Biosynthesis of silver and gold nanoparticles using thermophilic bacterium Geobacillus stearothermophilus

The Cd immobilization mechanisms in paddy soil through ureolysis-based microbial induced carbonate precipitation: Emphasis on the coexisting cations and metatranscriptome analysis

Microbial induced carbonate precipitation (MICP) can immobilize metals and reduce their bioavailability. However, little is known about the immobilization mechanism of Cd in the presence of soil cations and the triggered gene expression and metabolic pathways in paddy soil. Thus, microcosmic experiments were conducted to study the fractionation transformation of Cd and metatranscriptome analysis. Results showed that bioavailable Cd decreased from 0.62 to 0.29 mg/kg after 330 d due to the MICP immobilization. This was ascribed to the increase in carbonate bound, Fe-Mn oxides bound, and residual Cd. The underlying immobilization mechanisms could be attributed to the formation of insoluble Cd-containing precipitates, the complexation and lattice substitution with carbonate and Fe, Mn and Al (hydr)oxides, and the adsorption on functional group on extracellular polymers of cell. During the MICP immobilization process, up-regulated differential expression urease genes were significantly enriched in the paddy soil, corresponding to the arginine biosynthesis, purine metabolism and atrazine degradation. The metabolic pathway of bacterial chemotaxis, flagellum assembly, and peptidoglycan biosynthesis and the expression of cadA gene related to Cd excretion enhanced Cd resistance of soil microbiome. Therefore, this study provided new insights into the immobilization mechanisms of Cd in paddy soils through ureolysis-based MICP process.

Microbial nanotechnology for agriculture, food, and environmental sustainability: Current status and future perspective

The field of nanotechnology has the mysterious capacity to reform every subject it touches. Nanotechnology advancements have already altered a variety of scientific and industrial fields. Nanoparticles (NPs) with sizes ranging from 1 to 100 nm (nm) are of great scientific and commercial interest. Their functions and characteristics differ significantly from those of bulk metal. Commercial quantities of NPs are synthesized using chemical or physical methods. The use of the physical and chemical approaches remained popular for many years; however, the recognition of their hazardous effects on human well-being and conditions influenced serious world perspectives for the researchers. There is a growing need in this field for simple, non-toxic, clean, and environmentally safe nanoparticle production methods to reduce environmental impact and waste and increase energy productivity. Microbial nanotechnology is relatively a new field. Using various microorganisms, a wide range of nanoparticles with well-defined chemical composition, morphology, and size have been synthesized, and their applications in a wide range of cutting-edge technological areas have been investigated. Green synthesis of the nanoparticles is cost-efficient and requires low maintenance. The present review highlights the synthesis of the nanoparticles by different microbes, their characterization, and their biotechnological potential. It further deals with the applications in biomedical, food, and textile industries as well as its role in biosensing, waste recycling, and biofuel production.

Biosynthesis of metallic nanoparticles by bacterial cell-free extract

The biosynthesis of metallic nanoparticles (MNPs), encompassing noble metals, metal oxides, and sulfides, has gained significant attention in recent years due to their unique properties and wide-ranging applications. However, traditional chemical synthesis methods often involve extreme conditions, harsh chemicals, and negative environmental impacts. Consequently, developing a simple, non-toxic, and eco-friendly approach for MNP synthesis is paramount. One promising method that addresses these concerns is using a bacterial cell-free extract (CFE) as a mediator for biosynthesis. Compared with other biosynthesis production methods, the purification process of MNPs synthesized using bacterial CFEs is much simpler, and CFE production is easier to standardize and reproduce. Bacterial CFEs are rich in various biomolecules, including proteins, enzymes, and peptides, which serve as both reducing and oxidizing agents during MNP formation. These biomolecules act as capping agents, contributing to the stability and monodisperse nature of MNPs. Using bacterial CFEs for MNP synthesis offers several advantages. Firstly, it aligns with eco-friendly practices as a biosynthesis approach. The non-toxic process minimizes environmental damage. Additionally, bacterial CFEs are cost-effective, making large-scale production economically viable. This review provides insights into these mechanisms, highlighting the role of CFE biomolecules and their impact on MNP characteristics. It also investigates the correlation between synthesis parameters, morphologies, and physical, chemical, and biological properties, allowing for tailored MNP design through the biosynthesis conditions. Despite its advantages, bacterial CFE-mediated biosynthesis faces challenges. This review addresses these challenges and discusses potential solutions. It also explores future perspectives, emphasizing areas for further investigation and innovation. In summary, using bacterial CFEs to synthesize MNPs offers significant advantages over other methods. It ensures eco-friendly, non-toxic, and cost-effective production. The review emphasizes the mechanisms and biomolecules involved, showcasing the potential for tailored MNP design. It also addresses challenges and prospects, paving the way for advancements in this field. Furthermore, the originality of this work lies in the exploitation of bacterial CFEs as a highly efficient and scalable platform for MNP synthesis.

