Distribution and Influence on the Microbial Ecological Relationship of Antibiotic Resistance Genes in Soil at a Watershed Scale

Impact of land use on antibiotic resistance genes and bacterial communities in rivers

River ecosystems support essential ecosystem functions and services, including supplying water for domestic, agricultural, and industrial activities, provisioning of hydropower and fisheries, supporting navigation and recreational activities, and regulating water quality. In recent decades, the presence and spread of antibiotic resistance genes (ARGs) have emerged as a key threat to ecosystem health and human well-being. Rivers that are surrounded by human-modified landscapes serve as primary repositories and sources of ARGs. However, our understanding of the relationship between the diversity of ARGs and land use remain limited. We collected 30 sediment samples from five rivers in Ningbo, China, and then classified the sampling sites into two groups (i.e., group A with low levels of human impacts and group B with intense human impact) based on land use in their upstream areas. In total, we found 31 types of ARGs and 148 phyla of bacteria in the samples. ARGs abundance had a positive relationship with the levels of anthropogenic activities, and exhibited significant difference between the two groups. Co-occurrence networks showed that the interrelationship between bacteria and ARGs was more complex in group B than in group A. Moreover, Structural Equation Modeling (SEM) revealed that anthropogenic activity not only posed direct effect on ARGs but also indirectly affected ARGs through bacteria. Our results underscore the profound impacts of land-use changes on the diversity of ARGs, bacteria communities, and their relationships, which highlight the need for integrating ARGs in river assessments in regions with human-dominated land use.

Anthropogenic activities significantly interfered distribution and co-occurrence patterns of antibiotic resistance genes in a small rural watershed in Southwest China

The prevalence and spread of antibiotic resistance genes (ARGs) have been a significant concern for global public health in recent years. Small rural watersheds are the smallest units of factor mobility for agricultural production in China, and their ARG profiles are the best scale of the contamination status, but the mapping and the distribution and diffusion of ARGs in the water and soil of small rural watersheds are inadequate. In this study, based on microbial metagenomics, we invested prevalence maps of 209 ARGs corresponding to typical commonly used antibiotics (including multidrug, aminoglycoside, macrolide-lincosamide-streptogramin B (MLSB), and β-Lactamase) in water and soil in different agricultural types, as well as within water-soil interfaces in small rural watersheds in Southwest China. The results revealed that the most abundant ARGs in water and soil were consistent, but different in subtypes, and anthropogenic activities affect the transport of ARGs between water and soils. Livestock wastewater discharges influenced the diversity and abundance of ARGs in water, while in soil it is planting type and fertilizer management, and thus interfered with the co-occurrence patterns between bacteria and ARGs. Co-occurrence analysis revealed that Proteobacteria, Actinobacteria, and Bacteroidetes were the predominant ARG hosts in water and soil, but soil exhibited a more intricate ARG-bacterial association. Overall, this study provides integrated profiles of ARGs in water and soil influenced by anthropogenic activities at the small watershed scale in a typical rural area and provides a baseline for comparisons of ARGs.

Fate of high-risk antibiotic resistance genes in large-scale aquaculture sediments: Geographical differentiation and corresponding drivers

Antibiotic resistance genes (ARGs), emerging environmental contaminants, have become challenges of public health security. However, the distribution and drivers of ARGs, especially high-risk ARGs, in large-scale aquaculture sediments remain unknown. Here, we collected sediment samples from 40 crayfish ponds in seven main crayfish culture provinces in China and then investigated the distribution and risk of ARGs based on high-throughput sequencing and quantitative PCR techniques. Our results suggested that aquaculture sediment was potential reservoir of ARGs and the abundance of aadA-02 was the highest. High-risk ARG (floR) was also prevalent in the sediment and was the most abundant in Jiangsu Province, where opportunistic pathogens were also enriched. The abundance of floR was positively correlated with different environmental factors, such as total phosphorus in water and total carbon in sediment. In addition, Mycobacterium sp., opportunistic pathogenic bacteria, might be potential host for floR. Furthermore, the potential propagation pathway of ARGs was from sediment to crayfish gut, and Bacteroidetes and Proteobacteria might be the main bacterial groups responsible for the proliferation of ARGs. Generally, our results illustrate that pond sediment may be an ARG reservoir of aquatic animals. Meanwhile, our study helps develop valuable strategies for accessing risks and managing ARGs.

