Micro-interfacial behavior of antibiotic-resistant bacteria and antibiotic resistance genes in the soil environment: A review.

Overutilization and misuse of antibiotics in recent decades markedly intensified the rapid proliferation and diffusion of antibiotic resistance genes (ARGs) within the environment, thereby elevating ARGs to the status of a global public health crisis. Recognizing that soil acts as a critical reservoir for ARGs, environmental researchers have made great progress in exploring the sources, distribution, and spread of ARGs in soil. However, the microscopic state and micro-interfacial behavior of ARGs in soil remains inadequately understood. In this study, we reviewed the micro-interfacial behaviors of antibiotic-resistant bacteria (ARB) in soil and porous media, predominantly including migration-deposition, adsorption, and biofilm formation. Meanwhile, adsorption, proliferation, and degradation were identified as the primary micro-interfacial behaviors of ARGs in the soil, with component of soil serving as significant determinant. Our work contributes to the further comprehension of the microstates and processes of ARB and ARGs in the soil environments and offers a theoretical foundation for managing and mitigating the risks associated with ARG contamination.

Conductive black carbon promoted biotransformation of undissolved 2, 2'-dinitrobiphenyl by mediating electron transfer.

With low bioaccessbility, persistence of the undissolved organic pollutants in soil and sediments poses threat to health of the resident. Although ubiquitous black carbon catalyzes a wide range of biogeochemical reactions in nature, its role in biotransformation of the compounds in non-aqueous phase like 2, 2'-nitrobiphenyl remains unclear. Reduction rate constants of 2, 2'-dinitrobiphenyl by Shewanella oneidensis MR-1 increased from 0.0044 h-1 by 7-fold to 0.035 h-1 in the presence of black carbons produced at pyrolysis temperature of 250-900 °C. Accordingly, electrical conductivity of black carbon was enhanced from 0 to 5.56 S∙cm-1. The reactivity of black carbon for catalyzing the biotransformation positively correlated with its electrical conductivity (R2 > 0.89), which was strongly associated with conductive graphitic clusters in it. The surface oxygenated groups in black carbon were likely not involved in the bioreduction. This work attaches importance to role of the ubiquitous black carbon in natural biotransformation of the undissolved pollutants, and elucidates new mechanism for the biotransformation.

Catalyzed degradation of polycyclic aromatic hydrocarbons by recoverable magnetic chitosan immobilized laccase from Trametes versicolor.

The capability of laccase to oxidate a broad range of polyphenols and aromatic substrates in vitro offers a new technological option for the remediation of polycyclic aromatic hydrocarbon (PAH) pollution with high cytotoxicity. However, laccase application in the remediation of PAH-contaminated sites mainly suffers from a low oxidation rate and high cost because of the difficulty in its recovery. In this study, laccases were immobilized on magnetic Fe3O4 particles coated with chitosan (Fe3O4@SiO2-chitosan) to improve the operational stability and reusability in the treatment of PAH pollution. The enzyme fixation capacity reached 158 mg g-1, and 79.1% of free laccase activities were reserved under the optimum immobilized condition of 4% glutaraldehyde, 1.0 mg mL-1 laccase, 2 h covalent bonding time, and 6 h fixation time. The degradation efficiencies of anthracene (ANT) and benzo[a]pyrene (B(a)P) by Fe3O4@SiO2-chitosan immobilized laccase in 48 h were 81.9% and 69.2%, respectively. Furthermore, it is very easy to magnetically recover the immobilized laccase from reaction systems and reuse it in a new batch. The relative activities of immobilized laccase were over 50% for the degradation of ANT and B(a)P in three catalytic runs, reaching the goal of substantially reducing cost in practice. According to the results from quantum calculations and mass spectrum analyses, the degradation products of ANT and B(a)P by laccase were anthraquinone and B(a)P-dione, respectively. The findings from this study provide valuable insight in promoting the application of immobilized laccase technology in the remediation of PAH contamination.

Correlation and the concentrations of Pb, Cd, Hg and As in vegetables and soils of Chongqing, China.

This paper studies the concentration of Pb, Cd, Hg and As in vegetable and soil of 13 main vegetable base, Chongqing, China, as well as the correlation between them. Results show that the concentrations of heavy metals in different vegetables from 13 main vegetable bases of Chongqing are also significantly different. The order of Pb concentration is root vegetable (the average value is 0.203 mg/kg) > leaf vegetable (the average value is 0.065 mg/kg) > solanaceous vegetable (the average value is 0.004 mg/kg); the order of Cd concentration is leaf vegetable (the average value is 0.090 mg/kg) > solanaceous vegetable (the average value is 0.061 mg/kg) > root vegetable (the average value is 0.049 mg/kg); the order of Hg concentration is leaf vegetable (the average value is 0.004 mg/kg) > root vegetable (the average value is 0.003 mg/kg) > solanaceous vegetable (the average value is 0.001 mg/kg); the order of As concentration is root vegetable (the average value is 0.116 mg/kg) > solanaceous vegetable (the average value is 0.057 mg/kg) > leaf vegetable (the average value is 0.026 mg/kg). Significant positive correlation was found between the Cd concentration in vegetables and the Cd concentration in soil, and the linear equation was y = 0.065 + 0.012x. There was no significant correlation between the concentrations of Pb, Hg and As in vegetables and Pb, Hg and As in soil.

