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At least 19 recordsLinked to original sources

PubMed2024

Horizontal plasmid transfer promotes antibiotic resistance in selected bacteria in Chinese frog farms.

The emergence and dissemination of antibiotic resistance genes (ARGs) in the ecosystem are global public health concerns. One Health emphasizes the interconnectivity between different habitats and seeks to optimize animal, human, and environmental health. However, information on the dissemination of antibiotic resistance genes (ARGs) within complex microbiomes in natural habitats is scarce. We investigated the prevalence of antibiotic resistant bacteria (ARB) and the spread of ARGs in intensive bullfrog (Rana catesbeiana) farms in the Shantou area of China. Antibiotic susceptibilities of 361 strains, combined with microbiome analyses, revealed Escherichia coli, Edwardsiella tarda, Citrobacter and Klebsiella sp. as prevalent multidrug resistant bacteria on these farms. Whole genome sequencing of 95 ARB identified 250 large plasmids that harbored a wide range of ARGs. Plasmid sequences and sediment metagenomes revealed an abundance of tetA, sul1, and aph(3″)-Ib ARGs. Notably, antibiotic resistance (against 15 antibiotics) highly correlated with plasmid-borne rather than chromosome-borne ARGs. Based on sequence similarities, most plasmids (62%) fell into 32 distinct groups, indicating a potential for horizontal plasmid transfer (HPT) within the frog farm microbiome. HPT was confirmed in inter- and intra-species conjugation experiments. Furthermore, identical mobile ARGs, flanked by mobile genetic elements (MGEs), were found in different locations on the same plasmid, or on different plasmids residing in the same or different hosts. Our results suggest a synergy between MGEs and HPT to facilitate ARGs dissemination in frog farms. Mining public databases retrieved similar plasmids from different bacterial species found in other environmental niches globally. Our findings underscore the importance of HPT in mediating the spread of ARGs in frog farms and other microbiomes of the ecosystem.

Animals↗

PubMed2026

Dissemination of blaKPC-3-harbouring Klebsiella pneumoniae across ST48 and ST628 in multiple healthcare facilities in the Republic of Korea.

Klebsiella pneumoniae carbapenemase-3 (KPC-3) remains rare in South Korea, where KPC-2 is the dominant carbapenemase, making the repeated detection of a concentrated blaKPC-3 signal over five years notable. We performed genomic analyses of blaKPC-3-harbouring K. pneumoniae from a regional healthcare network. Two chromosomally distinct lineages with concordant capsule loci (ST628/KL15 and ST48/KL62) presented multidrug-resistant phenotypes, and the virulence-associated loci were confined to ST48. Single-nucleotide polymorphism (SNP) analyses revealed near-clonal relatedness within lineages, with 0-38 pairwise SNPs among ST628 isolates and 8 SNPs between the two ST48 isolates. Core-genome multilocus sequence typing (cgMLST) supported this structure, as ST628 isolates were assigned to complex type 19149 with 0-7 allelic differences, and ST48 isolates were assigned to complex type 19150 with 5 allelic differences. These patterns support vertical spread via clonal expansion across multiple facilities. Despite substantial chromosomal separation, most isolates carried the same IncFII(K) plasmid backbone and blaKPC-3, and they were nearly indistinguishable from a plasmid previously reported in South Korea. One isolate carried blaKPC-3 on a distinct multireplicon IncFIB(K)/IncFII(K) plasmid, indicating that the signal was not confined to a single plasmid backbone. In both plasmids, blaKPC-3 was embedded within Tn4401b. These findings indicate that a rare blaKPC-3 genotype can persist regionally through sustained clonal dissemination and that cross-lineage linkage is compatible with past horizontal transfer involving a conserved plasmid. These findings underscore the need for subtype-resolved, regionally coordinated genomic surveillance in connected healthcare networks to detect uncommon carbapenemase variants early.

Klebsiella pneumoniae↗

PubMed2025

Emergence of carbapenem-resistant Serratia marcescens co-harboring blaNDM-1, blaKPC-2, and blaSRT-2 in bloodstream infection.

