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PubMed2025

Global diversity of integrating conjugative elements (ICEs) in Helicobacter pylori and their influence on genome architecture.

Integrating conjugative elements (ICEs) are mobile genetic elements conferring a wide range of beneficial functions upon their bacterial hosts. Generally, they can be activated from their integrated states to undergo horizontal gene transfer via conjugation. In the case of the human gastric pathogen Helicobacter pylori, a paradigm for extensive genetic diversity, highly efficient natural transformation and recombination processes may superimpose canonical transfer of its two ICEs termed ICEHptfs3 and ICEHptfs4, and thus shape their composition substantially. Here, as a part of the Helicobacter pylori Genome Project (HpGP) initiative, we have analyzed high-quality genome sequences from 1011 clinical strains with respect to their ICE content and variability. We show that both elements are highly prevalent in all H. pylori populations, but have a strong tendency for gene erosion. ICE sequence variations reflect the population structure and show a clear signature of increased horizontal transfer. A detailed map of ICE integration sites revealed local preferences, but also how recombination processes result in hybrid elements or genome rearrangements. Population-specific differences in ICE cargo genes might reflect distinct requirements in the biological functions provided by these mobile elements.

Journal Article↗
PubMed2024

It's complicated: relationships between integrative and conjugative elements and their bacterial hosts.

Integrative and conjugative elements (ICEs) are typically found integrated in a bacterial host chromosome. They can excise, replicate, and transfer from cell to cell. Many contain genes that confer phenotypes to host cells, including antibiotic resistances, specialized metabolisms, phage defense, and symbiosis or pathogenesis determinants. Recent studies revealed that at least three ICEs (ICEclc, Tn916, and TnSmu1) cause growth arrest or death of host cells upon element activation. This review highlights the complex interactions between ICEs and their hosts, including the recent examples of the significant costs to host cells. We contrast two examples of killing, ICEclc and Tn916, in which killing, respectively, benefits or impairs conjugation and emphasize the importance of understanding the impacts of ICE-host relationships on conjugation. ICEs are typically only active in a small fraction of cells in a population, and we discuss how phenotypes normally occurring in a small subset of host cells can be uncovered.

Conjugation, Genetic↗
PubMed2025

Activation and modulation of the host response to DNA damage by an integrative and conjugative element.

Mobile genetic elements help drive horizontal gene transfer and bacterial evolution. Conjugative elements and temperate bacteriophages can be stably maintained in host cells. They can alter host physiology and regulatory responses and typically carry genes that are beneficial to their hosts. We found that ICEBs1, an integrative and conjugative element (ICE) of Bacillus subtilis, inhibits the host response to DNA damage (the SOS response). Activation of ICEBs1 before DNA damage reduced host cell lysis that was caused by SOS-mediated activation of two resident prophages. Further, activation of ICEBs1 itself activated the SOS response in a subpopulation of cells, and this activation was attenuated by the functions of the ICEBs1 genes ydcT and yddA (now ramT and ramA; ram for RecA modulator). Double-mutant analyses indicated that RamA functions to inhibit and RamT functions to both inhibit and activate the SOS response. Both RamT and RamA caused a reduction in RecA filaments, one of the early steps in activation of the SOS response. We suspect that there are several different mechanisms by which mobile genetic elements that generate single-stranded DNA (ssDNA) during their life cycle inhibit the host SOS response and RecA function, as RamT and RamA differ from the known SOS inhibitors encoded by conjugative elements.IMPORTANCEBacterial genomes typically contain mobile genetic elements, including bacteriophages (viruses) and integrative and conjugative elements, that affect host physiology. ICEs can excise from the chromosome and undergo rolling-circle replication, producing ssDNA, a signal that indicates DNA damage and activates the host SOS response. We found that following excision and replication, ICEBs1 of B. subtilis stimulates the host SOS response and that ICEBs1 encodes two proteins that limit the extent of this response. These proteins also reduce the amount of cell killing caused by resident prophages following their activation by DNA damage. These proteins are different from those previously characterized that inhibit the host SOS response and represent a new way in which ICEs can affect their host cells.

Bacillus subtilis↗
PubMed2025

The Arms Race Between Actinobacillus pleuropneumoniae and Its Genetic Environment: A Comprehensive Analysis of Its Defensome and Mobile Genetic Elements.

