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Radhey S. Gupta – One of the best experts on this subject based on the ideXlab platform.

  • Protein Signatures Distinctive of Alpha Proteobacteria and Its Subgroups and a Model for α –Proteobacterial Evolution
    Critical Reviews in Microbiology, 2020
    Co-Authors: Radhey S. Gupta
    Abstract:

    Alpha (α) Proteobacteria comprise a large and metabolically diverse group. No biochemical or molecular feature is presently known that can distinguish these bacteria from other groups. The evolutionary relationships among this group, which includes numerous pathogens and agriculturally important microbes, are also not understood. Shared conserved inserts and deletions (i.e., indels or signatures) in molecular sequences provide a powerful means for identification of different groups in clear terms, and for evolutionary studies (see www.bacterialphylogeny.com). This review describes, for the first time, a large number of conserved indels in broadly distributed proteins that are distinctive and unifying characteristics of either all α −Proteobacteria, or many of its constituent subgroups (i.e., orders, families, etc.). These signatures were identified by systematic analyses of proteins found in the Rickettsia prowazekii(RP) genome. Conserved indels that are unique to α −Proteobacteria are present in the foll…

  • Phylogenomics and signature proteins for the alpha Proteobacteria and its main groups
    BMC Microbiology, 2007
    Co-Authors: Radhey S. Gupta, Amy Mok
    Abstract:

    BackgroundAlpha Proteobacteria are one of the largest and most extensively studied groups within bacteria. However, for these bacteria as a whole and for all of its major subgroups (viz. Rhizobiales, Rhodobacterales, Rhodospirillales, Rickettsiales, Sphingomonadales and Caulobacterales), very few or no distinctive molecular or biochemical characteristics are known.ResultsWe have carried out comprehensive phylogenomic analyses by means of Blastp and PSI-Blast searches on the open reading frames in the genomes of several α-Proteobacteria (viz. Bradyrhizobium japonicum, Brucella suis, Caulobacter crescentus, Gluconobacter oxydans, Mesorhizobium loti, Nitrobacter winogradskyi, Novosphingobium aromaticivorans, Rhodobacter sphaeroides 2.4.1, Silicibacter sp. TM1040, Rhodospirillum rubrum and Wolbachia (Drosophila) endosymbiont). These studies have identified several proteins that are distinctive characteristics of all α-Proteobacteria, as well as numerous proteins that are unique repertoires of all of its main orders (viz. Rhizobiales, Rhodobacterales, Rhodospirillales, Rickettsiales, Sphingomonadales and Caulobacterales) and many families (viz. Rickettsiaceae, Anaplasmataceae, Rhodospirillaceae, Acetobacteraceae, Bradyrhiozobiaceae, Brucellaceae and Bartonellaceae). Many other proteins that are present at different phylogenetic depths in α-Proteobacteria provide important information regarding their evolution. The evolutionary relationships among α-Proteobacteria as deduced from these studies are in excellent agreement with their branching pattern in the phylogenetic trees and character compatibility cliques based on concatenated sequences for many conserved proteins. These studies provide evidence that the major groups within α-Proteobacteria have diverged in the following order: (Rickettsiales(Rhodospirillales (Sphingomonadales (Rhodobacterales (Caulobacterales-Parvularculales (Rhizobiales)))))). We also describe two conserved inserts in DNA Gyrase B and RNA polymerase beta subunit that are distinctive characteristics of the Sphingomonadales and Rhodosprilllales species, respectively. The results presented here also provide support for the grouping of Hyphomonadacea e and Parvularcula species with the Caulobacterales and the placement of Stappia aggregata with the Rhizobiaceae group.ConclusionThe α-Proteobacteria-specific proteins and indels described here provide novel and powerful means for the taxonomic, biochemical and molecular biological studies on these bacteria. Their functional studies should prove helpful in identifying novel biochemical and physiological characteristics that are unique to these bacteria.

