Regulation of membrane fixation and energy production/conversion for adaptation and recovery of ZnO nanoparticle impacted Nitrosomonas europaea

Nanoparticles and Their Antibacterial Application in Endodontics

Root canal treatment represents a significant challenge as current cleaning and disinfection methodologies fail to remove persistent bacterial biofilms within the intricate anatomical structures. Recently, the field of nanotechnology has emerged as a promising frontier with numerous biomedical applications. Among the most notable contributions of nanotechnology are nanoparticles, which possess antimicrobial, antifungal, and antiviral properties. Nanoparticles cause the destructuring of bacterial walls, increasing the permeability of the cell membrane, stimulating the generation of reactive oxygen species, and interrupting the replication of deoxyribonucleic acid through the controlled release of ions. Thus, they could revolutionize endodontics, obtaining superior results and guaranteeing a promising short- and long-term prognosis. Therefore, chitosan, silver, graphene, poly(lactic) co-glycolic acid, bioactive glass, mesoporous calcium silicate, hydroxyapatite, zirconia, glucose oxidase magnetic, copper, and zinc oxide nanoparticles in endodontic therapy have been investigated in the present review. The diversified antimicrobial mechanisms of action, the numerous applications, and the high degree of clinical safety could encourage the scientific community to adopt nanoparticles as potential drugs for the treatment of endodontic diseases, overcoming the limitations related to antibiotic resistance and eradication of the biofilm.

Enhanced anaerobic digestion of kitchen waste at different solids content by alkali pretreatment and bentonite addition: Methane production enhancement and microbial mechanism

High solid anaerobic digestion (AD) has been considered as a promising and sustainable technology for treating kitchen waste. To enhance AD of kitchen waste, alkali pretreatment and bentonite addition treatment (AP/Be) was performed on kitchen waste, and microbial community was investigated at different total solids (TS) content (10%, 13%, 19%, 22% and 25%). The results indicated that after AP/Be treatment, methane yield was as high as 198 mL CH₄/g volatile solid (VS), which increased by 236% as the control. Moreover, microbial community analysis revealed that AP/Be treatment enriched bacterial microbial diversity. At TS of 10%, AP/Be treatment enhanced the hydrogenotrophic methanogens (Methanobacterium) significantly. In addition, the dominant methanogenic pathways changed at different TS content. These results demonstrated AP/Be treatment had a positive effect on methanogenesis during kitchen waste anaerobic digestion process. This study threw new insights towards enhancing kitchen waste anaerobic digestion, as well as the microbial mechanism.

Assessing the effect of SiO2 and TiO2 nanoparticles on granule stability and microbial community shift in aerobic granular sludge process

The widely used SiO₂ and TiO₂ nanoparticles (NPs) can accumulate in industrial wastewaters, thereby posing challenge to biological wastewater treatment processes. In this work, the performance of aerobic granular sludge (AGS) reactors fed with wastewater containing 50 mg L^-1 SiO₂ and TiO₂ NPs were investigated. The results showed that the granules could resist the NPs in wastewater (no disintegration of granules was observed). SiO₂ NPs had a negative effect on the settleability of granules, with the SVI₃₀ increased by 64.5% and protein secretion decreased by 29.9%. To the contrary, the settleability of granules was improved in the presence of TiO₂ NPs due to the increase of the protein secretion. Possibly because of the compact and layered structure of granules, in the presence of both types of NPs, no obvious reduction of the overall removal efficiency of organics was found, and nanoparticle-resistant strains were enriched. The overall nitrification and denitrification efficiencies were hardly affected by SiO₂ NPs while significantly inhibited by TiO₂ NPs. Some functional genera, such as Hyphomicrobium and Acidovorax, showed growth inhibition with TiO₂ NPs, which might be responsible for the reduction of nitrification and denitrification efficiencies.

Static magnetic field enhances Cladosporium sp. XM01 growth and fungal Mn(II) oxidation

Fungal Mn oxidation is a crucial pathway in the biogeochemical cycling of toxic substances. However, few studies have aimed to promote the process of fungal Mn oxidation or systematically establish the mechanism of action. The effects of static magnetic field (SMF) treatment on the growth and Mn(II) oxidation capability of an Mn-oxidizing fungus, Cladosporium sp. XM01, were investigated. Results showed that 20.1 mT SMF treatment promoted the growth of strain XM01, and increased the Mn(II) removal rate by accelerating the adsorption and oxidation of Mn(II). In addition, the results of RNA sequencing suggested that SMF mainly stimulated energy metabolism and protein synthesis, accelerating the growth of strain XM01. Notably, KEGG pathway enrichment analysis found that SMF treatment significantly up-regulated the pathway of oxidative phosphorylation system, which is capable of stimulating the generation of superoxide (O₂^•-). Moreover, exposure to 20.1 mT SMF significantly promoted the activities of antioxidant enzymes including SOD and CAT. These results indicate that SMF treatment stimulates the generation of O₂^•- by strain XM01, and therefore, accelerates Mn(II) oxidation. This is a novel study using external SMF treatment to enhance fungal Mn(II) oxidation.

