Project FOMC4661 services include NGS sequencing of the V1V3 region of the 16S rRNA amplicons from the samples. First and foremost, please
download this report, as well as the sequence raw data from the download links provided below.
These links will expire after 60 days. We cannot guarantee the availability of your data after 60 days.
Full Bioinformatics analysis service was requested. We provide many analyses, starting from the raw sequence quality and noise filtering, pair reads merging, as well as chimera filtering for the sequences, using the
DADA2 denosing algorithm and pipeline.
We also provide many downstream analyses such as taxonomy assignment, alpha and beta diversity analyses, and differential abundance analysis.
For taxonomy assignment, most informative would be the taxonomy barplots. We provide an interactive barplots to show the relative abundance of microbes at different taxonomy levels (from Phylum to species) that you can choose.
If you specify which groups of samples you want to compare for differential abundance, we provide both ANCOM and LEfSe differential abundance analysis.
The samples were processed and analyzed with the ZymoBIOMICS® Service: Targeted
Metagenomic Sequencing (Zymo Research, Irvine, CA).
DNA Extraction: If DNA extraction was performed, one of three different DNA
extraction kits was used depending on the sample type and sample volume and were
used according to the manufacturer’s instructions, unless otherwise stated. The kit used
in this project is marked below:
☐
ZymoBIOMICS® DNA Miniprep Kit (Zymo Research, Irvine, CA)
☐
ZymoBIOMICS® DNA Microprep Kit (Zymo Research, Irvine, CA)
☐
ZymoBIOMICS®-96 MagBead DNA Kit (Zymo Research, Irvine, CA)
☑
N/A (DNA Extraction Not Performed)
Elution Volume: 50µL
Additional Notes: NA
Targeted Library Preparation: The DNA samples were prepared for targeted
sequencing with the Quick-16S™ NGS Library Prep Kit (Zymo Research, Irvine, CA).
These primers were custom designed by Zymo Research to provide the best coverage
of the 16S gene while maintaining high sensitivity. The primer sets used in this project
are marked below:
☐
Quick-16S™ Primer Set V1-V2 (Zymo Research, Irvine, CA)
☑
Quick-16S™ Primer Set V1-V3 (Zymo Research, Irvine, CA)
☐
Quick-16S™ Primer Set V3-V4 (Zymo Research, Irvine, CA)
☐
Quick-16S™ Primer Set V4 (Zymo Research, Irvine, CA)
☐
Quick-16S™ Primer Set V6-V8 (Zymo Research, Irvine, CA)
☐
Other: NA
Additional Notes: NA
The sequencing library was prepared using an innovative library preparation process in
which PCR reactions were performed in real-time PCR machines to control cycles and
therefore limit PCR chimera formation. The final PCR products were quantified with
qPCR fluorescence readings and pooled together based on equal molarity. The final
pooled library was cleaned up with the Select-a-Size DNA Clean & Concentrator™
(Zymo Research, Irvine, CA), then quantified with TapeStation® (Agilent Technologies,
Santa Clara, CA) and Qubit® (Thermo Fisher Scientific, Waltham, WA).
Control Samples: The ZymoBIOMICS® Microbial Community Standard (Zymo
Research, Irvine, CA) was used as a positive control for each DNA extraction, if
performed. The ZymoBIOMICS® Microbial Community DNA Standard (Zymo Research,
Irvine, CA) was used as a positive control for each targeted library preparation.
Negative controls (i.e. blank extraction control, blank library preparation control) were
included to assess the level of bioburden carried by the wet-lab process.
Sequencing: The final library was sequenced on Illumina® MiSeq™ with a V3 reagent kit
(600 cycles). The sequencing was performed with 10% PhiX spike-in.
The complete report of your project, including all links in this report, can be downloaded by clicking the link provided below. The downloaded file is a compressed ZIP file and once unzipped, open the file “REPORT.html” (may only shown as "REPORT" in your computer) by double clicking it. Your default web browser will open it and you will see the exact content of this report.