  • phylogenomics and signature proteins for the alpha Proteobacteria and its main groups
    BMC Microbiology, 2007
    Co-Authors: Radhey S. Gupta
    Abstract:

    Alpha Proteobacteria are one of the largest and most extensively studied groups within bacteria. However, for these bacteria as a whole and for all of its major subgroups (viz. Rhizobiales, Rhodobacterales, Rhodospirillales, Rickettsiales, Sphingomonadales and Caulobacterales), very few or no distinctive molecular or biochemical characteristics are known. We have carried out comprehensive phylogenomic analyses by means of Blastp and PSI-Blast searches on the open reading frames in the genomes of several α-Proteobacteria (viz. Bradyrhizobium japonicum, Brucella suis, Caulobacter crescentus, Gluconobacter oxydans, Mesorhizobium loti, Nitrobacter winogradskyi, Novosphingobium aromaticivorans, Rhodobacter sphaeroides 2.4.1, Silicibacter sp. TM1040, Rhodospirillum rubrum and Wolbachia (Drosophila) endosymbiont). These studies have identified several proteins that are distinctive characteristics of all α-Proteobacteria, as well as numerous proteins that are unique repertoires of all of its main orders (viz. Rhizobiales, Rhodobacterales, Rhodospirillales, Rickettsiales, Sphingomonadales and Caulobacterales) and many families (viz. Rickettsiaceae, Anaplasmataceae, Rhodospirillaceae, Acetobacteraceae, Bradyrhiozobiaceae, Brucellaceae and Bartonellaceae). Many other proteins that are present at different phylogenetic depths in α-Proteobacteria provide important information regarding their evolution. The evolutionary relationships among α-Proteobacteria as deduced from these studies are in excellent agreement with their branching pattern in the phylogenetic trees and character compatibility cliques based on concatenated sequences for many conserved proteins. These studies provide evidence that the major groups within α-Proteobacteria have diverged in the following order: (Rickettsiales(Rhodospirillales (Sphingomonadales (Rhodobacterales (Caulobacterales-Parvularculales (Rhizobiales)))))). We also describe two conserved inserts in DNA Gyrase B and RNA polymerase beta subunit that are distinctive characteristics of the Sphingomonadales and Rhodosprilllales species, respectively. The results presented here also provide support for the grouping of Hyphomonadacea e and Parvularcula species with the Caulobacterales and the placement of Stappia aggregata with the Rhizobiaceae group. The α-Proteobacteria-specific proteins and indels described here provide novel and powerful means for the taxonomic, biochemical and molecular biological studies on these bacteria. Their functional studies should prove helpful in identifying novel biochemical and physiological characteristics that are unique to these bacteria.

Dmitry A Rodionov – One of the best experts on this subject based on the ideXlab platform.

  • novel metabolic pathways and regulons for hexuronate utilization in Proteobacteria
    Journal of Bacteriology, 2018
    Co-Authors: J T Bouvier, Dmitry A Rodionov, Natalia V Sernova, Salehe Ghasempur, Irina A Rodionova, M W Vetting, Nawar Alobaidi, S C Almo, J A Gerlt
    Abstract:

    ABSTRACT We used comparative genomics to reconstruct d-galacturonic and d-glucuronic acid catabolic pathways and associated transcriptional regulons involving the tripartite ATP-independent periplasmic (TRAP) family transporters that bind hexuronates in Proteobacteria. The reconstructed catabolic network involves novel transcription factors, catabolic enzymes, and transporters for utilization of both hexuronates and aldarates (d-glucarate and meso-galactarate). The reconstructed regulons for a novel GntR family transcription factor, GguR, include the majority of hexuronate/aldarate utilization genes in 47 species from the Burkholderiaceae, Comamonadaceae, Halomonadaceae, and Pseudomonadaceae families. GudR, GulR, and UdhR are additional local regulators of some hexuronate/aldarate utilization genes in some of the above-mentioned organisms. The predicted DNA binding motifs of GguR and GudR regulators from Ralstonia pickettii and Polaromonas were validated by in vitro binding assays. Genes from the GulR- and GguR-controlled loci were differentially expressed in R. pickettii grown on hexuronates and aldarates. By a combination of bioinformatics and experimental techniques we identified a novel variant of the oxidative pathway for hexuronate utilization, including two previously uncharacterized subfamilies of lactone hydrolases (UxuL and UxuF). The genomic context of respective genes and reconstruction of associated pathways suggest that both enzymes catalyze the conversion of d-galactaro- and d-glucaro-1,5-lactones to the ring-opened aldarates. The activities of the purified recombinant enzymes, UxuL and UxuF, from four Proteobacterial species were directly confirmed and kinetically characterized. The inferred novel aldarate-specific transporter from the tripartite tricarboxylate transporter (TTT) family transporter TctC was confirmed to bind d-glucarate in vitro. This study expands our knowledge of bacterial carbohydrate catabolic pathways by identifying novel families of catabolic enzymes, transcriptional regulators, and transporters. IMPORTANCE Hexuronate catabolic pathways and their transcriptional networks are highly variable among different bacteria. We identified novel transcriptional regulators that control the hexuronate and aldarate utilization genes in four families of Proteobacteria. By regulon reconstruction and genome context analysis we identified several novel components of the common hexuronate/aldarate utilization pathways, including novel uptake transporters and catabolic enzymes. Two novel families of lactonases involved in the oxidative pathway of hexuronate catabolism were characterized. Novel transcriptional regulons were validated via in vitro binding assays and gene expression studies with Polaromonas and Ralstonia species. The reconstructed catabolic pathways are interconnected with each other metabolically and coregulated via the GguR regulons in Proteobacteria.

