Heavy Metal Resistance Genes Research Articles

Further Evidence of Anthropogenic Impact: High Levels of Multiple-Antimicrobial-Resistant Bacteria Found in Neritic-Stage Sea Turtles

Background/Objectives: Marine turtles are globally threatened and face daily anthropogenic threats, including pollution. Water pollution from emerging contaminants such as antimicrobials is a major and current environmental concern. Methods: This study investigated the phenotypic antimicrobial resistance and heavy metal resistance genes of 47 Vibrio isolates from different stages of sea turtles (oceanic stage vs neritic stage) from the Taiwanese coast. Results: The results show that a high proportion (48.9%; 23/47) of the Vibrio species isolated from sea turtles in our study had a multiple antimicrobial resistance (MAR) pattern. It was found that Vibrio spp. isolates with a MAR pattern and those with a MAR index value greater than 0.2 were both more likely to be observed in neritic-stage sea turtles. Furthermore, isolates from neritic-stage sea turtles exhibited greater resistance to the majority of antimicrobials tested (with the exception of beta-lactams and macrolides) than isolates from the oceanic-stage groups. Isolates from neritic sea turtles were found to be more resistant to nitrofurans and aminoglycosides than isolates from oceanic sea turtles. Furthermore, isolates with a MAR pattern (p = 0.010) and those with a MAR index value greater than 0.2 (p = 0.027) were both found to be significantly positively associated with the mercury reductase (merA) gene. Conclusions: The findings of our study indicate that co-selection of heavy metals and antimicrobial resistance may occur in aquatic bacteria in the coastal foraging habitats of sea turtles in Taiwan.

Two novel plasmids harbouring the multiresistance gene cfr in porcine Staphylococcus equorum

BackgroundThe emergence and transmission of the multidrug resistance gene cfr have raised public health concerns worldwide. ObjectivesMultidrug-resistant Staphylococcus equorum isolates can pose a threat to public health. In this study, we have characterised the whole-genome of one Staphylococcus equorum isolate harbouring two distinct cfr-carrying plasmids. MethodsAntimicrobial susceptibility testing was performed by broth microdilution. Genomic DNA was sequenced using both the Illumina HiSeq X Ten and Nanopore MinION platforms. De novo hybrid assembly was performed by Unicycler. Genomic data were assessed by in silico prediction and bioinformatic tools. ResultsStaphylococcus equorum isolate SN42 exhibited resistance or high MICs to linezolid, erythromycin, tetracycline, oxacillin, clindamycin, virginiamycin, tiamulin, chloramphenicol and florfenicol. It carried two cfr-harbouring plasmids: the RepA N-family plasmid pSN42–51 K and the Inc18-family plasmid pSN42–50 K. These two plasmids exhibited low structural similarities to the so far reported cfr-carrying plasmids. Both plasmids harboured an arsenic resistance operon, copper and cadmium resistance genes as well as the lincosamide-pleuromutilin-streptogramin A resistance gene lsa(B). In addition, plasmid pSN42–51 K carried two erm(B) genes for macrolide-lincosamide-streptogramin B resistance, the streptomycin resistance gene ant(6)-Ia as well as mercury resistance genes while pSN42–50 K was associated with the heavy metal translocating P-type ATPase gene hmtp. The co-carriage and co-existence of these antimicrobial resistance and heavy metal resistance genes increases the likelihood of co-selection of the cfr-carrying plasmids. ConclusionThis is the first report of S. equorum carrying two distinct cfr-carrying plasmids, underscoring the need for ongoing surveillance to address the potential dissemination of multi-drug resistance in bacteria from food-producing animals to ensure food safety and public health.

