Core Genome Phylogeny Research Articles

Campylobacter blaseri sp. nov., isolated from common seals (Phoca vitulina).

During a study to assess the faecal microbiome of common seals (Phoca vitulina) in a Dutch seal rehabilitation centre, 16S rRNA gene sequences of an unknown Campylobacter taxon were identified. Campylobacter isolates, which differed from the established Campylobacter taxa, were cultured and their taxonomic position was determined by a polyphasic study based on ten isolates. The isolates were characterized by 16S rRNA and atpA gene sequence analyses and by conventional phenotypic testing. Based on the whole genome sequences, the average nucleotide identity and core genome phylogeny were determined. The isolates formed a separate phylogenetic clade, divergent from all other Campylobacter taxa and most closely related to Campylobacter corcagiensis, Campylobacter geochelonis and Campylobacter ureolyticus. The isolates can be distinguished phenotypically from all other Campylobacter taxa based on their lack of motility, growth at 25 °C and growth on MacConkey agar. This study shows that these isolates represent a novel species within the genus Campylobacter, for which the name Campylobacter blaseri sp. nov. is proposed. The type strain for this novel species is 17S00004-5T (=LMG 30333T=CCUG 71276T).

Genomic epidemiology and population structure of Neisseria gonorrhoeae from remote highly endemic Western Australian populations

BackgroundNeisseria gonorrhoeae causes gonorrhoea, the second most commonly notified sexually transmitted infection in Australia. One of the highest notification rates of gonorrhoea is found in the remote regions of Western Australia (WA). Unlike isolates from the major Australian population centres, the remote community isolates have low rates of antimicrobial resistance (AMR).Population structure and whole-genome comparison of 59 isolates from the Western Australian N. gonorrhoeae collection were used to investigate relatedness of isolates cultured in the metropolitan and remote areas. Core genome phylogeny, multilocus sequencing typing (MLST), N. gonorrhoeae multi-antigen sequence typing (NG-MAST) and N. gonorrhoeae sequence typing for antimicrobial resistance (NG-STAR) in addition to hierarchical clustering of sequences were used to characterize the isolates.ResultsPopulation structure analysis of the 59 isolates together with 72 isolates from an international collection, revealed six population groups suggesting that N. gonorrhoeae is a weakly clonal species. Two distinct population groups, Aus1 and Aus2, represented 63% of WA isolates and were mostly composed of the remote community isolates that carried no chromosomal AMR genotypes. In contrast, the Western Australian metropolitan isolates were frequently multi-drug resistant and belonged to population groups found in the international database, suggesting international transmission of the isolates.ConclusionsOur study suggests that the population structure of N. gonorrhoeae is distinct between the communities in remote and metropolitan WA. Given the high rate of AMR in metropolitan regions, ongoing surveillance is essential to ensure the enduring efficacy of the empiric gonorrhoea treatment in remote WA.

Genomic Analysis of Rhodococcus sp. Br-6, a Bromate Reducing Bacterium Isolated From Soil in Chiba, Japan.

Bromate is a byproduct of the ozone disinfection of drinking water. It is a genotoxic carcinogen and causes renal cell tumors in rats. Physicochemical removal of bromate is very difficult, making microbial reduction of bromate to bromide a promising approach to eliminate bromate from water. Rhodococcus sp. Br-6, isolated from soil, can efficiently reduce bromate by using acetate as an electron donor. We determined the draft genome sequence of Rhodococcus sp. Br-6 for the potential practical application of the bromate-reducing bacterium. Core genome phylogeny suggests that the Br-6 strain is most closely related to R. equi. The Br-6 genome contains genes encoding multiple isoforms of diaphorase, previously found to be involved in Br-6-mediated bromate reduction. The genes identified in the present study could be effective targets for experimental studies of microbial bromate reduction in the future.

Acinetobacter dijkshoorniae is a later heterotypic synonym of Acinetobacter lactucae.