Serratia marcescens is an emerging opportunistic pathogen with high genetic diversity. The emergence and prevalence of carbapenem-resistant S. marcescens poses a major health threat due to its intrinsic resistance to multiple antibiotics, which severely restricts the selection and treatment of antibiotics for S. marcescens infection. This study presents the first documented case in China of a bloodstream infection caused by Staphylococcus epidermidis and S. marcescens strain (designated S96) co-producing blaNDM-1, blaKPC-2, and blaSRT-2. Strain S96 exhibited resistance to nearly all categories of β-lactam antimicrobials, β-lactam/inhibitor combinations, aminoglycosides, quinolones, and other clinical antibacterial agents, with the exception of tigecycline. Our main objective was to characterize the genetic mechanisms underlying its carbapenem resistance and plasmid transfer potential. Whole-genome sequencing revealed blaKPC-2 on a 44,047 bp "IncX6-like" plasmid and blaNDM-1 on a 100,081 bp IncFII(Yp)-type plasmid, alongside chromosomal blaSRT-2 and aac(6')-Ic. "IncX6-like" and IncFII(Yp)-type plasmids are widely distributed among carbapenem-resistant Enterobacteriaceae strains globally. Conjugation experiments demonstrated that the blaNDM-1-carrying plasmid could be successfully transferred to recipient Escherichia coli 600, with no significant fitness cost observed (P > 0.05). The experimental results demonstrate that carbapenem-resistant genes can disseminate among Enterobacteriaceae via plasmid-mediated horizontal transfer between bacterial cells. Comparative genomic analysis revealed plasmid structural homology with global counterparts, demonstrating IS-mediated recombination and horizontal gene transfer. The low adaptive cost of plasmid carriage and multidrug resistance phenotype pose significant challenges for clinical management. This study highlights the need for enhanced clinical surveillance and antibiotic stewardship to curb the spread of such multidrug-resistant pathogens.IMPORTANCECarbapenem resistance in Serratia marcescens is primarily mediated by Klebsiella pneumoniae carbapenemase (KPC), with New Delhi metallo-β-lactamase (NDM) being a relatively uncommon alternative resistance mechanism. KPC-2 and NDM-1 coexisting in S. marcescens is extremely rare clinically. This study reports the first clinical isolate of S. marcescens in China co-harboring blaNDM-1, blaKPC-2, and blaSRT-2. The isolate exhibits multidrug resistance to nearly all β-lactam antibiotics and β-lactam/inhibitor combinations, with low adaptive costs and high dissemination potential. The potential spread of resistance genes through mobile genetic elements poses a serious public health risk. The study underscores the need for enhanced surveillance, rational antibiotic use, and novel strategies to combat resistance. It also provides insights into the evolutionary mechanisms of bacterial resistance, emphasizing the urgent need for interventions to address the growing threat of antimicrobial resistance.

Humans↗

PubMed2025

Whole-Genome Sequencing Uncovers Chromosomal and Plasmid-Borne Multidrug Resistance and Virulence Genes in Poultry-Associated Escherichia coli from Nigeria.

BACKGROUND: Broad and unregulated antibiotic use in livestock production, particularly poultry farming, has increased the development and persistence of multidrug-resistant (MDR) bacterial strains in animals. These resistant pathogens and their antibiotic resistance genes (ARGs) can spread to humans through environmental exposure and the food chain, posing serious public health risks. Whole-genome sequencing (WGS), alongside phenotypic antimicrobial susceptibility testing (AST), enables a comprehensive understanding of resistance mechanisms and informs antimicrobial stewardship strategies, particularly in resource-limited settings. AIM: This study aimed to characterize the phenotypic and genotypic antimicrobial resistance profiles, plasmid content, and virulence factors of an MDR E. coli strain (S3) isolated from a poultry farm in Enugu State, Nigeria, to elucidate potential risks to public health and the role of poultry as a reservoir for resistance determinants. METHODS: E. coli strain S3 was isolated from chicken droppings using standard microbiological methods and confirmed by MALDI-TOF mass spectrometry. AST was assessed using disc diffusion and broth microdilution to determine minimum inhibitory concentrations (MICs) for ten antibiotics across multiple classes. WGS was performed with a hybrid approach combining Illumina and Nanopore platforms, followed by genome assembly and annotation. ARGs, plasmid replicons, and virulence factors were identified in silico using AMRFinderPlus, starAMR, RGI/CARD, PlasmidFinder, MOB-suite, and the Virulence Factor Database (VFDB). RESULTS: Phenotypic testing revealed extensive resistance, with complete resistance to six of seven tested antibiotics (cefotaxime, ampicillin, erythromycin, gentamicin, ciprofloxacin, and doxycycline). MICs exceeded clinical breakpoints for multiple classes, confirming an MDR phenotype. Genome analysis indicated a 5.33 Mb genome distributed across five contigs, including one chromosome and four plasmid-associated contigs. The strain harboured numerous ARGs, including bla CTX-M-15, bla OXA-1, bla TEM-1, aac(6')-Ib-cr, aadA5, aph(3")-Ib, sul1/sul2, tet(A), dfrA17, and mph(A), co-localized on plasmids indicative of horizontal gene transfer (HGT) potential. Plasmid types included Col156, IncF, and two rep clusters. Virulence profiling revealed genes associated with adhesion (pap cluster, ECP), iron acquisition (enterobactin, yersiniabactin, aerobactin, heme uptake), and toxins (sat, senB), highlighting the isolate's potential for urinary tract and intestinal infections. CONCLUSION: This study highlights the significant role of poultry-associated bacteria as reservoirs of AMR genes, particularly those harboured on mobile plasmids with potential for HGT. E. coli strain S3 exhibits extensive multidrug resistance and carries a complex plasmid repertoire facilitating horizontal transfer of ARGs. Coupled with a rich virulence gene profile, this strain underscores the public health risk posed by poultry-associated E. coli in Nigeria. These findings demonstrate the urgent need for stringent antimicrobial stewardship, regulatory oversight, and genomic surveillance in poultry production milieus to mitigate the dissemination of MDR pathogens.

