[Near-infrared excited graphene oxide/silver nitrate/chitosan coating for improving antibacterial properties of titanium implants].

Objective: To design and construct a graphene oxide (GO)/silver nitrate (Ag3PO4)/chitosan (CS) composite coating for rapidly killing bacteria and preventing postoperative infection in implant surgery. Methods: GO/Ag3PO4 composites were prepared by ion exchange method, and CS and GO/Ag3PO4 composites were deposited on medical titanium (Ti) sheets successively. The morphology, physical image, photothermal and photocatalytic ability, antibacterial ability, and adhesion to the matrix of the materials were characterized. Results: The GO/Ag3PO4 composites were successfully prepared by ion exchange method and the heterogeneous structure of GO/Ag3PO4 was proved by morphology phase test. The heterogeneous structure formed by Ag3PO4 and GO reduced the band gap from 1.79 eV to 1.39 eV which could be excited by 808 nm near-infrared light. The photothermal and photocatalytic experiments proved that the GO/Ag3PO4/CS coating had excellent photothermal and photodynamic properties. In vitro antibacterial experiments showed that the antibacterial rate of the GO/Ag3PO4/CS composite coating against Staphylococcus aureus reached 99.81% after 20 minutes irradiation with 808 nm near-infrared light. At the same time, the composite coating had excellent light stability, which could provide stable and sustained antibacterial effect. Conclusion: GO/Ag3PO4/CS coating can be excited by 808 nm near infrared light to produce reactive oxygen species, which has excellent antibacterial activity under light.

Contrasting response of fungal versus bacterial residue accumulation within soil aggregates to long-term fertilization.

Soil microorganisms are critical for soil carbon (C) cycling. They primarily regulate the turnover of the soil organic C (SOC) by adjusting their community structure, and contributing residues with a considerable amount to the resistant SOC. Nevertheless, how long-term fertilization (e.g., the combination of manure and chemical fertilizer) affects the spatial distribution of both living microbial communities and dead microbial residue within soil aggregate fractions remains largely unclear. In this study, we analyzed changes in microbial community (lipid biomarkers) and microbial residue retention (amino sugar biomarkers), and also calculated the contribution of microbial residue to organic C in bulk soil and different soil aggregates (> 2 mm, 1-2 mm, 0.25-1 mm, and < 0.25 mm) in Alfisols treated with 29 years fertilization or no fertilization (control). Our results showed that long-term fertilization significantly increased the mean weight diameter (MWD) of aggregates and organic C contents in all aggregate fractions. The fertilization treatment increased the contents of PLFAs and microbial residue C, but the relative contribution of microbial residue to SOC was higher in the control (56.8% vs. 49.0%), due to the low SOC background caused by much lower level of non-microbially derived C input. These results suggested that long-term fertilization could increase SOC by accumulating both plant- and microbial-derived C, while the C deficient soil is more dependent on the accumulation of microbial residues. Long-term fertilization promoted the enrichment of bacterial-derived muramic acid in micro aggregates, but increased the proportion of fungal-derived glucosamine in macro aggregates. Meanwhile, the contribution of bacterial residue to organic C in the fertilization treatment was higher in micro aggregates (7.6% for > 2 mm vs. 9.2% for < 0.25 mm aggregate), while the contribution of fungal residue was higher in macro aggregate fractions (40.9% for > 2 mm vs. 35.7% for < 0.25 mm aggregate). The above results indicated that long-term fertilization could drive the differentiation of heterogeneous microbial residue accumulation patterns that significantly alter the contribution of fungal- versus bacterial-derived C to organic C within soil aggregate fractions.

Microwave assisted antibacterial action of Garcinia nanoparticles on Gram-negative bacteria.

