Large-scale biogeographical patterns of antibiotic resistome in the forest soils across China.

Soil is a reservoir of environmental resistomes. Information about their distribution, profiles, and driving forces in undisturbed environments is essential for understanding and managing modern antibiotic resistance genes (ARGs) in human disturbed environments. However, knowledge about the resistomes in pristine soils is limited, particularly at national scale. Here, we conducted a national-scale investigation of soil resistomes in pristine forests across China. Although the antibiotics content was low and ranged from below limit of detection (LOD) to 0.290 µg/kg, numerous detected ARGs conferring resistance to major classes of modern antibiotics were identified and indicated forest soils as a potential source of resistance traits. ARGs ranged from 6.20 × 10-7 to 2.52 × 10-3 copies/16S-rRNA and were predominated by those resisting aminoglycoside and encoding deactivation mechanisms. Low abundance of mobile genetic elements (MGEs) and its scarcely positive connections with ARGs suggest the low potential of horizontal gene transfer. The geographic patterns of ARGs and ARG-hosts in pristine forest soils were mainly driven by soil physiochemical variables and followed a distance-decay relationship. This work focusing on pristine soils can provide valuably new information for our understanding of the ARGs in human disturbed environments.

Interactions between microplastics and organic compounds in aquatic environments: A mini review.

Microplastics (MPs) are widely distributed in aquatic environments. They may release toxic substances or act as carriers for other organic compounds and pathogens, with potential to cause harm to the ecological environment and human health. A key concern is how MPs interact with organic compounds. We reviewed related works conducted under both laboratory conditions and in field aquatic environments to investigate the mechanisms of interactions between MPs and organic compounds from three perspectives: MPs, organic compounds, and environmental factors. The crystallinity and specific surface area of the MPs, and the functional groups, ionic form and strength of both MPs and organic compounds are key factors affecting their interactions. Environmentally realistic concentration settings for both MPs and organic compounds are critical for interpretation of the results of sorption experiments. The effect of salinity on interactions is mainly due to changes in pH. These results contribute to a better understanding of the environmental behavior, and potential ecological and human health risks of microplastics.

Alleviated Antibiotic-Resistant Genes in the Rhizosphere of Agricultural Soils with Low Antibiotic Concentration.

The influence of the rhizosphere on the abundance and diversity of antibiotic resistance genes (ARGs) has been recognized but there is a lack of consensus because of broad ranges of plant species and antibiotic concentrations across different habitats and the elusive underlying mechanisms. Here, we profiled antibiotic concentrations and resistomes in the rhizosphere and bulk soils by cultivating 10 types of crops in manure-amended agricultural soils. Rhizosphere effects altered the antibiotic resistome structure, significantly increased the absolute abundance of the antibiotic resistome, and decreased their relative abundance, contrasting previous studies. Such plantation-driven variation in ARGs resulted from the boost of bacterial lineages with negative relationships with ARGs and the constraint of the potential ARG-hosts in the rhizosphere of plants cultivated in soils with low antibiotic concentrations as the selective pressure. This mechanism is not reported previously and deepens our understanding about the rhizosphere effects on ARGs.