Acinetobacter lactucae and Acinetobacter dijkshoorniae were recently described as novel species, and both were reported to be closely related to Acinetobacter pittii. Because they were reviewed and published almost concurrently, their descriptions did not include a specific comparison between these two novel species. Genomic data were provided in both initial descriptions, which simplifies the comparisons. Genome comparisons based on in silico DNA-DNA hybridizations, average nucleotide identity and core genome phylogeny of the type strain genomes establish that these strains are conspecific. Based on the rules of priority, A. dijkshoorniae should be reclassified as a later heterotypic synonym of A. lactucae.

High Prevalence of CTX-M-15-Type ESBL-Producing E. coli from Migratory Avian Species in Pakistan.

The increased presence of clinically relevant multidrug resistant bacteria in natural environments is an emerging challenge for global health care. Little is known regarding the occurrence of extended-spectrum beta-lactamase producing Escherichia coli (ESBL-E. coli) from environmental sentinels in Pakistan. The goal of the current study was to gain insights into the prevalence and phylogenetic relationships of ESBL-E. coli recovered from wild birds in Pakistan during winter migration. After initial screening of fecal samples on selective chromogenic agar, ESBL-E.coli were analyzed phenotypically using the Vitek-2 automated system. Genotypic characterization was performed using whole genome sequencing (WGS) followed by an in-depth in silico analysis. Of 150 birds screened, 26 (17.3%) were fecal carriers of ESBL-E. coli. Of these, 88.4% isolates exhibited multidrug resistance (MDR) phenotypes. Resistance to cefotaxime, ceftazidime, ampicillin, doxycycline, tetracycline and sulfamethoxazole/trimethoprim (CTX-CAZ-AM-DC-TE-SXT) represented the most common pattern of MDR (76.9%). WGS data analysis found blaCTX-M-15 as the predominant ESBL genotype (92.3%). Other genes encoding resistance to sulfonamides (sul1/sul2/sul3), aminoglycosides (strA, strB, aadA1, aadA2, aadA5, aac(3)-IId-like, aac(3)-IVa-like and aph(4)-Ia), trimethoprim (dfrA14 or dfrA17), tetracyclines [tet(A)/tet(B)], and fluoroquinolones (qnrS1) were detected commonly, often encoded on IncF-type plasmids (76.9%). ESBL-E. coli were assigned to 17 different sequence types (STs) of which ST10 and ST7097 (4 isolates each) were the most abundant followed by ST4720, ST93, and ST1139 (2 isolates each). Core-genome phylogeny of the isolates found low numbers (0–29) of single nucleotide polymorphisms (SNPs) in isolates belonged to ST7097 originated from two different locations (Chashma barrage and Rasul barrage). Similar trends were found among isolates belong to ST1139. In addition, WGS-based plasmid typing and S1-digestion found plasmids of the same pMLST type (IncF[F-:A-:B53]) and similar sizes in different bacterial and avian hosts suggesting horizontal gene transfer as another possibility for the spread of ESBL-E. coli in avian wildlife in Pakistan.

Evolutionary Context of Non-Sorbitol-Fermenting Shiga Toxin-Producing Escherichia coli O55:H7.

In July 2014, an outbreak of Shiga toxin–producing Escherichia coli (STEC) O55:H7 in England involved 31 patients, 13 (42%) of whom had hemolytic uremic syndrome. Isolates were sequenced, and the sequences were compared with publicly available sequences of E. coli O55:H7 and O157:H7. A core-genome phylogeny of the evolutionary history of the STEC O55:H7 outbreak strain revealed that the most parsimonious model was a progenitor enteropathogenic O55:H7 sorbitol-fermenting strain, lysogenized by a Shiga toxin (Stx) 2a–encoding phage, followed by loss of the ability to ferment sorbitol because of a non-sense mutation in srlA. The parallel, convergent evolutionary histories of STEC O157:H7 and STEC O55:H7 may indicate a common driver in the evolutionary process. Because emergence of STEC O157:H7 as a clinically significant pathogen was associated with acquisition of the Stx2a-encoding phage, the emergence of STEC O55:H7 harboring the stx2a gene is of public health concern.

Streptococcus bovimastitidis sp. nov., isolated from a dairy cow with mastitis.