Escherichia coli↗

PubMed2026

Concurrence of antibiotic resistance genes in plasmid genomes shape environmental resistomes.

Horizontal transfer of plasmid-associated antibiotic resistance genes (ARGs) plays a pivotal role in environmental antibiotic resistance dissemination. Here, we characterized ARG concurrence patterns in plasmid genomes and examined plasmid-associated ARGs across 106 environmental metagenomes. Approximately half of known ARG subtypes (257) occurred in plasmid genomes, and nearly one-quarter of plasmids carried ARGs, including "super plasmids" harboring over 20 ARG subtypes spanning 10 antibiotic categories. Aminoglycoside resistance genes (AmRGs) exhibited the highest concurrence frequency (CF) with other ARGs in plasmid genomes, followed by beta-lactam and sulfonamide resistance genes. Many high-risk ARGs preferentially coexisted with AmRGs (45.6% of total AmRGs CF). Environmental metagenomes revealed distinct plasmid-associated ARG profiles between polluted and relatively pristine environments, with significantly greater diversity and abundance under anthropogenic pollution. Five widespread ARG subtypes occurred across all environmental media, whereas polluted environments contained more unique ARGs. Co-occurrence networks identified AmRGs as "hubs" linking multiple ARG subtypes in environmental resistomes. Plasmid-ARG interaction networks further showed more complex potential plasmid-mediated concurrent dissemination in polluted environments. Collectively, use of aminoglycosides is more likely to cause co-transmission of multiple plasmid-related ARGs than other antibiotics, and CF of ARGs is proposed as an important supplementary factor for evaluating ARG dissemination under anthropogenic antibiotic stress.

Antibiotic resistance genes (ARGs)↗

PubMed2025

Mobile genetic elements in Klebsiella pneumoniae.

Klebsiella pneumoniae is a clinically important pathogenic bacteria that poses a serious threat to human health. In particular, the emergence of hypervirulent and multidrug-resistant K. pneumoniae has posed great challenges in clinical anti-infective therapy. In the K. pneumoniae genome, mobile genetic elements (MGEs), such as plasmids, prophages, transposons, and insertion sequences, enhance bacterial viability and adaptation by mediating the horizontal transfer of virulence genes, antibiotic resistance genes, and other adaptive genes. This paper reviews the types and characteristics of the main MGEs in K. pneumoniae, focusing on their effects on bacterial virulence and antibiotic resistance, with the aim of providing clues for developing infection control measures and new antibacterial drugs.

Klebsiella pneumoniae↗

PubMed2022

Ecological dynamics of plasmid transfer and persistence in microbial communities.

Plasmids are a major driver of horizontal gene transfer in prokaryotes, allowing the sharing of ecologically important accessory traits between distantly related bacterial taxa. Within microbial communities, interspecies transfer of conjugative plasmids can rapidly drive the generation genomic innovation and diversification. Recent studies are starting to shed light on how the microbial community context, that is, the bacterial diversity together with interspecies interactions that occur within a community, can alter the dynamics of conjugative plasmid transfer and persistence. Here, I summarise the latest research exploring how community ecology can both facilitate and impose barriers to the spread of conjugative plasmids within complex microbial communities. Ultimately, the fate of plasmids within communities is unlikely to be determined by any one individual host, rather it will depend on the interacting factors imposed by the community in which it is embedded.