Transcriptome analysis of an arsenite-/antimonite-oxidizer, Bosea sp. AS-1 reveals the importance of the type 4 secretion system in antimony resistance

Bosea sp. AS-1 is an arsenite [As(III)] and antimonite [Sb(III)] oxidizer previously isolated by our group from the Xikuangshan Antimony (Sb) Mine area. Our previous study showed that Bosea sp. AS-1 had a preference for oxidizing As(III) or Sb(III) with different carbon sources, which suggested that different metabolic mechanisms may be utilized by the bacteria to survive in As(III)- or Sb(III)-contaminated environments. Here, we conducted whole-genome and transcriptome sequencing to reveal the molecular mechanisms utilized by Bosea sp. AS-1 to resist As(III) or Sb(III). We discovered that AS-1 acquired various As- and Sb-resistant genes in its genome and might resist As(III) or Sb(III) through the regulation of multiple pathways, such as As and Sb metabolism, the bacterial secretion system, oxidative phosphorylation, the TCA cycle and bacterial flagellar motility. Interestingly, we discovered that genes of the type IV secretion system (T4SS) were activated in response to Sb(III), and inhibiting T4SS activity in AS-1 dramatically reduced its oxidation efficiency and tolerance to Sb(III). To our knowledge, this is the first study showing the activation of T4SS genes by Sb and a direct involvement of T4SS in bacterial Sb resistance. Our findings establish the T4SS as an important Sb resistance factor in bacteria and may help us understand the spread of Sb resistance genes in the environment.

Efficient removal of azo dyes by Enterococcus faecalis R1107 and its application in simulated textile effluent treatment

This study aimed to exploit the potential of Enterococcus faecalis R1107 in the bioremediation of azo dyes. The maximal decolorization of Congo Red (CR), Reactive Black 5 (RB5), and Direct Black 38 (DB38) were 90.17%, 96.82%, and 81.95%, respectively, with the bacterial treatment for 48 h. 65.57% of CR and 72.64% of RB5 could be decolorized by E. faecalis R1107 within 48 h when the concentration of azo dyes increased up to 1000 mg/L. FTIR analysis confirmed that E. faecalis R1107 could effectively break down the chemical structures of three azo dyes. E. faecalis R1107 alleviated the phytotoxicity of azo dyes and improved seed germination, which contributed to the increase in the lengths of roots, stems, and leaves of Vigna radiata seedlings. Transcriptomic analysis suggested that the gene regulatory networks in E. faecalis R1107 synergistically improved the degradation and detoxification of RB5, including the major metabolic pathways, the secondary metabolism, the transport system, the amino acid metabolic pathways, and the signal transduction systems. Simulated textile effluent (STE) was used to mimic real textile effluent to evaluate the bioremediation potential of E. faecalis R1107, and 72.79% STE can be decolorized after E. faecalis R1107 treatment for 48 h. In summary, our study demonstrated that E. faecalis R1107 might be well suitable for potential applications in the bioremediation of textile effluent.

Flux balance analysis of the ammonia-oxidizing bacterium Nitrosomonas europaea ATCC19718 unravels specific metabolic activities while degrading toxic compounds

The ammonia-oxidizing bacterium Nitrosomonas europaea has been widely recognized as an important player in the nitrogen cycle as well as one of the most abundant members in microbial communities for the treatment of industrial or sewage wastewater. Its natural metabolic versatility and extraordinary ability to degrade environmental pollutants (e.g., aromatic hydrocarbons such as benzene and toluene) enable it to thrive under various harsh environmental conditions. Constraint-based metabolic models constructed from genome sequences enable quantitative insight into the central and specialized metabolism within a target organism. These genome-scale models have been utilized to understand, optimize, and design new strategies for improved bioprocesses. Reduced modeling approaches have been used to elucidate Nitrosomonas europaea metabolism at a pathway level. However, genome-scale knowledge about the simultaneous oxidation of ammonia and pollutant metabolism of N. europaea remains limited. Here, we describe the reconstruction, manual curation, and validation of the genome-scale metabolic model for N. europaea, iGC535. This reconstruction is the most accurate metabolic model for a nitrifying organism to date, reaching an average prediction accuracy of over 90% under several growth conditions. The manually curated model can predict phenotypes under chemolithotrophic and chemolithoorganotrophic conditions while oxidating methane and wastewater pollutants. Calculated flux distributions under different trophic conditions show that several key pathways are affected by the type of carbon source available, including central carbon metabolism and energy production.