Performance of heavy metal-immobilizing bacteria combined with biochar on remediation of cadmium and lead co-contaminated soil

Heavy metal pollution of soil has become a public concern worldwide since it threats food safety and human health. Sustainable and environmental-friendly remediation technology is urgently needed. Therefore, we investigated the properties and heavy metal removal ability of Enterobacter asburiae G3 (G3), Enterobacter tabaci I12 (I12), and explored the feasibility of remediation Cd, Pb co-contaminated soil by the combination of G3/I12 and biochar. Our results indicated that both strains are highly resistant to Cd, Pb and maintain plant growth-promoting properties. The removal efficiency of G3 for Cd and Pb were 76.79-99.43%, respectively, while the removal efficiency of I12 for Cd and Pb were 62.57-99.55%, respectively. SEM-EDS and XRD analysis revealed that the morphological and structural changes occurred upon heavy metal exposure, metal precipitates were also detected on cell surface. FTIR analysis indicated that functional groups (-OH, -N-H, -C = O, -C-N, -PO4) were involved in Cd/Pb immobilization. Application of the bacteria, biochar, or their combination decreased the acid-extractable Cd, Pb in soil while increased the residual fractions, meanwhile, the bioavailability of both metal elements declined. Besides, these treatments increased soil enzyme (sucrase, catalase and urease) activity and accelerated pakchoi growth, heavy metal accumulation in pakchoi was depressed upon bacteria and/or biochar application, and a synergistic effect was detected when applying bacteria and biochar together. In BC + G3 and BC + I12 treated plants, the Cd and Pb accumulation decreased by 24.42% and 52.19%, 17.55% and 47.36%, respectively. Overall, our study provides an eco-friendly and promising in situ technology that could be applied in heavy metal remediation.

Effect of Biosynthesized Silver Nanoparticles on the Growth of the Green Microalga Haematococcus pluvialis and Astaxanthin Synthesis

Silver nanoparticles (AgNPs) are widely known for their antimicrobial activity in various systems from microorganisms to cell cultures. However, the data on their effects on microalgae are very limited. Unicellular green algae Haematococcus pluvialis is known for its ability to accumulate large amounts of astaxanthin under stress conditions. Therefore, it can be used as a suitable model system to test the influence of AgNPs on stress induction in unicellular algae, with visible phenotypic effects, such as astaxanthin synthesis and cell morphology. This study tested different AgNP concentrations (0-8 mg/L) effects on different growth stages (red and green) of H. pluvialis culture. Effects on cell morphology, culture productivity, and astaxanthin synthesis were evaluated. Data showed that the addition of high concentrations of AgNPs to the growing culture had a significant negative impact on culture productivity. Green-stage (HpG) cultures productivity was reduced by up to 85% by increasing AgNPs concentration to 8 mg/L while the impact on red-stage (HpR) culture was lower. Astaxanthin concentration measurements showed that AgNPs do not have any effect on astaxanthin concentration in HpG culture and caused decreased astaxanthin production rate in HpR culture. HpG culture astaxanthin concentration stayed constant at ~0.43% dry weight, while HpR culture astaxanthin concentration was significantly reduced from 1.89% to 0.60% dry weight by increasing AgNP concentration. AgNPs in the media lead to significant changes in cell morphology in both HpG and HpR cultures. Cell deformations and disrupted cytokinesis, as well as AgNPs and induced sexual reproduction, were observed.

Biosynthesis of Silver Nanoparticles Produced Using Geobacillus spp. Bacteria

Silver nanoparticles (AgNPs) are well known for their unique physical and chemical properties, which can be incorporated into a wide range of applications. The growing resistance of microorganisms to antimicrobial compounds promoted the use of AgNPs in antimicrobial therapy. AgNPs can be obtained using physical and chemical methods, but these technologies are highly unfriendly to nature and produce large amounts of side compounds (for example, sodium borohydride and N,N-dimethylformamide). Therefore, alternative technologies are required for obtaining AgNPs. This report focuses on the biosynthesis of silver nanoparticles through the reduction of Ag⁺ with the cell-free secretomes of four Geobacillus bacterial strains, namely, 18, 25, 95, and 612. Only a few studies that involved Geobacillus bacteria in the synthesis of metal nanoparticles, including AgNPs, have been reported to date. The silver nanoparticles synthesized through bio-based methods were characterized using UV-Vis spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS), and zeta potential measurements. UV-Vis spectroscopy showed a characteristic absorbance peak at 410-425 nm, indicative of AgNPs. SEM analysis confirmed that most nanoparticles were spherical. DLS analysis showed that the sizes of the obtained AgNPs were widely distributed, with the majority less than 100 nm in diameter, while the zeta potential values ranged from -25.7 to -31.3 mV and depended on the Geobacillus spp. strain.