Bacteria↗

PubMed2026

Farming reshapes the gut resistome, virulome, and mobilome of Cervidae.

The rapid expansion of cervid farming raises concerns about antimicrobial resistance (AMR) dissemination, yet its impact on the Cervidae gut microbiome remains poorly characterized. We integrated 89 newly sequenced fecal metagenomes with 599 publicly available datasets, comprising 285 metagenomes from farmed cervids and 370 from wild cervids, to construct a catalog of 15,494 non-redundant metagenome-assembled genomes (MAGs) representing 2,401 species. Our analysis demonstrates that farming profoundly reshapes the gut microbiome's functional composition. Specifically, farmed cervids exhibited significantly higher relative abundance, diversity, and heterogeneity of antimicrobial resistance genes (ARGs) compared to wild counterparts. We observed a robust synergistic relationship between ARGs, virulence factor genes, and mobile genetic element (MGE)-associated genes, identifying 70 ARG-MGE combinations as evidence of potential horizontal gene transfer. Plasmid profiling further suggested that a subset of ARGs may be associated with conjugative plasmids, with plasmid-associated ARGs being significantly more abundant in farmed than in wild cervids. Virome analyses indicated that bacteriophages, particularly Siphoviridae, may serve as mobile reservoirs for ARGs. Notably, Cervidae shared 268 ARG types with humans, including 23 high-risk genes associated with resistance to clinically important antibiotics (e.g. tetX1, vanRD, and bla-CTX-M-178), with Escherichia coli as a key cross-host carrier. These findings highlight that human-impacted cervid gut microbiomes are significant environmental reservoirs of clinically relevant AMR, underscoring the necessity for enhanced antibiotic stewardship and resistance surveillance in managed wildlife within a One Health framework.

Animals↗

PubMed2026

Hurdles to horizontal gene transfer: species-specific effects of synonymous variation and plasmid copy number determine antibiotic resistance phenotype.

Could codon composition condition the immediate success and the orientation of horizontal gene transfer? Horizontal gene transfer represents a change in the genome of expression of the transferred gene, and experimental evidence has accumulated indicating that the codon composition of a sequence is an important determinant of its compatibility with the translation machinery of the genome in which it is expressed. This suggests that codon composition influences the phenotype and the fitness conferred by a transferred gene and thus the immediate success of the transfer. To directly test this hypothesis, we characterized the resistance conferred by synonymous variants of a gentamicin resistance gene in three bacterial species: Escherichia coli, Acinetobacter baylyi and Pseudomonas aeruginosa. The strongest determinant of the resistance level conferred was the species in which the resistance gene was transferred, very likely because of important differences in the copy number of the plasmid carrying the gene. Significant differences in resistance were also found between synonymous variants within each of the three species, but more importantly, there was a strong interaction between species and variant: variants conferring high resistance in one species confer low resistance in another. However, the similarity in codon usage between the synonymous variants and the host genome only explained part of the phenotypic differences between variants in one species, P. aeruginosa. Further investigation of alternative explanations did not reveal common universal mechanisms across our three bacterial species. We conclude that codon composition can be a determinant of post-horizontal gene transfer success. However, there are multiple paths leading from synonymous sequence to phenotype, and sensitivity to these different paths is species-specific.

Gene Transfer, Horizontal↗

PubMed2026

GenBank mining reveals novel insights into Rhizobium phylogeny: Identical 16S rRNA sequences are mainly uncoupled from species designation, host plant, and geographic origin: How this search suggested the definition of a direct 'microbial h-index'.

