ars.els-cdn.com · web viewedgar, r.c. (2013) uparse: highly accurate otu sequences from microbial...
TRANSCRIPT
Supporting Information
Exploring abundance, diversity and variation of a widespread antibiotic
resistance gene in wastewater treatment plants
Ziyan Wei a,c, Kai Feng a,c, Shuzhen Li a,d, Yu Zhang b,c, Hongrui Chen b,c, Huaqun Yin e, Meiying
Xu f, Ye Deng a,c*
a Key Laboratory of Environmental Biotechnology of CAS, Research Center for Eco-
Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
b State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-
Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
c College of Resources and Environment, University of Chinese Academy of Sciences, Beijing
100049, China
d State Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of
Education, China), School of Environmental Science and Technology, Dalian University of
Technology, Dalian 116024, China
e School of Minerals Processing and Bioengineering, Central South University, Changsha 410083,
China
f State Key Laboratory of Applied Microbiology Southern China, Guangdong Institute of
Microbiology, Guangzhou 510070, China
Correspondence
Ye Deng
E-mail: [email protected]
Number of pages: 17
Number of additional text: 1
11 Tables and 1 Figures
Table of contents
Text S1 Methods
SPAGE \* MERGEFORMAT17
Table S1 Operational parameters of five urban sewage WWTPs
Table S2 Wastewater characteristics in five WWTPs in two seasons
Table S3 Primer pairs commonly used for the amplification of sul1 gene including target length
and primer coverage
Table S4 Quantitative amplification conditions and quality control of qPCR methods
Table S5 Dissimilarity test of bacterial communities among different sites and seasons based on
Bray-curtis
Table S6 Pearson correlations among different wastewater and operational parameters
Table S7 Correlations between bacterial community and environmental properties analyzed by
Mantel test based on Bray-curtis and Jaccard
Table S8 Initial and corrected bacterial quantity in different WWTPs between summer and winter
(average total abundance of OTUs)
Table S9 Dissimilarity test of total sul1-clusters in activated sludge among different sites and
seasons based on Bray-curtis
Table S10 Pearson correlation between relative abundance of dominant bacterial genera and major
clusters of sul1 gene
Table S11 The correlation between absolute abundance of sul1 and int1 genes in activated sludge
Fig. S1 Bacterial composition of activated sludge from five WWTPs in summer and winter at the
class-level
SPAGE \* MERGEFORMAT17
Text S1 Methods
DNA Extraction. 1 mL of each sample was centrifuged at 12,000×g for 10 min at 4 °C. Then 0.25
gram sediment (wet weight) after centrifugation was collected for DNA extraction in duplicate
with a FastDNA SPIN kit for soil (Qbiogene, Solon OH) according to the manufacturer’s manual.
During each sampling season, 6 replicate DNA samples (3 biological replicates × 2 experimental
replicates) were obtained from each wastewater treatment plant. The environmental DNA was
detected by 1% agarose gel electrophoresis and quantified with NanoDrop 2000 (Nanodrop,
USA).
Specificity assessment of the degenerate primers for sul1 gene. Experimentally, the PCR
products amplified with 51F and 280R were ligated to pMD18-T vector (TAKARA) and inserted
into E-coli., then plasmids were extracted from positive clones by the TIANpure Mini Plasmid kit
(TianGen, China) and sequenced by Sangon Biotech (Shanghai) Co., Ltd. The positive clones
were selected by penbritin and blue-white spot screening, they were annotated as sul1 gene and
there were no sequences annotated as other antibiotic resistance genes by BLASTn with the
Genbank nucleotide database. In this way, the specificity of the new primers was satisfactory, and
the standard plasmid of sul1 gene was obtained for further qPCR experiment.
Protocols of quantification of sul1, int1, and 16S rRNA genes by qPCR. Quantitative PCR was
performed with the CFX96 Touch Real-Time PCR Detection System (BioRad). The standard
plasmids were extracted from the Escherichia coli containing sul1, int1, and 16S rRNA genes by
the TIANpure Mini Plasmid kit (TianGen, China). The standard curves prepared from serial 10-
fold dilutions of standard plasmids covering 5-8 orders of magnitude, with high specificity of
primers, R2 value higher than 0.99, and proper amplification efficiencies (90 - 110%), could ensure
reliable quantification (Table S4).The qPCR program consisted of initial denaturing for 15 min at
95 C, followed by 40 cycles of 10 sec at 95 C, 30 sec at annealing temperatures (60 C, 58 C,
and 50 C for sul1, int1 and 16S rRNA genes, respectively), and a final melt curve stage with
temperature ramping form 50 C to 95 C (0.5 per read, 5 sec hold).