Combined Gold Recovery and Nanoparticle Synthesis in Microbial Systems Using Fractional Factorial Design

Green synthesis of gold nanoparticles (AuNPs) using microorganisms has been generally studied aiming for high-yield production and morphologies appropriated for various applications, such as bioremediation, (bio)sensors, and (bio)catalysis. Numerous approaches showed the individual effect of factors influencing the synthesis of AuNPs with limited analysis of the governing factors enhancing the production and desired quality of the precipitates. This study proposes a fractional-factorial design to investigate the simultaneous influence of seven environmental factors (cell concentration, temperature, anoxic/oxic conditions, pH, gold concentration, electron donor type, and bacterial species) on the recovery yield and synthesis of targeted AuNPs. Various sizes and morphologies of the AuNPs were obtained by varying the environmental factors studied. The factors with significant effects (i.e., 0.2 mM Au and pH 5) were selected according to statistical analysis for optimal removal of 88.2 ± 3.5% of gold and with the production of valuable 50 nm AuNPs, which are known for their enhanced sensitivity. Implications of the cytochrome-C on the bacterial mechanisms and the provision of electron donors via an electrochemical system are further discussed. This study helps develop gold recovery and nanoparticle synthesis methods, focusing on the determining factor(s) for efficient, low-cost, green synthesis of valuable materials.

Biologically Derived Gold Nanoparticles and Their Applications

Nanotechnology is a rapidly evolving discipline as it has a wide variety of applications in several fields. They have been synthesized in a variety of ways. Traditional processes such as chemical and physical synthesis have limits, whether in the form of chemical contamination during synthesis operations or in subsequent applications and usage of more energy. Over the last decade, research has focused on establishing easy, nontoxic, clean, cost-effective, and environmentally friendly techniques for nanoparticle production. To achieve this goal, biological synthesis was created to close this gap. Biosynthesis of nanoparticles is a one-step process, and it is ecofriendly in nature. The metabolic activities of biological agents convert dissolved metal ions into nanometals. For biosynthesis of metal nanoparticles, various biological agents like plants, fungus, and bacteria are utilized. In this review paper, the aim is to provide a summary of contemporary research on the biosynthesis of gold nanoparticles and their applications in various domains have been discussed.

Improvement of morpho-physiological, ultrastructural and nutritional profiles in wheat seedlings through astaxanthin nanoparticles alleviating the cadmium toxicity

Heavy metal accumulation in arable lands and water bodies has become one of the serious global issues among multitude of food security challenges. In particular, cadmium (Cd) concentration has been increasing substantially in the environment that negatively affects the growth and yield of important agricultural crops, especially wheat (Triticum aestivum L.). No doubt, nanotechnology is a revolutionary science but the comprehension of nanoparticle-plants interaction and its potential alleviatory role against metal stress is still elusive. Here, we investigated the mechanistic role of astaxanthin nanoparticles (AstNPs) in Cd stress amelioration and their interaction with wheat under Cd-spiked conditions. The AstNPs fabrication was confirmed through ultraviolet visible spectroscopy, where the particles showed characteristic peak at 423 nm. However, Fourier transform infrared, X-ray diffraction, scanning electron microscopy and transmission electron microscopy analyses confirmed the presence of stabilized spherical-shaped nanocrystals of AstNPs within the size range of 12.03-30.37 nm. The hydroponic application of AstNPs (100 mg L^-1) to Cd-affected wheat plants increased shoot height (59%), shoot dry weight (31%), nitrogen concentration (42%), and phosphorus concentration (26%) as compared to non-treated Cd affected seedlings. Moreover, AstNPs-treated plants showed reduction in acropetal Cd translocation (29%) in contrast to plants treated with Cd only. Under Cd-spiked conditions, AstNPs-treated plants displayed an improved nutrient profile (P, N, K⁺ and Ca²⁺) with a relative decrease in Na⁺ content in comparison with non-treated plants. Interestingly, it was found that AstNPs restricted the translocation of Cd to aerial plant parts by negatively regulating Cd transporter genes (TaHMA2 and TaHMA3), and relieved plants from oxidative burst by activating antioxidant machinery via triggering expressions of TaSOD and TaPOD genes. Consequently, it was observed that the application of AstNPs helped in maintaining the nutrient acquisition and ionic homeostasis in Cd-affected wheat plants, which subsequently improved the physiochemical profiles of plants under Cd-stress. This study suggests that AstNPs plausibly serve as stress stabilizers for plants under heavy metal-polluted environment.

Activity of Fusarium oxysporum-Based Silver Nanoparticles on Candida spp. Oral Isolates

Candida spp. resistant to commercially available antifungals are often isolated from patients with oral candidiasis, a situation that points to the need for the development of new therapies. Thus, we evaluated the activity of Fusarium oxysporum-based silver nanoparticles (AgNPs) on Candida spp. isolated from denture stomatitis lesions. Candida isolates were molecularly identified and submitted to susceptibility assays using AgNPs and commercial fungicides. The interference on biofilm formation and the mechanisms of action of AgNPs on Candida spp. were also investigated. Scanning electron microscopy was used to evaluate the morphology of AgNP-treated Candida. Candida albicans was the most frequent species isolated from denture stomatitis cases. All Candida spp. were susceptible to AgNPs at low concentrations, except Candida parapsilosis. AgNPs caused surface damage, cell disruption, and biofilm formation inhibition. The ergosterol supplementation protected C. albicans against the AgNP action. AgNPs are effective against Candida spp. and can be faced as a promising new therapeutic agent against oral candidiasis.

