Synthesis of silver nanoparticles and its contribution to the capability of Bacillus subtilis to deal with polluted waters

Green Synthesis and Characterization of Biologically Synthesized and Antibiotic-Conjugated Silver Nanoparticles followed by Post-Synthesis Assessment for Antibacterial and Antioxidant Applications

The paper presents the antibacterial and antioxidant activities of silver nanoparticles (AgNPs) when conjugated with two antibiotics levofloxacin and ciprofloxacin as well as biologically synthesized nanoparticles from Moringa oleifera and Curcuma longa. Leaves of Moringa and powder of Curcuma were used in the green synthesis of silver nanoparticles. Ultraviolet-visible spectroscopy (UV), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were used for the characterization of the synthesized silver nanoparticles. Comparison of levofloxacin and ciprofloxacin and their conjugated AgNPs was also studied for antibacterial and antioxidant activity. The synthesis of Moringa-AgNPs, turmeric-AgNPs, levofloxacin-AgNPs, and ciprofloxacin-AgNPs was confirmed by UV spectroscopy. An absorption peak value of 400-450 nm was observed, and light to dark brown color indicated the synthesis of AgNPs. Moringa-AgNPs revealed high antioxidant activity (80.3 ± 3.14) among all of the synthesized AgNPs. Lev-AgNPs displayed the highest zone of inhibition for Staphylococcus aureus, while in Escherichia coli, Cip-AgNPs showed high antibacterial activity. Furthermore, AgNPs synthesized using green methods exhibit high and efficient antimicrobial activities against two food-borne pathogens. Biologically synthesized nanoparticles exhibited antibacterial activity against E. coli (13.73 ± 0.46 with Tur-AgNPs and 13.53 ± 0.32 with Mor-AgNPs) and S. aureus (14.16 ± 0.24 with Tur-AgNPs and 13.36 ± 0.77 with Mor-AgNPs) by using a well diffusion method with significant shrinkage and damage of the bacterial cell wall, whereas antibiotic-conjugated nanoparticles showed high antibacterial activity compared to biologically synthesized nanoparticles with 14.4 ± 0.37 for Cip-AgNPs and 13.93 ± 0.2 for Lev-AgNPs for E. coli and 13.3 ± 0.43 for Cip-AgNPs and 14.33 ± 0.12 for Lev-AgNPs for S. aureus. The enhanced efficiency of conjugated silver nanoparticles is attributed to their increased surface area compared to larger particles. Conjugation of different functional groups contributes to improved reactivity, creating active sites for catalytic reactions. Additionally, the precise control over the size and shape of green-synthesized nanoparticles further augments their catalytic and antibiotic activities.

Synthesis of silver nanoparticles using Bacillus velezensis M3-7 lipopeptides: Enhanced antifungal activity and potential use as a biocontrol agent against Fusarium crown rot disease of wheat seedlings

Bacillus velezensis M3-7 is a hyperactive mutant, 12-fold improved in its antifungal activity, obtained during a previous study from the wild strain BLB371 after a combination of random mutagenesis and medium component optimization. This study explores the use of this mutant in synthesizing silver nanoparticles (Ag-NPs) for the control of Fusarium crown rot disease (FCR) in wheat seedlings. LC-MS/MS analysis proved that both strains co-produced different families of lipopeptides and that mutagenesis caused the hyper-production of iturin A C14 and C15, the liberation of iturin A C10 and C12, and the inhibition of fengycin release. Our aim was a further improvement in the antifungal activity of the wild strain and the mutant M3-7 in order to control Fusarium crown rot disease (FCR) in wheat seedlings. Therefore, a nanotechnology approach was adopted, and different lipopeptide concentrations produced by the wild strain and the mutant M3-7 were used as capping agents to synthesize silver nanoparticles (Ag-NPs) with enhanced antifungal activity. Ag-NPs formed using 3 mg·mL-1 of the mutant lipopeptides were found to exhibit a good distribution, improved antifungal activity, a promising potential to be used as a biofortified agent for seed germination, and an effective compound to control FCR in wheat seedlings.