Research Progress in the Joint Remediation of Plants–Microbes–Soil for Heavy Metal-Contaminated Soil in Mining Areas: A Review

Plants growing in heavy metal (HM)-contaminated soil have evolved a special detoxification mechanism. The rhizosphere gathers many living substances and their secretions at the center of plant roots, which has a unique ecological remediation effect. It is of great significance to thoroughly understand the ecological process of rhizosphere pollution under heavy metals (HMs) stress and develop biotechnology for joint remediation using plants and their coexisting microbial systems according to the mechanism of rhizosphere stress. Microbes can weaken the toxicity of HM pollutants by transforming the existing forms or reducing the bioavailability in the rhizosphere. Microbes survive in the HM-polluted soils through the production of stress-resistant substances, the participation of proteins, and the expression of heavy metal resistance genes, which strengthens the resistance of plants. Moreover, microbes can improve the nutritional status of plants to improve plant resistance to HMs. Plants, in turn, provide a habitat for microbes to survive and reproduce, which greatly accelerates the process of bioremediation. Briefly, the combined remediation of soil HMs pollution by plants and microbes is a promising, green, and sustainable strategy. Here, we mainly elucidate the joint remediation mechanism of plant–microbe symbiosis and introduce the coping characteristics of plants, microbes, and their symbiotic system, hoping to provide a scientific basis for the remediation of HM-contaminated soil in mining areas and the sustainable development of the ecological environment.

Insights on optimizing landfill site selection inspired by co-fermentation of weathered coal and landfill leachate

To develop new methods for transforming waste resources such as landfill leachate and weathered coal into clean energy, this research analyzed the co-fermentation effect and internal mechanism of methane production through gas chromatography, three-dimensional fluorescence, inducive coupling and metagenomics techniques. Our findings revealed that landfill leachate addition drives more than 70% increase in weathered coal biomethane production. Anaerobic fermentation collectively increased the tryptophan content in liquid-phase biodegradation, with the highest proportion reaching up to 72%. Paracoccus, Ralstonia, Aquamicrobium and other major microorganisms were in the range of 9–32%. Contamination of heavy metal diversity resistance genes has impacted microflora composition, with specialized heavy metal resistance genes such as NreB, CopD, NreB, and MerP altering the influence of heavy metals on anaerobic fermentation. The combined anaerobic fermentation of landfill leachate and weathered coal has expanded clean waste utilization and has broad application prospects.

Distribution and drivers of co−hosts of antibiotic and metal(loid) resistance genes in the fresh−brackish−saline groundwater

Groundwater is an essential source of drinking water and agricultural irrigation water, and its protection has become a global goal for public health. However, knowledge about heavy metal(loid) resistance genes (MRGs) in groundwater and the potential co−selection of antibiotic resistance genes (ARGs) have seldom been developed. Here, during the wet and dry seasons, we collected 66 groundwater samples (total dissolved solids = 93.9−9530 mg/L) adjacent to Baiyangdian Lake in Northern China, which presented the few metal(loid) and antibiotic contamination. We identified 160 MRGs whose composition exhibited significant seasonal variation, and dissolved metal(loid)s (particularly Ba) played a determinative role in promoting the MRGs proliferation though with relatively low concentrations, suggesting the relatively vulnerable groundwater ecosystems. Moreover, 27.4% of MRG−carrying metagenome−assembled genomes (MAGs) simultaneously carried ARGs, with the most frequently detected MRG types of Cu, Hg, and As, and ARG types of multidrug and bacitracin. Physicochemical variables, variables related to total dissolved solids, metal(loid)s, and antibiotics synthetically shaped the variation of MRG−ARG hosts in groundwater. We found that the increase of MRG−ARG hosts was critically responsible for the spread of MRGs and ARGs in groundwater. Our findings revealed the widespread co−occurrence of MRGs and ARGs in few−contaminated groundwater and highlighted the crucial roles of salinity in their propagation and transmission.

Genomics Insights into Mycolicibacterium Hassiacum Causing Infection in a Cat with Pyogranulomatous Dermatitis and Panniculitis.

Mycolicibacterium hassiacum (homotypic synonym: Mycobacterium hassiacum) represents an ungrouped thermotolerant rapidly growing mycobacteria (RGM) species occasionally associated with infections and disease in humans. In this report, we describe a case of pyogranulomatous dermatitis and panniculitis due to M. hassiacum in an immunocompetent adult cat. To the best of our knowledge, this represents the first report of M. hassiacum infection in animals. We also report the results of the in-depth genome characterization of the isolate using a combined short- and long-read whole-genome sequencing (WGS) approach. We observed the lack of acquired-resistance genes and no evidence of mutations in housekeeping genes associated with resistance to rifampicin and isoniazid. We detected some virulence factors in our isolate, such as some associated with the interaction of mycobacteria with host cells, and the presence of multiple copies of heavy metal resistance genes (arsB, arsR, and arsL/cadL). In conclusion, M. hassiacum should be included among the RGM species associated with feline subcutaneous atypical mycobacteriosis (SAM). A reliable and fast RGM laboratory identification and characterization is important not only for an accurate etiological diagnosis but also for a correct approach to SAM treatment options.