Curcumin-Chitosan Nanocomposite Formulation Containing Pongamia pinnata-Mediated Silver Nanoparticles, Wound Pathogen Control, and Anti-Inflammatory Potential

BACKGROUND

Because of its diverse range of use in several ethics of diagnosis and care of multiple diseases, nanotechnology has seen remarkable growth and has become a key component of medical sciences. In recent years, there has been rapid advancement in medicine and biomaterials. Nanomedicine aids in illness prevention, diagnosis, monitoring, and treatment.

AIM

The purpose of this work is to evaluate the antibacterial, anti-inflammatory, and cytotoxic capabilities of green produced silver nanoparticle with the addition of curcumin-assisted chitosan nanocomposite (SCCN) against wound pathogenic as reducing agents.

MATERIALS AND METHODS

The plant extract of Pongamia pinnata, silver nanoparticles, and its based curcumin nanoformulations was studied in this study utilizing UV visible spectrophotometer, selected area electron diffraction (SAED), and TEM. Anti-inflammatory, antimicrobial, and cytotoxic tests were performed on silver nanoparticles with the addition of curcumin-assisted chitosan nanocomposite (SCCN). Furthermore, these produced nanocomposites were coated on clinical silk and tested for antibacterial activity.

RESULTS

The produced silver nanoparticle with the addition of curcumin-assisted chitosan nanocomposite (SCCN) has significant antibacterial activities against Pseudomonas aeruginosa and staphylococcus aureus. They are as well as possess anti-inflammatory activity and furthermore prove to be biocompatible.

CONCLUSION

This advancement in the field of biomaterials, which means nanocomposite, not only helps to reduce the harmful effects of pathogenic organisms while representing an environmentally benign material but it also shows to be a material with zero danger to humans and the environment.

Response of Biological Gold Nanoparticles to Different pH Values: Is It Possible to Prepare Both Negatively and Positively Charged Nanoparticles?

The mycelium-free supernatant (MFS) of a five-day-old culture medium of Fusarium oxysporum was used to synthesize gold nanoparticles (AuNPs). The experimental design of the study was to answer the question: can this production process of AuNPs be controllable like classical chemical or physical approaches? The process of producing AuNPs from 1 mM tetrachloroauric (III) acid trihydrate in MFS was monitored visually by color change at different pH values and quantified spectroscopically. The produced AuNPs were analyzed by transmission electron microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The presence of capping agents was confirmed by Fourier transform infrared spectroscopy (FTIR). Two AuNP samples with acidic and alkaline pH were selected and adjusted with the pH gradient and analyzed. Finally, the size and zeta potential of all samples were determined. The results confirmed the presence of the proteins as capping agents on the surface of the AuNPs and confirmed the production of AuNPs at all pH values. All AuNP samples exhibited negative zeta potential, and this potential was higher at natural to alkaline pH values. The size distribution analysis showed that the size of AuNPs produced at alkaline pH was smaller than that at acidic pH. Since all samples had negative charge, we suspect that there were other molecules besides proteins that acted as capping agents on the surface of the AuNPs. We conclude that although the biological method of nanoparticle production is safe, green, and inexpensive, the ability to manipulate the nanoparticles to obtain both positive and negative charges is limited, curtailing their application in the medical field.

Biogenic Silver Nanoparticles: Synthesis and Application as Antibacterial and Antifungal Agents

The importance and need for eco-oriented technologies has increased worldwide, which leads to an enhanced development of methods for the synthesis of nanoparticles using biological agents. This review de-scribes the current approaches to the preparation of biogenic silver nanoparticles, using plant extracts and filtrates of fungi and microorganisms. The peculiarities of the synthesis of particles depending on the source of biocomponents are considered as well as physico-morphological, antibacterial and antifungal properties of the resulting nanoparticles which are compared with such properties of silver nanoparticles obtained by chemical synthesis. Special attention is paid to the process of self-assembly of biogenic silver nanoparticles.

Milking microalgae in conjugation with nano-biorefinery approach utilizing wastewater

In today's era, we need to replace chemical or physical processes of nanoparticle synthesis with biosynthesis processes to avoid environmental damage. These bioderived nanoparticles can help in addressing the problems of wastewater treatment and biofuels production. This review gives an insight into solving multiple problems using a nano-biorefinery approach in conjugation with wastewater treatment. The major advantage of using a bio-derivative method in nanoparticle synthesis is its low toxicity towards the environment. The current review discusses the development of nanoscience and its biogenic importance. It covers the usage of microalgae for (A) Nanoparticle's biosynthesis (B) Mechanism of nanoparticle biosynthesis (C) Nanoparticles in bio-refinery processes (D) Wastewater treatment with microalgae and bio-derived nanoparticles (E) A hypothetical mechanistic approach, which utilizes the photothermal effect of metallic nanoparticles to extract lipids from the cells without cell damage. The term "cell milking" has been around for quite some time, and the hypothesis discussed in the present study can help in this context. The current hypothesized process can pave ways for futuristic endeavors to conjugate nanoparticles and microalgae for viable and commercial production of biofuel, nanoparticles, and many other molecules.

