Open Access

Non-contiguous finished genome sequence and description of Salmonella enterica subsp. houtenae str. RKS3027

  • Songling Zhu,
  • , Hong-Liang Wang
  • , Chunxiao Wang,
  • , Le Tang,
  • , Xiaoyu Wang,
  • , Kai-Jiang Yu
  • and Shu-Lin Liu, ,
Corresponding author

DOI: 10.4056/sigs.3767427

Received: 25 May 2013

Accepted: 25 May 2013

Published: 15 June 2013

Abstract

Salmonella enterica subsp. houtenae serovar 16:z4, z32:-- str. RKS3027 was isolated from a human in Illinois, USA. S. enterica subsp. houtenae is a facultative aerobic rod-shaped Gram-negative bacterium. Here we describe the features of this organism, together with the draft genome sequence and annotation. The 4,404,136 bp long genome (97 contigs) contains 4,335 protein-coding gene and 28 RNA genes.

Keywords:

Salmonella entericasubspecieshoutenaegenome

Introduction

Salmonella is an important genus of human and animal pathogens [1], and more than 2,600 different serovars have been described. Currently, the genus Salmonella is divided into two species, S. enterica, and S. bongori [2]. S. enterica comprises seven subspecies: I (also called subspecies enterica), II (also called subspecies salamae), IIIa (also called subspecies arizonae), IIIb (also called subspecies diarizonae), IV (also called subspecies houtenae), VI (also called subspecies indica), and VII [3]. Most of Salmonella serovars belong to the S. enterica subspecies I and are responsible for disease in warm-blooded animals and humans [4]. Other serovars were usually isolated from cold-blooded organisms and the environment, but could also cause human disease occasionally. In contrast with S. enterica subspecies I, very limited information is available regarding pathogenicity of the other subspecies. When infecting humans, these serovars usually cause an intestinal infection (e.g., diarrhea), but previous reports in the literature [5] have shown that the serovars of Salmonella subspecies II–IV are capable of causing serious infections, including septicemia and abscesses. There has been an increase in case reports on extraintestinal infections caused by these subspecies [6]. S. enterica subsp. houtenae serovar 16:z4,z32:-- str. RKS3027 is a human isolate. This strain is of interest because of its pathogenicity as well as its divergent phylogenetic position among S. enterica.

Classification and features

Few 16S rRNA sequences of Salmonella subspecies are available except S. enterica subsp. enterica. Meanwhile, it is increasingly commonplace to construct the phylogenetic tree by using the whole-genome sequence for higher precision and robustness [7,8]. Therefore we used a total of 2,500 orthologs of 18 strains of Salmonella for constructing a genome-scale phylogenetic tree. Genetic relatedness of S. enterica subsp. houtenae strain RKS3027 to other Salmonella subspecies strains was shown in Figure 1. On the tree, all S. enterica subsp. enterica strains were clustered together, and S. enterica subsp. houtenae RKS3027 positioned between S. enterica subsp. enterica and S. bongori.

Figure 1

Phylogenetic tree highlighting the position of S. enterica subsp. houtenae strain RKS3027 relative to the other types and strains of Salmonella. GenBank accession numbers are indicated in the parentheses. The tree was built based on the comparison of concatenated nucleotide sequences of 2,500 orthologs conserved in all strains. Individual orthologous sequences were aligned by the MAFFT [9] and phylogenetic tree was constructed by using the neighbor-joining method within the MEGA software [10].

The Salmonella genus belongs to the bacterial family Enterobacteriaceae [11]. The bacteria are rod shaped, Gram-negative, with diameter of 0.7 to 1.5 µm and length of 2 to 5 µm (Table 1). They are facultative anaerobes, non-spore-forming, flagellated, and motile. They grow within the optimal temperature range 35 °C - 37 °C and within an optimal pH range of 7.2-7.6. S. enterica subsp. houtenae is salicin-positive and able to grow in KCB medium, two distinguishing characteristics when compared with S. enterica subsp. enterica. The strain is deposited in the Salmonella Genetic Stock Centre (SGSC), University of Calgary, Canada as S. enterica subsp. houtenae RKS3027 (= SGSC 3086).