Actinobacillus pleuropneumoniae is the causative agent of pleuropneumonia in swine, a highly contagious and economically significant disease. The genetic variability of A. pleuropneumoniae complicates disease control efforts, as it enables rapid adaptation to various stressors, including antimicrobial treatments. To better understand the molecular mechanisms underlying this adaptability, we investigated the role of the bacterial defensome and its relationship with mobile genetic elements (MGEs), such as prophages, plasmids, and integrative conjugative elements (ICEs). Using bioinformatic tools, we identified a diverse and rich defensome in A. pleuropneumoniae, with an average of 16 different defense systems per strain. We found that CRISPR-Cas systems, along with other defense mechanisms, are actively involved in restricting the entry of foreign genetic material, playing a crucial role in bacterial adaptation. Additionally, we characterized several novel prophages and examined their distribution across different strains, revealing their potential contribution to the bacterium's evolutionary success. Our findings underscore the complex interplay between the bacterium's defense systems and MGEs, shedding light on how A. pleuropneumoniae maintains genetic diversity while also safeguarding itself against external threats. These insights provide a better understanding of the genetic factors that influence the pathogen's adaptability and highlight potential avenues for more effective disease control strategies.

Actinobacillus pleuropneumoniae↗
PubMed2026

Interspecies Exchange of Mobile Genetic Elements During a Plant Disease Outbreak.

Outbreak sequencing provides insight into the origin and evolutionary processes acting on emerging pathogens. Sequencing a historic multihost outbreak of Ralstonia spp. in Martinique shows the outbreak was caused by two lineages that diverged at separate times from mainland populations. One lineage (Ralstonia pseudosolanacearum I-18) was originally introduced from Asia to South America, where it became well established prior to its dissemination to Martinique, where it retains a signature of specialization on solanaceous hosts. The novel lineage first identified during the outbreak (Ralstonia solanacearum IIB-4NPB) arose from a mainland population endemic to the Americas prior to its arrival in Martinique, where host-range expansion was observed. In contrast to minor changes in secreted effector protein repertoires, the emergent R. solanacearum IIB-4NPB acquired a novel integrative and conjugative element (ICERsoRUN1145). After identifying all Ralstonia spp. ICEs and mapping their spatial and phylogenetic distribution among Ralstonia spp. sampled during the outbreak, we found closely related ICEs circulating in mainland populations of R. pseudosolanacearum, indicating likely exchange between introduced and endemic Ralstonia spp. The family of ICEs in Ralstonia (ICERs) has a conserved bipartite structure and display a striking pattern of functional specialization in each cargo gene insertion hotspot: the first hotspot is a target for metabolic gene acquisition, and the second is a target for defense element acquisition. This work provides unparalleled phylogenetic and spatial resolution of an unusual outbreak and highlights the role of horizontal transfer in shaping the ecological success of an emerging pathogen.

Plant Diseases↗
PubMed2026

The Convergence of Antimicrobial Resistance and Virulence in Streptococcus pneumoniae: A Molecular and Clinical Perspective.

Antimicrobial resistance (AMR) and virulence have traditionally been viewed as competing traits in bacterial evolution due to fitness costs. However, Streptococcus pneumoniae has emerged as a paradigm of successful coevolution, with multidrug-resistant clones simultaneously maintaining or enhancing pathogenic potential. This review examines the molecular mechanisms, epidemiological patterns, and clinical consequences of the convergence between AMR and virulence in Streptococcus pneumoniae. Resistance to β-lactams is driven by mosaic penicillin-binding protein genes (pbp1a, pbp2b, pbp2x), while macrolide resistance is mediated primarily by the erm(B) gene (MLS phenotype) and mef(A/E)-msr(D) genes encoding an efflux system. These determinants are frequently co-localized on integrative and conjugative elements, ICEs, (e.g., Tn916 family) within successful clonal complexes such as CC271/320 and lineages including ST320 and GPSC10. Contrary to the classical fitness cost hypothesis, compensatory epistasis, capsular recombination, metabolic adaptations, and intra-serotype phenotypic variation enable certain clones to combine high-level resistance to β-lactams, macrolides, and tetracyclines with enhanced colonization, biofilm formation, immune evasion, and invasive capacity. Post-pneumococcal conjugate vaccine (PCV) surveillance reveals the persistence and expansion of these high-risk lineages, contributing to treatment-refractory invasive pneumococcal disease (IPD), increased morbidity, and mortality. Although PCVs have reduced vaccine-type resistant strains in some settings, serotype replacement and emerging metabolic genotypes continue to drive adaptation. This review highlights the need for integrated genomic surveillance, novel therapeutics (e.g., omadacycline, lefamulin, endolysins), monoclonal antibodies, and next-generation vaccines targeting both resistance and conserved virulence determinants. A multifaceted strategy combining antimicrobial stewardship, strengthened surveillance, and innovative interventions is essential to curb the evolving threat of resistant and virulent S. pneumoniae.