Please download and save the file to your computer storage device. The download link will expire after 60 days upon your receiving of this report.
Complete report download link:
To view the report, please follow the following steps:
1.
Download the .zip file from the report link above.
2.
Extract all the contents of the downloaded .zip file to your desktop.
3.
Open the extracted folder and find the "REPORT.html" (may shown as only "REPORT").
4.
Open (double-clicking) the REPORT.html file. Your default browser will open the top age of the complete report. Within the
report, there are links to view all the analyses performed for the project.
The raw NGS sequence data is available for download with the link provided below. The data is a compressed ZIP file and can be unzipped to individual sequence files.
Since this is a pair-end sequencing, each of your samples is represented by two sequence files, one for READ 1,
with the file extension “*_R1.fastq.gz”, another READ 2, with the file extension “*_R1.fastq.gz”.
The files are in FASTQ format and are compressed. FASTQ format is a text-based data format for storing both a biological sequence
and its corresponding quality scores. Most sequence analysis software will be able to open them.
The Sample IDs associated with the R1 and R2 fastq files are listed in the table below:
Sample ID
Read 1 File Name
Read 2 File Name
S10
zr4661_10V1V3_R1.fastq.gz
zr4661_10V1V3_R2.fastq.gz
S11
zr4661_11V1V3_R1.fastq.gz
zr4661_11V1V3_R2.fastq.gz
S12
zr4661_12V1V3_R1.fastq.gz
zr4661_12V1V3_R2.fastq.gz
S13
zr4661_13V1V3_R1.fastq.gz
zr4661_13V1V3_R2.fastq.gz
S14
zr4661_14V1V3_R1.fastq.gz
zr4661_14V1V3_R2.fastq.gz
S15
zr4661_15V1V3_R1.fastq.gz
zr4661_15V1V3_R2.fastq.gz
S16
zr4661_16V1V3_R1.fastq.gz
zr4661_16V1V3_R2.fastq.gz
S17
zr4661_17V1V3_R1.fastq.gz
zr4661_17V1V3_R2.fastq.gz
S18
zr4661_18V1V3_R1.fastq.gz
zr4661_18V1V3_R2.fastq.gz
S19
zr4661_19V1V3_R1.fastq.gz
zr4661_19V1V3_R2.fastq.gz
S01
zr4661_1V1V3_R1.fastq.gz
zr4661_1V1V3_R2.fastq.gz
S20
zr4661_20V1V3_R1.fastq.gz
zr4661_20V1V3_R2.fastq.gz
S21
zr4661_21V1V3_R1.fastq.gz
zr4661_21V1V3_R2.fastq.gz
S22
zr4661_22V1V3_R1.fastq.gz
zr4661_22V1V3_R2.fastq.gz
S23
zr4661_23V1V3_R1.fastq.gz
zr4661_23V1V3_R2.fastq.gz
S24
zr4661_24V1V3_R1.fastq.gz
zr4661_24V1V3_R2.fastq.gz
S25
zr4661_25V1V3_R1.fastq.gz
zr4661_25V1V3_R2.fastq.gz
S26
zr4661_26V1V3_R1.fastq.gz
zr4661_26V1V3_R2.fastq.gz
S27
zr4661_27V1V3_R1.fastq.gz
zr4661_27V1V3_R2.fastq.gz