The acquired pco gene cluster in Salmonella enterica mediates resistance to copper.

The pervasive environmental metal contamination has led to selection of heavy-metal resistance genes in bacteria. The pco and sil clusters are located on a mobile genetic element and linked to heavy-metal resistance. These clusters have been found in Salmonella enterica serovars isolated from human clinical cases and foods of animal origin. This may be due to the use of heavy metals, such as copper, in animal feed for their antimicrobial and growth promotion properties. The sil cluster can be found alone or in combination with pco cluster, either in the chromosome or on a plasmid. Previous reports have indicated that sil, but not pco, cluster contributes to copper resistance in S. enterica Typhimurium. However, the role of the pco cluster on the physiology of non-typhoidal S. enterica remains poorly understood. To understand the function of the pco gene cluster, a deletion mutant of pcoABCD genes was constructed using allelic exchange mutagenesis. Deletion of pcoABCD genes inhibited growth of S. enterica in high-copper medium, but only under anaerobic environment. Complementation of the mutant reversed the growth phenotype. The survival of S. enterica in RAW264.7 macrophages was not affected by the loss of pcoABCD genes. This study indicates that the acquired pco cluster is crucial for copper detoxification in S. enterica, but it is not essential for intracellular replication within macrophages.

Comprehensive analysis of antibiotic and heavy metal resistance, and virulence factors in Aeromonas veronii CTe-01: Implications for global antimicrobial resistance

ObjectivesThis study aimed to characterize Aeromonas veronii CTe-01 focusing on its resistance to heavy metal and antibiotics. MethodsA. veronii CTe-01 was characterized using standard microbiological and molecular techniques. Antibiotic susceptibility and heavy metal resistance were tested per standard protocols. Genomic analysis, including plasmid characterization, was conducted in silico. ResultsA. veronii CTe-01 showed resistance to various heavy metals and antibiotics. Multiple resistance genes were identified, including those for beta-lactamases, heavy metal resistance, and type III secretion system components. The bacterium carries a 9 kb plasmid with repA/repB replication genes, parA/parB partitioning genes, and a type II toxin-antitoxin system for stability. ConclusionsA. veronii CTe-01 is a genetic reservoir for antibiotic resistance, heavy metal resistance genes, and virulence factors. The study offers insights into its dual role as a pathogen and heavy metal remediator in aquatic environments.

Repercussions of Prolonged Pesticide Use on Natural Soil Microbiome Dynamics Using Metagenomics Approach.

The residual pesticides in soil can affect the natural microbiome composition and genetic profile that drive nutrient cycling and soil fertility. In the present study, metagenomic approach was leveraged to determine modulations in nutrient cycling and microbial composition along with connected nexus of pesticide, antibiotic, and heavy metal resistance in selected crop and fallow soils having history of consistent pesticide applications. GC-MS analysis estimated residuals of chlorpyrifos, hexachlorbenzene, and dieldrin showing persistent nature of pesticides that pose selective pressure for microbial adaptation. Taxonomic profiling showed increased abundance of pesticide degrading Streptomyces, Xanthomonas, Cupriavidus, and Pseudomonas across the selected soils. Genes encoding for pesticide degrading cytochrome p450, organophosphorus hydrolase, aldehyde dehydrogenase, and oxidase were predominant and positively correlated with Bacillus, Sphingobium, and Burkholderia. Nitrogen-fixing genes (nifH, narB, and nir) were relatively less abundant in crop soils, correlating to the decrease in nitrogen-fixing bacteria (Anabaena, Pantoea, and Azotobacter). Microbial enzymes involved in carbon (pfkA, gap, pgi, and tpiA) and phosphorus cycle (gmbh and phnJ) were significantly higher in crop soils indicating extensive utilization of pesticide residuals as a nutrient source by the indigenous soil microbiota. Additionally, presence of antibiotic and heavy metal resistance genes suggested potential cross-resistance under pressure from pesticide residues. The results implied selective increase in pesticide degrading microbes with decrease in beneficial bacteria that resulted in reduced soil health and fertility. The assessment of agricultural soil microbial profile will provide a framework to develop sustainable agriculture practices to conserve soil health and fertility.