Deciphering the Role of WWTPs in Cold Environments as Hotspots for the Dissemination of Antibiotic Resistance Genes

Cold environments are the most widespread extreme habitats in the world. However, the role of wastewater treatment plants (WWTPs) in the cryosphere as hotspots in antibiotic resistance dissemination has not been well established. Hence, a snapshot of the resistomes of WWTPs in cold environments, below 5 °C, was provided to elucidate their role in disseminating antibiotic resistance genes (ARGs) to the receiving waterbodies. The resistomes of two natural environments from the cold biosphere were also determined. Quantitative PCR analysis of the aadA, aadB, ampC, blaSHV, blaTEM, dfrA1, ermB, fosA, mecA, qnrS, and tetA(A) genes indicated strong prevalences of these genetic determinants in the selected environments, except for the mecA gene, which was not found in any of the samples. Notably, high abundances of the aadA, ermB, and tetA(A) genes were found in the influents and activated sludge, highlighting that WWTPs of the cryosphere are critical hotspots for disseminating ARGs, potentially worsening the resistance of bacteria to some of the most commonly prescribed antibiotics. Besides, the samples from non-disturbed cold environments had large quantities of ARGs, although their ARG profiles were highly dissimilar. Hence, the high prevalences of ARGs lend support to the fact that antibiotic resistance is a common issue worldwide, including environmentally fragile cold ecosystems.

A new insight into the potential drivers of antibiotic resistance gene enrichment in the collembolan gut association with antibiotic and non-antibiotic agents

Effects of non-antibiotic pharmaceuticals on antibiotic resistance genes (ARGs) in soil ecosystem are still unclear. In this study, we explored the microbial community and ARGs variations in the gut of the model soil collembolan Folsomia candida following soil antiepileptic drug carbamazepine (CBZ) contamination, while comparing with antibiotic erythromycin (ETM) exposure. Results showed that, CBZ and ETM all significantly influenced ARGs diversity and composition in the soil and collembolan gut, increasing the relative abundance of ARGs. However, unlike ETM, which influences ARGs via bacterial communities, exposure to CBZ may have primarily facilitated enrichment of ARGs in gut through mobile genetic elements (MGEs). Although soil CBZ contamination did not pose an effect on the gut fungal community of collembolans, it increased the relative abundance of animal fungal pathogens contained therein. Soil ETM and CBZ exposure both significantly increased the relative abundance of Gammaproteobacteria in the collembolan gut, which may be used to indicate soil contamination. Together, our results provide a fresh perspective for the potential drivers of non-antibiotic drugs on ARG changes based on the actual soil environment, revealing the potential ecological risk of CBZ on soil ecosystems involving ARGs dissemination and pathogens enrichment.

Evaluating the impact of heavy metals on antimicrobial resistance in the primary food production environment: A scoping review

Heavy metals are naturally occurring environmental compounds, which can influence antimicrobial resistance (AMR) dissemination. However, there is limited information on how heavy metals may act as a selective pressure on AMR in the primary food production environment. This review aims to examine the literature on this topic in order to identify knowledge gaps. A total of 73 studies, which met pre-established criteria, were included. These investigations were undertaken between 2008 and 2021, with a significant increase in the last three years. The majority of studies included were undertaken in China. Soil, water and manure were the most common samples analysed, and the sampling locations varied from areas with a natural presence of heavy metals, areas intentionally amended with heavy metals or manure, to areas close to industrial activity or mines. Fifty-four per cent of the investigations focused on the analysis of four or more heavy metals, and copper and zinc were the metals most frequently analysed (n = 59, n = 49, respectively). The findings of this review highlight a link between heavy metals and AMR in the primary food production environment. Heavy metals impacted the abundance and dissemination of mobile genetic elements (MGEs) and antimicrobial resistance genes (ARGs), with MGEs also observed as playing a key role in the spread of ARGs and metal resistance genes (MRGs). Harmonization of methodologies used in future studies would increase the opportunity for comparison between studies. Further research is also required to broaden the availability of data at a global level.

Spatio-vertical distribution of riverine microplastics: Impact of the textile industry

Microplastics (MPs) contamination in rivers and lakes is of paramount environmental importance as freshwater systems transport MPs from land to ocean. However, information regarding the spatio-vertical distributions of MPs in rivers, and their associations with surrounding industrial activities, is scarce and unclear. This study investigated MPs in the Taipu River, where there is a highly developed textile industry in Yangtze River Delta, China. Results showed a widespread occurrence of MPs particles with concentrations in the range of 0.65-6.07 items/L and 0.30-3.63 items/L in surface and bottom waters. A higher abundance of MPs was observed in surface waters than in bottom waters (t = 5.423, p = 0.024). The MPs distributions varied markedly in space, with the highest abundances being found in textile manufacturing zones as a consequence of industrial release (F = 14.642, p < 0.001). Transparent fibers were the major MPs compositions with 100-500 μm in size. Polyethylene terephthalate (PET) accounted for 71.4% and 59.73% of the total MPs identified in surface and bottom water, respectively. These PET polymers were predominantly presented in "fibrous" shapes, further reflecting the point sources of textile wastewater. Moreover, polyvinyl acetate (PVAC), used as fabric coating and resin matrix to form nonwoven fabrics, was firstly highlighted at a watershed scale. Although risk assessments revealed a light to moderate risks of MPs in the Taipu River, textile wastewater appears to cause a high "grey water" footprint and increase the risks of MPs pollution from textile life-cycle production. This study bridged gaps between field data and policy-making for MPs control and shed insight into the cleaner production of the textile industry.