[Effects of Nano-magnesium Hydroxide on the Forms of Cadmium in Different Types of Soil].

The effects of nano-magnesium hydroxide and common magnesium hydroxide (100, 200, and 300 mg·kg-1) on the forms of cadmium in different types of cadmium contaminated soils (1, 5, 10, and 15 mg·kg-1) were studied under 28 days of continuous culture experiment. In the neutral soil, during the 28 days of culture, soil exchange Cd (EX-Cd) form distribution ratio (FDC) decreased at first and then increased with the culture time increasing under treatment of 1, 5, 10, and 15 mg·kg-1 Cd. The minima of soil EX-Cd FDC were found on the 14th day under 1 mg·kg-1 Cd and 5 mg·kg-1 Cd treatments, whereas the minima of soil EX-Cd FDC were observed on the 4th day under 10 mg·kg-1 Cd and 15 mg·kg-1 Cd treatments. The FDC of soil carbonate bound Cd (CAB-Cd), iron manganese oxidized Cd (FeMn-Cd), and organic bound Cd (OM-Cd) increased at first, then decreased, and finally, became stable, and the maxima of soil CAB-Cd, FeMn-Cd, and OM-Cd FDC were found on the 4th day, whereas the minima of soil CAB-Cd, FeMn-Cd, and OM-Cd FDC were observed on the 14th day. Soil residual Cd (RES-Cd) FDC increased gradually and then tended to becomes stable during the 28 days of culture. The soil EX-Cd FDC was 66.7%-81.8% at 1, 5, 10, and 15 mg·kg-1 Cd treatments, which was the main form of the soil. The FDC of soil Cd forms was in the order of EX-Cd > CAB-Cd > RES-Cd > FeMn-Cd > OM-Cd. Soil EX-Cd FDC reached the lowest value on the 14th Day. Soil EX-Cd FDC was reduced by nano-magnesium hydroxide and common magnesium hydroxide, and it decreased with the increase of the amount of magnesium hydroxide. During 0-28 days of culture, the soil EX-Cd FDC decreased by 11.4%-67.7%, 7.8%-37.2%, 7.7%-36.4%, 5.0%-28.8% (nano-magnesium hydroxide) and 0.5%-49.5%, 0.6%-15.0%, 1.0%-18.1%, 0.7%-14.6% (ordinary magnesium hydroxide) at 1, 5, 10, and 15 mg·kg-1 Cd treatments, respectively. The EX-Cd content of alkaline soil reached the lowest value on the 7th day of culture, and the EX-Cd content of acidic soil reached the lowest value on the 21st day under 1, 5, and 10 mg·kg-1 Cd treatments. The content of EX-Cd in neutral, acidic, and alkaline soils decreased with the increase of magnesium hydroxide content, and the content of EX-Cd in soil decreased with the increase of magnesium hydroxide amount. At the same amount, the effect of passivating soil EX-Cd under nanometer magnesium hydroxide treatment was superior to ordinary magnesium hydroxide treatment.

[Differences in the Cadmium-Enrichment Capacity and Subcellular Distribution and Chemical Form of Cadmium in Different Varieties of Pepper].

In a preliminary experiment, 91 pepper varieties were screened, and one variety each with high Cd accumulation (X55), medium Cd accumulation (Daguo 99), and low Cd accumulation (Luojiao 318) were selected to study the effect of different cadmium levels (0, 5, and 10 mg·kg-1 Cd) on cadmium migration and enrichment ability, and its subcellular distribution and chemical form. The results showed that under the stress of Cd, shoot dry weight of pepper plants was in the order X55>17>27. At the same level of Cd, the Cd transfer coefficient of fruit was 17>27 and X55. Cadmium concentrations in each subcellular component of the pepper fruits were 27 > 17 > X55. Cadmium concentration in subcellular component of the roots, stems, leaves, and fruits of the pepper plants was in order of cell wall (F1) > organelle (F2) > cell soluble component (F3). Cadmium was limited in cell wall and plays an important role in detoxification mechanism and resistance of Cd in pepper plants. The morphological content of various Cd forms in the pepper fruits of the three varieties increased with the increase of Cd treatment level, in the order CdNaCl > CdHAC > CdR > CdHCl > CdW > CdE. CdNaCl and CdHAC account for a large proportion of Cd in pepper fruits, which may be an important defense mechanism for reducing the biological toxicity of Cd.