Amplification of 16S rRNA, sul1 genes before sequencing. PCR amplification was performed
in a mixture of 50 μL, including 5 μL DNA template, 2.5 U of Taq DNA Polymerase (TaKaRa), 1
× Taq buffer, 75 μM dNTP and 0.3 μM of each primer. Total 30 cycles (94 C for 20 sec, annealing
SPAGE \* MERGEFORMAT17
temperature (57 C for 16S rRNA gene or 60 C for sul1 gene) for 25 sec, and 68 C for 45 sec)
were performed after 1 min of denaturation at 94 C, followed by final extension at 68 C for 10
min. PCR products were detected by agarose gel electrophoresis, and purified by recovering the
gel using Gel Extraction Kit (OMEGA BioTek).
Sequence data processing. Raw sequencing data were preprocessed and analyzed by the
following tools integrated in an in-house Galaxy Pipeline (http://mem.rcees.ac.cn:8080/),
including FLASH program (Magoc and Salzberg 2011) for combination of paired-end reads,
Btrim (Kong 2011) for sequence quality trimming, Uparse (Edgar 2013) and Uclust (Edgar 2010)
for chimeras detection and operational taxonomy units (OTUs) generation, and taxonomy
assignment of 16S rRNA sequences against the Greengenes database (DeSantis et al. 2006).
SPAGE \* MERGEFORMAT17
Table S1 Operational parameters of five urban sewage WWTPs
WWTPsSecondary
treatment
HRT
(h)
SRT
(d)
Actual
treatment
capacity (m3/d)
Population
equivalent
(104)
Sludge
yield
(kg/d)
Influent
composition
BJ MBR 16.5 20 150,000 22 88,000 domestic sewage
QDN A/A/O 21 19 170,000 80 126,000
mainly domestic
sewage and part of
industrial sewage
QDS A/A/O 21 13 100,000 26 11,800
mainly domestic
sewage and part of
industrial sewage
WXNC-orbal
OD20 15 150,000 50 120,000
mainly domestic
sewage and part of
industrial sewage
WXS A/A/O 18 19 100,000 82 89,000 domestic sewage
MBR: Membrane bio-reactor; A/A/O: Anaerobic-anoxic-oxic; C-orbal OD: Combined orbal oxidation ditch; HRT:
Hydraulic retention time; SRT: Sludge Retention Time
SPAGE \* MERGEFORMAT17
Table S2 Wastewater characteristics in five WWTPs in two seasons
SampleDO
(mg/L)pH
Temper
ature
(C)
COD_
inflow
(mg/L)
COD_
effluent
(mg/L)
TN_
inflow
(mg/L)
TN_
effluent
(mg/L)
TP_
inflow
(mg/L)
TP_
effluent
(mg/L)
BJ6 2.14 7.15 21.30 225.00 30.00 65.09 8.34 5.50 0.50
BJ12 2.02 7.19 11.57 225.00 30.00 65.09 8.34 5.50 0.50
QDN6 1.77 7.04 23.90 950.00 50.00 80.00 8.00 13.00 0.50
QDN12 2.20 7.13 11.17 950.00 50.00 80.00 8.00 13.00 0.50
QDS6 1.89 7.14 25.40 1000.00 50.00 100.00 15.00 15.00 0.50
QDS12 2.17 7.02 12.87 1000.00 50.00 100.00 15.00 15.00 0.50
WXN6 2.05 6.83 24.47 344.28 28.44 34.39 13.58 3.68 0.23
WXN12 1.72 7.33 14.93 344.28 28.44 34.39 13.58 3.68 0.23
WXS6 1.91 7.17 25.70 220.92 30.69 37.82 12.84 6.92 0.38
WXS12 1.81 7.17 14.80 220.92 30.69 37.82 12.84 6.92 0.38
DO: dissolved oxygen; COD: chemical oxygen demand; TN: total nitrogen; TP: total phosphorus.