Streptococcus pneumoniae↗
PubMed2026

Optimizing a culture-enriched hybrid metagenomics pipeline to assess the AMR footprint of livestock manure in anaerobic digestate.

The role of environmental samples from livestock production systems, including manure and anaerobic digestate, as reservoirs of antimicrobial resistance genes (ARGs) is likely underestimated because conventional metagenomic approaches can overlook low-abundance ARGs and often lack the resolution to associate these genes with their microbial hosts and co-localized mobile genetic elements (MGEs). We evaluated whether culture-enriched metagenomics (CEMG), with and without antibiotic selection, enhances ARG detection in anaerobic digestate and improves the resolution of ARG-MGE-host associations using hybrid short- and long-read metagenomic assembly. CEMG increased ARG recovery; mean ARG abundance rose from 15.4 counts per million (CPM) in metagenomic fresh digestate (FD) to 124 CPM in CEMG without antibiotics and 160 CPM in antibiotic-selective CEMG. In FD, only 9 unique ARGs were detected, whereas CEMG recovered 112, including ARGs of clinical importance, such as glycopeptide resistance, beta-lactamase genes, and the cfr 23S rRNA methyltransferase conferring cross-resistance to multiple antibiotic classes. Antibiotic selection induced targeted, class-specific shifts in ARG profiles, with ARGs associated with tetracycline resistance consistently enriched across treatments. Hybrid metagenomic assembly resolved the genomic context of 784 ARGs, of which 59.3% were co-localized with at least one class of MGEs, predominantly plasmids and integrative conjugative elements/integrative mobilizable elements. Biocide and metal resistance genes frequently co-occurred with ARGs on the same contigs. Together, these findings demonstrate that antibiotic-selective culture enrichment enhances resistome surveillance by improving detection of low-abundance ARGs, while hybrid assembly provides critical genomic context for assessing their mobility and host associations.IMPORTANCELivestock manure and its byproducts, such as anaerobic digestate, are recognized as important environmental reservoirs of antimicrobial resistance genes (ARGs) and resistant bacteria, yet current metagenomic approaches may underestimate this risk by failing to detect low-abundance but clinically relevant ARGs. Here, we show that integrating culture enrichment with hybrid metagenomics improves ARG recovery and reveals ARG co-localization with mobile genetic elements and putative bacterial hosts. This approach captures a cultivable and condition-responsive fraction of the resistome that is not readily accessible through direct metagenomic sequencing alone, providing a more informative framework for environmental AMR surveillance.

anaerobic digestion↗
PubMed2026

Complete genome of multiply antibiotic resistant ST10 Acinetobacter baumannii isolate NL6 from Vietnam and relationship to available ST10 genomes.

The genome of NL6, a multiply antibiotic-resistant Acinetobacter baumannii ST10:KL49:OCL2 carriage isolate from Vietnam, was sequenced using Nanopore technology, and complete chromosome and plasmid sequences were assembled from the long reads and available short reads. Resistance genes and their locations were identified, and transfer of a conjugative plasmid carrying several resistance genes into a new host was tested. The acquired resistance genes in NL6 were distributed between the chromosome and two of three plasmids present. The chromosome carries multiple copies of several insertion sequences, an incomplete copy of the ISAba1-bounded Tn6250 that includes the sul2 and strAB genes, and an integrative element carrying copper resistance genes designated IECuR. Plasmid pNL6-2 (r3-T5; 15 Kbp) is a Rep_3/OrfX plasmid that includes a tet39 dif module, and pNL6-3 (r3-T20; 66.9 Kbp) carries aacC2d, aphA6, and blaCARB-16 and a second ampC gene preceded by an ISAba1. Conjugation of pNL6-3 into derivatives of ATCC17978 was demonstrated, confirming that the ampC gene confers resistance to third-generation cephalosporins. NL6 was compared to other complete ST10 genomes. Several acquired elements in the chromosome were shared with the ST10 isolate LAC-4 (USA), indicating shared ancestry, but the plasmid content differed. The KL and plasmid content were variable in 17 further complete ST10 genomes downloaded from GenBank. Tn6250 and IECuR were only found together in the chromosome of two further KL49 isolates. Antibiotic resistance in ST10 A. baumannii was acquired mainly via plasmid acquisition, but resistance genes varied, and a variety of plasmids was involved.IMPORTANCEMembers of the CC10 clonal complex of Acinetobacter baumannii comprising ST10 plus single and double locus variants are known to be particularly virulent. However, antibiotic resistance in members of this group has rarely been examined. Here, determination of the complete genome (chromosome and plasmids) of a representative ST10 isolate from Vietnam allowed the context and location of acquired antibiotic resistance genes and of other mobile genetic elements to be determined. Mobile genetic element locations in completed chromosomes facilitate comparisons of potentially related genomes, revealing those with recent shared ancestry. Differences in plasmid content can also be examined.