  • Comparative Genomics of Transcriptional Regulation of Methionine Metabolism in Proteobacteria
    PLOS ONE, 2014
    Co-Authors: Semen A Leyn, Mikhail S. Gelfand, Inna A. Suvorova, Tatiana D. Kholina, Sofia S. Sherstneva, Pavel S. Novichkov, Dmitry A Rodionov
    Abstract:

    Methionine metabolism and uptake genes in Proteobacteria are controlled by a variety of RNA and DNA regulatory systems. We have applied comparative genomics to reconstruct regulons for three known transcription factors, MetJ, MetR, and SahR, and three known riboswitch motifs, SAH, SAM-SAH, and SAM_alpha, in ∼200 genomes from 22 taxonomic groups of Proteobacteria. We also identified two novel regulons: a SahR-like transcription factor SamR controlling various methionine biosynthesis genes in the Xanthomonadales group, and a potential RNA regulatory element with terminator-antiterminator mechanism controlling the metX or metZ genes in beta-Proteobacteria. For each analyzed regulator we identified the core, taxon-specific and genome-specific regulon members. By analyzing the distribution of these regulators in bacterial genomes and by comparing their regulon contents we elucidated possible evolutionary scenarios for the regulation of the methionine metabolism genes in Proteobacteria.

  • n acetylgalactosamine utilization pathway and regulon in Proteobacteria genomic reconstruction and experimental characterization in shewanella
    Journal of Biological Chemistry, 2012
    Co-Authors: Semen A Leyn, Dmitry A Rodionov, Chen Yang
    Abstract:

    Abstract We used a comparative genomics approach to reconstruct the N-acetyl-D-galactosamine (Aga) and galactosamine (Gam) utilization pathways and transcriptional regulons in Proteobacteria. The reconstructed Aga/Gam utilization pathways include multiple novel genes with specific functional roles. Most of the pathway variations were attributed to the amino sugar transport, phosphorylation, and deacetylation steps, whereas the downstream catabolic enzymes in the pathway were largely conserved. The predicted Aga kinase AgaK, the novel variant of Aga-6-P deacetylase AgaA-II and the Gam-6-P deaminase AgaS from Shewanella sp. ANA-3 were validated in vitro using individual enzymatic assays and reconstitution of the three-step pathway. By using genetic techniques, we confirmed that AgaS but not AgaI functions as the main Gam-6-P deaminase in the Aga/Gam utilization pathway in Escherichia coli. Regulons controlled by AgaR repressors were reconstructed by bioinformatics in most Proteobacterial genomes encoding Aga pathways. Candidate AgaR binding motifs share a common sequence with consensus CTTTC that was found in multiple copies and arrangements in regulatory regions of aga genes. This study provides comprehensive insights into the common and distinctive features of the Aga/Gam catabolism and its regulation in diverse Proteobacteria.

Rudolf I. Amann – One of the best experts on this subject based on the ideXlab platform.