Here we describe a new species of the genus Streptococcus that was isolated from a dairy cow with mastitis in New Zealand. Strain NZ1587T was Gram-positive, coccus-shaped and arranged as chains, catalase and coagulase negative, γ-haemolytic and negative for Lancefield carbohydrates (A-D, F and G). The 16S rRNA sequence did not match sequences in the NCBI 16S rRNA or GreenGenes databases. Taxonomic classification of strain NZ1587T was investigated using 16S rRNA and core genome phylogeny, genome-wide average nucleotide identity (ANI) and predicted DNA-DNA hybridisation (DDH) analyses. Phylogeny based on 16S rRNA was unable to resolve the taxonomic position of strain NZ1587T, however NZ1587T shared 99.4 % identity at the 16S rRNA level with a distinct branch of S. pseudoporcinus. Importantly, core genome phylogeny demonstrated that NZ1587T grouped amongst the 'pyogenic' streptococcal species and formed a distinct branch supported by a 100 % bootstrap value. In addition, average nucleotide identity and inferred DNA-DNA hybridisation analyses showed that NZ1587T represents a novel species. Biochemical profiling using the rapid ID 32 strep identification test enabled differentiation of strain NZ1587T from closely related streptococcal species. In conclusion, strain NZ1587T can be classified as a novel species, and we propose a novel taxon named Streptococcus bovimastitidis sp. nov.; the type strain is NZ1587T. NZ1587T has been deposited in the Culture Collection University of Gothenburg (CCUG 69277T) and the Belgian Co-ordinated Collections of Micro-organisms/LMG (LMG 29747).

Associations among Antibiotic and Phage Resistance Phenotypes in Natural and Clinical Escherichia coli Isolates.

ABSTRACTThe spread of antibiotic resistance is driving interest in new approaches to control bacterial pathogens. This includes applying multiple antibiotics strategically, using bacteriophages against antibiotic-resistant bacteria, and combining both types of antibacterial agents. All these approaches rely on or are impacted by associations among resistance phenotypes (where bacteria resistant to one antibacterial agent are also relatively susceptible or resistant to others). Experiments with laboratory strains have shown strong associations between some resistance phenotypes, but we lack a quantitative understanding of associations among antibiotic and phage resistance phenotypes in natural and clinical populations. To address this, we measured resistance to various antibiotics and bacteriophages for 94 natural and clinical Escherichia coli isolates. We found several positive associations between resistance phenotypes across isolates. Associations were on average stronger for antibacterial agents of the same type (antibiotic-antibiotic or phage-phage) than different types (antibiotic-phage). Plasmid profiles and genetic knockouts suggested that such associations can result from both colocalization of resistance genes and pleiotropic effects of individual resistance mechanisms, including one case of antibiotic-phage cross-resistance. Antibiotic resistance was predicted by core genome phylogeny and plasmid profile, but phage resistance was predicted only by core genome phylogeny. Finally, we used observed associations to predict genes involved in a previously uncharacterized phage resistance mechanism, which we verified using experimental evolution. Our data suggest that susceptibility to phages and antibiotics are evolving largely independently, and unlike in experiments with lab strains, negative associations between antibiotic resistance phenotypes in nature are rare. This is relevant for treatment scenarios where bacteria encounter multiple antibacterial agents.

PanX: pan-genome analysis and exploration.

Horizontal transfer, gene loss, and duplication result in dynamic bacterial genomes shaped by a complex mixture of different modes of evolution. Closely related strains can differ in the presence or absence of many genes, and the total number of distinct genes found in a set of related isolates—the pan-genome—is often many times larger than the genome of individual isolates. We have developed a pipeline that efficiently identifies orthologous gene clusters in the pan-genome. This pipeline is coupled to a powerful yet easy-to-use web-based visualization for interactive exploration of the pan-genome. The visualization consists of connected components that allow rapid filtering and searching of genes and inspection of their evolutionary history. For each gene cluster, panX displays an alignment, a phylogenetic tree, maps mutations within that cluster to the branches of the tree and infers gain and loss of genes on the core-genome phylogeny. PanX is available at pangenome.de. Custom pan-genomes can be visualized either using a web server or by serving panX locally as a browser-based application.

Differentiation and Structure in Sulfolobus islandicus Rod-Shaped Virus Populations.