S28
zr4661_28V1V3_R1.fastq.gz
zr4661_28V1V3_R2.fastq.gz
S29
zr4661_29V1V3_R1.fastq.gz
zr4661_29V1V3_R2.fastq.gz
S02
zr4661_2V1V3_R1.fastq.gz
zr4661_2V1V3_R2.fastq.gz
S30
zr4661_30V1V3_R1.fastq.gz
zr4661_30V1V3_R2.fastq.gz
S31
zr4661_31V1V3_R1.fastq.gz
zr4661_31V1V3_R2.fastq.gz
S32
zr4661_32V1V3_R1.fastq.gz
zr4661_32V1V3_R2.fastq.gz
S33
zr4661_33V1V3_R1.fastq.gz
zr4661_33V1V3_R2.fastq.gz
S34
zr4661_34V1V3_R1.fastq.gz
zr4661_34V1V3_R2.fastq.gz
S35
zr4661_35V1V3_R1.fastq.gz
zr4661_35V1V3_R2.fastq.gz
S36
zr4661_36V1V3_R1.fastq.gz
zr4661_36V1V3_R2.fastq.gz
S37
zr4661_37V1V3_R1.fastq.gz
zr4661_37V1V3_R2.fastq.gz
S38
zr4661_38V1V3_R1.fastq.gz
zr4661_38V1V3_R2.fastq.gz
S39
zr4661_39V1V3_R1.fastq.gz
zr4661_39V1V3_R2.fastq.gz
S03
zr4661_3V1V3_R1.fastq.gz
zr4661_3V1V3_R2.fastq.gz
S40
zr4661_40V1V3_R1.fastq.gz
zr4661_40V1V3_R2.fastq.gz
S41
zr4661_41V1V3_R1.fastq.gz
zr4661_41V1V3_R2.fastq.gz
S42
zr4661_42V1V3_R1.fastq.gz
zr4661_42V1V3_R2.fastq.gz
S43
zr4661_43V1V3_R1.fastq.gz
zr4661_43V1V3_R2.fastq.gz
S44
zr4661_44V1V3_R1.fastq.gz
zr4661_44V1V3_R2.fastq.gz
S45
zr4661_45V1V3_R1.fastq.gz
zr4661_45V1V3_R2.fastq.gz
S46
zr4661_46V1V3_R1.fastq.gz
zr4661_46V1V3_R2.fastq.gz
S47
zr4661_47V1V3_R1.fastq.gz
zr4661_47V1V3_R2.fastq.gz
S48
zr4661_48V1V3_R1.fastq.gz
zr4661_48V1V3_R2.fastq.gz
S49
zr4661_49V1V3_R1.fastq.gz
zr4661_49V1V3_R2.fastq.gz
S04
zr4661_4V1V3_R1.fastq.gz
zr4661_4V1V3_R2.fastq.gz
S50
zr4661_50V1V3_R1.fastq.gz
zr4661_50V1V3_R2.fastq.gz
S51
zr4661_51V1V3_R1.fastq.gz
zr4661_51V1V3_R2.fastq.gz
S52
zr4661_52V1V3_R1.fastq.gz
zr4661_52V1V3_R2.fastq.gz
S53
zr4661_53V1V3_R1.fastq.gz
zr4661_53V1V3_R2.fastq.gz
S54
zr4661_54V1V3_R1.fastq.gz
zr4661_54V1V3_R2.fastq.gz
S55
zr4661_55V1V3_R1.fastq.gz
zr4661_55V1V3_R2.fastq.gz
S56
zr4661_56V1V3_R1.fastq.gz
zr4661_56V1V3_R2.fastq.gz
S57
zr4661_57V1V3_R1.fastq.gz
zr4661_57V1V3_R2.fastq.gz
S58
zr4661_58V1V3_R1.fastq.gz
zr4661_58V1V3_R2.fastq.gz
S59
zr4661_59V1V3_R1.fastq.gz
zr4661_59V1V3_R2.fastq.gz
S05
zr4661_5V1V3_R1.fastq.gz
zr4661_5V1V3_R2.fastq.gz
S60
zr4661_60V1V3_R1.fastq.gz
zr4661_60V1V3_R2.fastq.gz
S06
zr4661_6V1V3_R1.fastq.gz
zr4661_6V1V3_R2.fastq.gz
S07
zr4661_7V1V3_R1.fastq.gz
zr4661_7V1V3_R2.fastq.gz
S08
zr4661_8V1V3_R1.fastq.gz
zr4661_8V1V3_R2.fastq.gz
S09
zr4661_9V1V3_R1.fastq.gz
zr4661_9V1V3_R2.fastq.gz
Please download and save the file to your computer storage device. The download link will expire after 60 days upon your receiving of this report.
