Open Access

Genome sequence of the haloarchaeon Haloterrigena jeotgali type strain A29T isolated from salt-fermented food

  • In-Tae Cha1, 2,
  • Mi-Hwa Lee3,
  • Byung-Yong Kim4,
  • Yong-Joon Cho4,
  • Dae-Won Kim5,
  • Kyung June Yim1,
  • Hye Seon Song1,
  • Myung-Ji Seo2,
  • Jin-Kyu Rhee6,
  • Jong-Soon Choi1, 7,
  • Hak-Jong Choi8,
  • Changmann Yoon1,
  • Seong Woon Roh1, 9Email author and
  • Young-Do Nam3, 9Email author
Contributed equally
Standards in Genomic Sciences201510:49

DOI: 10.1186/s40793-015-0047-4

Received: 22 September 2014

Accepted: 21 July 2015

Published: 5 August 2015

Abstract

Haloterrigena jeotgali is a halophilic archaeon within the family Natrialbaceae that was isolated from shrimp jeotgal, a traditional Korean salt-fermented food. A29T is the type strain of H. jeotgali, and is a Gram-negative staining, non-motile, rod-shaped archaeon that grows in 10 %–30 % (w/v) NaCl. We present the annotated H. jeotgali A29T genome sequence along with a summary of its features. The 4,131,621 bp genome with a GC content of 64.9 % comprises 4,215 protein-coding genes and 127 RNA genes. The sequence can provide useful information on genetic mechanisms that enable haloarchaea to endure a hypersaline environment.

Keywords

Haloarchaeon Haloterrigena jeotgali Genome sequence Salt-fermented food Jeotgal

Introduction

An extremely halophilic archaeon, called a haloarchaeon, that is a member of the family Natrialbaceae [1] was isolated from various hypersaline environments such as soda and salt lakes, solar salterns, salt mines, salted soils, deep-sea brine, and various salt-fermented foods. Although high salinity is toxic to most cells, extreme halophiles are adapted to their hypersaline environments [2]. Most halophilic archaea require at least 1.5 M NaCl for growth and optimum growth occurs in the range of 3.1 to 3.4 M NaCl [3]. Since halophilic enzymes from the haloarchaea are generally considered to be active and stable at high salt concentrations, they have potential for biotechnological applications such as engineering for salt-resistant plants in agriculture, environmental bioremediation of organic pollutants and production of fermented foods. The genus Haloterrigena was first proposed by Ventosa et al. [4] with the reclassification of Halococcus turkmenicus as Haloterrigena turkmenica [4], and presently includes nine species: H. turkmenica [4], H. thermotolerans [5], H. longa , H. limicola [6], H. saccharevitans [7], H. hispanica [8], H. jeotgali [9], H. salina [10], and H. daqingensis [11], all of which are pleomorphic, Gram-negative staining, and red- or light pink-pigmented. However, the genus Haloterrigena is poorly characterized at the genome level.

A29T (= KCTC 4020T = DSM 18794T = JCM 14585T = CECT 7218T) is the type strain of H. jeotgali and was isolated from shrimp jeotgal, a traditional Korean salt-fermented food [9]. Although little is known about the roles of the haloarchaea during the fermentation process, the increasing genome information is expected to contribute to expansion of the understanding of their roles and halotolerant features. Here, we present a summary of the classification and features of H. jeotgali A29T along with the annotated genome sequence.

Organism information

Classification and features

A taxonomic analysis was conducted by comparing the H. jeotgali A29T 16S rRNA gene sequence with the most recent release of the EzTaxon-e database [12]. Phylogenetic relationships between strain A29T and closely related species were evaluated using MEGA6 program [13], and dendrograms were generated by the neighbor-joining [14], minimum evolution [15], and maximum likelihood [16] methods. A bootstrap analysis investigating the stability of the dendrogram was performed by obtaining a consensus tree based on 1,000 randomly generated trees. Strain A29T showed the highest level of the 16S rRNA gene similarity to H. thermotolerans PR5T (99.0 %), H. saccharevitans AB14T (98.3 %), H. limicola AX-7T (97.1 %), H. turkmenica 4kT (96.8 %), H. salina XH-65T (96.6 %), H. hispanica FP1T (96.1 %), H. longa ABH32T (94.9 %), and H. daqingensis JX313T (94.6 %). The DNA-DNA relatedness between strain A29T and the related strains H. thermotolerans PR5T, H. saccharevitans AB14T, and H. limicola AX-7T was 23.2 %, 22.0 %, and 17.9 %, respectively. The 16S rRNA gene sequence similarity data and DNA–DNA relatedness value of less than 70 % [17] suggested that strain A29T represents a distinct genospecies [9] (Table 1). The consensus phylogenetic tree based on the 16S rRNA gene sequences indicated that strain A29T was clustered in a branch with other species of the genus Haloterrigena (Fig. 1).
Table 1