Copper mining bacteria: Converting toxic copper ions into a stable single-atom copper

The chemical synthesis of monoatomic metallic copper is unfavorable and requires inert or reductive conditions and the use of toxic reagents. Here, we report the environmental extraction and conversion of CuSO₄ ions into single-atom zero-valent copper (Cu⁰) by a copper-resistant bacterium isolated from a copper mine in Brazil. Furthermore, the biosynthetic mechanism of Cu⁰ production is proposed via proteomics analysis. This microbial conversion is carried out naturally under aerobic conditions eliminating toxic solvents. One of the most advanced commercially available transmission electron microscopy systems on the market (NeoArm) was used to demonstrate the abundant intracellular synthesis of single-atom zero-valent copper by this bacterium. This finding shows that microbes in acid mine drainages can naturally extract metal ions, such as copper, and transform them into a valuable commodity.

Copper nanoparticles: Green synthesis and managing fruit rot disease of chilli caused by Colletotrichum capsici

The present study was focused on synthesis and characterization of copper nanoparticles to evaluate their efficacy against fruit rot pathogen of chilli crop. The green synthesis of nanoparticles was carried out by using extracts of Eucalyptus and Mint leaves. The synthesis of copper nanoparticles was confirmed by XRD, PSA, SEM and TEM. The average size of these particles synthesized by Eucalyptus leaf extract (CuNP-E) ranged from 10 to 130 nm, while as size of Mint leaf extract synthesized particles (CuNP-M) ranged from 23 to 39 nm, thus confirming their nano size. These green synthesized copper nanoparticles were evaluated against Colletotrichum capsici where Carbendazim 50 WP @ 500 ppm and copper oxychloride 50 WP @ 2500 ppm served as standard checks. The mycelia inhibition of Colletotrichum capsici caused by copper nanoparticles was studied on PDA medium. CuNP-M @ 1000 ppm showed highest mycelial inhibition of 99.78% followed by 93.75% at 500 ppm and CuNP-E @ 1000 ppm compared to standard fungicides, carbendazim 50 WP @ 500 ppm (72.82%), and copper oxychloride 50 WP @ 2500 ppm (85.85%). The CuNP-M @ 500 ppm were significantly superior to carbendazim 50 WP @ 500 ppm and copper oxychloride 50 WP @ 2500 ppm, but was statistically at par with CuNP-E @ 1000 ppm. This shows effectiveness of much lower concentration of copper nanoparticles compared to conventional fungicides. In detached fruit method, nanoparticles applied before inoculation of pathogen showed better results with regard to incubation period, lesion number and lesion size than after inoculation of pathogen. The present study reveals a simple, convenient, non-toxic and cost-efficient technique for the synthesis of nanoparticles and their effectiveness against Colletotrichum capsici. CuNP-M first time synthesized and evaluated against Colletotrichum capsici performed better than CuNP-E.

Biogenic copper nanoparticles synthesized by using a copper-resistant strain Shigella flexneri SNT22 reduced the translocation of cadmium from soil to wheat plants

The mechanistic role of green copper nanoparticles (CuNPs) in cadmium (Cd) toxicity alleviation in plants is poorly understood. Here, the CuNPs, synthesized by using a bacterium Shigella flexneri SNT22, were confirmed through UV-vis spectroscopy with a characteristic peak at 334.50 nm. Moreover, FT-IR, XRD, SEM, and TEM techniques revealed that the spherical shaped crystals of CuNPs with a size range of 17.24 nm to 38.03 nm were stabilized by coating proteins. Diff ;erent levels of CuNPs (e.g., 25, 50, and 100 mg kg^-1 of soil) were examined in pots having Cd-mixed soil to evaluate their effect on wheat plants in a growth chamber under optimal environmental conditions. Treatment of soil with 100 mg kg^-1 of CuNPs increased plant length by 44.4 %, shoot dry weight by 28.26 %, nitrogen contents by 41.60 %, and phosphorus contents by 58.79 %, whereas decreased the acropetal Cd translocation by 49.62 %. An increase in the N, P, K⁺, Ca²⁺, K⁺/Na⁺, and Ca²⁺/Na⁺ contents and decrease in the Na⁺ concentration in wheat plants treated with CuNPs was also recorded. Overall, the results are valuable to establish a green CuNPs-based approach for sustainable wheat growth in metal-contaminated soils.

Phytochemical screening, metabolite profiling and enhanced antimicrobial activities of microalgal crude extracts in co-application with silver nanoparticle

Background

Microalgae is one of the major sources of natural compounds with antimicrobial activity. The metabolite profiling of the extracts could identify the bioactive compounds based on methanol (MET), ethanol (ETH), chloroform (CHL), hexane (HEX) and water (W) solvent systems. The microalgal crude extracts in co-application with silver nanoparticles (AgNPs) had enhanced antimicrobial activity with potential to overcome the global problem of microbial antibiotic resistance.

