Genome sequence of a commensal bacterium, Enterococcus faecalis CBA7120, isolated from a Korean fecal sample
- Joon Yong Kim1,
- Hye Seon Song1, 2,
- Yeon Bee Kim1, 2,
- Joseph Kwon1,
- Jong-Soon Choi1,
- Yong-Joon Cho3,
- Byung-Yong Kim3,
- Jin-Kyu Rhee2,
- Jinjong Myoung4,
- Young-Do Nam†5, 6 and
- Seong Woon Roh†1, 6Email author
© The Author(s) 2016
Received: 24 August 2016
Accepted: 19 November 2016
Published: 25 November 2016
Enterococcus faecalis, the type strain of the genus Enterococcus, is not only a commensal bacterium in the gastrointestinal tract in vertebrates and invertebrates, but also causes serious disease as an opportunistic pathogen. To date, genome sequences have been published for over four hundred E. faecalis strains; however, pathogenicity of these microbes remains complicated. To increase our knowledge of E. faecalis virulence factors, we isolated strain CBA7120 from the feces of an 81-year-old female from the Republic of Korea and performed a comparative genomic analysis.
The genome sequence of E. faecalis CBA7120 is 3,134,087 bp in length, with a G + C content of 37.35 mol%, and is comprised of four contigs with an N50 value of 2,922,046 bp. The genome showed high similarity with other strains of E. faecalis, including OG1RF, T13, 12107 and T20, based on OrthoANI values. Strain CBA7120 contains 374 pan-genome orthologous groups (POGs) as singletons, including “Phages, Prophages, Transposable elements, Plasmids,” “Carbohydrates,” “DNA metabolism,” and “Virulence, Disease and Defense” subsystems. Genes related to multidrug resistance efflux pumps were annotated in the genome.
The comparative genomic analysis of E. faecalis strains presented in this study was performed using a variety of analysis methods and will facilitate future identification of hypothetical proteins.
KeywordsEnterococcus faecalis Genome sequence Comparative genomics Virulence factors
Genus Enterococcus is a common member of the normal intestinal flora in various species, both vertebrates and invertebrates. However, some species in the genus Enterococcus are leading causes of highly contagious hospital-acquired infections, including urinary tract, intra-abdominal, pelvic, and soft tissue infections, as well as bacteremia and endocarditis. Thus, members of the genus Enterococcus have been extensively studied. The genus Enterococcus was first described by Schleifer and Kilpper-Balz  and species of the genus Enterococcus are Gram-positive, non-spore-forming, facultative anaerobic microbes that produce lactic acid. Enterococcus faecalis DSM 20478T is the type species for the genus .
The first genome sequence of Enterococcus was published by Paulsen in 2003 with E. faecalis V583 . To date, more than 400 strains of E. faecalis have been sequenced and analyzed. The virulence factors present in E. faecalis are well established, and include aggregation substances, surface adhesins, sex pheromones, lipoteichoic acid, extracellular superoxide, the lytic enzymes gelatinase and hyaluronidase, and the toxin cytolysin, but novel virulence factors continue to be reported . In this study, we performed sequencing and genomic analysis of E. faecalis CBA7120, isolated from the feces of an 81-year-old female. Comparison of genomic data from E. faecalis CBA7120 with other genomes of E. faecalis may improve our understanding of the virulence factors and pathogenesis present in Enterococcus.
Strain isolation and DNA extraction
Enterococcus faecalis CBA7120 was isolated from the feces of an 81-year-old healthy female living in the Republic of Korea and cultivated on modified Eggerth–Gagnon (EG) medium [containing per liter of distilled water: peptone 10 g, Na2HPO4 4 g, porcine gastric mucin 2 g, sheep blood 50 ml, agar 15 g] at 37 °C for 24 h in an anaerobic chamber (Coy Laboratory Products). Once a pure culture was obtained, strain CBA7120 was preserved at −80 °C in a suspension of 20% glycerol for long-term storage. Genomic DNA for sequencing was prepared using QuickGene DNA tissue kit S (Kurabo, Japan) and QIAamp DNA extraction Kits (Qiagen, USA).
Whole genome sequencing, assembly, and gene annotation
A SMRTbell library was constructed according to the Pacific Biosciences protocol “20-kb Template Preparation Using BluePippin Size-selection system (15-kb Size Cutoff)”. The library was sequenced using P6-C4 chemistry on a Pacific Biosciences RS II instrument. The PacBio RS II sequencing system generated 150,292 reads, with an average read length of 8095 bp from one SMRT cell. For the assembly, filtering was performed by Hierarchical Genome Assembly Process (HGAP) version 2 protocol with default parameter. Assembly was performed using the HGAP 2 protocol with default parameters in SMRT Analysis version 2.3 . The assembly was polished with three successive passes through Quiver to reach a final consensus accuracy of >99.988% at 232.798 × coverage. Finally, finished assembly consisted of four contigs. Using RS_Modification_and_Motif_analysis protocol with default parameter in PacBio SMRT analysis pipeline, 4 N6-methyladenine and other six unidentified methylated motifs were identified. Gene prediction was accomplished using Glimmer3  on the Rapid Annotation using Subsystem Technology (RAST; http://rast.nmpdr.org/) server , and gene annotation was performed using the SEED and Clusters of Orthologous Groups (COG; http://www.ncbi.nlm.nih.gov/COG/) databases [7, 8]. RNAmmer 1.2  and tRNAscan-SE 1.21  were used to identify rRNA and tRNA sequences, respectively.