Classification and general features of Haloterrigena jeotgali A29T [19]

MIGS ID

Property

Term

Evidence codea

 

Classification

Domain Archaea

TAS [25]

 

Phylum Euryarchaeota

TAS [26]

 

Class Halobacteria

TAS [27, 28]

 

Order Natrialbales

TAS [1]

 

Family Natrialbaceae

TAS [1]

 

Genus Haloterrigena

TAS [4]

 

Species Haloterrigena jeotgali

TAS [9]

 

(Type) strain A29T (KCTC 4020, DSM 18794, JCM 14585, CECT 7218)

TAS [9]

 

Gram stain

Negative

TAS [9]

 

Cell shape

Rod

TAS [9]

 

Motility

Non-motile

TAS [9]

 

Sporulation

Not reported

 
 

Temperature range

17–50 °C

TAS [9]

 

Optimum temperature

37–45 °C

TAS [9]

 

pH range; Optimum

6.5–8.5; 7.0 − 7.5

TAS [9]

 

Carbon source

Fructose, lactose, acetate

TAS [9]

MIGS-6

Habitat

Salt-fermented food

TAS [9]

MIGS-6.3

Salinity

35 % NaCl (w/v)

TAS [9]

MIGS-22

Oxygen requirement

Aerobic

TAS [9]

MIGS-15

Biotic relationship

Free-living

TAS [9]

MIGS-14

Pathogenicity

Not reported

 

MIGS-4

Geographic location

South Korea

TAS [9]

MIGS-5

Sample collection

2006

NAS

MIGS-4.1

Latitude

Not reported

 

MIGS-4.2

Longitude

Not reported

 

MIGS-4.4

Altitude

Not reported

 

aEvidence codes - 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 [29]

Fig. 1

Phylogenetic tree based on the neighbor-joining (NJ) algorithm for the 16S rRNA gene sequences of strain A29T and closely related taxa. Numbers at the nodes indicate bootstrap values calculated using NJ/minimum evolution (ME)/maximum likelihood (ML) probabilities. Filled and open circles represent nodes recovered by both ME and ML methods or by either method, respectively. Methanospillum hangatei JF-1T served as an outgroup

H. jeotgali A29T is Gram-negative staining, non-motile, rod-shaped (0.4 μm wide and 1.0 μm long) (Fig. 2), and grows in irregular clusters. Colonies cultured on complex agar medium were light red, circular, and measured 0.5 mm in diameter after 7 days at 37 °C. Growth occurred in the presence of 10–30 % (w/v) NaCl at temperatures ranging from 17–50 °C and in the pH range of 6.5–8.5. Optimal conditions for growth were; a NaCl concentration of 15–20 % (w/v), a temperature ranging from 37–45 °C, and a pH of 7.0–7.5. The isolate was catalase-positive and oxidase-negative and did not reduce nitrate to nitrite. Mg2+ was not required for growth. Cell lysis occurred in distilled water. This strain was able to hydrolyze casein and Tween 80 but not starch, gelatin, urea, or DNA. Anaerobic growth occurred in the presence of nitrate but not of sulfate, thiosulfate, dimethyl sulfoxide, or trimethylamine N-oxide. Fructose, lactose, and acetate—but not sucrose, glucose, citrate, or formate—were utilized as carbon and energy sources. Acid was not produced from fructose, lactose, acetate, sucrose, glucose, citrate, or formate. Strain A29T was resistant to bacitracin, penicillin, ampicillin, chloramphenicol, and erythromycin, but was sensitive to novobiocin, anisomycin, and aphidicolin. The major polar lipids were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, and mannose-2,6-disulfate(1–2)-glucose glycerol diether [9].
Fig. 2