Acinetobacter baumannii↗
PubMed2026

Characteristics of an NDM-1-producing Klebsiella pneumoniae strain belonging to ST105.

Uncommon multilocus sequence types (MLSTs) of NDM-producing Klebsiella pneumoniae may pose a significant threat to patients, although they are often overlooked in surveillance studies. Characterizing these isolates is therefore important for infection control. In this study, the antimicrobial susceptibility and pathogenicity of K. pneumoniae strain KP_WXD, pertaining to the atypical sequence type ST105, were evaluated, including capsular polysaccharide (CPS) production, biofilm formation, and resistance to serum killing. Whole-genome sequencing (WGS) was performed to analyze its genomic features. K. pneumoniae KP_WXD strain was resistant to all tested β-lactam agents. Its virulence was lower than that of K. pneumoniae strains ST11-KL64 and NTUH-k2044 used as references, while its biofilm formation ability was stronger than that of both strains. WGS analysis revealed carriage of IncF and IncN plasmids carrying multiple antibiotic resistance genes, alongside blaNDM-1 and blaCTX-M, integrated into well-characterized mobile genetic elements. Moreover, both blaNDM-1 and blaCTX-M-harboring plasmids were transferable to E. coli J53 by conjugation without significant fitness cost on the recipient strain.

Klebsiella pneumoniae↗
PubMed2026

Genome-Wide Characterization of β-Glucosidase (TaBGLU) Genes in Bread Wheat and Their Expression Under Drought, Cold, and Combined Stress.

Glycoside hydrolase 1 (GH1) β-glucosidases were known to activate hormone conjugates and defense metabolites, yet their genomic organization and stress-response dynamics in wheat remained incompletely defined. We therefore performed an integrated characterization of TaBGLUs spanning phylogeny, gene structure and conserved motifs, subcellular localization, promoter cis-elements, Gene Ontology enrichment, protein-protein interaction networks, and targeted expression profiling. Wheat TaBGLUs partitioned into well-supported clades that shared canonical GH1 catalytic residues and a largely conserved motif scaffold. Subcellular localization predictions indicated predominant nuclear and chloroplast targeting, with a smaller cohort directed to secretory or endomembrane compartments. Promoters were enriched for light-responsive, hormone-related (ABA, JA/SA, auxin, GA) and stress-associated (MYB/WRKY, heat, low temperature) cis-elements, and functional annotations were consistent with roles in carbohydrate and cell-wall metabolism, hormone homeostasis, and defense. Network analysis revealed a densely connected TaBGLU submodule embedded within broader carbohydrate and defense interaction networks, suggesting coordinated or cooperative functions. Expression profiling under cold, drought, and combined drought and cold demonstrated broad stress inducibility, with early activation detected by 6 h, cold-responsive maxima typically at 12 h, drought-responsive peaks predominating at 24 h, and combined stress eliciting both earlier and more sustained expression maxima between 12-24 h. Representative strongly responsive genes included TaBGLU20, TaBGLU44, TaBGLU6, and TaBGLU23, which showed pronounced late induction under combined stress, TaBGLU30, which exhibited an earlier combined-stress peak, and TaBGLU12, which displayed a marked late drought-specific response. Taken together, this integrated genomic, regulatory, and expression atlas refined the wheat BGLU repertoire relative to previous gene model inventories, highlighted candidate TaBGLUs with central network positions and strong stress inducibility, and provided concrete entry points for functional validation and breeding for improved stress resilience.

Triticum↗
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

Global lessons from antibiotic resistance: Metformin-hydrolysing genes in transposable elements, a new threat for type II diabetic patients?