SPAGE \* MERGEFORMAT17
Table S3 Primer pairs commonly used for the amplification of sul1 gene including target length
and primer coverage
Primer name
Targeted
length
(bp)
Primer sequences (5′-3′)
Primer coverage (%)
(0 Mismatch)
Updated sul1
gene sequence
database
Sul1-
ARDB
Degenerate Primer 23551F: AAATGCTGCGAGTYGGMKCA 86.41 99.07
280R: AACMACCAKCCTRCAGTCCG 83.39 93.81
sul1_1
(Van et al. 2008)822
F: TTCGGCATTCTGAATCTCAC 85.25 97.83
R: ATGATCTAACCCTCGGTCTC 70.62 79.57
sul1_2
(Ma et al. 2007)793
F: TTTCCTGACCCTGCGCTCTAT 85.02 97.21
R: GTGCGGACGTAGTCAGCGCCA 76.66 88.24
sul1_3
(Kerrn et al. 2002)433
F: CGGCGTGGGCTACCTGAACG 84.55 97.21
R: GCCGATCGCGTGAAGTTCCG 77.24 89.16
sul1_4
(Pyatov et al. 2014)160
F: GACGAGATTGTGCGGTTCTT 82.11 92.88
R: CCGACTTCAGCTTTTGAAGG 77.93 89.16
sul1_5
(Toleman et al. 2006)840
F: ATGGTGACGGTGTTCGGCATTCTGA 81.04 93.81
R: CTAGGCATGATCTAACCCTCGGTCT 70.17 79.26
sul1_6
(Sáenz et al. 2004)789
F: TGGTGACGGTGTTCGGCATTC 81.42 93.81
R: GCGAGGGTTTCCGAGAAGGTG 67.83 76.78
sul1_7
(Song et al. 2010)134
F: GATTTTTCTTGAGCCCCGC 79.67 90.71
R: TGGACCCAGATCCTTTACAGG 77.70 89.47
sul1_8
(Chang et al. 2007)201
F: GGATTTTTCTTGAGCCCCGC 79.67 90.71
R: CATTGCCGATCGCGTGAAGT 76.66 88.54
sul1_9
(Luo et al. 2010)158
F: CACCGGAAACATCGCTGCA 79.21 91.33
R: AAGTTCCGCCGCAAGGCT 77.47 89.16
sul1_10
(Czekalski et al. 2014)67
F: CCGTTGGCCTTCCTGTAAAG 77.58 89.16
R: TTGCCGATCGCGTGAAGT 77.12 89.16
Table S4 Quantitative amplification conditions and quality control of qPCR methods
Target Primers Amplicon Annealing R2 Efficiency Slope
SPAGE \* MERGEFORMAT17
gene size (bp) temperature (C) (%)
16S
rRNA
341F, 534R
(Koike et al. 2007)193 50 0.99 101 -3.307
int1int-F, int-R
(Zhao et al. 2001)280 58 0.99 102 -3.270
sul1
51F, 280R 235 60 0.99 99 -3.339
sul1_1 822 55 0.99 100 -3.313
sul1_2 793 55 0.99 91 -3.568
sul1_3 433 60 0.99 90 -3.602
sul1_4 160 60 0.99 109 -3.131
SPAGE \* MERGEFORMAT17
Table S5 Dissimilarity test of bacterial communities among different sites and seasons based on
Bray-curtis index
SampleMRPP ANOSIM PERMANOVA
Delta P R P F P
BJ-QDN 0.343 0.001 0.470 0.001 0.286 0.001
BJ-QDS 0.343 0.002 0.470 0.001 0.286 0.001
BJ-WXN 0.343 0.001 0.470 0.003 0.286 0.001
BJ-WXS 0.343 0.002 0.470 0.001 0.286 0.001
QDN-QDS 0.332 0.001 0.847 0.001 0.499 0.001
QDN-WXN 0.363 0.001 0.718 0.001 0.474 0.001
QDN-WXS 0.330 0.001 0.847 0.001 0.493 0.001
QDS-WXN 0.316 0.001 0.847 0.001 0.633 0.001
QDS-WXS 0.283 0.001 0.847 0.001 0.703 0.001
WXN-WXS 0.314 0.001 0.847 0.001 0.475 0.001
BJ6-BJ12 0.258 0.005 0.563 0.002 0.523 0.001
QDN6-QDN12 0.246 0.004 0.722 0.004 0.476 0.001
QDS6-QDS12 0.148 0.003 0.723 0.001 0.790 0.001
WXN6-WXN12 0.282 0.002 0.709 0.002 0.282 0.001
WXS6-WXS12 0.178 0.002 0.470 0.001 0.663 0.001
Values in bold indicate significant difference
SPAGE \* MERGEFORMAT17
Table S6 Pearson correlations among different wastewater and operational parameters
SampleCOD
_inflow
COD
_effluent