In the past decade, molecular surveys of viral diversity have revealed that viruses are the most diverse and abundant biological entities on Earth. In culture, however, most viral isolates that infect microbes are represented by a few variants isolated on type strains, limiting our ability to study how natural variation affects virus-host interactions in the laboratory. We screened a set of 137 hot spring samples for viruses that infect a geographically diverse panel of the hyperthemophilic crenarchaeon Sulfolobus islandicus. We isolated and characterized eight SIRVs (Sulfolobus islandicus rod-shaped viruses) from two different regions within Yellowstone National Park (USA). Comparative genomics revealed that all SIRV sequenced isolates share 30 core genes that represent 50–60% of the genome. The core genome phylogeny, as well as the distribution of variable genes (shared by some but not all SIRVs) and the signatures of host-virus interactions recorded on the CRISPR (clustered regularly interspaced short palindromic repeats) repeat-spacer arrays of S. islandicus hosts, identify different SIRV lineages, each associated with a different geographic location. Moreover, our studies reveal that SIRV core genes do not appear to be under diversifying selection and thus we predict that the abundant and diverse variable genes govern the coevolutionary arms race between SIRVs and their hosts.

Comparative Phylogenomic Analysis of Escherichia coli ST131 Isolates and IncF-type Plasmids from North Carolina Community Hospitals and Other Regions of the United States

Background Escherichia coli sequence type 131 (ST131), associated with CTX-M-15-type extended-spectrum β-lactamases (ESBLs), predominates globally among multidrug-resistant (MDR) E. coli. Among MDR E. coli ST131 isolates from North Carolina and other US regions, we explored genetic associations of the H30Rx and H30R1 subclones with IncF-type plasmid variants.MethodsSequence data from 144 clinical E. coli isolates, including 39 MDR ST131 isolates from our 7 NC community hospitals and previous 104 ST131 isolates from other US regions, were analyzed and compared. Specific genes were sought using a bioinformatic pipeline at the Center for Genomic Epidemiology and BLAST. Evolutionary analyses were performed using MEGA7. Plasmid incompatibility groups and its STs were identified using PlasmidFinder and pMLST. Comparisons of the completed sequences of 2 ST131 reference plasmids with 144 ST131 draft genome assemblies were performed using CGView Comparison Tool, and circular comparison maps were generated. Among 31 blaCTX-M-containing contigs, blaCTX-M gene insertion sites were examined.ResultsIn the core genome phylogeny, the H30R1 and H30Rx clades were placed within a larger H30R clade (Figure 1). pMLST revealed association of IncF[F2:A1:B-] plasmids (mostly blaCTX-M-15-positive) with H30Rx, and IncF[F1:A2:B20] plasmids (all blaCTX-M-15-negative) with H30R1. The ST131-associated IncF[F2:A1:B-] plasmids from NC generally resembled those from other US regions (Figure 2). However, in contrast to the others, some of the NC plasmids lacked regions previously described as gisland 1 h and/or the gColla-region, h in addition to gisland 2 h (Figure 3). Among the 31 NC ST131 isolates producing CTX-M (26 H30Rx and 5 H30R1 isolates), blaCTX-M-15 was inserted at the same chromosomal site in 3 H30Rx isolates, at different chromosomal sites in 3 H30Rx isolates, and on IncF plasmids in 1 H30Rx and 1 H30R1 isolates, suggesting that the blaCTX-M-containing gene cassette has moved around among and/or within these strains.ConclusionOur genomic and plasmid analysis of community hospital-source ST131 isolates demonstrated fixation and ongoing evolution of specific plasmids within the separate but closely related H30Rx and H30R1 sublineages.Disclosures J. R. Johnson, Crucell/Janssen: Consultant, Consulting fee Merck: Grant Investigator, Grant recipient Tetraphase: Grant Investigator, Research grant Actavis/Allergan: Grant Investigator, Grant recipient

Household Clustering of Escherichia coli Sequence Type 131 Clinical and Fecal Isolates According to Whole Genome Sequence Analysis.