Owing to the existence of the outer membrane barrier, most antibacterial agents cannot penetrate Gram-negative bacteria and are ineffective. Here, we report a general method for narrow-spectrum antibacterial Garcinia nanoparticles that can only be effective to kill Gram-positive bacteria, to effectively eliminate Gram-negative bacteria by creating transient nanopores in bacterial outer membrane to induce drug entry under microwaves assistance. In vitro, under 15 min of microwaves irradiation, the antibacterial efficiency of Garcinia nanoparticles against Escherichia coli can be enhanced from 6.73% to 99.48%. In vivo, MV-assisted GNs can effectively cure mice with bacterial pneumonia. The combination of molecular dynamics simulation and experimental results reveal that the robust anti-E. coli effectiveness of Garcinia nanoparticles is attributed to the synergy of Garcinia nanoparticles and microwaves. This work presents a strategy for effectively treating both Gram-negative and Gram-positive bacteria co-infected pneumonia using herbal medicine nanoparticles with MV assistance as an exogenous antibacterial auxiliary.

Influence of environmental factors on soil organic carbon in different soil layers for Chinese Mollisols under intensive maize cropping.

The Mollisol region of Northeast China has a large soil organic carbon (SOC) storage which is important for maintaining soil fertility. SOC is susceptible to various environmental factors; however, the responses of SOC content to environmental factors in different soil layers of cropland remain unclear, particularly in deep soil layers. In this study, we collected 138 soil samples from the surface, subsurface, and subsoil layers among 46 sample sites with monocropping maize and intensive conventional tillage in this region. We assessed the relative importance and effect paths of 12 environmental factors (including geography, climate, and soil properties) on SOC content in different layers using redundancy analysis (RDA), structural equation model (SEM), and variation partitioning analysis (VPA). The VPA results showed that SOC content was mainly affected by climatic factors that explained 68% and 57% for the surface and subsurface layers, respectively. However, SOC content in the subsoil layer was greatly affected by soil properties that explained 27%. Furthermore, the SEMs results suggested that geographical factors indirectly affected SOC content by influencing the climatic factors. Mean annual temperature was the most important factor affecting SOC content directly or indirectly, and its negative effects significantly diminished with soil depth, as it explained 63%, 52%, and 17% of the variation in SOC content for the surface, subsurface and subsoil layers, respectively. In addition, the effects of soil water-holding capacity on SOC content also decreased with soil depth, whereas pH and clay content showed a contrasting pattern. This implies that pH and clay content play important roles in the sequestration of SOC in deep soil layers. Moreover, the organic C content within >53 µm aggregates was more sensitive to environmental factors. This study can be useful for forecasting SOC dynamics and establishing reasonable C management strategies under climate change conditions.

Quantitative characterization of non-DLVO factors in the aggregation of black soil colloids.

The variable role and fate of soil colloids under different environmental conditions are derived from their dispersion and aggregation properties. In this work, dynamic and static light scattering were used to characterize the original size, aggregation kinetics of natural black soil colloids (BSCs) and structural features of aggregates in electrolytes with different cations (K+, Mg2+, Ca2+), respectively. For these three cations, the aggregation kinetics followed the trend of Ca2+ > Mg2+ > K+ and the critical coagulation concentration (CCC) followed the sequence: K+ (134.30 mmol L-1) > Mg2+ (13.27 mmol L-1) > Ca2+ (4.19 mmol L-1). The results indicated that the aggregation behavior in different valence cation systems followed the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) model qualitatively. However, the quantitative differences of CCC suggest the existence of ion-specific effects. The effective ionic charge coefficient 1.31, 2.20, and 2.78 of K+, Mg2+ and Ca2+ were proposed to consider of all the non-DLVO factors, which were obtained by forming a relationship based on mathematic between the electrostatic repulsion and the van der Waals attractive interaction at the CCC. The non-classical polarization of cations in a strong soil electric field is a primary mechanism of cation effects on soil colloid interactions, causing the difference in colloid interaction energy and further affecting soil colloid aggregation. This result is crucial for enriching the theory of charged colloidal interactions.

Distributions of straw-derived carbon in Mollisol's aggregates under different fertilization practices.