Optimization of the biosynthesis of silver nanoparticles using bacterial extracts and their antimicrobial potential

In the present study, silver nanoparticles (AgNPs) were biosynthesized using the supernatant and the intracellular extract of Cupriavidus necator, Bacillus megaterium, and Bacillus subtilis. The characterization of the AgNPs was carried out using UV-Vis spectroscopy, FTIR, DLS and TEM. Resazurin microtiter-plate assay was used to determine the antimicrobial action of AgNPs against Escherichia coli. UV-Visible spectra showed peaks between 414 and 460 nm. TEM analysis revealed that the synthesized AgNPs showed mostly spherical shapes. DLS results determined sizes from 20.8 to 118.4 nm. The highest antimicrobial activity was obtained with the AgNPs synthesized with supernatant rather than those using the intracellular extract. Therefore, it was determined that the bacterial species, temperature, pH, and type of extract (supernatant or intracellular) influence the biosynthesis. This synthesis thus offers a simple, environmentally friendly, and low-cost method for the production of AgNPs, which can be used as antibacterial agents.

Biocidal and synergistic effect of three types of biologically synthesised silver/silver chloride nanoparticles

Three types of silver/silver chloride nanoparticles were obtained by green synthesis from three types of microbial biomass. Their biocidal capacity was tested against six microorganisms. Two filamentous fungi were used that had previously demonstrated the ability to synthesise nanoparticles, Penicillium sp. 8L2 and Botryosphaeria rhodina MAMB-05. Also, the synthesis capacity of a yeast, Rhodotorula mucilaginosa 1S1, was evaluated. The original protocols underwent slight modifications. At the same time, the fractional inhibitory concentration was obtained. The interaction between specific antibiotics and the nanoparticles that showed the greatest biocidal capacity came from Penicillium sp.8L2, and it was studied further. All nanoparticles were characterised by UV-vis spectrophotometry and transmission electron microscopy (TEM). Also, their size distribution was analysed, which was in the range of 4 to 34 nm. The biocidal capacity of the nanoparticles for a group of bacteria and fungi was studied, presenting very low values in the range of 2.5-10 µg/mL for bacteria and 4-256 µg/mL for fungi. The interactions between the nanoparticles synthesised by Penicillium sp. 8L2 and a group of specific antibiotics for the tested microorganisms were also studied, proving that there was a synergistic interaction with vancomycin and ciprofloxacin and Staphylococcus epidermidis CECT 4183 and Escherichia coli CECT 101 bacteria, respectively.

New aspects of lipopeptide-incorporated nanoparticle synthesis and recent advancements in biomedical and environmental sciences: a review

The toxicity of metal nanoparticles has introduced promising research in the current scenario since an enormous number of people have been potentially facing this problem in the world. The extensive attention on green nanoparticle synthesis has been focussed on as a vital step in bio-nanotechnology to improve biocompatibility, biodegradability, eco-friendliness, and huge potential utilization in various environmental and clinical assessments. Inherent influence on the study of green nanoparticles plays a key role to synthesize the controlled and surface-influenced molecule by altering the physical, chemical, and biological assets with the provision of various precursors, templating/co-templating agents, and supporting solvents. However, in this article, the dominant characteristics of several kinds of lipopeptide biosurfactants are discussed to execute a critical study of factors affecting synthesis procedure and applications. The recent approaches of metal, metal oxide, and composite nanomaterial synthesis have been deliberated as well as the elucidation of the reaction mechanism. Furthermore, this approach shows remarkable boosts in the production of nanoparticles with the very less employed harsh and hazardous processes as compared to chemical or physical method-based nanoparticle synthesis. This study also shows that the advances in strain selection for green nanoparticle production could be a worthwhile and strong economical approach in futuristic medical science research.

Multifunctional chitosan/grape seed extract/silver nanoparticle composite for food packaging application

Food-borne fungi present significant hazards to food preservation and human health. Oxidation causes spoilage and the inedibility of the fruit. However, traditional packaging films without antimicrobial or antioxidant activities do not satisfy the active packaging requirements. Films with antimicrobial and antioxidant activities are urgently required. In this study, silver nanoparticles (AgNPs) were synthesized from fruit waste grape seed extracts (GSE). The antimicrobial and antioxidant activities of GSE-silver nanoparticles (GSE-AgNPs) and AgNPs (average size 20 nm) stabilized by polyvinyl pyrrolidone (PVP-AgNPs) were evaluated in vitro. The effect of chitosan (CS)-coated GSE-AgNPs and PVP-AgNPs on the postharvest quality of grape was studied during storage at 20 °C for 5 days. The results confirmed that grapes treated with CS and GSE-AgNPs showed significantly reduced decay percentage, weight loss, and maintained titratable acidity at high levels compared with those of untreated fruit and fruit treated with PVP-AgNPs. Moreover, CS and GSE-AgNPs significantly inhibited the total mold count during storage. Our results suggest that CS coating enriched with GSE-AgNPs has the potential to preserve the quality and extend the shelf life of grapes.