OBJECTIVES: To investigate the evolutionary origin, genomic mobility, and potential dissemination of metformin-hydrolysing genes (mfmAB), and to assess whether environmental selection by metformin pollution may drive the emergence of transferable pharmaceutical-degrading traits analogous to antibiotic resistance. METHODS: Large-scale comparative genomics was performed using publicly available bacterial genomes carrying mfmAB homologs. Phylogenomic reconstruction, average nucleotide identity analysis, genomic context comparison, plasmid characterization, and insertion sequence mapping were used to infer evolutionary history and identify mechanisms of horizontal gene transfer. RESULTS: mfmAB homologs were identified in twelve Aminobacter and three Pseudomonas genomes within a conserved ∼8.2 kb gene cluster. Phylogenomic analyses showed that metformin-degrading capacity emerged independently in multiple Aminobacter lineages across distinct continents, consistent with convergent evolution under anthropogenic selective pressure. Genomic comparisons indicated a chromosomal origin of mfmAB, followed by mobilization onto conjugative plasmids through IS1182-mediated transposition. In Pseudomonas, additional IS3/IS6-mediated transposition events integrated mfmAB into diverse plasmid backbones, frequently within composite transposons also encoding guanylurea and biguanide degradation pathways (guuH, bguH). These findings reveal a dynamic modular assembly of metabolic functions facilitating adaptation to pharmaceutical pollutants. CONCLUSIONS: Metformin pollution appears to promote the emergence and mobilization of pharmaceutical-degrading genes through mechanisms paralleling antibiotic resistance evolution. Although no clinical impact has yet been demonstrated, the potential spread of such genes into human-associated microbiomes and their possible co-selection with antibiotic resistance determinants represent an emerging One Health concern. Environmental surveillance of pharmaceutical-degrading genes is warranted to anticipate future threats to drug efficacy.

Convergent evolution↗
PubMed2026

Transferable IncHI2-Associated blaLAP-2 and blaCTX-M-55 Resistance Platforms in Foodborne Salmonella.

Extended-spectrum β-lactamase genes in foodborne Salmonella enterica can disseminate through mobile multidrug-resistance platforms. IncHI2 plasmids are important resistance vehicles capable of carrying complex resistance regions and facilitating their horizontal transfer across diverse bacterial backgrounds, but the transfer and genomic organization of IncHI2 elements co-carrying blaLAP-2 and blaCTX-M-55 remain insufficiently characterized. This study investigated two multidrug-resistant foodborne isolates recovered in Shanghai in 2022: Salmonella Agona ST13 isolate Sal22C150 and Salmonella Havana ST1527 isolate Sal22P208. Antimicrobial susceptibility testing, whole-genome sequencing, conjugation, plasmid-retention analysis, comparative genomics, as well as strain- and plasmid-level phylogenetic analyses were performed. Both isolates exhibited broad antimicrobial resistance, including resistance to extended-spectrum cephalosporins. In both isolates, blaLAP-2 and blaCTX-M-55 co-transferred with the IncHI2 replicon to Escherichia coli J53 at frequencies of (4.95 ± 0.41) × 10-5 and (4.46 ± 0.42) × 10-6 transconjugants per donor cell, respectively. All tested plasmid markers remained detectable through 20 passages without antimicrobial selection. Complete assembly of Sal22P208 confirmed the location of the three β-lactamase genes on the 275,096 bp IncHI2 plasmid pSal22P208. The plasmid contained a conserved conjugative backbone and mosaic accessory regions carrying 15 antimicrobial-resistance determinants together with mercury- and tellurium-resistance loci. SNP-based analysis placed pSal22P208 within a closely related cluster containing six reference IncHI2 plasmids differing by fewer than 30 SNPs and recovered from Salmonella and E. coli of animal, food, and human origin, suggesting a broad distribution of this plasmid lineage across diverse bacterial and ecological backgrounds. Sal22P208 additionally contained a Tn3-associated chromosomal multidrug-resistance region between rpmJ and rpmE that shared extensive structural similarity with a region in Citrobacter braakii LBA3. These findings highlight the role of transferable IncHI2 resistance platforms in the horizontal dissemination and short-term post-transfer maintenance of linked resistance determinants, while chromosomally integrated resistance regions may provide an additional route for the accumulation and inheritance of multidrug resistance in foodborne Salmonella.

IncHI2 plasmid↗