  • Archaea-Like Genes for C_1-Transfer Enzymes in Planctomycetes: Phylogenetic Implications of Their Unexpected Presence in This Phylum
    Journal of Molecular Evolution, 2004
    Co-Authors: Margarete Bauer, Rudolf I. Amann, Thierry Lombardot, Hanno Teeling, Naomi L. Ward, Frank O. Glöckner
    Abstract:

    The unexpected presence of archaea-like genes for tetrahydromethanopterin (H_4MPT)-dependent enzymes in the completely sequenced genome of the aerobic marine planctomycete Pirellula sp. strain 1 (“ Rhodopirellula baltica ”) and in the currently sequenced genome of the aerobic freshwater planctomycete Gemmata obscuriglobus strain UQM2246 revives the discussion on the origin of these genes in the bacterial domain. We compared the genomic arrangement of these genes in Planctomycetes and methylotrophic Proteobacteria and performed a phylogenetic analysis of the encoded protein sequences to address the question whether the genes have been present in the common ancestor of Bacteria and Archaea or were transferred laterally from the archaeal to the bacterial domain and therein. Although this question could not be solved using the data presented here, some constraints on the evolution of the genes involved in archaeal and bacterial H_4MPT-dependent C_1-transfer may be proposed: (i) lateral gene transfer (LGT) from Archaea to a common ancestor of Proteobacteria and Planctomycetes seems more likely than the presence of the genes in the common ancestor of Bacteria and Archaea ; (ii) a single event of interdomain LGT can be favored over two independent events; and (iii) the archaeal donor of the genes might have been a representative of the Methanosarcinales . In the bacterial domain, the acquired genes evolved according to distinct environmental and metabolic constraints, reflected by specific rearrangements of gene order, gene recruitment, and gene duplication, with subsequent functional specialization. During the course of evolution, genes were lost from some planctomycete genomes or replaced by orthologous genes from Proteobacterial lineages.

  • Predominance of β‐Proteobacteria in summer melt pools on Arctic pack ice
    Limnology and Oceanography, 2004
    Co-Authors: Robin Brinkmeyer, Frank Oliver Glöckner, Elisabeth Helmke, Rudolf I. Amann
    Abstract:

    The diversity and community structure of bacteria in melt pools on Arctic pack ice floes were dominated by bProteobacteria. Thirty-five percent of the pure cultures isolated in 1997 from pack ice floes north of Svalbard and in the Fram Strait were from the b-Proteobacteria group. Within this group, there were only two phylotypes clustering within the widespread Beta I cluster, also known as the Comamonadaceae clade. One phylotype, most closely related to Aquaspirillum arcticum(96.0‐97.3% identical), was frequent among cultures isolated from 10 melt pools. A 16S riboribosomal RNA (rRNA) gene clone library, constructed from a melt pool that was sampled 2 yr later in the Fram Strait, was also dominated by b-Proteobacteria, in particular the same recurrent isolate phylotype designated ‘‘MP-BetaI’’. Fluorescence in situ hybridization of 20 melt pools corroborated the cultivation and cloning data. bProteobacteria were the most abundant bacterial group, constituting ;49% of the bacteria that were stained by 496diamidino-2-phenylindole (DAPI). a- and g-Proteobacteria accounted for only 2% each, the Cytophaga‐Flavobacterium group accounted for 9%, and the Actinobacteria spp. accounted for 9%. Approximately 63% of the b-Proteobacterial fraction that was found in the melt pools was determined with a newly developed probe to be the recurrent b-Proteobacterial MP-BetaI phylotypes, indicating that it is particularly adapted for success in this extreme environment.

  • Flow sorting of marine bacterioplankton after fluorescence in situ hybridization
    Applied and Environmental Microbiology, 2004
    Co-Authors: Ramanan Sekar, B M Fuchs, Rudolf I. Amann, Jakob Pernthaler
    Abstract:

    We describe an approach to sort cells from coastal North Sea bacterioplankton by flow cytometry after in situ hybridization with rRNA-targeted horseradish peroxidase-labeled oligonucleotide probes and catalyzed fluorescent reporter deposition (CARD-FISH). In a sample from spring 2003 >90% of the cells were detected by CARD-FISH with a bacterial probe (EUB338). Approximately 30% of the microbial assemblage was affiliated with the Cytophaga-Flavobacterium lineage of the Bacteroidetes (CFB group) (probe CF319a), and almost 10% was targeted by a probe for the β-Proteobacteria (probe BET42a). A protocol was optimized to detach cells hybridized with EUB338, BET42a, and CF319a from membrane filters (recovery rate, 70%) and to sort the cells by flow cytometry. The purity of sorted cells was >95%. 16S rRNA gene clone libraries were constructed from hybridized and sorted cells (S-EUB, S-BET, and S-CF libraries) and from unhybridized and unsorted cells (UNHYB library). Sequences related to the CFB group were significantly more frequent in the S-CF library (66%) than in the UNHYB library (13%). No enrichment of β-Proteobacterial sequence types was found in the S-BET library, but novel sequences related to Nitrosospira were found exclusively in this library. These bacteria, together with members of marine clade OM43, represented >90% of the β-Proteobacteria in the water sample, as determined by CARD-FISH with specific probes. This illustrates that a combination of CARD-FISH and flow sorting might be a powerful approach to study the diversity and potentially the activity and the genomes of different bacterial populations in aquatic habitats.