Small RNAs as a New Platform for Tuning the Biosynthesis of Silver Nanoparticles for Enhanced Material and Functional Properties

Genetic engineering of nanoparticle biosynthesis in bacteria could help facilitate the production of nanoparticles with enhanced or desired properties. However, this process remains limited due to the lack of mechanistic knowledge regarding specific enzymes and other key biological factors. Herein, we report on the ability of small noncoding RNAs (sRNAs) to affect silver nanoparticle (AgNP) biosynthesis using the supernatant from the bacterium Deinococcus radiodurans. Deletion strains of 12 sRNAs potentially involved in the oxidative stress response were constructed, and the supernatants from these strains were screened for their effect on AgNP biosynthesis. We identified several sRNA deletions that drastically decreased AgNP yield compared to the wild-type (WT) strain, suggesting the importance of these sRNAs in AgNP biosynthesis. Furthermore, AgNPs biosynthesized using the supernatants from three of these sRNA deletion strains demonstrated significantly enhanced antimicrobial and catalytic activities against environmentally relevant dyes and bacteria relative to AgNPs biosynthesized using the WT strain. Characterization of these AgNPs using electron microscopy (EM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) revealed that the deletion of these small RNAs led to changes within the supernatant composition that altered AgNP properties such as the surface chemistry, surface potential, and overall composition. Taken together, our results demonstrate that modulating specific sRNA levels can affect the composition of supernatants used to biosynthesize AgNPs, resulting in AgNPs with unique material properties and improved functionality; as such, we introduce sRNAs as a new platform for genetically engineering the biosynthesis of metal nanoparticles using bacteria. Many of the sRNAs examined in this work have potential regulatory roles in oxidative stress responses; further studies into their targets could help provide insight into the specific molecular mechanisms underlying bacterial biosynthesis and metal reduction, enabling the production of nanoparticles with enhanced properties.

Antifungal activity of silver nanoparticles synthesized by iturin against Candida albicans in vitro and in vivo

Candida albicans (C. albicans) is a fungal pathogen that is difficult to cure clinically due to lack of effective antifungal agents with low toxicity. In this study, iturin, a cyclic peptide having wide antifungal spectrum, was used to synthesize nanosilver particles (AgNPs), and a complex of iturin-AgNPs was formed. The antifungal activity of iturin-AgNPs against C. albicans and its mechanisms were tested in vitro. Iturin-AgNPs were also loaded in chitosan (CS) composite dressing and applied to skin wound healing in mice. As results, iturin-AgNPs showed excellent antifungal activity with the minimum inhibitory concentrations (MIC) of 1.25, 2.5, and 5 μg/mL at C. albicans concentrations of 1×10⁵, 1×10⁶, and 1×10⁷ CFU/mL, respectively. The MIC value still kept at 2.5 μg/mL against C. albicans (10⁵ CFU/mL) after 15 regeneration, showing less induction of drug resistance to the pathogenic fungus. The antifungal mechanisms of iturin-AgNPs against C. albicans were identified as the increase of membrane permeability, damage of cell membrane integrity, and leakage of cellular protein and nucleic acids. No toxicity was found for iturin-AgNPs to HaCaT cells at concentrations of lower than 10 μg/mL. In wound healing application, iturin-AgNP CS composite dressing significantly accelerated the healing of C. albicans infected skin wounds at the early 10 days. In conclusion, iturin-AgNPs were developed as an efficient antifungal agent against C. albicans in vitro and in vivo and showed potential application in wound healing promotion.

Antibacterial and wound healing-promoting effect of sponge-like chitosan-loaded silver nanoparticles biosynthesized by iturin

Silver nanoparticles (AgNPs) are widely used in wound dressing, but are limited in the application due to its high toxicity at effective concentrations. iturin-AgNPs was previously found to have much higher antibacterial activity at lower AgNPs content than the commercial AgNPs. To verify its potential application in the promotion of wound healing, a chitosan (CS) composite sponge dressing-loaded iturin-AgNPs was developed and evaluated for their antibacterial activity in vitro and used for wound healing in vivo. As results, the synthesized CS dressing had high porosity and water absorption. As expected, the antibacterial activity of CS dressing was significantly promoted by the incorporation of iturin-AgNPs. The CS dressing-loaded iturin-AgNPs showed more effective inhibition of bacterial infection and promotion of wound healing processing and quality than the commercial wound dressing loaded AgNPs in vivo. The mechanisms for the promotion of wound healing by the CS dressing-loaded iturin-AgNPs were found as the enhancement of re-epithelialization and collagen formation, as well as the increased antibacerial activity. No toxicity was found to all organs of mice. The study developed an efficient way to enhance the antibacterial activity of CS dressing loaded AgNPs at low toxicity, which has great potential in wound care application.