Background. Within-household sharing of strains from the resistance-associated H30R1 and H30Rx subclones of Escherichia coli sequence type 131 (ST131) has been inferred based on conventional typing data, but it has been assessed minimally using whole genome sequence (WGS) analysis. Methods. Thirty-three clinical and fecal isolates of ST131-H30R1 and ST131-H30Rx, from 20 humans and pets in 6 households, underwent WGS analysis for comparison with 52 published ST131 genomes. Phylogenetic relationships were inferred using a bootstrapped maximum likelihood tree based on core genome sequence polymorphisms. Accessory traits were compared between phylogenetically similar isolates. Results. In the WGS-based phylogeny, isolates clustered strictly by household, in clades that were distributed widely across the phylogeny, interspersed between H30R1 and H30Rx comparison genomes. For only 1 household did the core genome phylogeny place epidemiologically unlinked isolates together with household isolates, but even there multiple differences in accessory genome content clearly differentiated these 2 groups. The core genome phylogeny supported within-household strain sharing, fecal-urethral urinary tract infection pathogenesis (with the entire household potentially providing the fecal reservoir), and instances of host-specific microevolution. In 1 instance, the household's index strain persisted for 6 years before causing a new infection in a different household member. Conclusions. Within-household sharing of E coli ST131 strains was confirmed extensively at the genome level, as was long-term colonization and repeated infections due to an ST131-H30Rx strain. Future efforts toward surveillance and decolonization may need to address not just the affected patient but also other human and animal household members.

Increasing genomic diversity and evidence of constrained lifestyle evolution due to insertion sequences in Aeromonas salmonicida.

BackgroundAeromonads make up a group of Gram-negative bacteria that includes human and fish pathogens. The Aeromonas salmonicida species has the peculiarity of including five known subspecies. However, few studies of the genomes of A. salmonicida subspecies have been reported to date.ResultsWe sequenced the genomes of additional A. salmonicida isolates, including three from India, using next-generation sequencing in order to gain a better understanding of the genomic and phylogenetic links between A. salmonicida subspecies. Their relative phylogenetic positions were confirmed by a core genome phylogeny based on 1645 gene sequences. The Indian isolates, which formed a sub-group together with A. salmonicida subsp. pectinolytica, were able to grow at either at 18 °C and 37 °C, unlike the A. salmonicida psychrophilic isolates that did not grow at 37 °C. Amino acid frequencies, GC content, tRNA composition, loss and gain of genes during evolution, pseudogenes as well as genes under positive selection and the mobilome were studied to explain this intraspecies dichotomy.ConclusionInsertion sequences appeared to be an important driving force that locked the psychrophilic strains into their particular lifestyle in order to conserve their genomic integrity. This observation, based on comparative genomics, is in agreement with previous results showing that insertion sequence mobility induced by heat in A. salmonicida subspecies causes genomic plasticity, resulting in a deleterious effect on the virulence of the bacterium. We provide a proof-of-concept that selfish DNAs play a major role in the evolution of bacterial species by modeling genomes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2381-3) contains supplementary material, which is available to authorized users.

TGS-TB: Total Genotyping Solution for Mycobacterium tuberculosis Using Short-Read Whole-Genome Sequencing

Whole-genome sequencing (WGS) with next-generation DNA sequencing (NGS) is an increasingly accessible and affordable method for genotyping hundreds of Mycobacterium tuberculosis (Mtb) isolates, leading to more effective epidemiological studies involving single nucleotide variations (SNVs) in core genomic sequences based on molecular evolution. We developed an all-in-one web-based tool for genotyping Mtb, referred to as the Total Genotyping Solution for TB (TGS-TB), to facilitate multiple genotyping platforms using NGS for spoligotyping and the detection of phylogenies with core genomic SNVs, IS6110 insertion sites, and 43 customized loci for variable number tandem repeat (VNTR) through a user-friendly, simple click interface. This methodology is implemented with a KvarQ script to predict MTBC lineages/sublineages and potential antimicrobial resistance. Seven Mtb isolates (JP01 to JP07) in this study showing the same VNTR profile were accurately discriminated through median-joining network analysis using SNVs unique to those isolates. An additional IS6110 insertion was detected in one of those isolates as supportive genetic information in addition to core genomic SNVs. The results of in silico analyses using TGS-TB are consistent with those obtained using conventional molecular genotyping methods, suggesting that NGS short reads could provide multiple genotypes to discriminate multiple strains of Mtb, although longer NGS reads (≥300-mer) will be required for full genotyping on the TGS-TB web site. Most available short reads (~100-mer) can be utilized to discriminate the isolates based on the core genome phylogeny. TGS-TB provides a more accurate and discriminative strain typing for clinical and epidemiological investigations; NGS strain typing offers a total genotyping solution for Mtb outbreak and surveillance. TGS-TB web site: https://gph.niid.go.jp/tgs-tb/.

