacterial activity and minimal inhibitory concentration of the AgNPs against certain Gram-positive and Gram-negative bacteria were determined by the agar well diffusion and broth microdilution methods. The AgNPs had a considerable antibacterial effect compared to chloramphenicol as a broad-spectrum antibiotic.