Open Access

Draft genome sequence of Enterococcus faecium strain LMG 8148

  • Joran E. Michiels1,
  • Bram Van den Bergh1,
  • Maarten Fauvart1, 2 and
  • Jan Michiels1Email author
Standards in Genomic Sciences201611:63

https://doi.org/10.1186/s40793-016-0187-1

Received: 23 March 2016

Accepted: 27 August 2016

Published: 7 September 2016

Abstract

Enterococcus faecium, traditionally considered a harmless gut commensal, is emerging as an important nosocomial pathogen showing increasing rates of multidrug resistance. We report the draft genome sequence of E. faecium strain LMG 8148, isolated in 1968 from a human in Gothenburg, Sweden. The draft genome has a total length of 2,697,490 bp, a GC-content of 38.3 %, and 2,402 predicted protein-coding sequences. The isolation of this strain predates the emergence of E. faecium as a nosocomial pathogen. Consequently, its genome can be useful in comparative genomic studies investigating the evolution of E. faecium as a pathogen.

Keywords

Draft genome Gut commensal Nosocomial pathogen Enterococcus faecium Human isolate

Introduction

Enterococci commonly reside in the gastro-intestinal tract of a wide variety of invertebrate and vertebrate hosts, including humans. Since they produce bacteriocins, Enterococcus spp. are widely used as starter cultures for food fermentations or probiotic supplements [1]. Since the 1970s however, they have enigmatically progressed from commensal organisms of little clinical interest to leading nosocomial pathogens causing infections of the urinary tract, bloodstream, and surgical wounds, among others [2]. The large majority of human enterococcal infections are caused by two species: E. faecalis and E. faecium . Worryingly, acquired antibiotic resistance against a multitude of drugs is increasingly being reported in these organisms [3].

Here, we report the draft genome of E. faecium LMG 8148, a strain of human origin isolated in 1968 in Gothenburg, Sweden [4].

Organism information

Classification and features

Enterococcus is a large genus of Gram-positive, non-sporulating, facultative anaerobic, round-shaped, lactic acid-producing bacteria (Table 1) [5]. E. faecium belongs to the family Enterococcaceae , order Lactobacillales , class Bacilli , and phylum Firmicutes . Microscopically, enterococci are often observed as pairs or short chains of cells (Fig. 1) [5]. They were classified as group D streptococci until assigned a separate genus in 1984 [6]. E. faecalis and E. faecium are the two most prominent species within the genus. Enterococci can grow in a wide range of environmental conditions, including temperature (5-50 °C), pH (4.6-9.9), 40 % (w/v) bile salts, and 6.5 % NaCl [7]. To investigate evolutionary relationships with other Enterococcus species and E. faecium strains, a phylogenetic tree was constructed using 16S rDNA sequences (Fig. 2). As expected, E. faecium LMG 8148 forms a cluster with the other E. faecium strains.
Table 1

Classification and general features of Enterococcus faecium strain LMG 8148 according to the MIGS recommendations [8]

MIGS ID

Property

Term

Evidence codea

 

Classification

Domain Bacteria

TAS [16]

  

Phylum Firmicutes

TAS [17]

  

Class Bacilli

TAS [18, 19]

  

Order Lactobacillales

TAS [19, 20]

  

Family Enterococcaceae

TAS [19, 21]

  

Genus Enterococcus

TAS [6]

  

Species Enterococcus faecium

TAS [6]

  

Strain LMG 8148

NAS

 

Gram stain

Positive

TAS [22]

 

Cell shape

Coccus

TAS [22]

 

Motility

Non-motile

NAS

 

Sporulation

Non-sporulating

TAS [7]

 

Temperature range

5-50 °C

TAS [7]

 

Optimum temperature

37 °C

TAS [23]

 

pH range; Optimum

4.6-9.9; 7.5

TAS [23]

 

Carbon source

Glucose, citrate, complex carbon sources

TAS [24, 25]

MIGS-6

Habitat

Gastro-intestinal tracts of humans and other mammals

TAS [5]

MIGS-6.3

Salinity

0-6.5 %

TAS [7]

MIGS-22

Oxygen requirement

Facultatively anaerobic

TAS [7]

MIGS-15

Biotic relationship

Commensal

TAS [5]

MIGS-14

Pathogenicity

Pathogenic

TAS [5]

MIGS-4

Geographic location

Sweden

NAS

MIGS-5

Sample collection

1961

TAS [4]