DADA2 is a software package that models and corrects Illumina-sequenced amplicon errors.
DADA2 infers sample sequences exactly, without coarse-graining into OTUs,
and resolves differences of as little as one nucleotide. DADA2 identified more real variants
and output fewer spurious sequences than other methods.
DADA2’s advantage is that it uses more of the data. The DADA2 error model incorporates quality information,
which is ignored by all other methods after filtering. The DADA2 error model incorporates quantitative abundances,
whereas most other methods use abundance ranks if they use abundance at all.
The DADA2 error model identifies the differences between sequences, eg. A->C,
whereas other methods merely count the mismatches. DADA2 can parameterize its error model from the data itself,
rather than relying on previous datasets that may or may not reflect the PCR and sequencing protocols used in your study.
DADA2 pipeline includes several tools for read quality control, including quality filtering, trimming, denoising, pair merging and chimera filtering. Below are the major processing steps of DADA2:
Step 1. Read trimming based on sequence quality
The quality of NGS Illumina sequences often decreases toward the end of the reads.
DADA2 allows to trim off the poor quality read ends in order to improve the error
model building and pair mergicing performance.
Step 2. Learn the Error Rates
The DADA2 algorithm makes use of a parametric error model (err) and every
amplicon dataset has a different set of error rates. The learnErrors method
learns this error model from the data, by alternating estimation of the error
rates and inference of sample composition until they converge on a jointly
consistent solution. As in many machine-learning problems, the algorithm must
begin with an initial guess, for which the maximum possible error rates in
this data are used (the error rates if only the most abundant sequence is
correct and all the rest are errors).
Step 3. Infer amplicon sequence variants (ASVs) based on the error model built in previous step. This step is also called sequence "denoising".
The outcome of this step is a list of ASVs that are the equivalent of oligonucleotides.
Step 4. Merge paired reads. If the sequencing products are read pairs, DADA2 will merge the R1 and R2 ASVs into single sequences.
Merging is performed by aligning the denoised forward reads with the reverse-complement of the corresponding
denoised reverse reads, and then constructing the merged “contig” sequences.
By default, merged sequences are only output if the forward and reverse reads overlap by
at least 12 bases, and are identical to each other in the overlap region (but these conditions can be changed via function arguments).
Step 5. Remove chimera.
The core dada method corrects substitution and indel errors, but chimeras remain. Fortunately, the accuracy of sequence variants
after denoising makes identifying chimeric ASVs simpler than when dealing with fuzzy OTUs.
Chimeric sequences are identified if they can be exactly reconstructed by
combining a left-segment and a right-segment from two more abundant “parent” sequences. The frequency of chimeric sequences varies substantially
from dataset to dataset, and depends on on factors including experimental procedures and sample complexity.
Results
1. Read Quality Plots NGS sequence analaysis starts with visualizing the quality of the sequencing. Below are the quality plots of the first
sample for the R1 and R2 reads separately. In gray-scale is a heat map of the frequency of each quality score at each base position. The mean
quality score at each position is shown by the green line, and the quartiles of the quality score distribution by the orange lines.
The forward reads are usually of better quality. It is a common practice to trim the last few nucleotides to avoid less well-controlled errors
that can arise there. The trimming affects the downstream steps including error model building, merging and chimera calling. FOMC uses an empirical
approach to test many combinations of different trim length in order to achieve best final amplicon sequence variants (ASVs), see the next
section “Optimal trim length for ASVs”.