Transmission electron micrograph of H. jeotgali A29T. The scale bar represents 200 nm

Genome sequencing and annotation

Genome project history

H. jeotgali strain A29T genome was sequenced to obtain information regarding mechanism(s) or molecule(s) that confer adaption to a hypersaline environment and to identify the primary structure of potentially novel halophilic enzymes with relatively low similarity to those in the sequence database. The genome project and sequence were deposited in the Genomes OnLine Database [18] and GenBank (JDTG00000000), respectively. Sequencing and annotation were performed by ChunLab Inc. (Seoul, Korea). Project information and associated MIGS version 2.0 compliance levels [19] are shown in Table 2.
Table 2

Project information

MIGS ID

Property

Term

MIGS-31

Finishing quality

Improved-high-quality draft

MIGS-28

Libraries used

300-bp paired end (Illumina); 400-bp single end (Ion Torrent); 10 kb (PacBio RS)

MIGS-29

Sequencing platforms

Illumina MiSeq, Ion Torrent PGM, PacBio RS system

MIGS-31.2

Fold coverage

700.5×

MIGS-30

Assemblers

CLC Genomics Workbench 6.5.1, SMRT Analysis 2.1

MIGS-32

Gene calling method

GLIMMER 3.02

 

Locus Tag

HL44

 

GenBank ID

JDTG00000000

 

GenBank Date of Release

June 20, 2014

 

GOLD ID

Gi0069863

 

BIOPROJECT

PRJNA236631

MIGS-13

Source material identifier

A29T

 

Project relevance

Environmental and biotechnological

Growth conditions and genomic DNA preparation

H. jeotgali A29T was grown aerobically in DSM Medium 954 at 37°C. Genomic DNA was extracted and purified using a G-spin™ DNA extraction kit (iNtRON Biotechnology, Sungnam, Korea) according to the manufacturer’s instructions.

Genome sequencing and assembly

The genome of H. jeotgali A29T was sequenced from a total of 9,473,809 quality-trimmed sequencing reads (700.5-fold coverage) that combined 6,797,702 reads (473.8-fold coverage) from the Illumina MiSeq. 300 bp paired-end library (Illumina, San Diego, CA, USA); 2,617,102 reads (181.1-fold coverage) obtained using an Ion Torrent Personal Genome Machine (PGM) 318v2 chip (Life Technologies, Carlsbad, CA, USA); and 59,005 reads (45.7-fold coverage) from a PacBio RS 10 kb library (Pacific Biosciences, Menlo Park, CA, USA). Illumina and PGM data were assembled de novo with CLC Genomics Workbench 6.5.1 (CLC bio, Boston, MA, USA) and PacBio data were assembled with the HGAP2 algorithm in SMRT Analysis 2.1 (Pacific Biosciences). Resultant contigs were assembled with CodonCode Aligner 3.7 (CodonCode Corporation, Centerville, MA, USA). The final assembly yielded three scaffolds with 20 contigs spanning 4.1 Mb.

Genome annotation

Open reading frames of the assembled genome were predicted using the Integrated Microbial Genomes-Expert Review platform as part of the Joint Genome Institute genome annotation pipeline [20]. Additional gene prediction and functional annotation were achieved using the Rapid Annotation using Subsystem Technology pipeline. Predicted ORFs were compared during gene annotation using NCBI Clusters of Orthologous Groups [21], Pfam [22], and EzTaxon-e [12] databases. rRNA and tRNA genes were identified using RNAmmer 1.2 [23] and tRNAscan-SE 1.23 [24] tools, respectively. Genomic features were visualized with CLgenomics 1.06 (ChunLab Inc.).