MIGS-4.1

Latitude

Unknown

NAS

MIGS-4.2

Longitude

Unknown

NAS

MIGS-4.4

Altitude

Unknown

NAS

aEvidence codes - IDA inferred from direct assay, TAS traceable author statement (i.e., a direct report exists in the literature); NAS: Non-traceable VAuthor Statement (i.e., not directly observed for the living, isolated sample, but based on a generally accepted property for the species, or anecdotal evidence). These evidence codes are from the Gene Ontology project [26]

Fig. 1

Phase-contrast micrograph of E. faecium LMG 8148

Fig. 2

16S rRNA phylogenetic tree indicating the position of E. faecium LMG 8148 relative to other E. faecium strains and other enterococcal species (type strain = T). Lactobacillus plantarum was included as an outgroup. Genbank accession numbers of the aligned sequences are indicated between brackets. 16S rDNA sequences were aligned using MUSCLE, and the phylogenetic tree was determined using the neighbour-joining algorithm with the Kimura 2-parameter distance model in MEGA (version 7) [27]. A gamma distribution (shape parameter = 1) was used for rate variation among sites. The optimal tree with the sum of branch lengths = 0.1983 is shown, and nodes that appeared in more than 50 % of replicate trees in the bootstrap test (1000 replicates) are marked with their bootstrap support values

Genome sequencing information

Genome project history

The strain LMG 8148 was isolated from a human in Gothenburg (Sweden) in 1968 [4]. The strain was obtained through the Belgian Coordinated Collection of Microorganisms. DNA samples were sequenced at the EMBL GeneCore facility (Heidelberg, Germany) and assembled using CLC Genomics Workbench (version 7.5.1). The draft genome was annotated using the NCBI Prokaryotic Genome Annotation Pipeline. This draft whole-genome sequence has been deposited at DDBJ/ENA/GenBank under the accession LOHT00000000. The project information, and its association with MIGS version 2.0 [8], is summarised in Table 2.
Table 2

Project information

MIGS-ID

Property

Term

MIGS-31

Finishing quality

High-quality draft

MIGS-28

Libraries used

One paired-end Illumina library (Nextera)

MIGS-29

Sequencing platforms

Illumina HiSeq 2000

MIGS-31.2

Fold coverage

317

MIGS-30

Assemblers

CLC NGS Cell 7.5.1

MIGS-32

Gene calling method

GeneMarkS+

 

Locus Tag

AUC59

 

Genbank ID

LOHT00000000

 

GenBank Date of Release

2016/02/26

 

GOLD ID

-

 

BIOPROJECT

PRJNA305395

MIGS-13

Source Material Identifier

LMG 8148

 

Project relevance

Evolution

Growth conditions and genomic DNA preparation

Bacterial cultures were inoculated from single colonies on lysogeny broth agar in 5 ml of lysogeny broth and grown overnight at 37 °C, with 200 rpm orbital shaking. The DNeasy Blood&Tissue Kit (Qiagen) was used for DNA isolation, following the manufacturer’s instructions and pre-treatment protocol for Gram-positive bacteria. Concentration and purity of isolated DNA was determined spectrophotometrically using the Nanodrop ND-1000 and fluorometrically using Qubit analysis (ThermoFisher Scientific).

Genome sequencing and assembly

100 bp paired-end sequencing was performed on an Illumina HiSeq 2000 machine at the EMBL GeneCore facility in Heidelberg (Germany). The total number of paired reads was 9,317,630. Sequencing data was analysed with the Qiagen CLC Genomics workbench version 7.5.1. After a trimming step for quality (score limit: 0.05) and ambiguous nucleotides (maximum 2 ambiguities), reads were assembled de novo using a mismatch cost of 2, a deletion cost of 3, an insertion cost of 3, length fraction 0.5, and similarity fraction 0.8. The assembly yielded 366 contigs (minimum length 200 bp) with an average coverage of 317× and an average contig length of 7,370 bp (N50 length of 41,184 bp). The total length of the draft genome is 2,697,490 bp with a GC-content of 38.3 %.

