Effect of Ag Nanoparticles on Denitrification and Microbial Community in a Paddy Soil

Advancing food safety with biogenic silver nanoparticles: Addressing antimicrobial resistance, sustainability, and commercial viability

The escalating threat of antimicrobial resistance (AMR), particularly among foodborne pathogens such as Escherichia coli, Salmonella enterica, and Listeria monocytogenes, necessitates innovative solutions beyond conventional antimicrobials. Silver nanoparticles (AgNPs) have garnered significant attention for their broad-spectrum antimicrobial efficacy, ability to target multidrug-resistant strains, and versatile applications across the food sector. This review critically examines AgNPs' integration into food safety strategies, including their roles in antimicrobial food packaging, agricultural productivity enhancement, and livestock disease mitigation. Key advancements in eco-friendly synthesis methods, leveraging algae, agricultural byproducts, and microbial systems, are highlighted as pathways to address scalability, sustainability, and cost constraints. However, the potential risks of silver bioaccumulation, environmental toxicity, and regulatory challenges present significant barriers to their widespread implementation. By reviewing cutting-edge research, this review provides a comprehensive analysis of AgNP efficacy, safety, and commercial viability, proposing a roadmap for overcoming current limitations. It calls for collaborative, interdisciplinary efforts to bridge technological, ecological, and regulatory gaps, positioning AgNPs as a transformative solution for combating AMR and ensuring global food security.

Reveal molecular mechanism on the effects of silver nanoparticles on nitrogen transformation and related functional microorganisms in an agricultural soil

Silver nanoparticles (AgNPs) are widely present in aquatic and soil environment, raising significant concerns about their impacts on creatures in ecosystem. While the toxicity of AgNPs on microorganisms has been reported, their effects on biogeochemical processes and specific functional microorganisms remain relatively unexplored. In this study, a 28-day microcosmic experiment was conducted to investigate the dose-dependent effects of AgNPs (10 mg and 100 mg Ag kg-1 soil) on nitrogen transformation and functional microorganisms in agricultural soils. The molecular mechanisms were uncovered by examining change in functional microorganisms and metabolic pathways. To enable comparison, the toxicity of positive control with an equivalent Ag+ dose from CH3COOAg was also included. The results indicated that both AgNPs and CH3COOAg enhanced nitrogen fixation and nitrification, corresponding to increased relative abundances of associated functional genes. However, they inhibited denitrification via downregulating nirS, nirK, and nosZ genes as well as reducing nitrate and nitrite reductase activities. In contrast to high dose of AgNPs, low levels increased bacterial diversity. AgNPs and CH3COOAg altered the activities of associated metabolic pathways, resulting in the enrichment of specific taxa that demonstrated tolerance to Ag. At genus level, AgNPs increased the relative abundances of nitrogen-fixing Microvirga and Bacillus by 0.02 %-629.39 % and 14.44 %-30.10 %, respectively, compared with control group (CK). The abundances of denitrifying bacteria, such as Rhodoplanes, Pseudomonas, and Micromonospora, decreased by 19.03 % to 32.55 %, 24.73 % to 50.05 %, and 15.66 % to 76.06 %, respectively, compared to CK. CH3COOAg reduced bacterial network complexity, diminished the symbiosis mode compared to AgNPs. The prediction of genes involved in metabolic pathways related to membrane transporter and cell motility showed sensitive to AgNPs exposure in the soil. Further studies involving metabolomics are necessary to reveal the essential effects of AgNPs and CH3COOAg on biogeochemical cycle of elements in agricultural soil.

Silver Bionanocomposites as Active Food Packaging: Recent Advances & Future Trends Tackling the Food Waste Crisis

Food waste is a pressing global challenge leading to over $1 trillion lost annually and contributing up to 10% of global greenhouse gas emissions. Extensive study has been directed toward the use of active biodegradable packaging materials to improve food quality, minimize plastic use, and encourage sustainable packaging technology development. However, this has been achieved with limited success, which can mainly be attributed to poor material properties and high production costs. In the recent literature, the integration of silver nanoparticles (AgNPs) has shown to improve the properties of biopolymer, prompting the development of bionanocomposites. Furthermore, the antibacterial properties of AgNPs against foodborne pathogens leads towards food shelf-life improvement and provides a route towards reducing food waste. However, few reviews have analyzed AgNPs holistically throughout a portfolio of biopolymers from an industrial perspective. Hence, this review critically analyses the antibacterial, barrier, mechanical, thermal, and water resistance properties of AgNP-based bionanocomposites. These advanced materials are also discussed in terms of food packaging applications and assessed in terms of their performance in enhancing food shelf-life. Finally, the current barriers towards the commercialization of AgNP bionanocomposites are critically discussed to provide an industrial action plan towards the development of sustainable packaging materials to reduce food waste.