Straw incorporation is an effective measure for increasing soil organic carbon (SOC) thereby improving soil quality and crop productivity. However, quantitative assessments of the transformation and distribution of exogenous carbon (C) in soil aggregates under various field fertilization practices have been lacking. In this study, we collected topsoil samples (0-20 cm) from three fertilization treatments (no fertilization control, CK; inorganic fertilizer, IF; inorganic fertilizer plus manure, IFM) at a 29-year long-term Mollisol experiment in Northeast China. We then mixed the soil samples with 13C-labeled maize straw (δ13C = 246.9‰), referred as CKS, IFS, and IFMS, and incubated them in-situ for 360 days. Initial and incubated soil samples were separated into four aggregate fractions (> 2, 1-2, 0.25-1, and < 0.25 mm) using the dry-sieving method, which counted 18%, 17%, 45%, and 21% (averages from the three initial soil samples), respectively. Organic C content was highest in 0.25-1 mm aggregate (6.9-9.6 g kg-1) prior to incubation, followed by > 2 mm aggregates (2.2-5.8 g kg-1), 1-2 mm aggregates (2.4-4.6 g kg-1), and < 0.25 mm aggregates (3.3-4.5 g kg-1). After 360-day incubation with straw incorporation, organic C content was 2.3-4.5 g kg-1, 2.9-5.0 g kg-1, 7.2-11 g kg-1 and 1.8-3.0 g kg-1 in > 2, 1-2, 0.25-1, and < 0.25 mm aggregates, respectively, with the highest in the IFMS treatment. Straw-derived C content was 0.02-0.05 g kg-1, 0.03-0.04 g kg-1, 0.11-0.13 g kg-1, and 0.05-0.10 g kg-1 in > 2, 1-2, 0.25-1, and < 0.25 mm aggregates, respectively. The relative distribution of straw-derived C was highest (40-49%) in 0.25-1 mm aggregate, followed by < 0.25 mm aggregates (21-31%), 1-2 mm aggregates (13-15%), and > 2 mm aggregates (9.4-16%). During the incubation, the relative distribution of straw-derived C exhibited a decrease in > 2 mm and 1-2 mm aggregates, but an increase in the < 0.25 mm aggregate. At the end of incubation, the relative distribution of straw-derived C showed a decrease in the 0.25-1 mm aggregate but an increase in the < 0.25 mm aggregate under the IFMS treatment. This study indicates that more straw-derived C would be accumulated in smaller aggregates over longer period in Mollisols, and combined inorganic and organic fertilization is an effective measure for C sequestration in Northeast China.

Ag3PO4 decorated black urchin-like defective TiO2 for rapid and long-term bacteria-killing under visible light.

Both phototherapy via photocatalysts and physical puncture by artificial nanostructures are promising substitutes for antibiotics when treating drug-resistant bacterial infectious diseases. However, the photodynamic therapeutic efficacy of photocatalysts is seriously restricted by the rapid recombination of photogenerated electron-hole pairs. Meanwhile, the nanostructures of physical puncture are limited to two-dimensional (2D) platforms, and they cannot be fully used yet. Thus, this research developed a synergistic system of Ag3PO4 nanoparticles (NPs), decorated with black urchin-like defective TiO2 (BU-TiO2-X/Ag3PO4). These NPs had a decreased bandgap compared to BU-TiO2-X, and BU-TiO2-X/Ag3PO4 (3:1) exhibited the lowest bandgap and the highest separation efficiency for photogenerated electron-hole pairs. After combination with BU-TiO2-X, the photostability of Ag3PO4 improved because the oxygen vacancy of BU-TiO2-X retards the reduction of Ag+ in Ag3PO4 into Ag0, thus reducing its toxicity. In addition, the nanospikes on the surface of BU-TiO2-X can, from all directions, physically puncture bacterial cells, thus assisting the hybrid's photodynamic therapeutic effects, alongside the small amount of Ag+ released from Ag3PO4. This achieves synergy, endowing the hybrid with high antibacterial efficacy of 99.76 ± 0.15% and 99.85 ± 0.09% against Escherichia coli and Staphylococcus aureus, respectively, after light irradiation for 20 min followed by darkness for 12 h. It is anticipated that these findings may bring new insight for developing synergistic treatment strategies against bacterial infectious diseases or pathogenic bacterial polluted environments.