Genome annotation

All contigs were annotated using NCBI’s Prokaryotic Genome Annotation Pipeline. Pfam domains [9] in the predicted protein sequences were identified using the Batch Web CD-Search Tool from NCBI [10]. Predicted proteins were classified into COG [11] functional categories using the WebMGA web server for metagenomic analysis [12]. For further characterization of the predicted genes, CRISPRFinder [13], the SignalP 4.1 server [14], and the TMHMM server [15] were used to predict CRISPR repeats, signal peptides, and transmembrane domains, respectively. For the CRISPRFinder tool, only confirmed CRISPRs and not questionable CRISPRs were taken into account.

Genome properties

The properties of this draft genome are summarised in Table 3. Assembly yielded 366 contigs containing 2,697,490 bp with a 38.3 % GC-content. The total number of 2,772 genes predicted by PGAP includes 2,402 protein coding genes (totalling 2,136,945 base pairs), 303 pseudo genes, and 67 RNA genes (56 tRNA and 11 rRNA genes). For 19.37 % of the protein-coding genes, no putative function was assigned, and these were annotated as hypothetical proteins. Further characteristics of the predicted genes are given in Table 3, and classification into functional COG categories is shown in Table 4.
Table 3

Genome statistics

Attribute

Value

% of Total

Genome size (bp)

2,697,490

100.00

DNA coding (bp)

2,136,945

79.22

DNA G + C (bp)

1,034,256

38.34

DNA scaffolds

366

100.00

Total genes

2,772

100.00

Protein coding genes

2,402

86.65

RNA genes

67

2.42

Pseudo genes

303

10.93

Genes in internal clusters

-

-

Genes with function prediction

2,235

80.63

Genes assigned to COGs

2,153

77.67

Genes with Pfam domains

2,078

74.96

Genes with signal peptides

120

4.33

Genes with transmembrane helices

631

22.76

CRISPR repeats

1

-

Table 4

Number of genes associated with general COG functional categories

Code

Value

%age

Description

J

150

6.24

Translation, ribosomal structure and biogenesis

A

0

0.00

RNA processing and modification

K

185

7.70

Transcription

L

148

6.16

Replication, recombination and repair

B

0

0.00

Chromatin structure and dynamics

D

21

0.87

Cell cycle control, cell division, chromosome partitioning

V

49

2.04

Defense mechanisms

T

88

3.66

Signal transduction mechanisms

M

114

4.75

Cell wall/membrane biogenesis

N

13

0.54

Cell motility

U

27

1.12

Intracellular trafficking and secretion

O

58

2.41

Posttranslational modification, protein turnover, chaperones

C

74

3.08

Energy production and conversion

G

253

10.53

Carbohydrate transport and metabolism

E

144

6.00

Amino acid transport and metabolism

F

78

3.25

Nucleotide transport and metabolism

H

55

2.29

Coenzyme transport and metabolism

I

57

2.37

Lipid transport and metabolism

P

109

4.54

Inorganic ion transport and metabolism

Q

22

0.92

Secondary metabolites biosynthesis, transport and catabolism

R

263

10.95

General function prediction only

S

245

10.20

Function unknown

-

249

10.37

Not in COGs

The total is based on the total number of protein coding genes in the genome

Conclusions

The presented genome sequence is from a strain isolated in 1968, and thus precedes the emergence of enterococci as important causative agents of hospital-acquired infections in the 1970s and 1980s [2]. Consequently, this genome could be useful for comparative genomic studies looking to solve the remarkable recent emergence of E. faecium as a notorious nosocomial pathogen.

Abbreviations

COG: 

Clusters of Orthologous Groups

PGAP: 

Prokaryotic genome annotation pipeline

Declarations

Acknowledgements

JEM and BVDB are recipients of a fellowship from the Agency for Innovation by Science and Technology (IWT) and the Research Foundation Flanders (FWO), respectively. This work was supported by grants from the KU Leuven Research Council (PF/10/010 “NATAR”, IDO/09/01), the Interuniversity Attraction Poles program initiated by the Belgian Science Policy Office (IAP P7/28) and the FWO (grants G.0413.10, G.0471.12 N, G.0B25.15 N). The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Authors' contributions

JEM performed the experiments, analysed the data, and wrote the manuscript. BVDB and MF helped analysing the data and edited the manuscript. JM initiated and supervised the study, and edited the manuscript. All authors read and approved the final manuscript.

Competing interests

The authors declare that they have no competing interests.

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Authors’ Affiliations

(1)
Centre of Microbial and Plant Genetics, KU Leuven
(2)
Department of Life Science Technologies, imec, Smart Systems and Emerging Technologies Unit

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Copyright

© The Author(s). 2016