Recovery of Ag+ by cyclic lipopeptide iturin A and corresponding chain peptide: reaction mechanisms, kinetics, toxicity reduction, and applications

Iturin A, a cyclic lipopeptide produced by Bacillus subtilis, has great potential in removal of Ag⁺ from water, but the mechanisms and kinetic remain unclear. By comparison with the chain peptide (CP) that has the same amino acid sequence as iturin A, the mechanisms were found as iturin A reduced Ag⁺ to Ag⁰ and formed silver nanoparticles (AgNPs) via the groups of Ar-OH, CO, -NH-, O=C-O, and -C(CH).The cycle peptide fraction played an important role for the faster formation of AgNPs by iturin A than by CP. The overall Ag⁺ removal process by iturin A and CP could be well described by a Freundlich isotherm, with the equilibrium Ag⁺ removal capacity ranging from 58.41 to 61.03 mg/g within 293.15-333.15 K for iturin A. With the application of iturin A, the overall removal rate of Ag⁺ reached 91.8% in wastewater, the formed AgNPs could be easily recovered via charging the direct electric current, and the toxicity of Ag⁺ to paddy growth was greatly reduced.

The investigation of bioremediation potential of Bacillus subtilis and B. thuringiensis isolates under controlled conditions in freshwater

Bioremediation is widely used to remove water pollution as environmentally friendly smart solutions. In this study, Bacillus isolates were investigated in terms of the effectiveness of single and multiple cultures in eliminating aquatic pollution related to aquaculture activities. In the established experimental setups, the environments where Bacillus isolates were inoculated with single and multiple cultures at 1 × 10⁷ CFU/mL were evaluated comparatively with control groups without these isolates, and total aerobic mesophilic bacterial counts were performed in the petri dish by inoculation method. At the end of the 6 days of the experiment, in the environment in which single and multiple cultures of Bacillus isolates were presented with 17-20 ± 0.05 °C temperature and 5.1-8.1 pH 2-4.6 mg/l dissolved oxygen values (O₂), 2% increase in total phosphorus (TP) value was observed. On the other hand, 4% removal of Ammonia-nitrogen (NH₃-N), 80% removal of Nitrite-nitrogen (NO₂-N), and 100% removal of Nitrate-nitrogen (NO₃-N) were observed. In the changes in heavy metal concentrations, the removal of Ni, Cr, Se, Al, Cd, Mn, Fe, and B was observed from highest to lowest as 57%, 50%, 50%, 43%, 40%, 23%, 5%, and 2%, respectively. It also has been seen that B. thuringiensis isolate was observed to be more effective than B. subtilis in metal removal.

Capability of Bacillus Subtilis to remove Pb2+ via producing lipopeptides

Lead contamination is widely found in soil and waters, which makes great threat to animal and human health. Environmentally friendly, efficient, and economical methods for the removal of Pb²⁺ pose significant challenges for environmental protection. Bacillus subtilis lipopeptide was firstly used to remove Pb²⁺ from water. In mechanisms, the lipopeptides formed complexes and chelated with Pb²⁺ via OH, CO, OCO, and NH. In kinetics, the Pb²⁺ removal process closely followed a pseudo-first-order model, and the equilibrium Pb²⁺ adsorption capacity ranged from 112.6 to 113.7 mg/g within a temperature range of 293.13-313.13 K. The Pb²⁺ removal process could be well described by a Langmuir isotherm. The maximum Pb²⁺ removal capability of lipopeptides was 164.4 mg/g in manually metal contaminated water and 130.4 mg/g in actual wastewater. Furthermore, the lipopeptides can not only decrease the amount of lead in oats grown, but also promote oat growth under Pb²⁺ stress. The results showed that lipopeptides can be used as a highly efficient adsorbent to remove Pb²⁺ from water, which means the great potential of lipopeptides in practical environments.