Results

Chlorella sp. exhibited the highest lipid, N. oculata the highest total saturated fatty acids (TSFA), and T. suecica the highest mono-unsaturated (MUFA) and poly-unsaturated fatty acids (PUFA). The highest carbohydrate, protein and total phenolics contents (TPCs) were attained by N. oculata. The highest total flavonoids contents (TFCs), and chlorophyll a and b were in T. suecica, while comparable level of carotenoids were found in all species. For high-performance thin-layer chromatography (HPTLC) analyses, the eicosapentaenoic acid (EPA) with high peaks were detected in T. suecica-HEX and N. oculata-CHL; and β-carotene in Chlorella sp.-ETH. The gas chromatography–mass spectrometry (GC–MS) analyses showed high 13-docosenamide (Z)- in T. suecica-HEX; phytol in N. oculata-HEX; and neophytadiene in Chlorella sp.-ETH. The AgNPs–MCEs–MET and HEX at the 1.5:1 ratios exhibited strong activities against Bacillus subtilis, Streptococcus uberis, and Salmonella sp.; and the AgNPs–T. suecica-HEX and MET and AgNPs–Chlorella sp.-HEX at the 1.5:1 ratios exhibited activities against Klebsiella pneumoniae.

Conclusion

Different bioactive components were detected in the MCEs based on the HPTLC and GC–MS analyses. Significant antimicrobial activities against the pathogenic microbes were demonstrated by the synergistic effects of the MCEs in co-application with the AgNPs. This could be beneficial in the fight against sensitive and multidrug-resistant bacteria.

Green Synthesis of AuNPs by Acinetobacter sp. GWRVA25: Optimization, Characterization, and Its Antioxidant Activity

Bacteriogenic synthesis of metal nanoparticles is ecofriendly and greatly influenced by physico-chemical reaction parameters with respect to shape and size. Thus, present work aimed to synthesize and optimization of bacteriogenic gold nanoparticles (AuNPs) and study their antioxidant activity. Acinetobacter sp. cells were able to synthesize AuNPs, when challenged with tetra-chloroauric acid (HAuCl₄). By physicochemical optimization, maximum synthesis was obtained with 72 h old culture using 2.1 × 10⁹ CFU/ml cell density. Whereas, pH-7 is suitable for AuNPs synthesis. HAuCl₄ concentration (0.5 mM) enhanced the formation of monodispersed and spherical nanoparticles (15 ± 10 nm). At 37°C temperature, Acinetobacter sp. released nanoparticles in supernatant. From characterization, AuNPs were found to be crystalline in nature with negative surface charge. AuNPs showed up to 86% different radical scavenging ability, exhibiting antioxidant activity. In conclusion, spherical AuNPs can be synthesized using Acinetobacter sp. through physicochemical optimization. This is the first report of antioxidant activity exhibited by monodispersed bacteriogenic AuNPs synthesized using Acinetobacter sp.

Use of biogenic copper nanoparticles synthesized from a native Escherichia sp. as photocatalysts for azo dye degradation and treatment of textile effluents

Textile wastewater contains a huge amount of azo dyes and heavy metals and catastrophically deteriorates the agricultural field by affecting its phyisco-chemical/biological and nutritional properties when directly drained to agricultural lands without any treatment. Recently, biogenic copper nanoparticles (CuNPs) have gained considerable attention for photocatalytic degradation of wastewater pollutants owing to their unique physico-chemical and biological properties, low cost and environmental sustainability. The current study reports the synthesis of CuNPs by a native copper-resistant bacterial strain Escherichia sp. SINT7 and evaluation of the photocatalytic activity of the biogenic CuNPs for azo dye degradation and treatment of textile effluents. Scanning electron microscopy and transmission electron microscopy revealed the spherical shape of biogenic CuNPs with particle size ranging from 22.33 to 39 nm. Moreover, X-ray diffraction data revealed that the CuNPs have spherical crystalline shapes with an average particle size of 28.55 nm. FTIR spectra showed the presence of coating proteins involved in the stabilization of nanomaterial. Azo dye degradation assays indicated that CuNPs decolorized congo red (97.07%), malachite green (90.55%), direct blue-1 (88.42%) and reactive black-5 (83.61%) at a dye concentration of 25 mg L^-1 after 5 h of sunlight exposure. However, at 100 mg L^-1 dye concentration, the degradation percentage was found to be 83.90%, 31.08%, 62.32% and 76.84% for congo red, malachite green, direct blue-1 and reactive black-5, respectively. Treatment of textile effluents with CuNPs resulted in a significant reduction in pH, electrical conductivity, turbidity, total suspended solids, total dissolved solids, hardness, chlorides and sulfates as compared to the non-treated samples. Thus, the promising dye detoxification and textile effluent recycling efficiency of biogenic CuNPs may lead to the development of eco-friendly and cost-efficient process for large-scale wastewater treatment.

Gold nanorods: from anisotropy to opportunity. An evolution update

Gold nanoparticles have drawn attention to nanomedicine for many years due to their physicochemical properties, which include: good stability; biocompatibility; easy surface chemistry and superior magnetic; and last, electronic properties. All of these properties distinguish gold nanoparticles as advantageous carriers to be exploited. The challenge to develop new gold nanostructures has led to anisotropy, a new property to exploit for various medical applications: diagnostic and imaging strategies as well as therapeutic options. Gold nanorods are the most studied anisotropic gold nanoparticles because of the presence of two absorption peaks according to their longitudinal and transversal plasmon resonances. The longitudinal surface plasmonic resonance can provide the absorption in the near-infrared region and this is an important aspect of using gold nanorods for medical purposes.