16S rDNA is the historical gold standard for bacterial identification, particularly in metabarcoding approaches reliant on sequence similarity thresholds. We analyzed 6,660 Rhizobium 16S rRNA gene sequences from GenBank to examine the relationship between sequence identity and three metadata: species name, host plant, and geographic origin. Using an iterative BLAST-based pipeline, we detected 116,069 pairwise matches and assessed concordance among sequences (average length 1,328 bp) sharing 100% identity. For those in which the organism name, host plant and country of isolation were present in the record, surprisingly, 66.59% of identical sequence pairs showed full discordance across all three metadata, while only 1.40% shared the same name, host, and country. The most widespread sequence, detected 371 times, was associated with over 56 different host plants across 25 countries and bore multiple species name designations. These results highlight a striking mismatch between the 16S barcode and the taxonomic, ecological, and phenotypic variability it is assumed to reflect, likely arising from the slow evolution of rRNA genes contrasted with the mobility of ecologically relevant genes via horizontal transfer on plasmids, transposons, and phages. Our findings further challenge the limitations of relying on 16S rRNA alone for fine-scale taxonomic and metadata-based inference in capturing the true functional and ecological diversity of bacteria, endorsing the critical importance of polyphasic taxonomic approaches that integrate genomic, phenotypic, and ecological data. An interesting byproduct of the analysis was to realize the possibility of treating these data as if they were 'citations.' The more one finds the same query sequence, the more that sequence can be considered biologically 'cited', i.e., re-proposed elsewhere in the world. Thus, one can also analyze the h-index of such a ranking. In our Rhizobium dataset, we calculated an h-index = 201, meaning the sequence ranked 201st had 202 identical homologues in GenBank. Although the research effort on given species is directly connected with it, this number provides a quantitative indicator of a taxon's sequence recurrence and distribution within public databases, independent of nomenclatural inconsistencies, offering a novel framework for assessing bacterial representation across global datasets.

RNA, Ribosomal, 16S↗

PubMed2026

Mobile genetic elements-driven partitions of mega-plasmids resistome in Salmonella Infantis.

Salmonella enterica serovar Infantis (S. Infantis) becomes the primary pathogen among the top Salmonella serotypes, contributing to numerous cases of foodborne illness annually in the United States. S. Infantis infection has spread rapidly worldwide, especially the clones with pESI-like plasmids. However, the underlying mechanisms regarding the transmission of S. Infantis, particularly mobile genetic elements (MGEs), mediated horizontal gene transfer, are limited. The objective of this study was to evaluate the relationship, if any, among MGEs, antibiotic-resistant genes (ARGs), and virulence factors (VFs) within S. Infantis via genomic analysis. A total of 91 S. Infantis complete genomes with high sequencing quality were selected for downstream bioinformatic analysis. The results showed that the majority of VFs were located in the bacterial chromosomes, while most ARGs were carried by S. Infantis mega-plasmids in an MGE-favored manner. Integrons and transposons were closely associated with certain ARGs, but prophages within mega-plasmids displayed a diverse ARG profile. Collectively, MGE-mediated horizontal gene transfer might lead to ARG acquisition by mega-plasmids, subsequently contributing to the resistome of S. Infantis. Our findings provide insights into the development of MGE-associated resistome in S. Infantis that could inform more effective prevention and intervention strategies to control this pathogen, further ensuring public health and safety.IMPORTANCEThe rapid emergence and transmission of antibiotic-resistant foodborne pathogens pose a significant risk to public health, necessitating the discovery of underlying mechanisms to control multidrug-resistant pathogens. Salmonella enterica serovar Infantis (S. Infantis) has become a pathogen of clinical and epidemiological relevance in recent years, ranking as the top prevalent serovar associated with foodborne illnesses and exhibiting resistance to several antibiotics. The current investigation of multidrug resistance (MDR) S. Infantis strains primarily emphasized the presence of mega-plasmids. However, the question of how mega-plasmids contribute to the transmission of antibiotic-resistant genes (ARG) is unaddressed. Utilizing the genomic characterization of S. Infantis complete genomes with high quality, our study revealed that the resistome of S. Infantis mega-plasmids-the primary ARG reservoirs of S. Infantis-followed a specific pattern of mobile genetic elements (MGEs). Monitoring the spread of MGE-carried ARGs within mega-plasmids should be considered in future surveillance.

Interspersed Repetitive Sequences↗

PubMed2025

Co-existence of the oxazolidinone resistance genes cfr and optrA on a novel multiresistance plasmid from a methicillin-resistant Macrococcoides bohemicum strain.