Genome properties

The draft genome sequence of H. jeotgali A29T was 4,131,621 bp and comprised three scaffolds including 20 contigs, and had a GC content of 64.9 % (Fig. 3 and Table 3). Of the 4,342 predicted genes, 4,215 were protein-coding and 2,636 ORFs (60.7 %) were assigned putative functions, whereas the remaining genes were annotated as hypothetical proteins. The genome contained 127 ORFs assigned to RNA genes, including 47 predicted for tRNA, 14 for rRNA (five 5S, two 16S, and seven 23S), and 66 for miscellaneous RNA (one archaeal signal recognition particle; five for the HgcC family; one archaeal RNA P; and 59 clustered regularly interspaced short palindromic direct repeat elements). The distribution of genes across COG functional categories is presented in Table 4.
Fig. 3

Graphical circular map of the H. jeotgali A29T genome. RNA genes (red, tRNA and blue, rRNA) and genes on the reverse and forward strands (colored according to COG categories) are shown from the outside to the center. The inner circle shows the GC skew; yellow and blue indicate positive and negative values, respectively. GC content is indicated in red and green

Table 3

Genomic statistics

Attribute

Value

% of Total

Genome size (bp)

4,131,621

100.00

DNA coding (bp)

3,538,864

85.65

DNA G + C (bp)

2,682,192

64.92

DNA scaffolds

20

100.00

Total genes

4,342

100.00

Protein-coding genes

4,215

97.08

RNA genes

127

2.92

Genes in internal clusters

3,412

78.58

Genes with function prediction

2,636

60.71

Genes assigned to COGs

2,144

49.38

Genes with Pfam domains

2,638

60.76

Genes with signal peptides

79

1.82

Genes with transmembrane helices

984

22.66

CRISPR repeats

1

 
Table 4

Number of genes associated with general COG functional categories

Code

Value

% age

Description

J

154

6.53

Translation, ribosomal structure, and biogenesis

A

1

0.04

RNA processing and modification

K

107

4.54

Transcription

L

129

5.47

Replication, recombination, and repair

B

3

0.13

Chromatin structure dynamics

D

19

0.81

Cell cycle control, mitosis, and meiosis

Y

0

0.00

Nuclear structure

V

31

1.31

Defense mechanisms

T

78

3.31

Signal transduction mechanisms

M

69

2.93

Cell wall/membrane biogenesis

N

17

0.72

Cell motility

Z

0

0.00

Cytoskeleton

W

0

0.00

Extracellular structures

U

21

0.89

Intracellular trafficking, secretion, and vesicular transport

O

101

4.28

Posttranslational modification, protein turnover, chaperones

C

167

7.08

Energy production conversion

G

88

3.73

Carbohydrate transport metabolism

E

217

9.20

Amino acid transport metabolism

F

66

2.80

Nucleotide transport metabolism

H

131

5.56

Coenzyme transport metabolism

I

125

5.30

Lipid transport metabolism

P

158

6.70

Inorganic ion transport metabolism

Q

50

2.12

Secondary metabolites biosynthesis, transport catabolism

R

400

16.96

General function prediction only

S

226

9.58

Function unknown

-

2198

50.62

Not in COGs

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

Conclusions

H. jeotgali A29T encoded the genes associated with the mechanisms of salinity tolerance, biosynthesis and transport of compatible solutes such as glycine betaine (N,N,N-trimethylglycine) (choline sulfatase, choline dehydrogenase, betaine reductase, and glycine betaine transporter OpuD), ion exclusion using cation (Mg2+ and Cu2+) transport and K+ transport and Na+/H+ antiporter systems. The sequences may contribute to expansion of our knowledge of complex osmoregulation mechanism of the haloarchaea that should facilitate biotechnological applications of the haloarchaea and provide useful information on genetic mechanisms that enable haloarchaea to endure hypersaline environments.

Notes

Abbreviations

ME: 

Minimum evolution

ML: 

Maximum likelihood

NJ: 

Neighbor-joining

PGM: 

Personal Genome Machine

Declarations

Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning (2012R1A1A2040922 and 2014R1A1A1002980) and a Korea Basic Science Institute NAP grant (T34780).