Below is the link to a PDF file for viewing the quality plots for all samples:
2. Optimal trim length for ASVs The final number of merged and chimera-filtered ASVs depends on the quality filtering (hence trimming) in the very beginning of the DADA2 pipeline.
In order to achieve highest number of ASVs, an empirical approach was used -
Create a random subset of each sample consisting of 5,000 R1 and 5,000 R2 (to reduce computation time)
Trim 10 bases at a time from the ends of both R1 and R2 up to 50 bases
For each combination of trimmed length (e.g., 300x300, 300x290, 290x290 etc), the trimmed reads are
subject to the entire DADA2 pipeline for chimera-filtered merged ASVs
The combination with highest percentage of the input reads becoming final ASVs is selected for the complete set of data
Below is the result of such operation, showing ASV percentages of total reads for all trimming combinations (1st Column = R1 lengths in bases; 1st Row = R2 lengths in bases):
R1/R2
281
271
261
251
241
231
321
39.78%
46.45%
46.60%
47.99%
48.84%
44.42%
311
41.66%
47.98%
48.40%
49.35%
45.84%
32.40%
301
41.98%
48.20%
48.63%
44.77%
32.84%
19.38%
291
41.62%
47.73%
43.51%
31.38%
19.48%
14.18%
281
42.43%
44.23%
31.41%
18.87%
14.37%
5.42%
271
38.26%
32.05%
19.05%
13.96%
5.27%
2.67%
Based on the above result, the trim length combination of R1 = 311 bases and R2 = 251 bases (highlighted red above), was chosen for generating final ASVs for all sequences.
This combination generated highest number of merged non-chimeric ASVs and was used for downstream analyses, if requested.
3. Error plots from learning the error rates
After DADA2 building the error model for the set of data, it is always worthwhile, as a sanity check if nothing else, to visualize the estimated error rates.
The error rates for each possible transition (A→C, A→G, …) are shown below. Points are the observed error rates for each consensus quality score.
The black line shows the estimated error rates after convergence of the machine-learning algorithm.
The red line shows the error rates expected under the nominal definition of the Q-score.
The ideal result would be the estimated error rates (black line) are a good fit to the observed rates (points), and the error rates drop
with increased quality as expected.
Forward Read R1 Error Plot
Reverse Read R2 Error Plot
The PDF version of these plots are available here:
4. DADA2 Result Summary The table below shows the summary of the DADA2 analysis,
tracking paired read counts of each samples for all the steps during DADA2 denoising process -
including end-trimming (filtered), denoising (denoisedF, denoisedF), pair merging (merged) and chimera removal (nonchim).
Sample ID
F4661.S01
F4661.S02
F4661.S03
F4661.S04
F4661.S05
F4661.S06
F4661.S07
F4661.S08
F4661.S09
F4661.S10
F4661.S11
F4661.S12
F4661.S13
F4661.S14
F4661.S15
F4661.S16
F4661.S17
F4661.S18
F4661.S19
F4661.S20
F4661.S21
F4661.S22
F4661.S23
F4661.S24
F4661.S25
F4661.S26
F4661.S27
F4661.S28
F4661.S29
F4661.S30
F4661.S31
F4661.S32
F4661.S33
F4661.S34
F4661.S35
F4661.S36
F4661.S37
F4661.S38
F4661.S39
F4661.S40
F4661.S41
F4661.S42
F4661.S43
F4661.S44
F4661.S45
F4661.S46
F4661.S47
F4661.S48
F4661.S49
F4661.S50
F4661.S51
F4661.S52
F4661.S53
F4661.S54