Multilocus sequence typing (MLST)
MLST was performed using the following seven housekeeping genes: glucose-6-phosphate dehydrogenase (gdh), glyceraldehyde-3-phosphate dehydrogenase (gyd), phosphate ATP binding cassette transporter (pstS), glucokinase (gki), shikimate-5-dehydrogenase (aroE), xanthine phosphoribosyltransferase (xpt), and acetyl-CoA acetyltransferase (yiqL) using PubMLST (http://pubmlst.org/efaecalis/).
Comparative genomic analysis
Using data in the NCBI genome database (http://www.ncbi.nlm.nih.gov/genome/), four E. faecalis strains were selected as the closest neighbors of strain CBA7120 (>89% symmetric identity): E. faecalis strain 12107, T13, OG1RF, and T20, and these genomes were used for comparative genomic analysis. The genome of E. faecalis TX0031 also showed high symmetric identity, but it was excluded from further analysis because the genome contains a large number of contigs. For whole-genome comparison, the genomes of strain CBA7120 and the other related strains were aligned using the progressive MAUVE algorithm in the MAUVE multiple genome alignment software 2.4.0 . The OrthoANI algorithm was used to assess overall similarity between two genome sequences . OrthoANI values were obtained and a phylogenetic tree was constructed based on OrthoANI analysis of the E. faecalis strains CBA7120, 12107, T13, OG1RF, and T20 using the orthologous average nucleotide identity tool . Orthologs in the genomes of strain CBA7120 and other related strains were identified using reciprocal best hit (RBH) in the UBLAST program . Pan-genome orthologous groups (POGs) were constructed using the EzBioCloud Comparative Genomics Database (http://cg.ezbiocloud.net/). For the visualization heat map and the dendrogram based on the gene content (presence or absence) of the genomes of strain CBA7120 and the other four strains, Jaccard coefficients and UPGMA clustering were used to calculate the presence of POGs and genome clustering, respectively. The Venn diagram based on POGs shared between strain CBA7120 and related strains was constructed using the jvenn program .
Results and discussion
General genome features of Enterococcus faecalis CBA7120
PacBio SMRT Analysis 2.3.0
Assembly size (bp)
DNA G + C content (%)
4 16S-23S-5S rRNA operon
Multilocus sequence typing (MLST)
Enterococcus faecalis CBA7120 was typed with MLST at loci gdh 1, gyd 7, pstS 9, gki 1, aroE 1, xpt 3, and yqiL 1, and was classified as sequence type 5 (ST 5) containing solely strain B343 that was isolated from a chicken product in Spain.
Comparative genomics of strain CBA7120 with other E. faecalis strains
Summary of protein coding sequences annotated as belonging to the “Virulence, Disease, and Defense” subsystem in the SEED database
Streptococcus pyogenes recombinatorial zone
Chaperonin (heat shock protein 33)
Colicin V and bacteriocin production cluster
Acetyl-coenzyme A carboxyl transferase beta chain
Colicin V production protein
tRNA pseudouridine synthase A
Negative transcriptional regulator-copper transport operon
Copper-translocating P-type ATPase
DNA-binding heavy metal response regulator
Cobalt-zinc-cadmium resistance protein
Transcriptional regulator, MerR family
Resistance to fluoroquinolones
DNA gyrase subunit B
DNA gyrase subunit A
Topoisomerase IV subunit B
Topoisomerase IV subunit A
Copper homeostasis: copper tolerance
Cytoplasmic copper homeostasis protein CutC
Magnesium and cobalt efflux protein CorC
Beta-lactamase class C and other penicillin-binding proteins
Metal-dependent hydrolases of the beta-lactamase superfamily I
Cadmium resistance protein
Cadmium efflux system accessory protein
Multidrug resistance efflux pumps
Multidrug resistance efflux pump PmrA
Multi antimicrobial extrusion protein [Na(+)/drug antiporter], MATE family of MDR efflux pumps
Multidrug and toxin extrusion (MATE) family efflux pump YdhE/NorM, homolog
Multidrug-efflux transporter, major facilitator superfamily (MFS)
Genomic analysis based on ortholog analysis may be a powerful comparative genomics tool. Additional study of the virulence factors present in E. faecalis CBA7120 will guide further research on E. faecalis virulence.
coding DNA sequences
clusters of orthologous groups
locally collinear block
multidrug and toxin extrusion
multilocus sequence typing
pan-genome orthologous group
rapid annotation using subsystem technology
reciprocal best hit
YDN and SWR designed and coordinated all the experiments. HSS characterized the strain and prepared the high-quality DNA. JYK, YJC, BYK performed the sequence assembly, gene prediction, gene annotation, comparative genomic analysis and wrote manuscript. YBK, JK, JSC, JKR and JM checked and edited the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Availability of data and materials
This Whole Genome Shotgun project has been deposited at DDBJ under the accession numbers BDEN01000001–BDEN01000004.
Ethics approval and consent to participate
This study was approved by the Institutional Review Board of the Korea National Institutes of Health (NIH) under approval number 2015-02-EXP-05-3C-A.
This research was supported from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (2015R1D1A1A09061039), from the Center for Analytical Research of Disaster Science of the Korea Basic Science Institute (C36703), from Korean Food Research Institute (E0131600-04) and from Korea Centers for Disease Control and Prevention (4847-311-210-13, 2015).
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