Nitrosomonas europaea catalyzes the first step of the nitrification process (ammonia to nitrite). It has been recognized as one of the most important members of microbial communities of wastewater treatment processes. Genome-scale models are powerful tools in process optimization since they can predict the organism’s behavior under different growth conditions. The final genome-scale model of N. europaea ATCC19718, iGC535, can predict growth and oxygen uptake rates with 90.52% accuracy under chemolithotrophic and chemolitoorganotrophic conditions. Moreover, iGC535 can predict the simultaneous oxidation of ammonia and wastewater pollutants, such as benzene, toluene, phenol and, chlorobenzene. iGC535 represents the most comprehensive knowledge-base for a nitrifying organism available to date. The genome-scale model reconstructed in this work brings us closer to understanding N. europaea’s role in a community with other nitrifying bacteria.

Comprehensive genomic and proteomic profiling reveal Acinetobacter johnsonii JH7 responses to Sb(III) toxicity

Antimony (Sb) pollution poses a severe health threat to ecosystems. However, the toxic effects of Sb on biota are far from being elucidated. One of the unresolved questions is the molecular signal pathways underlying microbial adaptation to excess antimonite or Sb(III) exposure. The response of a Sb(III)-resistant bacterium Acinetobacter. johnsonii JH7 to Sb(III) stress was investigated using genomic and proteomic profiling. Sb(III) induced the formation of reactive oxygen species thereby leading to oxidative stress and the up-regulation of antioxidant enzyme activities. In addition, two important operons (ars and pst) playing critical roles in this cellular response were identified. The ars proteins functioned cooperatively to expel Sb(III) thereby decreasing antimonite toxicity. Downregulation of the phosphate-specific transporter might reduce the uptake of Sb(V) while hindering phosphorus assimilation. Interaction of Sb(III) with JH7 strain cells also affected peptide syntheses and folding, energy conversion, and stability of the cellular envelope. The present study provides for the first time a global map of cellular adaptation to excess Sb(III). Such information is potentially useful to future Sb pollution remediation strategies.

Advances in Using Nanotechnology Structuring Approaches for Improving Food Packaging

Recent advances in food packaging materials largely rely on nanotechnology structuring. Owing to several unique properties of nanostructures that are lacking in their bulk forms, the incorporation of nanostructures into packaging materials has greatly improved the performance and enriched the functionalities of these materials. This review focuses on the functions and applications of widely studied nanostructures for developing novel food packaging materials. Nanostructures that offer antimicrobial activity, enhance mechanical and barrier properties, and monitor food product freshness are discussed and compared. Furthermore, the safety and potential toxicity of nanostructures in food products are evaluated by summarizing the migration activity of nanostructures to different food systems and discussing the metabolism of nanostructures at the cellular level and in animal models.

Effects of Exogenous N-Acyl-Homoserine Lactone as Signal Molecule on Nitrosomonas Europaea under ZnO Nanoparticle Stress

Despite the adverse effects of emerging ZnO nanoparticles (nano-ZnO) on wastewater biological nitrogen removal (BNR) systems being widely documented, strategies for mitigating nanoparticle (NP) toxicity impacts on nitrogen removal have not been adequately addressed. Herein, N-acyl-homoserine lactone (AHL)-based quorum sensing (QS) was investigated for its effects against nano-ZnO toxicity to a model nitrifier, Nitrosomonas europaea. The results indicated that AHL-attenuated nano-ZnO toxicity, which was inversely correlated with the increasing dosage of AHL from 0.01 to 1 µM. At 0.01 µM, AHL notably enhanced the tolerance of N. europaea cells to nano-ZnO stress, and the inhibited cell proliferation, membrane integrity, ammonia oxidation rate, ammonia monooxygenase activity and amoA gene expression significantly increased by 18.2 ± 2.1, 2.4 ± 0.9, 58.7 ± 7.1, 32.3 ± 1.7, and 7.3 ± 5.9%, respectively, after 6 h of incubation. However, increasing the AHL dosage compromised the QS-mediated effects and even aggravated the NPs’ toxicity effects. Moreover, AHLs, at all tested concentrations, significantly increased superoxide dismutase activity, indicating the potential of QS regulations to enhance cellular anti-oxidative stress capacities when facing NP invasion. These results provide novel insights into the development of QS regulation strategies to reduce the impact of nanotoxicity on BNR systems.