F4661.S55
F4661.S56
F4661.S57
F4661.S58
F4661.S59
F4661.S60
Row Sum
Percentage
input
42,727
69,877
58,362
56,802
51,877
54,019
59,514
63,978
45,293
51,599
46,450
50,365
46,662
46,172
53,905
55,722
42,320
55,070
45,737
51,538
46,616
50,955
54,221
49,517
38,634
52,620
43,599
50,820
42,114
49,086
44,481
51,233
50,457
59,514
52,401
61,346
61,269
65,321
62,549
63,133
47,936
50,573
50,652
52,737
52,349
59,412
56,211
57,881
42,420
50,888
45,767
52,497
48,261
48,568
52,093
53,427
39,413
48,837
53,903
60,785
3,122,485
100.00%
filtered
22,878
45,719
37,914
35,940
32,733
32,456
38,231
42,241
27,985
32,160
25,362
33,115
28,568
28,134
33,195
36,365
24,900
35,455
28,202
32,802
29,276
30,694
34,479
30,771
21,543
33,104
25,910
32,307
26,061
30,227
26,743
32,366
31,588
37,839
33,852
40,001
38,904
42,012
40,735
42,023
29,269
32,142
32,381
33,607
33,164
37,954
32,932
38,751
24,524
30,890
28,266
32,547
29,279
27,443
28,087
32,797
23,055
29,370
35,231
38,213
1,944,692
62.28%
denoisedF
22,059
44,244
36,427
34,585
31,632
31,350
36,916
40,546
27,318
31,132
24,915
32,535
27,956
27,610
32,014
35,061
24,301
34,493
27,569
31,664
28,764
29,893
33,608
29,661
20,839
31,780
25,245
31,481
25,092
29,641
26,084
31,024
30,112
36,432
32,940
38,200
38,022
40,597
39,845
40,445
28,852
31,349
31,158
32,592
32,137
36,931
32,103
37,805
23,843
29,854
27,222
31,420
28,521
26,838
27,478
31,669
22,502
28,355
34,027
37,119
1,885,807
60.39%
denoisedR
22,350
44,658
36,635
35,143
32,035
31,488
37,362
40,677
27,453
31,532
25,007
32,487
28,010
27,827
32,275
35,418
24,602
34,946
27,839
31,997
28,735
30,214
33,853
29,946
21,045
32,201
25,394
31,763
25,391
29,711
26,428
31,327
30,522
36,612
33,092
38,777
38,294
40,871
40,125
41,163
29,142
31,641
31,476
32,904
32,467
37,105
32,390
37,953
24,072
30,216
27,440
31,879
28,700
27,134
27,510
31,852
22,534
28,694
34,320
37,623
1,902,257
60.92%
merged
20,281
40,406
32,298
29,335
28,416
26,659
33,088
32,956
24,553
27,539
22,870
29,548
25,112
25,839
27,737
29,950
22,109
31,741
25,019
27,985
26,583
27,839
31,584
25,176
17,841
28,335
22,537
28,917
19,989
27,446
24,617
26,101
25,938
32,022
29,198
33,387
34,733
35,500
37,032
35,731
27,793
26,053
27,132
29,847
29,161
33,434
28,849
33,157
21,477
26,380
23,127
28,418
25,784
24,175
24,204
26,664
20,198
25,096
30,018
33,837
1,678,751
53.76%
nonchim
10,592
20,865
17,101
13,358
15,481
14,504
18,708
16,716
14,034
15,581
16,023
13,699
14,011
13,766
14,713
14,969
12,131
15,671
11,310
15,501
15,123
16,628
17,464
14,634
9,551
15,454
11,522
14,649
11,125
14,833
11,297
13,993
14,756
15,862
14,383
18,180
19,232
17,876
20,898
18,116
21,087
12,401
13,954
15,229
14,135
17,971
15,435
15,235
11,270
13,497
12,575
15,469
15,859
13,647
12,743
13,066
10,084
11,636
14,528
16,854
890,985
28.53%
This table can be downloaded as an Excel table below:
5. DADA2 Amplicon Sequence Variants (ASVs). A total of 14342 unique merged and chimera-free ASV sequences were identified, and their corresponding
read counts for each sample are available in the "ASV Read Count Table" with rows for the ASV sequences and columns for sample. This read count table can be used for
microbial profile comparison among different samples and the sequences provided in the table can be used to taxonomy assignment.