Table 1

Classification and general features of S. enterica subsp. houtenae RKS3027 according to the MIGS recommendations [12]

MIGS ID

    Property

    Term

   Evidence codea

    Current classification

    Domain Bacteria

   TAS [13]

    Phylum Proteobacteria

   TAS [14]

    Class Gammaproteobacteria

   TAS [15,16]

    Order Enterobacteriales

   TAS [17]

    Family Enterobacteriaceae

   TAS [18-20]

    Genus Salmonella

   TAS [18,21-23]

    Species Salmonella enterica

   TAS [23,24]

    Subspecies Salmonella enterica subsp. houtenae

   TAS [23,24]

    Strain RKS3027

   IDA

    Serovar 16:z3, z32:--

   IDA

    Gram stain

    Negative

   IDA

    Cell shape

    Rod-shaped

   IDA

    Motility

    Motile

   IDA

    Sporulation

    Non-sporulating

   IDA

    Temperature range

    Mesophilic

   IDA

    Optimum temperature

    35 °C - 37 °C

   IDA

    Carbon source

    Glucose

   IDA

    Energy source

    Chemoorganotrophic

   IDA

MIGS-6

    Habitat

    Reptiles

   IDA

MIGS-6.3

    Salinity

    Medium

   IDA

MIGS-22

    Oxygen

    Facultative anaerobes

   IDA

MIGS-15

    Biotic relationship

    Endophyte

   IDA

MIGS-14

    Pathogenicity

    Pathogenic

   IDA

MIGS-4

    Geographic location

    Illinois, USA

   NAS

MIGS-5

    Sample collection time

    1986

   NAS

MIGS-4.1

    Latitude

    Not report

   NAS

MIGS-4.2

    Longitude

    Not report

   NAS

MIGS-4.3

    Depth

    Not report

   NAS

MIGS-4.4

    Altitude

    Not report

   NAS

a) Evidence codes - IDA: Inferred from Direct Assay; TAS: Traceable Author Statement (i.e., a direct report exists in the literature); NAS: Non-traceable Author 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 [25].

Genome sequencing information

Genome project history

This organism was selected for sequencing on the basis of its phylogenetic position and its serious virulence in humans compared to the reptiles. This Whole Genome Shotgun project has been deposited at DDBJ/EMBL/GenBank under the accession ANHR00000000. The version described in this paper is the first version, ANHR01000000, and the sequence consists of 97 large contigs. Table 2 presents the project information and its association with MIGS version 2.0 compliance [12].

Table 2

Project information

MIGS ID

   Property

    Term

MIGS-31

   Finishing quality

    Draft

MIGS-28

   Libraries used

    Illumina Paired-End library

MIGS-29

   Sequencing platforms

    Illumina HiSeq 2000

MIGS-31.2

   Fold coverage

    100 ×

MIGS-30

   Assemblers

    SOAPdenovo v1.05

MIGS-32

   Gene calling method

    RAST

   Genbank ID

    ANHR00000000

   GOLD ID

    Gi21447

   Project relevance

    Evolution in bacteria, human pathogen

Growth conditions and DNA isolation

S. enterica subsp. houtenae strain RKS3027 was grown Luria Broth (LB) medium at 37°C. The DNA was extracted from the cell, concentrated and purified using the Qiamp kit (Qiagen), as detailed in the manual for the instrument.

Genome sequencing and assembly

The genome of S. enterica subsp. houtenae RKS3027 was sequenced using the Illumina sequencing platform by the paired-end strategy (2×100bp). The details of library construction and sequencing can be found at the Illumina web site [26]. The final coverage reached 100-fold for an estimated genome size of 4.5 Mb. The sequence data from Illumina HiSeq 2000 were assembled with SOAPdenovo v1.05. The final assembly contained 97 large contigs (>3000 bp) in 59 scaffolds generating a genome size of 4.4 Mb.