Denitrification contributes to N2O emission in paddy soils

Denitrification is vital to nitrogen removal and N₂O release in ecosystems; in this regard, paddy soils exhibit strong denitrifying ability. However, the underlying mechanism of N₂O emission from denitrification in paddy soils is yet to be elucidated. In this study, the potential N₂O emission rate, enzymatic activity for N₂O production and reduction, gene abundance, and community composition during denitrification were investigated using the ¹⁵N isotope tracer technique combined with slurry incubation, enzymatic activity detection, quantitative polymerase chain reaction (qPCR), and metagenomic sequencing. Results of incubation experiments showed that the average potential N₂O emission rates were 0.51 ± 0.20 μmol⋅N⋅kg^-1⋅h^-1, which constituted 2.16 ± 0.85% of the denitrification end-products. The enzymatic activity for N₂O production was 2.77-8.94 times than that for N₂O reduction, indicating an imbalance between N₂O production and reduction. The gene abundance ratio of nir to nosZ from qPCR results further supported the imbalance. Results of metagenomic analysis showed that, although Proteobacteria was the common phylum for denitrification genes, other dominant community compositions varied for different denitrification genes. Gammaproteobacteria and other phyla containing the norB gene without nosZ genes, including Actinobacteria, Planctomycetes, Desulfobacterota, Cyanobacteria, Acidobacteria, Bacteroidetes, and Myxococcus, may contribute to N₂O emission from paddy soils. Our results suggest that denitrification is highly modular, with different microbial communities collaborating to complete the denitrification process, thus resulting in an emission estimation of 13.67 ± 5.44 g N₂O⋅m^-2⋅yr^-1 in surface paddy soils.

Multifunctional Starch-Based Sensor with Non-Covalent Network to Achieve "3R" Circulation

With the consumption of disposable electronic devices increasing, it is meaningful but also a big challenge to develop reusable and sustainable materials to replace traditional single-use sensors. Herein, a clever strategy for constructing a multifunctional sensor with 3R circulation (renewable, reusable, pollution-reducing biodegradable) is presented, in which silver nanoparticles (AgNPs) with multiple interactions are introduced into a reversible non-covalent cross-linking network composed of biocompatible and degradable carboxymethyl starch (CMS) and polyvinyl alcohol (PVA) to simultaneously obtain high mechanical conductivity and long-term antibacterial properties by a one-pot method. Surprisingly, the assembled sensor shows high sensitivity (gauge factor up to 4.02), high conductivity (0.1753 S m^-1 ), low detection limit (0.5%), long-term antibacterial ability (more than 7 days), and stable sensing performance. Thus, the CMS/PVA/AgNPs sensor can not only accurately monitor a series of human behavior, but also identify handwriting recognition from different people. More importantly, the abandoned starch-based sensor can form a 3R circulation. Especially, the fully renewable film still shows excellent mechanical performance, achieving reusable without sacrificing its original function. Therefore, this work provides a new horizon for multifunctional starch-based materials as sustainable substrates for replacing traditional single-use sensors.

The impact of Ag nanoparticles on methane emission in two typical paddy soils

Numerous applications of Ag nanoparticles (AgNPs) have increased the likelihood of their release and accumulation in agroecosystem. Thus far, few studies have evaluated the impacts of AgNPs to soil methane emissions and the microbial dynamics. In this study, microcosmic experiments were conducted to investigate the responses of methanogenic processes from two paddy soils (Cambisols and Ultisols) subjected to four AgNPs doses (0.1, 1, 10 and 50 mg/kg). The results showed that 0.1 and 1 mg/kg AgNPs had no significant effects on CH₄ emissions, but 50 mg/kg AgNPs increased soil CH₄ emissions in both paddy soils. The aggravation effect of AgNPs on CH₄ emissions was more apparent in Ultisols compared to Cambisols paddy soils. Real-time PCR suggested that 50 mg/kg AgNPs significantly increased the ratio of methanogenic to bacterial gene for both paddy soils. Amplicon sequencing indicated that methanogenic community was clustered into a separate group after 50 mg/kg AgNPs exposure. Structural equation model illustrated that Methanosarcinales was both significantly responded to AgNPs in Cambisols and Ultisols soils; however, Methanocellales significantly responded to AgNPs only in Cambisols soils. Subsequently, uncontrolled use of AgNPs may account as an environmental risk due to the potentially increased soil CH₄ emissions in paddy ecosystems.

Microbial silver resistance mechanisms: recent developments

In this mini-review, after a brief introduction into the widespread antimicrobial use of silver ions and nanoparticles against bacteria, fungi and viruses, the toxicity of silver compounds and the molecular mechanisms of microbial silver resistance are discussed, including recent studies on bacteria and fungi. The similarities and differences between silver ions and silver nanoparticles as antimicrobial agents are also mentioned. Regarding bacterial ionic silver resistance, the roles of the sil operon, silver cation efflux proteins, and copper-silver efflux systems are explained. The importance of bacterially produced exopolysaccharides as a physiological (biofilm) defense mechanism against silver nanoparticles is also emphasized. Regarding fungal silver resistance, the roles of metallothioneins, copper-transporting P-type ATPases and cell wall are discussed. Recent evolutionary engineering (adaptive laboratory evolution) studies are also discussed which revealed that silver resistance can evolve rapidly in bacteria and fungi. The cross-resistance observed between silver resistance and resistance to other heavy metals and antibiotics in bacteria and fungi is also explained as a clinically and environmentally important issue. The use of silver against bacterial and fungal biofilm formation is also discussed. Finally, the antiviral effects of silver and the use of silver nanoparticles against SARS-CoV-2 and other viruses are mentioned. To conclude, silver compounds are becoming increasingly important as antimicrobial agents, and their widespread use necessitates detailed understanding of microbial silver response and resistance mechanisms, as well as the ecological effects of silver compounds. Figure created with BioRender.com.