OBJECTIVES: To identify and characterize the oxazolidinone resistance genes cfr and optrA from a methicillin-resistant Macrococcoides bohemicum strain of chicken origin. METHODS: The presence of mobile oxazolidinone resistance genes was detected by PCR. Antimicrobial susceptibility testing was conducted by broth microdilution. Transfer experiments were carried out to evaluate horizontal transferability of the plasmid. WGS was performed using a combination of Illumina NovaSeq/Oxford Nanopore PromethION platforms. RESULTS: The M. bohemicum strain HLJ23 exhibited an MDR phenotype and was positive for both cfr and optrA genes. WGS revealed that the genes cfr and optrA co-exist on the novel MDR plasmid pHLJ23-71kb. Although conjugation experiments were unsuccessful, plasmid pHLJ23-71kb could be transferred to Staphylococcus aureus RN4220 by electrotransformation. Genetic context analysis showed that the cfr and optrA together with another four antimicrobial resistance genes are located in an MDR region on plasmid pHLJ23-71kb. Sequence analysis suggested that this MDR region possibly originated from Mammaliicoccus or Staphylococcus spp. CONCLUSIONS: To the best of our knowledge, this study represents the first report of the oxazolidinone resistance genes cfr and optrA in the genus Macrococcoides. Furthermore, attention should be paid to the exchange of resistance determinants between members of the genera Staphylococcus, Mammaliicoccus and Macrococcoides.

Plasmids↗

PubMed2026

From commensal to pathobiont: The emergence of virulence-enhanced Escherichia coli in China's food-animal systems - insights with future implications.

A fundamental shift in Escherichia coli epidemiology is being driven by convergence of virulence determinants and antimicrobial resistance within linked human-animal-environment systems. In China, the rapid growth of food-animal production, extensive antimicrobial use, and complex food networks are accelerating the emergence and dissemination of virulence-enhanced E. coli pathobionts. This review synthesizes recent epidemiological, genomics, and outbreak data to characterize China's evolving landscape of food-animal-associated E. coli. We highlight a significant shift from classical pathotypes to hybrid lineages that simultaneously carry virulence factors and last-resort antibiotic resistance determinants, including mcr-1, tet(X4), and blaNDM. These traits disseminate rapidly via plasmid-mediated horizontal gene transfer, facilitating rapid adaptation and enabling cross-sectoral One Health transmission. National surveillance, foodborne outbreak investigations, and whole-genome sequencing data show that food-animal reservoirs are active evolutionary niches that drive pathogen diversity and fitness, rather than serving merely as contamination sources. Whole-genome sequencing also pinpoints high-risk clones (e.g., ST394) and plasmid-mediated co-selection of virulence and AMR. The emergence of hybrid pathotypes (e.g., STEC/ETEC) and AMR-virulence co-selection challenges traditional classification and limits the effectiveness of conventional surveillance approaches. The 2017 colistin ban reduced mcr-1, yet ongoing resistance and emerging tet(X4) demand integrated surveillance. Collectively, these findings call for reconceptualizing E. coli as a dynamic genomic entity embedded within a unified ecological network. Addressing this threat requires an integrated One Health strategy including genomic surveillance, agricultural antimicrobial stewardship, and coordinated food-environment-clinical monitoring to prevent high-risk clone emergence and global spread.

Animals↗

PubMed2026

Variations in carbapenem resistance associated with the VIM-1 metallo-β-lactamase across the Enterobacterales.

The VIM-1 metallo-β-lactamase enzyme, encoded within class 1 integrons, is found in Gram-negative clinical isolates worldwide and has been linked to outbreaks of bacterial pathogens in nosocomial settings. Six vim-1+ clinical isolates, from the genera Escherichia, Klebsiella and Enterobacter, were obtained from Kingston, Ontario, Canada. Whole-genome sequencing revealed that vim-1 was plasmid-borne in all strains and situated as the first gene in In916 or In110 integrons. Analysis of related plasmids suggested that these vim-1-containing plasmids are globally disseminated and have spread via horizontal gene transfer and autochthonous vertical spread within Ontario. Interestingly, the MICs of ertapenem and meropenem, two clinically relevant carbapenem antibiotics, against these six isolates varied more than tenfold, suggesting that the effects of VIM-1 are dependent on the genomic content of the host microbe. Introducing vim-1 into three common Enterobacterales laboratory strains was not sufficient to confer resistance to ertapenem and meropenem. Instead, adaptive laboratory evolution of the vim-1 + laboratory strains revealed that vim-1-mediated carbapenem resistance in these strains was dependent on epistatic interactions with ompC mutations, likely due to decreased outer membrane permeability to these antibiotics. Together, these results provide additional support for the role of gene epistasis in modulating the antimicrobial resistance phenotypes of acquired resistance genes, as well as previous results suggesting that the presence of a β-lactamase gene is insufficient to confer strong resistance to carbapenems without being paired with reduced outer membrane permeability.

beta-Lactamases↗

PubMed2026

Mesorhizobium bavaricum sp. nov. and Mesorhizobium monacense sp. nov., two novel Lotus-associated species harbouring symbiotic plasmids.