Escherichia coli novel sequence type 11873 harbours a new CTX-M-15–carrying multidrug resistance type 1/2 hybrid IncC plasmid

ObjectiveThe aim of the current study was to determine the genomic map of the resistance genes of two CTX-M-15–carrying Escherichia coli strains belonging to novel sequence type (ST) 11873. Complete, closed genome sequences of the E. coli strains were obtained by applying a combination of short-read Illumina and long-read Oxford Nanopore-based sequencing. MethodsIsolation of E. coli was performed using ECC CHROMagar and antibiotic sensitivity patterns were determined using Sensititre EUVSEC plates. Whole-genome sequencing was performed for two E. coli strains (3–338 and 5–325) using Illumina MiSeq- and Oxford Nanopore MinION-based sequencing. ResultsThe complete genome of strain 3–338 (GenBank accession no. CP130007–17) was assembled into a circular chromosome of 4.65 Mb and 10 plasmids (between 2 and 148 kb). Strain 5–325 (CP130018–27) exhibited a circular chromosome of 4.7 Mb and 9 plasmids (between 2 and 148 kb). Both strains carried an identical type 1/2 hybrid IncC plasmid (∼148 kb) harbouring multiple antibiotic resistance genes (ARGs), including blaCTX−M-15, blaOXA-1, blaTEM-1, qnrS1, sul2, aphA1, aacC2, mph(A) and floR. This plasmid also carried heavy metal resistance genes, such as chrA and arsR. Strain 5–325 carried an additional IncFIB plasmid (∼78 kb) harbouring additional ARGs, including blaTEM-1, qnrS1, tet(A), dfrA14, sul2, strA and strB. ConclusionsOur study shows the emergence of a CTX-M-15–carrying type 1/2 hybrid IncC plasmid in novel E. coli ST11873. These findings emphasise the need for population-based sewage surveillance for understanding the prevalence of antibiotic resistance in pathogens in order to mitigate the further spread of such resistance factors.

Insight into response mechanism of aerobic granular sludge to combined nanoparticle stress: Nitrogen removal, microbial community and heavy metal resistance genes

Multiple nanoparticles presented in wastewater treatment plants can produce comprehensive ecotoxicity. In this study, copper oxide nanoparticles (nCuO) and zinc oxide nanoparticles (nZnO) were investigated for their co-toxicity to aerobic granular sludge (AGS) systems. The combined stress of nCuO and nZnO performed significant antagonistic effects on nitrogen removal both under acute and chronic stress. Under chronic stress, nCuO and nZnO co-existence performed significant antagonistic effects on cell membrane, adenosine triphosphate (ATP) activity and microbial community structure. PICRUSt analysis indicated that nCuO (15 mg/L) co-existence alleviated nZnO (10 mg/L) inhibition on energy production and membrane transport metabolic pathways. In addition, nCuO addition to single nZnO weakened the toxicity of nZnO to nitrogen metabolism, glucose metabolism, and electron transfer genes, contributing to an alleviation in nitrogen removal inhibition. As compared with individual stress, combined stress decreased Cu(II) release from nCuO, but increased Zn(II) release from nZnO. The combination of nCuO and nZnO increased zinc resistance gene amplification and czcC gene proportion, and promoted Zn(II) efferent from cells, also with AGS resistance.