The Widespread Multidrug-Resistant Serotype O12 Pseudomonas aeruginosa Clone Emerged through Concomitant Horizontal Transfer of Serotype Antigen and Antibiotic Resistance Gene Clusters.

ABSTRACTThe O-specific antigen (OSA) in Pseudomonas aeruginosa lipopolysaccharide is highly varied by sugar identity, side chains, and bond between O-repeats. These differences classified P. aeruginosa into 20 distinct serotypes. In the past few decades, O12 has emerged as the predominant serotype in clinical settings and outbreaks. These serotype O12 isolates exhibit high levels of resistance to various classes of antibiotics. Here, we explore how the P. aeruginosa OSA biosynthesis gene clusters evolve in the population by investigating the association between the phylogenetic relationships among 83 P. aeruginosa strains and their serotypes. While most serotypes were closely linked to the core genome phylogeny, we observed horizontal exchange of OSA biosynthesis genes among phylogenetically distinct P. aeruginosa strains. Specifically, we identified a “serotype island” ranging from 62 kb to 185 kb containing the P. aeruginosa O12 OSA gene cluster, an antibiotic resistance determinant (gyrAC248T), and other genes that have been transferred between P. aeruginosa strains with distinct core genome architectures. We showed that these genes were likely acquired from an O12 serotype strain that is closely related to P. aeruginosa PA7. Acquisition and recombination of the “serotype island” resulted in displacement of the native OSA gene cluster and expression of the O12 serotype in the recipients. Serotype switching by recombination has apparently occurred multiple times involving bacteria of various genomic backgrounds. In conclusion, serotype switching in combination with acquisition of an antibiotic resistance determinant most likely contributed to the dissemination of the O12 serotype in clinical settings.

Phylogenomics of Xanthomonas field strains infecting pepper and tomato reveals diversity in effector repertoires and identifies determinants of host specificity.

Bacterial spot disease of pepper and tomato is caused by four distinct Xanthomonas species and is a severely limiting factor on fruit yield in these crops. The genetic diversity and the type III effector repertoires of a large sampling of field strains for this disease have yet to be explored on a genomic scale, limiting our understanding of pathogen evolution in an agricultural setting. Genomes of 67 Xanthomonas euvesicatoria (Xe), Xanthomonas perforans (Xp), and Xanthomonas gardneri (Xg) strains isolated from diseased pepper and tomato fields in the southeastern and midwestern United States were sequenced in order to determine the genetic diversity in field strains. Type III effector repertoires were computationally predicted for each strain, and multiple methods of constructing phylogenies were employed to understand better the genetic relationship of strains in the collection. A division in the Xp population was detected based on core genome phylogeny, supporting a model whereby the host-range expansion of Xp field strains on pepper is due, in part, to a loss of the effector AvrBsT. Xp-host compatibility was further studied with the observation that a double deletion of AvrBsT and XopQ allows a host range expansion for Nicotiana benthamiana. Extensive sampling of field strains and an improved understanding of effector content will aid in efforts to design disease resistance strategies targeted against highly conserved core effectors.

Some (bacilli) like it hot: genomics of Geobacillus species.

Biotechnology and Biological Sciences Research Council (BBSRC). Grant Numbers: BB/H016120/1, BB/I024631/1, BB/I025956/1, BB/K003240/2, BB/L012499/1

The extent of genome flux and its role in the differentiation of bacterial lineages.