TN
_inflow
TN
_effluent
TP
_inflow
TP
_effluentDO pH
temperat
ure
COD_
inflow1 0.979* 0.842* 0.067 0.933* 0.503* 0.142 -0.153 -0.025
COD_
effluent1 0.876* -0.031 0.976* 0.638* 0.161 -0.123 -0.040
TN_inflow 1 -0.084 0.889* 0.821* 0.320 -0.077 -0.105
TN_effluent 1 0.069 -0.462* -0.184 -0.064 0.206
TP_inflow 1 0.689* 0.160 -0.098 -0.022
TP_effluent 1 0.337 0.033 -0.059
DO 1 0.069 -0.462*
pH 1 0.689*
temperature 1
COD: chemical oxygen demand; TN: total nitrogen; TP: total phosphorus; DO: dissolved oxygen.
Values in bold indicate significant correlation, * Correlation is significant at 0.05 level.
SPAGE \* MERGEFORMAT17
Table S7 Correlations between bacterial community and environmental properties analyzed by
Mantel test based on Bray-curtis and Jaccard
Environmental factorsBray-curtis Jaccard
rM P rM P
Geographical distance 0.499 0.001 0.482 0.001
DO 0.110 0.005 0.093 0.008
pH 0.041 0.164 0.028 0.196
Temperature 0.181 0.001 0.143 0.001
COD_inflow 0.579 0.001 0.651 0.001
TP_effluent 0.403 0.001 0.388 0.001
Values in bold indicate significant difference
SPAGE \* MERGEFORMAT17
Table S8 Initial and corrected bacterial quantities in different WWTPs between summer and winter
(average total abundance of OTUs)
WWTPsInitial bacterial quantity Corrected bacterial quantity
Ratios of corrected bacterial
quantity / initial bacterial quantity
summer winter summer winter summer winter
BJ 108483.67 82898.83 50730.95 37730.19 46.66% 45.54%
QDN 36222.00 36564.33 14850.43 16081.74 42.33% 44.08%
QDS 59496.67 82652.33 25440.60 34639.84 42.62% 42.52%
WXN 36435.17 64572.17 17188.18 27375.40 47.15% 46.25%
WXS 75808.50 40543.83 34933.23 18318.36 45.90% 45.19%
SPAGE \* MERGEFORMAT17
Table S9 Dissimilarity test of total sul1-clusters in activated sludge among different sites and
seasons based on Bray-curtis
SampleMRPP ANOSIM PERMANOVA
Delta P R P F P
BJ-QDN 0.008 0.111 0.094 0.062 0.045 0.333
BJ-QDS 0.008 0.115 0.094 0.075 0.045 0.317
BJ-WXN 0.008 0.091 0.094 0.069 0.045 0.358
BJ-WXS 0.108 0.128 0.094 0.061 0.045 0.349
QDN-QDS 0.008 0.465 0.005 0.345 0.022 0.634
QDN-WXN 0.009 0.587 0.034 0.696 0.031 0.482
QDN-WXS 0.008 0.323 0.029 0.226 0.041 0.366
QDS-WXN 0.008 0.595 0.026 0.636 0.040 0.408
QDS-WXS 0.006 0.511 0.030 0.639 0.034 0.457
WXN-WXS 0.008 0.092 0.063 0.116 0.093 0.110
BJ6-BJ12 0.009 0.180 0.131 0.136 0.071 0.417
QDN6-QDN12 0.009 0.121 0.186 0.112 0.219 0.085
QDS6-QDS12 0.006 0.028 0.269 0.032 0.239 0.058
WXN6-WXN12 0.010 0.683 0.036 0.553 0.058 0.553
WXS6-WXS12 0.006 0.635 0.102 0.830 0.065 0.476
Values in bold indicate significant difference
SPAGE \* MERGEFORMAT17
Table S10 Pearson correlation between relative abundance of dominant bacterial genera and major
clusters of sul1 gene
Genus Relative abundanceCluster_109 Cluster_130 Cluster_108
r P r P r P
Caldilinea 8.32% 0.347 0.326 0.374 0.287 0.356 0.312
Nitrospira 8.14% -0.393 0.261 -0.434 0.210 -0.461 0.180