Legumes establish a mutualistic interaction with nitrogen-fixing rhizobia. Lotus japonicus is a model for studying this symbiosis; however, only a limited number of rhizobial species nodulating this host have been taxonomically described. Here, we characterise four Mesorhizobium strains (DC-1.1T, Qj1B1, DC-1.5T, and Qj2B2) isolated from root nodules of Lotus japonicus and Lotus burttii. Multi-locus phylogeny and phylogenomic analyses resolved these isolates into two well-supported monophyletic clades. Genome-based comparisons supported their classification as distinct taxa, with strains DC-1.1T and Qj1B1 showing 95.2% average nucleotide identity (ANI) and 62.9-63.5% digital DNA-DNA hybridisation (dDDH) values relative to Mesorhizobium newzealandense ICMP 19545T, whereas DC-1.5T and Qj2B2 exhibited 92.5-92.8% ANI and 49.9-50.5% dDDH compared with Mesorhizobium waimense ICMP 19557T. Together with chemotaxonomic and physiological traits, these data support the proposal of two novel species, Mesorhizobium bavaricum sp. nov. (DC-1.1T and Qj1B1) and Mesorhizobium monacense sp. nov. (DC-1.5T and Qj2B2). Metagenomic analyses predicted high environmental prevalence for these novel taxa, particularly within soil habitats. Isolates DC-1.1T, Qj1B1, and DC-1.5T effectively nodulated Lotus burttii and significantly promoted plant growth, whereas Qj2B2 neither nodulated nor enhanced growth. Comparative genomic analysis revealed that the nodulating isolates harbour symbiotic genes (nod, fix, and nif) on symbiotic plasmids, a rare feature in Mesorhizobium strains, whereas Qj2B2 lacks essential nod and nif genes. Consistent with these genomic features, symbiotaxonomic analysis assigned the nodulating isolates to symbiovar loti. These results highlight the potential of these isolates as models for comparative analyses of symbiotic plasmid evolution and horizontal gene transfer.

Mesorhizobium↗

PubMed2026

Giants within: a new class of microbial mobile elements.

Prokaryotes harbor a diverse spectrum of extrachromosomal elements (ECEs), which are intracellular replicons maintained independently of the primary chromosome. Historically, the ECE research field has focused on relatively small ECEs, such as plasmids. However, the advent of long-read sequencing has revealed that prokaryotes also harbor various types of giant ECEs, spanning hundreds of kilobases to over 1 Mb, that were not hitherto recognized. In this review, we describe how long-read sequencing has enabled the discovery of giant ECEs and compare the genetic architectures and functional repertoires of several recently characterized examples. The functions of most genes in these ECEs remain uncharacterized, and current computational tools frequently misclassify or overlook them. We further discuss how the discovery of these giant ECEs challenges existing classification frameworks that attempt to distinguish megaplasmids, chromids, and chromosomes. Together, these findings highlight giant ECEs as a largely unexplored layer of microbial genetics, whose characterization will have broad implications for our understanding of microbial adaptation and horizontal gene transfer.

Extrachromosomal DNA↗

PubMed2025

Diversity and distribution of the lanthanome in aerobic methane-oxidising bacteria.

