Sam:LabNotes/Microbiome-new/2011-2-15

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Bowtie mapping on E.coli SAG Nextera libraries HC-MDA-Ecoli-SAGs(NX1-NX8)-Jan09[edit]

Background[edit]

  • These libraries were equally pulled (20ng per library) and sequenced in pair-end(PE) mode.
  • The sequenced data processed by Dr. Zhang for base-calling and saved into FASTQ files.
Wiki(12-29-'10)

Sample no.   Sample name          Total DNA(ng)
-----------------------------------------------
NX01         WGA102710-(1-4)- 3hr     288.50ng
NX02         WGA102710-(1-4)-10hr     500.00ng
NX03         WGA110310-(5)-   3hr     114.50ng
NX04         WGA110310-(5)-  10hr     500.00ng
Wiki(01-06-'11)

Sample no.   Sample name          Total DNA(ng)
-----------------------------------------------
NX05         WGA122010-(1-2)-3hr       181.50ng
NX06         WGA122010-(1-2)-10hr      200.00ng
NX07         WGA122110-(2-3)-3hr        50.00ng
NX08         WGA122110-(2-3)-10hr      200.00ng

Analysis approaches[edit]

Data pooling[edit]

  • Using "gunzip" command to unzip SE files.
  • Combine two SE data(read1 + read2) into one PE data
e.g. samchiang@genemapster:~/Raw-Read-backup/110120_HL087$ cat s_4_1_ID8.txt s_4_2_ID8.txt > s_4_pe_ID8.txt &

Genome coverage analysis (whole reads and 1000000 down-sampled reads)[edit]

  • Script: Read2coverage-kz-3
  • Data resource: pooled pe reads data from HC-MDA-Ecoli-SAGs(NX1-NX8)-Jan09
  • Command
perl Read2coverage-kz-3 /media/disk-2/samchiang/Raw-Read-backup/110120_HL087/pooled_pe/s_4_pe_ID8_3074085.txt /media/disk-2/samchiang/Tools/bowtie-0.12.5/indexes/e_coli_k12_mg1655/e_coli_k12_mg1655 &
  • Bowtie setting
samchiang@genemapster:~/Scripts$ /media/disk-2/samchiang/Tools/bowtie-0.12.5/bowtie -k 1 -l 28 -n 2 -m 1 --best --best --phred64-quals

Results[edit]


Sequence Read Name s_4_pe_ID1_NX s_4_pe_ID2_NX s_4_pe_ID3_NX s_4_pe_ID4_NX s_4_pe_ID5_NX s_4_pe_ID6_NX s_4_pe_ID7_NX s_4_pe_ID8_NX
Library Nick Name NX01 NX02 NX03 NX04 NX05 NX06 NX07 NX08
Library Sample Name WGA102710_(1_4)_3hr WGA102710_(1_4)_10hr WGA102710_(5)_3hr WGA102710_(5)_10hr WGA122010_(1-2)_3hr WGA122010_(1-2)_10hr WGA122010_(2-3)_3hr WGA122010_(2-3)_10hr
DNA starting amount (ng) 288.5 500.0 114.5 500.0 181.5 200.0 50.0 200.0
Proccessed reads 13395058 8843072 6451756 15366518 5071132 7353034 6647566 4888674
Mapped read, no. (unique) 2707193 (20.21%) 5734751 (64.85%) 1988199 (30.82%) 8571871 (55.78%) 742103 (14.63%) 2963238 (40.30%) 1048466 (15.77%) 1590418 (32.53%)
Failed to align, no. 10515640 (78.50%) 2512119 (28.41%) 4285220 (66.42%) 4736204 (30.82%) 4311962 (85.03%) 4338695 (59.01%) 5549873 (83.49%) 3176843 (64.98%)
Mapped read, no (non-unique) 172225 (1.29%) 596202 (6.74%) 178337 (2.76%) 2058443 (13.40%) 17067 (0.34%) 51101 (0.69%) 49227 (0.74%) 121413 (2.48%)
Total bps coverred, bp 2146219 2001793 797791 835527 914841 767267 1282002 738538
Genome coverage 46.26% 43.15% 17.20% 18.01% 19.72% 16.54% 27.63% 15.92%


Sequence Read Name s_4_pe_ID1_NX s_4_pe_ID2_NX s_4_pe_ID3_NX s_4_pe_ID4_NX s_4_pe_ID5_NX s_4_pe_ID6_NX s_4_pe_ID7_NX s_4_pe_ID8_NX
1000000 uniqe reads 4948046 1542020 3244646 1792757 6835270 2481390 6341154 3074085
700000 uniqe reads 4784689 1736973
Proccessed reads 4948046 1542020 3244646 1792757 4784689 1736973 6341154 3074085
Mapped read, no. (unique) 1028262 (20.78%) 1047304 (67.92%) 1032729 (31.83%) 1060752 (59.17%) 701069 (14.65%) 721899 (41.56%) 1001553 (15.79%) 1029838 (33.50%)
Failed to align, no. 3853931 (77.89%) 381914 (24.77%) 2118408 (65.29%) 467033 (26.05%) 4067507 (85.01%) 1002826 (57.73%) 5292536 (83.46%) 1965747 (63.95%)
Mapped read, no (non-unique) 65853 (1.33%) 112802 (7.32%) 93509 (2.88%) 264972 (14.78%) 16113 (0.34%) 12248 (0.71%) 47065 (0.74%) 78500 (2.55%)
Total bps coverred, bp 1890835 1445489 652120 310201 897507 456971 1267625 676415
Genome coverage 40.76% 31.16% 14.06% 6.69% 19.35% 9.85% 27.32% 14.58%

Discussions[edit]

Mappalbe rates[edit]

  • The mappalbe rates are very low in these Nextera libraries (NX_ID_1 ~ NX_ID8), even worse then previous standard Illumina libraries (E.coli SAG) http://genome-tech.ucsd.edu/LabNotes/index.php/Sam:LabNotes/Microbiome-new/2010-12-8.
  • The low mappable rates are due to high failed-to-align rates, which could be caused by:
    • 1. Exogeneous DNA contamination -> Validate failed-to-align reads (or de novo assembled contigs) by BLASTn or MEGAN.
    • 2. Low quality of reads or containing sequencing tail -> Manually check the read structure

If it is true that exogeneous DNA contamination is the major issue of libraries quality, then using Nexteral-libraries construction were not albe to reduce DNA contamination effectively. It is possible that the primary exogeneous DNA contamination came from prior MDA amplificaiont, so changing library construction won't help much.

Genome coverage[edit]

  • Genome coverage were compared under the same number of unique reads (down-sampled to 1,000,000 unique reads).
    • Libraries NX-ID5 and NX-ID6 were down-sampled to 700,000 unique reads due to the insufficient available mappalbe reads.
  • In the short-vs-long paired comparisons (NX-ID1 vs NX-ID2, NX-ID3 vs NX-ID4, NX-ID5 vs NX-ID6, NX-ID7 vs NX-ID8), short-amplified libraries always showed higher (1.5~2 fold) genome coverage than long-amplified libraries.