Hyphomicrobium 5.91% -0.297 0.404 -0.301 0.398 -0.326 0.359
SMB53 5.70% -0.182 0.615 -0.167 0.645 -0.203 0.574
Candidatus
Microthrix4.89% 0.173 0.632 0.156 0.666 0.130 0.720
Dechloromonas 3.73% -0.040 0.913 -0.077 0.833 -0.099 0.785
Mycobacterium 2.75% 0.371 0.292 0.375 0.286 0.395 0.259
Rubrivivax 2.33% -0.375 0.285 -0.375 0.285 -0.377 0.283
Turicibacter 1.67% -0.101 0.782 -0.085 0.816 -0.117 0.747
Planctomyces 1.65% 0.317 0.372 0.342 0.333 0.356 0.313
Rhodobacter 1.57% 0.144 0.691 0.096 0.791 0.046 0.900
Dokdonella 1.56% 0.357 0.311 0.321 0.365 0.343 0.331
Gemmata 1.54% -0.280 0.433 -0.249 0.487 -0.198 0.584
Allochromatium 1.48% 0.313 0.379 0.336 0.342 0.395 0.258
Thermomonas 1.46% 0.422 0.224 0.375 0.285 0.358 0.310
Paracoccus 1.37% -0.006 0.987 -0.030 0.935 -0.098 0.788
Phycicoccus 1.27% 0.119 0.743 0.120 0.741 0.088 0.809
Clostridium 1.21% 0.174 0.630 0.179 0.622 0.204 0.573
Dok59 1.01% -0.183 0.612 -0.177 0.626 -0.216 0.550
SPAGE \* MERGEFORMAT17
Table S11 The correlation between absolute abundance of sul1 and int1 genes in activated sludge
CorrelationPearson Kendall Spearman
r P r P r P
All 0.200 0.126 0.165 0.063 0.248 0.056
BJ 0.832 0.001 0.595 0.007 0.729 0.007
QDN 0.409 0.186 0.121 0.583 0.210 0.513
QDS 0.282 0.375 0.212 0.337 0.413 0.183
WXN -0.185 0.564 0.121 0.583 0.196 0.542
WXS 0.290 0.360 0.273 0.217 0.357 0.255
BJ6 0.753 0.084 0.600 0.091 0.714 0.111
BJ12 0.873 0.023 0.600 0.091 0.771 0.072
QDN6 0.022 0.967 -0.333 0.348 -0.486 0.329
QDN12 0.584 0.224 0.333 0.348 0.486 0.329
QDS6 -0.264 0.613 -0.333 0.348 -0.371 0.468
QDS12 0.547 0.262 0.467 0.188 0.714 0.111
WXN6 0.446 0.375 0.200 0.573 0.257 0.623
WXN12 -0.658 0.156 -0.333 0.348 -0.374 0.468
WXS6 0.367 0.475 0.467 0.188 0.600 0.208
WXS12 -0.214 0.683 -0.067 0.851 -0.086 0.872
Values in bold indicate significant correlation
SPAGE \* MERGEFORMAT17
Fig. S1 Bacterial composition of activated sludge from five WWTPs in summer and winter at the
class-level
SPAGE \* MERGEFORMAT17
References:
Chang, L.L., Lin, H.H., Chang, C.Y. and Lu, P.L. (2007) Increased incidence of class 1 integrons in trimethoprim/sulfamethoxazole-resistant clinical isolates of Stenotrophomonas maltophilia. Journal of Antimicrobial Chemotherapy 59(5), 1038-1039.Czekalski, N., Gascon Diez, E. and Burgmann, H. (2014) Wastewater as a point source of antibiotic-resistance genes in the sediment of a freshwater lake. ISME J 8(7), 1381-1390.DeSantis, T.Z., Hugenholtz, P., Larsen, N., Rojas, M., Brodie, E.L., Keller, K., Huber, T., Dalevi, D., Hu, P. and Andersen, G.L. (2006) Greengenes, a chimera-checked 16S rRNA gene database and workbench compatible with ARB. Applied and Environmental Microbiology 72(7), 5069-5072.Edgar, R.C. (2010) Search and clustering orders of magnitude faster than BLAST. Bioinformatics 26(19), 2460-2461.Edgar, R.C. (2013) UPARSE: highly accurate OTU sequences from microbial amplicon reads. Nature Methods 10(10), 