Horizontal gene transfer (HGT) and gene loss are key processes in bacterial evolution. However, the role of gene gain and loss in the emergence and maintenance of ecologically differentiated bacterial populations remains an open question. Here, we use whole-genome sequence data to quantify gene gain and loss for 27 lineages of the plant-associated bacterium Pseudomonas syringae. We apply an extensive error-control procedure that accounts for errors in draft genome data and greatly improves the accuracy of patterns of gene occurrence among these genomes. We demonstrate a history of extensive genome fluctuation for this species and show that individual lineages could have acquired thousands of genes in the same period in which a 1% amino acid divergence accrues in the core genome. Elucidating the dynamics of genome fluctuation reveals the rapid turnover of gained genes, such that the majority of recently gained genes are quickly lost. Despite high observed rates of fluctuation, a phylogeny inferred from patterns of gene occurrence is similar to a phylogeny based on amino acid replacements within the core genome. Furthermore, the core genome phylogeny suggests that P. syringae should be considered a number of distinct species, with levels of divergence at least equivalent to those between recognized bacterial species. Gained genes are transferred from a variety of sources, reflecting the depth and diversity of the potential gene pool available via HGT. Overall, our results provide further insights into the evolutionary dynamics of genome fluctuation and implicate HGT as a major factor contributing to the diversification of P. syringae lineages.

Draft genome sequences of the type strains of Shigella flexneri held at Public Health England: comparison of classical phenotypic and novel molecular assays with whole genome sequence

BackgroundPublic Health England (PHE) holds a collection of Shigella flexneri Type strains isolated between 1949 and 1972 representing 15 established serotypes and one provisional type, E1037. In this study, the genomes of all 16 PHE Type strains were sequenced using the Illumina HiSeq platform. The relationship between core genome phylogeny and serotype was examined.ResultsThe most common target gene for the detection of Shigella species in clinical PCR assays, ipaH, was detected in all genomes. The type-specific target genes were correctly identified in each genome sequence. In contrast to the S. flexneri in serotype 5 strain described by Sun et al. (2012), the two PHE serotype 5 Type strains possessed an additional oac gene and were differentiated by the presence (serotype 5b) or absence (serotype 5a) of gtrX. The somatic antigen structure and phylogenetic relationship were broadly congruent for strains expressing serotype specific antigens III, IV and V, but not for those expressing I and II. The whole genome phylogenies of the 15 isolates sequenced showed that the serotype 6 Type Strain was phylogenetically distinct from the other S. flexneri serotypes sequenced. The provisional serotype E1037 fell within the serotype 4 clade, being most closely related to the Serotype 4a Type Strain.ConclusionsThe S. flexneri genome sequences were used to evaluate phylogenetic relationships between Type strains and validate genotypic and phenotypic assays. The analysis confirmed that the PHE S. flexneri Type strains are phenotypically and genotypically distinct. Novel variants will continue to be added to this archive.

Genome Sequencing Reveals the Environmental Origin of Enterococci and Potential Biomarkers for Water Quality Monitoring

Enterococci are common members of the gut microbiome and their ease of culturing has facilitated worldwide use as indicators of fecal pollution of waters. However, enterococci were recently shown to persist in environmental habitats, often in the absence of fecal input, potentially confounding water quality assays. Toward resolving this issue and providing a more complete picture of natural enterococci diversity, 11 isolates of Enterococcus faecalis recovered from freshwater watersheds (environmental) were sequenced and compared to 59 available enteric genomes. Phenotypically and phylogenetically the environmental E. faecalis were indistinguishable from their enteric counterparts. However, distinct environmental- and enteric-associated gene signatures, encoding mostly accessory nutrient utilization pathways, were detected among the variable genes. Specifically, a nickel uptake operon was over-represented in environmental genomes, while genes for utilization of sugars thought to be abundant in the gut such as xylose were over-represented in enteric genomes. The distribution and phylogeny of these identified signatures suggest that ancestors of E. faecalis resided in extra-enteric habitats, challenging the prevailing commensal view of enterococci ecology. Thus, habitat-associated gene content changes faster than core genome phylogeny and may include biomarkers for reliably detecting fecal contaminants for improved microbial water quality monitoring.