A review on biosynthesis of silver nanoparticles and their biocidal properties

Use of silver and silver salts is as old as human civilization but the fabrication of silver nanoparticles (Ag NPs) has only recently been recognized. They have been specifically used in agriculture and medicine as antibacterial, antifungal and antioxidants. It has been demonstrated that Ag NPs arrest the growth and multiplication of many bacteria such as Bacillus cereus, Staphylococcus aureus, Citrobacter koseri, Salmonella typhii, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumonia, Vibrio parahaemolyticus and fungus Candida albicans by binding Ag/Ag+ with the biomolecules present in the microbial cells. It has been suggested that Ag NPs produce reactive oxygen species and free radicals which cause apoptosis leading to cell death preventing their replication. Since Ag NPs are smaller than the microorganisms, they diffuse into cell and rupture the cell wall which has been shown from SEM and TEM images of the suspension containing nanoparticles and pathogens. It has also been shown that smaller nanoparticles are more toxic than the bigger ones. Ag NPs are also used in packaging to prevent damage of food products by pathogens. The toxicity of Ag NPs is dependent on the size, concentration, pH of the medium and exposure time to pathogens.

Strategies to Combat Antibiotic Resistance in the Wastewater Treatment Plants

The main goal of this manuscript is to review different treatment strategies and mechanisms for combating the antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs) in the wastewater environment. The high amount of antibiotics is released into the wastewater that may promote selection of ARB and ARGs which find their way into natural environments. Emerging microbial pathogens and increasing antibiotic resistance among them is a global public health issue. The propagation and spread of ARB and ARGs in the environment may result in an increase of antibiotic resistant microbial pathogens which is a worldwide environmental and public health concern. A proper treatment of wastewater is essential before its discharge into rivers, lake, or sewage system to prevent the spread of ARB and ARGs into the environment. This review discusses various treatment options applied for combating the spread of ARB and ARGs in wastewater treatment plants (WWTPs). It was reported that low-energy anaerobic-aerobic treatment reactors, constructed wetlands, and disinfection processes have shown good removal efficiencies. Nanomaterials and biochar combined with other treatment methods and coagulation process are very recent strategies regarding ARB and ARGs removal and need more investigation and research. Based on current studies a wide-ranging removal efficiency of ARGs can be achieved depending on the type of genes present and treatment processes used, still, there are gaps that need to be further investigated. In order to find solutions to control dissemination of antibiotic resistance in the environment, it is important to (1) study innovative strategies in large scale and over a long time to reach an actual evaluation, (2) develop risk assessment studies to precisely understand occurrence and abundance of ARB/ARGs so that their potential risks to human health can be determined, and (3) consider operating and environmental factors that affect the efficiency of each treatment mechanism.

Lignin peroxidase mediated silver nanoparticle synthesis in Acinetobacter sp

Metals present in environment render the bacteria to attain certain resistance machinery to survive, one of which is transformation of metal ions to nano forms. Various enzymes and proteins have been suggested to play significant role in synthesis of silver nanoparticles (AgNPs) in bacteria. In present study, we have purified lignin peroxidase from secreted enzyme extract of Acinetobacter sp. employing diethyl aminoethyl cellulose ion exchange and Biogel P-150 gel filtration column chromatography. The purified fraction has a specific activity of 1.571 U/mg with substrate n-propanol and 6.5-fold purification. The tetrameric enzyme, with molecular weight of 99 kDa, consisted of dimers of two polypetides of 23.9 and 24.6 kDa as revealed by native and SDS-PAGE. On exposure to purified enzyme, spherical polydispersed AgNPs of ~ 50 nm were obtained as observed under transmission electron microscope. Optimum activity of the purified enzyme was obtained at pH 2 and 60 °C with n-propanol as substrate. This is the first report describing the reduction of extracellular silver ions by lignin peroxidase purified from Acinetobacter sp.

Biosynthesis of gold nanoparticles using cell-free extracts of Magnusiomyces ingens LH-F1 for nitrophenols reduction

A green and eco-friendly method for the synthesis of gold nanoparticles (AuNPs) was developed using the cell-free extracts of a yeast strain Magnusiomyces ingens LH-F1. UV-vis spectra showed a distinct absorption band at ~ 540 nm, corresponding to the surface plasmon resonance of AuNPs. Transmission electron microscopy images revealed that the shapes of AuNPs were almost spherical and pseudo-spherical. Fourier transform infrared spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses suggested that some proteins containing amino- and carboxyl-groups in the cell-free extracts were absorbed on the surface of nanoparticles, which could act as reducing and capping agents for AuNPs synthesis. Furthermore, with the concentration of cell-free extracts increasing from 25 to 200 mg L^-1, the average size of AuNPs decreased from 28.3 to 20.3 nm. Meanwhile, the morphology became more uniform with less irregular shapes. In addition, the as-synthesized AuNPs showed an excellent catalytic activity for nitrophenols reduction (i.e., 4-nitrophenol, 3-nitrophenol and 2-nitrophenol) in the presence of excess NaBH₄. The catalytic rate constant of nitrophenols reduction was also dependent on cell-free extract concentration. The larger AuNPs synthesized by less cell-free extracts were covered with a thinner corona and showed better capacity for reducing nitrophenols. This study suggested that the as-synthesized AuNPs could be employed as efficient catalysts in reduction of organic contaminants.