Adaption and recovery of Nitrosomonas europaea to chronic TiO2 nanoparticle exposure

Although the adverse impacts of emerging nanoparticles (NPs) on the biological nitrogen removal (BNR) process have been broadly reported, the adaptive responses of NP-impaired nitrifiers and the related mechanisms have seldom been addressed to date. Here, we systematically explored the adaption and recovery capacities of the ammonia oxidizer Nitrosomonas europaea under chronic TiO₂ NP exposure and different dissolved oxygen (DO) conditions at the physiological and transcriptional levels in a chemostat reactor. N. europaea cells adapted to 50 mg/L TiO₂ NP exposure after 40-d incubation and the inhibited cell growth, membrane integrity, nitritation rate, and ammonia monooxygenase activity all recovered regardless of the DO concentrations. Transmission electron microscope imaging indicated the remission of the membrane distortion after the cells' 40-d adaption to the NP exposure. The microarray results further suggested that the metabolic processes associated with the membrane repair were pivotal for cellular adaption/recovery, such as the membrane efflux for toxicant exclusion, the structural preservation or stabilization, and the osmotic equilibrium adjustment. In addition, diverse metabolic and stress-defense pathways, including aminoacyl-tRNA biosynthesis, respiratory chain, ATP production, toxin-antitoxin 'stress-fighting', and DNA repair were activated for the cellular adaption coupled with the metabolic activity recovery, probably via recovering the energy production/conversion efficiency and mediating the non-photooxidative stress. Finally, low DO (0.5 mg/L) incubated cells were more susceptible to TiO₂ NP exposure and required more time to adapt to and recover from the stress, which was probably due to the stimulation limitation of the oxygen-dependent energy metabolism with a lower oxygen supply. The findings of this study provide new insights into NP contamination control and management adjustments during the BNR process.

Responses and recovery assessment of continuously cultured Nitrosomonas europaea under chronic ZnO nanoparticle stress: Effects of dissolved oxygen

Although the antibacterial performances of emerging nanoparticles (NPs) have been extensively explored in the nitrifying systems, the impacts of dissolved oxygen (DO) levels on their bio-toxicities to the nitrifiers and the impaired cells' recovery potentials have seldom been addressed yet. In this study, the physiological and transcriptional responses of the typical ammonia oxidizers - Nitrosomonas europaea in a chemostat to the chronic ZnO NP exposure under different DO conditions were investigated. The results indicated that the cells in steady-growth state in the chemostat were more persevering than batch cultured ones to resist ZnO NP stress despite the dose-dependent NP inhibitory effects were observed. In addition, the occurred striking over-expressions of amoA and hao genes at the initial NP exposure stage suggested the cells' self-regulation potentials at the transcriptional level. The low DO (0.5 mg/L) cultured cells displayed higher sensitivity to NP stress than the high DO (2.0 mg/L) cultured ones, probably owning to the inefficient oxygen-dependent electron transfer from ammonia oxidation for energy conversion/production. The following 12-h NP-free batch recovery assays revealed that both high and low DO cultured cells possessed the physiological and metabolic activity recovery potentials, which were in negative correlation with the NP exposure time. The duration of NP stress and the resulting NP dissolution were critical for the cells' damage levels and their performance recoverability. The membrane preservation processes and the associated metabolism regulations were expected to actively participate in the cells' self-adaption to NP stress and thus be responsible for their metabolic activities recovery.

Reviews of the toxicity behavior of five potential engineered nanomaterials (ENMs) into the aquatic ecosystem

Presently, engineered nanomaterials (ENMs) are used in a wide variety of commercial applications, resulting in an uncontrolled introduction into the aquatic environment. The purpose of this review is to summarize the pathways and factors that controlling the transport and toxicity of five extensively used ENMs. These toxicological pathways are of great importance and need to be addressed for sustainable implications of ENMs without environmental liabilities. Here we discuss five potentially utilized ENMs with their possible toxicological risk factors to aquatic plants, vertebrates model and microbes. Moreover, the key effect of ENMs surface transformations by significant reaction with environmental objects such as dissolved natural organic matter (DOM) and the effect of ENMs surface coating and surface charge will also be debated. The transformations of ENMs are subsequently facing a major ecological transition that is expected to create a substantial toxicological effect towards the ecosystem. These transformations largely involve chemical and physical processes, which depend on the properties of both ENMs and the receiving medium. In this review article, the critical issues that controlling the transport and toxicity of ENMs are reviewed by exploiting the latest reports and future directions and targets are keenly discussed to minimize the pessimistic effects of ENMs.