Genetic features of BEL-1-producing and KPC-2-producing E. coli from hospital wastewater: human source or sewages adaptation

Hospital sewage is an ecosystem that facilitates the transfer of antibiotic and heavy metal resistance genes and the interaction of human and environmental bacteria. In this environment, we have detected the presence of 7 KPC-2 and BEL-1 co-producing E. coli isolates of two different clones over a 10-month period in the same hospital. All isolates carried blaKPC-2 and the operon mer on the same IncP plasmid of similar size and an IncN plasmid of different size each clone carrying blaBEL-1. Both IncN-blaBEL-1 plasmids shared a 77 kb region containing blaBEL-1 alongside with fosE, blaOXA-10 and aac(6’)-1b genes in a class 3 integron within a Tn3 transposon. The major IncN plasmid contained in addition a region homolog to P1-like bacteriophage RCS47, including the lytic RepL and lysogenic proteins, but other phage regions were incomplete. The characters such as the temporal persistence in sewage, the absence of colonized patients in the hospital or in the region, the presence of a p1 phage-plasmid fusion and the infrequent class 3 integron as genetic platform would indicate that BEL-1-producing isolates could have been generated in situ by adaptation to human sewage. Part of the microbiota in these discharges could be explained by the interactions of sewage ecosystems and not derive directly from the hospital.

Nano- and microplastics drive the dynamic equilibrium of amoeba-associated bacteria and antibiotic resistance genes

As emerging pollutants, microplastics have become pervasive on a global scale, inflicting significant harm upon ecosystems. However, the impact of these microplastics on the symbiotic relationship between protists and bacteria remains poorly understood. In this study, we investigated the mechanisms through which nano- and microplastics of varying sizes and concentrations influence the amoeba-bacterial symbiotic system. The findings reveal that nano- and microplastics exert deleterious effects on the adaptability of the amoeba host, with the magnitude of these effects contingent upon particle size and concentration. Furthermore, nano- and microplastics disrupt the initial equilibrium in the symbiotic relationship between amoeba and bacteria, with nano-plastics demonstrating a reduced ability to colonize symbiotic bacteria within the amoeba host when compared to their microplastic counterparts. Moreover, nano- and microplastics enhance the relative abundance of antibiotic resistance genes and heavy metal resistance genes in the bacteria residing within the amoeba host, which undoubtedly increases the potential transmission risk of both human pathogens and resistance genes within the environment. In sum, the results presented herein provide a novel perspective and theoretical foundation for the study of interactions between microplastics and microbial symbiotic systems, along with the establishment of risk assessment systems for ecological environments and human health.

Heavy metal tolerance and detoxification mechanism mediated by heavy metal resistance genes in compost habitat.

Heavy metal pollution from compost is one of the most concerned environmental problems, which poses a threat to the ecosystem and human health. This study aims to reveal the heavy metal tolerance and detoxification mechanism mediated by heavy metal resistance genes (HMRGs) in compost habitat through metagenomics combined with chemical speciation analysis of heavy metals. The results showed that there were 37 HMRGs corresponding to 7 common heavy metal(loid)s in composting, and they had the ability to transform heavy metals into stable or low-toxic speciation by regulating enzyme transport, redox, methylation, etc. This study summarized the heavy metal metabolism pathway mediated by HMRGs, providing a new perspective for understanding the transformation of heavy metals in the composting process.

Genomic and environmental controls on Castellaniella biogeography in an anthropogenically disturbed subsurface

Castellaniella species have been isolated from a variety of mixed-waste environments including the nitrate and multiple metal-contaminated subsurface at the Oak Ridge Reservation (ORR). Previous studies examining microbial community composition and nitrate removal at ORR during biostimulation efforts reported increased abundances of members of the Castellaniella genus concurrent with increased denitrification rates. Thus, we asked how genomic and abiotic factors control the Castellaniella biogeography at the site to understand how these factors may influence nitrate transformation in an anthropogenically impacted setting. We report the isolation and characterization of several Castellaniella strains from the ORR subsurface. Five of these isolates match at 100% identity (at the 16S rRNA gene V4 region) to two Castellaniella amplicon sequence variants (ASVs), ASV1 and ASV2, that have persisted in the ORR subsurface for at least 2 decades. However, ASV2 has consistently higher relative abundance in samples taken from the site and was also the dominant blooming denitrifier population during a prior biostimulation effort. We found that the ASV2 representative strain has greater resistance to mixed metal stress than the ASV1 representative strains. We attribute this resistance, in part, to the large number of unique heavy metal resistance genes identified on a genomic island in the ASV2 representative genome. Additionally, we suggest that the relatively lower fitness of ASV1 may be connected to the loss of the nitrous oxide reductase (nos) operon (and associated nitrous oxide reductase activity) due to the insertion at this genomic locus of a mobile genetic element carrying copper resistance genes. This study demonstrates the value of integrating genomic, environmental, and phenotypic data to characterize the biogeography of key microorganisms in contaminated sites.