Gundelia tournefortii L.: a natural source for the green synthesis of silver nanoparticles

The present study focused on the synthesis of spherical silver nanoparticles (Ag NPs) using Gundelia tournefortii L. aerial part extract. The plant extract could reduce silver ions into Ag NPs. To identify the compounds responsible for the reduction of silver ions, functional groups present in plant extract were investigated by Fourier transform infrared spectroscopy. Techniques used to characterise synthesised nanoparticles included field emission scanning electron microscopy, X‐ray diffraction and transmission electron microscopy. UV‐visible spectrophotometer showed the absorbance peak in the range of 400–450 nm. The Ag NPs showed antibacterial activities against both gram positive (Staphylococcus aureus and Bacillus Cereus) and gram negative (Salmonella typhimurium and Escherichia coli) microorganisms. The results confirmed that this protocol was simple, rapid, eco‐friendly, low‐priced and non‐toxic; therefore, it could be used as an alternative to conventional physical/chemical methods. Only 5 min were required for the conversion of silver ions into Ag NPs at room temperature, without the involvement of any hazardous chemical.

Kinetics of Synthesis of Gold Nanoparticles by Acinetobacter sp. SW30 Isolated from Environment

Cell biomass and metal salt concentration have great influence on morphology of biosynthesized nanoparticle. The aim of present study was to evaluate the effect of varying cell density and gold salt concentrations on synthesis of nanoparticles and its morphology, which has not been studied in bacteria till now. When cells of Acinetobacter sp. SW30 were incubated with different cell density and gold chloride concentrations, tremendous variation in color of colloidal solution containing gold nanoparticles (AuNP) was observed indicating variation in their size and shapes. Surprisingly, monodispersed spherical AuNP of size ~19 nm were observed at lowest cell density and HAuCl₄ salt concentration while increase in cell number resulted in formation of polyhedral AuNP (~39 nm). Significance of this study lays in the fact that the shape and dispersity of AuNP can be customized depending up on the requirement. FTIR spectrum revealed shift from 3221 to 3196 cm^-1 indicating the presence and role of amino acids in Au³⁺ reduction while possible involvement of amide I and II groups in stabilization of AuNP. The rate constant was calculated for cell suspension of 2.1 × 10⁹ cfu/ml challenged with 1.0 mM HAuCl₄, incubated at 30 °C and pH 7 using the slopes of initial part of the plot log (A_α - A_t) versus time as 1.99 × 10^-8 M. Also, this is the first study to report the kinetics of gold nanoparticle synthesis by Acinetobacter sp. SW30.

Biosynthesis of gold nanoparticles: A green approach

Nanotechnology is an immensely developing field due to its extensive range of applications in different areas of technology and science. Different types of methods are employed for synthesis of nanoparticles due to their wide applications. The conventional chemical methods have certain limitations with them either in the form of chemical contaminations during their syntheses procedures or in later applications and use of higher energy. During the last decade research have been focussed on developing simple, clean, non-toxic, cost effective and eco-friendly protocols for synthesis of nanoparticles. In order to get this objective, biosynthesis methods have been developed in order to fill this gap. The biosynthesis of nanoparticles is simple, single step, eco-friendly and a green approach. The biochemical processes in biological agents reduce the dissolved metal ions into nano metals. The various biological agents like plant tissues, fungi, bacteria, etc. are used for biosynthesis for metal nanoparticles. In this review article, we summarised recent literature on biosynthesis of gold nanoparticles which have revolutionised technique of synthesis for their applications in different fields. Due to biocompatibility of gold nanoparticles, it has find its applications in biomedical applications. The protocol and mechanism of biosynthesis of gold nanoparticles along with various applications have also been discussed.

A review of the influence of treatment strategies on antibiotic resistant bacteria and antibiotic resistance genes

Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARG) in the aquatic environment have become an emerging contaminant issue, which has implications for human and ecological health. This review begins with an introduction to the occurrence of ARB and ARG in different environmental systems such as natural environments and drinking water resources. For example, ARG or ARB with resistance to ciprofloxacin, sulfamethoxazole, trimethoprim, quinolone, vancomycin, or tetracycline (e.g., tet(A), tet(B), tet(C), tet(G), tet(O), tet(M), tet(W), sul I, and sul II) have been detected in the environment. The development of resistance may be intrinsic, may be acquired through spontaneous mutations (de novo), or may occur due to horizontal gene transfer from donor bacteria, phages, or free DNA to recipient bacteria. An overview is also provided of the current knowledge regarding inactivation of ARB and ARG, and the mechanism of the effects of different disinfection processes in water and wastewater (chlorination, UV irradiation, Fenton reaction, ozonation, and photocatalytic oxidation). The effects of constructed wetlands and nanotechnology on ARB and ARG are also summarized.