BACKGROUND: Lanthanides (Ln) play important and often regulatory roles in the metabolism of methylotrophs, including methanotrophs, particularly through their involvement in methanol oxidation. However, the diversity, distribution, and ecological relevance of Ln-associated proteins (the lanthanome) in aerobic methane-oxidising bacteria (MOB) remain underexplored. This study investigates the lanthanome using genome, plasmid, and proteome data, alongside metatranscriptome data from methane-rich lake sediments. RESULTS: We surveyed 179 genomes spanning Proteobacterial, Verrucomicrobial, and Actinobacterial MOBs to examine the distribution of Ln-dependent methanol dehydrogenases (MDHs) and Ln transport proteins. Distinct lineage-specific patterns were observed: XoxF5 was the most widespread MDH variant in Proteobacteria, while XoxF2 was restricted to Verrucomicrobia. Transporter systems also showed distinct patterns, with LanM restricted to Alphaproteobacteria, LanPepSY and LanA confined to Gammaproteobacteria, and LutH-like receptors broadly distributed across all lineages. Homologues of these genes were also detected on plasmids, indicating potential for horizontal gene transfer. In Lake Washington sediment metatranscriptomes, lanthanome transcripts were detected, with Proteobacteria as dominant contributors. Notably, a large fraction of xoxF transcripts were affiliated with non-MOB Methylophilaceae, consistent with known cooperative interactions with MOB. Using Methylosinus trichosporium OB3b as a model, we assessed methane oxidation and proteomic responses to soluble CeCl3 and a mixed-lanthanide ore. Lag phases were prolonged in the presence of lanthanides, particularly with ore, but methane oxidation rates converged across treatments after acclimation. Proteomic analysis revealed extensive condition-specific responses, with 724 proteins differentially expressed in Ore treatment compared to 60 under CeCl3. XoxF3 and XoxF5 were upregulated while MxaF and its accessory proteins were downregulated, consistent with the "lanthanide switch". Notably, LanM was not expressed despite being encoded, whereas LutH-like receptor was downregulated under both treatments, likely reflecting regulatory control to prevent excess metal uptake. Additional upregulation of a TonB-dependent receptor and ABC transporter suggests a potential lanthanophore-mediated uptake strategy. CONCLUSION: This study highlights the diversity and ecological activity of Ln-binding and transport systems in MOBs, their plasmid localisation and potential mobility, and their distinct regulation under different Ln sources. The strong proteomic response to complex ore underscores the physiological flexibility of MOBs in coping with natural lanthanide forms. These findings provide a framework for ecological studies and candidate targets for biotechnological applications in methane bioconversion and sustainable lanthanide recovery from complex materials.

Horizontal gene transfer↗

PubMed2026

Hypervirulence-associated pseudo-compound transposons as fundamental mobile units driving cross-species virulence dissemination in Enterobacteriaceae.

BACKGROUND: The rapid global spread of hypervirulence in Enterobacteriaceae, particularly in carbapenem-resistant Klebsiella pneumoniae, poses a significant public health threat. However, the key genetic vehicles and mechanisms driving horizontal transfer of hypervirulence-associated genes (iucA, iroB, rmpA, rmpA2, and peg-344) remain poorly defined, limiting effective surveillance. METHODS: We performed a large-scale genomic survey of 2,869 virulence-associated plasmid sequences and 2,337 complete Enterobacteriaceae chromosomes. Using comparative genomics and evolutionary analyses, we systematically identified and characterized Hypervirulence-associated Pseudo-Compound Transposons (Hva-PCTs), defined as structured mobile elements in which hypervirulence-associated genes are flanked by insertion sequences. RESULTS: Our results demonstrate that hypervirulence-associated genes are transmitted primarily as discrete IS-bounded units, which we term Hva-PCTs. We identified 29 distinct plasmid-borne Hva-PCTs (pHva-PCTs) and 30 chromosomal Hva-PCTs (cHva-PCTs). These modules show clear species-specific patterns: iucA/iroB-associated Hva-PCTs mainly originate in Escherichia coli and spread through IncFIB-containing multi-replicon plasmids (commonly combined with IncFIC(FII) and/or IncFII, while rmpA/rmpA2/peg-344-containing modules originate in K. pneumoniae and are disseminated via IncHI1B/repB plasmids. Three Hva-PCTs were detected on both plasmids and chromosomes (xHva-PCTs). In one clinical K. pneumoniae isolate (LS356), the identical composite module was present on both replicons. Simpler sub-modules, such as ISKqu3-rmpA2-iucA_1-IS102 and IS102-rmpA-peg-344-iroB_1-IS1A, frequently co-occur on the same plasmid; when positioned in tandem, they reconstitute the full composite structure. This assembly pattern is further supported by a partial duplication event in plasmid pP901. CD-HIT clustering (80% nucleotide identity and 90% coverage) showed that 13 of 22 major clusters contained both plasmid and chromosomal copies, with intra-cluster identities >80% across multiple sequence types and host species. CONCLUSION: Hypervirulence-associated genes in Enterobacteriaceae are disseminated mainly as IS-flanked Hva-PCTs rather than solely through intact virulence plasmids. These modules exhibit strong but not absolute host specificity. The presence of identical Hva-PCTs on plasmids and chromosomes suggests inter-replicon mobility, while their stepwise assembly from simpler sub-modules highlights modular accretion as a key evolutionary process. Tracking Hva-PCTs as distinct mobile units may complement existing plasmid- and gene-centric surveillance approaches for hypervirulent and convergent strains. Experimental validation of their transposition activity and phenotypic effects is still required.

Virulence↗