Authors’ Affiliations

(1)
Biological Disaster Analysis Team, Korea Basic Science Institute
(2)
Division of Bioengineering, Incheon National University
(3)
Research Group of Gut Microbiome, Korea Food Research Institute
(4)
ChunLab Inc., Seoul National University
(5)
Systems Biology Team, Center for Immunity and Pathology, Korea National Institute of Health
(6)
Department of Food Science and Engineering, Ewha Womans University
(7)
Graduate School of Analytical Science and Technology, Chungnam National University
(8)
World Institute of Kimchi
(9)
Korea University of Science and Technology

References

  1. Gupta RS, Naushad S, Baker S. Phylogenomic analyses and molecular signatures for the class Halobacteria and its two major clades: a proposal for division of the class Halobacteria into an emended order Halobacteriales and two new orders, Haloferacales ord. nov. and Natrialbales ord. nov. Int J Syst Evol Microbiol. 2015;65:1050–69.PubMedView ArticleGoogle Scholar
  2. Grant WD. Life at low water activity. Philos Trans R Soc Lond B Biol Sci. 2004;59:1249–66.View ArticleGoogle Scholar
  3. Oren A. Sensitivity of selected members of the family Halobacteriaceae to quinolone antimicrobial compounds. Arch Microbiol. 1996;165:354–8.PubMedView ArticleGoogle Scholar
  4. Ventosa A, Gutierrez MC, Kamekura M, Dyall-Smith ML. Proposal to transfer Halococcus turkmenicus, Halobacterium trapanicum JCM 9743 and strain GSL-11 to Haloterrigena turkmenica gen. nov., comb. nov. Int J Syst Bacteriol. 1999;49:131–6.PubMedView ArticleGoogle Scholar
  5. Montalvo-Rodriguez R, Lopez-Garriga J, Vreeland RH, Oren A, Ventosa A, Kamekura M. Haloterrigena thermotolerans sp. nov., a halophilic archaeon from Puerto Rico. Int J Syst Evol Microbiol. 2000;50:1065–71.PubMedView ArticleGoogle Scholar
  6. Cui HL, Tohty D, Zhou PJ, Liu SJ. Haloterrigena longa sp. nov. and Haloterrigena limicola sp. nov., extremely halophilic archaea isolated from a salt lake. Int J Syst Evol Microbiol. 2006;56:1837–40.PubMedView ArticleGoogle Scholar
  7. Xu XW, Liu SJ, Tohty D, Oren A, Wu M, Zhou PJ. Haloterrigena saccharevitans sp. nov., an extremely halophilic archaeon from Xin-Jiang, China. Int J Syst Evol Microbiol. 2005;55:2539–42.PubMedView ArticleGoogle Scholar
  8. Romano I, Poli A, Finore I, Huertas FJ, Gambacorta A, Pelliccione S, et al. Haloterrigena hispanica sp. nov., an extremely halophilic archaeon from Fuente de Piedra, southern Spain. Int J Syst Evol Microbiol. 2007;57:1499–503.PubMedView ArticleGoogle Scholar
  9. Roh SW, Nam YD, Chang HW, Kim KH, Sung Y, Kim MS, et al. Haloterrigena jeotgali sp. nov., an extremely halophilic archaeon from salt-fermented food. Int J Syst Evol Microbiol. 2009;59:2359–63.PubMedView ArticleGoogle Scholar
  10. Gutierrez MC, Castillo AM, Kamekura M, Ventosa A. Haloterrigena salina sp. nov., an extremely halophilic archaeon isolated from a salt lake. Int J Syst Evol Microbiol. 2008;58:2880–4.PubMedView ArticleGoogle Scholar
  11. Wang S, Yang Q, Liu ZH, Sun L, Wei D, Zhang JZ, et al. Haloterrigena daqingensis sp. nov., an extremely haloalkaliphilic archaeon isolated from a saline-alkaline soil. Int J Syst Evol Microbiol. 2010;60:2267–71.PubMedView ArticleGoogle Scholar
  12. Kim OS, Cho YJ, Lee K, Yoon SH, Kim M, Na H, et al. Introducing EzTaxon-e: a prokaryotic 16S rRNA gene sequence database with phylotypes that represent uncultured species. Int J Syst Evol Microbiol. 2012;62:716–21.PubMedView ArticleGoogle Scholar