Genome annotation

Genes were predicted using RAST (Rapid Annotation using Subsystem Technology) [27] with gene caller GLIMMER3 [28] followed by manual curation. The predicted bacterial protein sequences were compared with the annotated genes from four available Salmonella genomes, i.e., S. enterica subsp. enterica Typhi P-stx-12, S. enterica subsp. enterica Heidelberg B182, S. enterica subsp. enterica Typhimurium UK-1 and S. enterica subsp. enterica Typhimurium 4/74 and searched against the Clusters of Orthologous Groups (COG) databases using BLASTP. The BLAST results were filtered with the following parameters: identities >90% and compared length >70%. CGViewer was used for visualization of genomic features [29].

Genome properties

The genome of S. enterica subsp. houtenae RKS3027 is 4,404,136 bp long (97 contigs) with a 51.68% G + C content (Table 3 and Figure 2). Of the 4,363 predicted genes, 4,335 were protein-coding genes, and 28 were RNAs (1 5S rRNA gene and 27 predicted tRNA genes). A total of 3,378 genes (77.42%) were assigned a putative function. The remaining genes were annotated as hypothetical proteins. The properties and statistics of the genome are summarized in Table 3. The distribution of genes into COGs functional categories is presented in Table 4.

Table 3

Nucleotide content and gene count levels of the genome

Attribute

   Value

      % of totala

Genome size (bp)

   4,404,136

DNA coding region (bp)

   3,824,952

      86.85

DNA G+C content (bp)

   2,276,005

      51.68

Total genes

   4,363

      100

RNA genes

   28

      0.06

Protein-coding genes

   4,335

      99.36

Genes assigned to COGs

   3,378

      77.42

a) The total is based on either the size of the genome in base pairs or the total number of protein coding genes in the annotated genome.

Figure 2

Graphical circular map of the S. enterica subsp. houtenae strain RKS 3027 genome. From the outside to the center: genes on forward strand (color by COG categories), genes on reverse strand (color by COG categories), GC content, GC skew. The map was generated with the CGviewer software.

Table 4

Number of genes associated with the 25 general COG functional categories

Code

   Value

   %agea

    Description

J

   163

   3.76

    Translation

A

   1

   0.02

    RNA processing and modification

K

   281

   6.48

    Transcription

L

   176

   4.06

    Replication, recombination and repair

B

   0

   0.00

    Chromatin structure and dynamics

D

   32

   0.74

    Cell cycle control, mitosis and meiosis

Y

   0

   0.00

    Nuclear structure

V

   48

   1.11

    Defense mechanisms

T

   103

   2.38

    Signal transduction mechanisms

M

   235

   5.42

    Cell wall/membrane biogenesis

N

   95

   2.19

    Cell motility

Z

   0

   0.00

    Cytoskeleton

W

   0

   0.00

    Extracellular structures

U

   41

   0.95

    Intracellular trafficking and secretion

O

   138

   3.18

    Posttranslational modification, protein turnover, chaperones

C

   254

   5.86

    Energy production and conversion

G

   343

   7.91

    Carbohydrate transport and metabolism

E

   319

   7.36

    Amino acid transport and metabolism

F

   77

   1.78

    Nucleotide transport and metabolism

H

   131

   3.02

    Coenzyme transport and metabolism

I

   89

   2.05

    Lipid transport and metabolism

P

   175

   4.04

    Inorganic ion transport and metabolism

Q

   47

   1.08

    Secondary metabolites biosynthesis, transport and catabolism

R

   318

   7.34

    General function prediction only

S

   312

   7.20

    Function unknown

-

   957

   22.08

    Not in COGs

a) The total is based on the total number of protein coding genes in the annotated genome.

Declarations

Acknowledgments

This work was supported by grants of the National Natural Science Foundation of China (NSFC30970119, 81030029, 81271786, NSFC-NIH 81161120416) to SLL.


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