Effect of aqueous phase from hydrothermal carbonization of sewage sludge on heavy metals and heavy metal resistance genes during chicken manure composting

Livestock manure is often contaminated with heavy metals (HMs) and HM resistance genes (HMRGs), which pollute the environment. In this study, we aimed to investigate the effects of the aqueous phase (AP) produced by hydrothermal carbonization (HTC) of sewage sludge (SS) alone and the AP produced by co-HTC of rice husk (RH) and SS (RH-SS) on humification, HM bioavailability, and HMRGs during chicken manure composting. RH-SS and SS increased the humic acid content of the compost products by 18.3 % and 9.7 %, respectively, and significantly increased the humification index (P < 0.05) compared to the CK (addition of tap water). The passivation of HMs (Zn, Cu, As, Pb, and Cr) increased by 12.17–23.36 % and 9.74–15.95 % for RH-SS and SS, respectively, compared with that for CK. RH-SS and SS reduced the HMRG abundance in composted products by 22.29 % and 15.07 %, respectively. The partial least squares path modeling results showed that SS and RH-SS promoted compost humification while simultaneously altering the bacterial community and reducing the bioavailability of metals and host abundance of HMRGs, which has a direct inhibitory effect on the production and distribution of HMRGs. These findings support a new strategy to reduce the environmental risk of HMs and HMRGs in livestock manure utilization.

Strategic implementation of upflow microbubble airlift photocatalytic process to control heavy metal resistant-MDR bacteria and the associated genes in wastewater

The emergence of multidrug resistance (MDR) and heavy metal resistance (HMR) in bacterial pathogens and genes through mobile genetic elements (MGEs) from wastewater effluents needs to be eradicated using green technology. HMR is critical to controlling antimicrobial resistance but has been neglected in most photocatalytic disinfection (PCD) studies. Advanced photocatalysis in antimicrobial studies requires a strategic approach to enhance the disinfection efficiency. This study applied an optimized upflow airlift photocatalytic reactor (UAPR) with microbubble air and blue light to remove the antimicrobial resistance (HMR–MDR bacteria (HMR–MDRB), HMR genes (HMRGs), antibiotic resistant genes (ARGs) and MGEs) and inhibit pathogenicity in a mixed culture of high-strength HMR–MDRB isolated from wastewater. Stable dissolved oxygen (DO) supplementation and blue light significantly affected the HMRGs and MGE reduction, resulting in enhanced disinfection activity (30 %) and reaction time (60 min) required for the complete inactivation of HMR-MDRB mixed culture. The process effectively reduced the blaNDM-1 (3.37 log), pbrT (2.18 log), intl1 (2.16 log), and tn916/1545 (4.07 log), with a PCD rate constant (kg) of 0.0515 min−1, 0.0359 min−1, 0.0292 min−1, and 0.0662 min−1, respectively. Process mechanism studies showed that the stable supplementation of DO was a critical factor in controlling the type of reactive oxygen species (ROS), resulting in type II ROS, 1O2, as the critical free radical contributing to the reduction of ARGs and integron, whereas h+ was the ROS for pbrT and transposon.

Crucifer Lesion-Associated Xanthomonas Strains Show Multi-Resistance to Heavy Metals and Antibiotics.