  13. Tamura K, Stecher G, Peterson D, Filipski A, Kumar S. MEGA6: Molecular Evolutionary Genetics Analysis version 6.0. Mol Biol Evol. 2013;30:2725–9.PubMed CentralPubMedView ArticleGoogle Scholar
  14. Saitou N, Nei M. The neighbor-joining method: a new method for reconstructing phylogenetic trees. Mol Biol Evol. 1987;4:406–25.PubMedGoogle Scholar
  15. Rzhetsky A, Nei M. A simple method for estimating and testing minimum-evolution trees. Mol Biol Evol. 1992;9:945–67.Google Scholar
  16. Felsenstein J. Evolutionary trees from DNA sequences: a maximum likelihood approach. J Mol Evol. 1981;17:368–76.PubMedView ArticleGoogle Scholar
  17. Wayne LG, Brenner DJ, Colwell RR, Grimont PAD, Kandler O, Krichevsky MI, et al. International Committee on Systematic Bacteriology. Report of the ad hoc committee on reconciliation of approaches to bacterial systematics. Int J Syst Bacteriol. 1987;37:463–4.View ArticleGoogle Scholar
  18. Liolios K, Chen IM, Mavromatis K, Tavernarakis N, Hugenholtz P, Markowitz VM, et al. The Genomes On Line Database (GOLD) in 2009: status of genomic and metagenomic projects and their associated metadata. Nucleic Acids Res. 2010;38:346–54.View ArticleGoogle Scholar
  19. Field D, Garrity G, Gray T, Morrison N, Selengut J, Sterk P, et al. The minimum information about a genome sequence (MIGS) specification. Nat Biotechnol. 2008;26:541–7.PubMed CentralPubMedView ArticleGoogle Scholar
  20. Markowitz VM, Mavromatis K, Ivanova NN, Chen IM, Chu K, Kyrpides NC. IMG ER: a system for microbial genome annotation expert review and curation. Bioinformatics. 2009;25:2271–8.PubMedView ArticleGoogle Scholar
  21. Tatusov RL, Galperin MY, Natale DA, Koonin EV. The COG database: a tool for genome-scale analysis of protein functions and evolution. Nucleic Acids Res. 2000;28:33–6.PubMed CentralPubMedView ArticleGoogle Scholar
  22. Finn RD, Bateman A, Clements J, Coggill P, Eberhardt RY, Eddy SR, et al. Pfam: the protein families database. Nucleic Acids Res. 2014;42:222–30.View ArticleGoogle Scholar
  23. Lagesen K, Hallin P, Rodland EA, Staerfeldt HH, Rognes T, Ussery DW. RNAmmer: consistent and rapid annotation of ribosomal RNA genes. Nucleic Acids Res. 2007;35:3100–8.PubMed CentralPubMedView ArticleGoogle Scholar
  24. Lowe TM, Eddy SR. tRNAscan-SE: a program for improved detection of transfer RNA genes in genomic sequence. Nucleic Acids Res. 1997;25:955–64.PubMed CentralPubMedView ArticleGoogle Scholar
  25. Woese CR, Kandler O, Wheelis ML. Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya. Proc Natl Acad Sci U S A. 1990;87:4576–9.PubMed CentralPubMedView ArticleGoogle Scholar
  26. Garrity GM, Holt JG. Phylum AII. Euryarchaeota phy. nov. In: Boone DR, Castenholz RW, Garrity GM, editors. Bergey’s Manual of Systematic Bacteriology, vol. 2. 2nd ed. New York: Springer; 2001. p. 211.View ArticleGoogle Scholar
  27. Editor L. Validation List no. 85. Validation of publication of new names and new combinations previously effectively published outside the IJSEM. Int J Syst Evol Microbiol. 2002;52:685–90.View ArticleGoogle Scholar
  28. Grant WD, Kamekura M, McGenity TJ, Ventosa A. Class III. Halobacteria class nov. In: Boone DR, Castenholz RW, Garrity GM, editors. Bergey’s Manual of Systematic Bacteriology, vol. 2. 2nd ed. New York: Springer; 2001. p. 294–334.Google Scholar
  29. Ashburner M, Ball CA, Blake JA, Botstein D, Butler H, Cherry JM, et al. Gene ontology: tool for the unification of biology. The Gene Ontology Consortium. Nat Genet. 2000;25:25–9.PubMed CentralPubMedView ArticleGoogle Scholar

Copyright

© Cha et al. 2015

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