Christophe Carnoy – One of the best experts on this subject based on the ideXlab platform.

  • the dif xer recombination systems in Proteobacteria
    PLOS ONE, 2009
    Co-Authors: Christophe Carnoy, Claudealain H Roten
    Abstract:

    In E. coli, 10 to 15% of growing bacteria produce dimeric chromosomes during DNA replication. These dimers are resolved by XerC and XerD, two tyrosine recombinases that target the 28-nucleotide motif (dif) associated with the chromosome’s replication terminus. In streptococci and lactococci, an alternative system is composed of a unique, Xer-like recombinase (XerS) genetically linked to a dif-like motif (difSL) located at the replication terminus. Preliminary observations have suggested that the dif/Xer system is commonly found in bacteria with circular chromosomes but that assumption has not been confirmed in an exhaustive analysis. The aim of the present study was to extensively characterize the dif/Xer system in the Proteobacteria, since this taxon accounts for the majority of genomes sequenced to date. To that end, we analyzed 234 chromosomes from 156 Proteobacterial species and showed that most species (87.8%) harbor XerC and XerD-like recombinases and a dif-related sequence which (i) is located in non-coding sequences, (ii) is close to the replication terminus (as defined by the cumulative GC skew) (iii) has a palindromic structure, (iv) is encoded by a low G+C content and (v) contains a highly conserved XerD binding site. However, not all Proteobacteria display this dif/XerCD system. Indeed, a sub-group of pathogenic e-Proteobacteria (including Helicobacter sp and Campylobacter sp) harbors a different recombination system, composed of a single recombinase (XerH) which is phylogenetically distinct from the other Xer recombinases and a motif (difH) sharing homologies with difSL. Furthermore, no homologs to dif or Xer recombinases could be detected in small endosymbiont genomes or in certain bacteria with larger chromosomes like the Legionellales. This raises the question of the presence of other chromosomal deconcatenation systems in these species. Our study highlights the complexity of dif/Xer recombinase systems in Proteobacteria and paves the way for systematic detection of these components in prokaryotes.

  • The dif/Xer recombination systems in Proteobacteria.
    PLOS ONE, 2009
    Co-Authors: Christophe Carnoy, Claudealain H Roten
    Abstract:

    In E. coli, 10 to 15% of growing bacteria produce dimeric chromosomes during DNA replication. These dimers are resolved by XerC and XerD, two tyrosine recombinases that target the 28-nucleotide motif (dif) associated with the chromosome’s replication terminus. In streptococci and lactococci, an alternative system is composed of a unique, Xer-like recombinase (XerS) genetically linked to a dif-like motif (difSL) located at the replication terminus. Preliminary observations have suggested that the dif/Xer system is commonly found in bacteria with circular chromosomes but that assumption has not been confirmed in an exhaustive analysis. The aim of the present study was to extensively characterize the dif/Xer system in the Proteobacteria, since this taxon accounts for the majority of genomes sequenced to date. To that end, we analyzed 234 chromosomes from 156 Proteobacterial species and showed that most species (87.8%) harbor XerC and XerD-like recombinases and a dif-related sequence which (i) is located in non-coding sequences, (ii) is close to the replication terminus (as defined by the cumulative GC skew) (iii) has a palindromic structure, (iv) is encoded by a low G+C content and (v) contains a highly conserved XerD binding site. However, not all Proteobacteria display this dif/XerCD system. Indeed, a sub-group of pathogenic e-Proteobacteria (including Helicobacter sp and Campylobacter sp) harbors a different recombination system, composed of a single recombinase (XerH) which is phylogenetically distinct from the other Xer recombinases and a motif (difH) sharing homologies with difSL. Furthermore, no homologs to dif or Xer recombinases could be detected in small endosymbiont genomes or in certain bacteria with larger chromosomes like the Legionellales. This raises the question of the presence of other chromosomal deconcatenation systems in these species. Our study highlights the complexity of dif/Xer recombinase systems in Proteobacteria and paves the way for systematic detection of these components in prokaryotes.