996-+.Kerrn, M.B., Klemmensen, T., Frimodt-Moller, N. and Espersen, F. (2002) Susceptibility of Danish Escherichia coli strains isolated from urinary tract infections and bacteraemia, and distribution of sul genes conferring sulphonamide resistance. Journal of Antimicrobial Chemotherapy 50(4), 513-516.Koike, S., Krapac, I.G., Oliver, H.D., Yannarell, A.C., Chee-Sanford, J.C., Aminov, R.I. and Mackie, R.I. (2007) Monitoring and source tracking of tetracycline resistance genes in lagoons and groundwater adjacent to swine production facilities over a 3-year period. Appl Environ Microbiol 73(15), 4813-4823.Kong, Y. (2011) Btrim: A fast, lightweight adapter and quality trimming program for next-generation sequencing technologies. Genomics 98(2), 152-153.Luo, Y., Mao, D., Rysz, M., Zhou, Q., Zhang, H., Xu, L. and P, J.J.A. (2010) Trends in antibiotic resistance genes occurrence in the Haihe River, China. Environmental Science & Technology 44(19), 7220-7225.Ma, M.G., Wang, H.N., Yu, Y., Zhang, D. and Liu, S.G. (2007) Detection of antimicrobial resistance genes of pathogenic Salmonella from swine with DNA microarray. Journal of Veterinary Diagnostic Investigation 19(2), 161-167.Magoc, T. and Salzberg, S.L. (2011) FLASH: fast length adjustment of short reads to improve genome assemblies. Bioinformatics 27(21), 2957-2963.Pyatov, V., Vrtkova, I. and Knoll, A. (2014) Detection of Aminoglycoside, Sulfonamide and Tetracycline resistance genes in Escherichia coli isolated from bovine milk samples. Mendelnet 2014, 504-506.Sáenz, Y., Briñas, L., Domínguez, E., Ruiz, J., Zarazaga, M., Vila, J. and Torres, C. (2004) Mechanisms of Resistance in Multiple-Antibiotic-Resistant Escherichia coli Strains of Human, Animal, and Food Origins. Antimicrobial Agents and Chemotherapy 48(10), 3996-4001.Song, J.S., Jang, S.J., Lee, J.J., Lee, J.H., Bae, I.K., Jeong, B.C., Cha, S.S., Lee, J.H., Hong, S.K. and Lee, S.H. (2010) Association of the blaCMY-10 gene with a novel complex class 1 integron carrying an ISCR1 element in clinical isolates from Korea. Clinical Microbiology and Infection 16(7), 1013-1017.Toleman, M.A., Bennett, P.M. and Walsh, T.R. (2006) Common regions e.g. orf513 and
SPAGE \* MERGEFORMAT17
antibiotic resistance: IS91-like elements evolving complex class 1 integrons. Journal of Antimicrobial Chemotherapy 58(1), 1-6.Van, T.T.H., Chin, J., Chapman, T., Tran, L.T. and Coloe, P.J. (2008) Safety of raw meat and shellfish in Vietnam: an analysis of Escherichia coli isolations for antibiotic resistance and virulence genes. International Journal of Food Microbiology 124(3), 217-223.Zhao, S., White, D.G., Ge, B., Ayers, S., Friedman, S., English, L., Wagner, D., Gaines, S. and Meng, J. (2001) Identification and Characterization of Integron-Mediated Antibiotic Resistance among Shiga Toxin-Producing Escherichia coli Isolates. Appl Environ Microbiol 67(4), 1558-1564.
SPAGE \* MERGEFORMAT17