Copper resistance in phytopathogens is a major challenge to crop production globally and is known to be driven by excessive use of copper-based pesticides. However, recent studies have shown co-selection of multiple heavy metal and antibiotic resistance genes in bacteria exposed to heavy metal and xenobiotics, which may impact the epidemiology of plant, animal, and human diseases. In this study, multi-resistance to heavy metals and antibiotics were evaluated in local Xanthomonas campestris pv. campestris (Xcc) and co-isolated Xanthomonas melonis (Xmel) strains from infected crucifer plants in Trinidad. Resistance to cobalt, cadmium, zinc, copper, and arsenic (V) was observed in both Xanthomonas species up to 25 mM. Heavy metal resistance (HMR) genes were found on a small plasmid-derived locus with ~ 90% similarity to a Stenotrophomonas spp. chromosomal locus and a X. perforans pLH3.1 plasmid. The co-occurrence of mobile elements in these regions implies their organization on a composite transposon-like structure. HMR genes in Xcc strains showed the lowest similarity to references, and the cus and ars operons appear to be unique among Xanthomonads. Overall, the similarity of HMR genes to Stenotrophomonas sp. chromosomal genomes suggest their origin in this genus or a related organism and subsequent spread through lateral gene transfer events. Further resistome characterization revealed the presence of small multidrug resistance (SMR), multidrug resistance (MDR) efflux pumps, and bla (Xcc) genes for broad biocide resistance in both species. Concurrently, resistance to antibiotics (streptomycin, kanamycin, tetracycline, chloramphenicol, and ampicillin) up to 1000 µg/mL was confirmed.

Long-term and combined heavy-metal contamination forms a unique microbiome and resistome: A case study in a Yellow River tributary sediments

Microorganisms have developed mechanisms to adapt to environmental stress, but how microbial communities adapt to long-term and combined heavy-metal contamination under natural environmental conditions remains unclear. Specifically, this study analyzed the characteristics of heavy metal composition, microbial community, and heavy metal resistance genes (MRGs) in sediments along Mang River, a tributary of the Yellow River, which has been heavily polluted by industrial production for more than 40 years. The results showed that the concentrations of Cr, Zn, Pb, Cu and As in most sediments were higher than the ambient background values. Bringing the heavy metals speciation and concentration into the risk evaluation method, two-thirds of the sediment samples were at or above the moderate risk level, and the ecological risk of combined heavy metals in the sediments decreased along the river stream. The high ecological risk of heavy metals affected the microbial community structure, metabolic pathways and MRG distribution. The formation of a HM-resistant microbiome possibly occurred through the spread of insertion sequences (ISs) carrying multiple MRGs, the types of ISs carrying MRGs outnumber those of plasmids, and the quantity of MRGs on ISs is also higher than that on plasmids. These findings could improve our understanding of the adaptation mechanism of microbial communities to long-term combined heavy metal contamination.

Landscape of plasmids encoding β-lactamases in disinfection residual Enterobacteriaceae from wastewater treatment plants

Conventional disinfection processes, such as chlorination and UV radiation, are ineffective in controling antibiotic-resistant bacteria, especially disinfection residual Enterobacteriaceae (DRE) encoding β-lactamases, some of which have been classified as “critical priority pathogens” by the World Health Organization. However, few studies have focused on the transferability, phenotype, and genetic characteristics of DRE-derived plasmids encoding β-lactamases, especially extended-spectrum β-lactamases and carbapenemases. In this study, we isolated 10 typical DRE harboring plasmid-mediated blaNDM, blaCTX-M, or blaTEM in post-disinfection effluent from two wastewater treatment plants (WWTPs), with transfer frequency ranging from 1.69 × 10−6 to 3.02 × 10−5. According to genomic maps of plasmids, all blaNDM and blaTEM were cascaded with IS26, and blaCTX-M was adjacent to ISEcp1 or IS26, indicating the important role of these elements in the movement of β-lactamase-encoding genes. The presence of intact class 1 integrons on pWTPN-01 and pWTPC-03 suggested the ability of these DRE-derived plasmids to integrate other exogenous antibiotic resistance genes (ARGs). The coexistence of antibiotic, disinfectant, and heavy metal resistance genes on the same plasmid (e.g., pWTPT-03) implied the facilitating role of disinfectants and heavy metals in the transmission of DRE-derived ARGs. Notably, two plasmid transconjugants exhibited no discernible competitive fitness cost, suggesting a heightened environmental persistence. Furthermore, enhanced virulence induced by β-lactamase-encoding plasmids in their hosts was confirmed using Galleria mellonella infection models, which might be attributed to plasmid-mediated virulence genes. Overall, this study describes the landscape of β-lactamase-encoding plasmids in DRE, and highlights the urgent need for advanced control of DRE to keep environmental and ecological security.