Claudealain H Roten – One of the best experts on this subject based on the ideXlab platform.

  • the dif xer recombination systems in Proteobacteria
    PLOS ONE, 2009
    Co-Authors: Christophe Carnoy, Claudealain H Roten
    Abstract:

    In E. coli, 10 to 15% of growing bacteria produce dimeric chromosomes during DNA replication. These dimers are resolved by XerC and XerD, two tyrosine recombinases that target the 28-nucleotide motif (dif) associated with the chromosome’s replication terminus. In streptococci and lactococci, an alternative system is composed of a unique, Xer-like recombinase (XerS) genetically linked to a dif-like motif (difSL) located at the replication terminus. Preliminary observations have suggested that the dif/Xer system is commonly found in bacteria with circular chromosomes but that assumption has not been confirmed in an exhaustive analysis. The aim of the present study was to extensively characterize the dif/Xer system in the Proteobacteria, since this taxon accounts for the majority of genomes sequenced to date. To that end, we analyzed 234 chromosomes from 156 Proteobacterial species and showed that most species (87.8%) harbor XerC and XerD-like recombinases and a dif-related sequence which (i) is located in non-coding sequences, (ii) is close to the replication terminus (as defined by the cumulative GC skew) (iii) has a palindromic structure, (iv) is encoded by a low G+C content and (v) contains a highly conserved XerD binding site. However, not all Proteobacteria display this dif/XerCD system. Indeed, a sub-group of pathogenic e-Proteobacteria (including Helicobacter sp and Campylobacter sp) harbors a different recombination system, composed of a single recombinase (XerH) which is phylogenetically distinct from the other Xer recombinases and a motif (difH) sharing homologies with difSL. Furthermore, no homologs to dif or Xer recombinases could be detected in small endosymbiont genomes or in certain bacteria with larger chromosomes like the Legionellales. This raises the question of the presence of other chromosomal deconcatenation systems in these species. Our study highlights the complexity of dif/Xer recombinase systems in Proteobacteria and paves the way for systematic detection of these components in prokaryotes.

  • The dif/Xer recombination systems in Proteobacteria.
    PLOS ONE, 2009
    Co-Authors: Christophe Carnoy, Claudealain H Roten
    Abstract:

    In E. coli, 10 to 15% of growing bacteria produce dimeric chromosomes during DNA replication. These dimers are resolved by XerC and XerD, two tyrosine recombinases that target the 28-nucleotide motif (dif) associated with the chromosome’s replication terminus. In streptococci and lactococci, an alternative system is composed of a unique, Xer-like recombinase (XerS) genetically linked to a dif-like motif (difSL) located at the replication terminus. Preliminary observations have suggested that the dif/Xer system is commonly found in bacteria with circular chromosomes but that assumption has not been confirmed in an exhaustive analysis. The aim of the present study was to extensively characterize the dif/Xer system in the Proteobacteria, since this taxon accounts for the majority of genomes sequenced to date. To that end, we analyzed 234 chromosomes from 156 Proteobacterial species and showed that most species (87.8%) harbor XerC and XerD-like recombinases and a dif-related sequence which (i) is located in non-coding sequences, (ii) is close to the replication terminus (as defined by the cumulative GC skew) (iii) has a palindromic structure, (iv) is encoded by a low G+C content and (v) contains a highly conserved XerD binding site. However, not all Proteobacteria display this dif/XerCD system. Indeed, a sub-group of pathogenic e-Proteobacteria (including Helicobacter sp and Campylobacter sp) harbors a different recombination system, composed of a single recombinase (XerH) which is phylogenetically distinct from the other Xer recombinases and a motif (difH) sharing homologies with difSL. Furthermore, no homologs to dif or Xer recombinases could be detected in small endosymbiont genomes or in certain bacteria with larger chromosomes like the Legionellales. This raises the question of the presence of other chromosomal deconcatenation systems in these species. Our study highlights the complexity of dif/Xer recombinase systems in Proteobacteria and paves the way for systematic detection of these components in prokaryotes.