The species-level, open-reference 16S rRNA NGS reads taxonomy assignment pipeline
Version 20210310
1. Raw sequences reads in FASTA format were BLASTN-searched against a combined set of 16S rRNA reference sequences.
It consists of MOMD (version 0.1), the HOMD (version 15.2 http://www.homd.org/index.php?name=seqDownload&file&type=R ),
HOMD 16S rRNA RefSeq Extended Version 1.1 (EXT), GreenGene Gold (GG)
(http://greengenes.lbl.gov/Download/Sequence_Data/Fasta_data_files/gold_strains_gg16S_aligned.fasta.gz) ,
and the NCBI 16S rRNA reference sequence set (https://ftp.ncbi.nlm.nih.gov/blast/db/16S_ribosomal_RNA.tar.gz).
These sequences were screened and combined to remove short sequences (<1000nt), chimera, duplicated and sub-sequences,
as well as sequences with poor taxonomy annotation (e.g., without species information).
This process resulted in 1,015 from HOMD V15.22, 495 from EXT, 3,940 from GG and 18,044 from NCBI, a total of 25,120 sequences.
Altogether these sequence represent a total of 15,601 oral and non-oral microbial species.
The NCBI BLASTN version 2.7.1+ (Zhang et al, 2000) was used with the default parameters.
Reads with ≥ 98% sequence identity to the matched reference and ≥ 90% alignment length
(i.e., ≥ 90% of the read length that was aligned to the reference and was used to calculate
the sequence percent identity) were classified based on the taxonomy of the reference sequence
with highest sequence identity. If a read matched with reference sequences representing
more than one species with equal percent identity and alignment length, it was subject
to chimera checking with USEARCH program version v8.1.1861 (Edgar 2010). Non-chimeric reads with multi-species
best hits were considered valid and were assigned with a unique species
notation (e.g., spp) denoting unresolvable multiple species.
2. Unassigned reads (i.e., reads with < 98% identity or < 90% alignment length) were pooled together and reads < 200 bases were
removed. The remaining reads were subject to the de novo
operational taxonomy unit (OTU) calling and chimera checking using the USEARCH program version v8.1.1861 (Edgar 2010).
The de novo OTU calling and chimera checking was done using 98% as the sequence identity cutoff, i.e., the species-level OTU.
The output of this step produced species-level de novo clustered OTUs with 98% identity.
Representative reads from each of the OTUs/species were then BLASTN-searched
against the same reference sequence set again to determine the closest species for
these potential novel species. These potential novel species were pooled together with the reads that were signed to specie-level in
the previous step, for down-stream analyses.
Reference:
Edgar RC. Search and clustering orders of magnitude faster than BLAST.
Bioinformatics. 2010 Oct 1;26(19):2460-1. doi: 10.1093/bioinformatics/btq461. Epub 2010 Aug 12. PubMed PMID: 20709691.
3. Designations used in the taxonomy:
1) Taxonomy levels are indicated by these prefixes:
k__: domain/kingdom
p__: phylum
c__: class
o__: order
f__: family
g__: genus
s__: species
Example:
k__Bacteria;p__Firmicutes;c__Clostridia;o__Clostridiales;f__Lachnospiraceae;g__Blautia;s__faecis
2) Unique level identified – known species:
k__Bacteria;p__Firmicutes;c__Clostridia;o__Clostridiales;f__Lachnospiraceae;g__Roseburia;s__hominis
The above example shows some reads match to a single species (all levels are unique)
3) Non-unique level identified – known species:
k__Bacteria;p__Firmicutes;c__Clostridia;o__Clostridiales;f__Lachnospiraceae;g__Roseburia;s__multispecies_spp123_3
The above example “s__multispecies_spp123_3” indicates certain reads equally match to 3 species of the
genus Roseburia; the “spp123” is a temporally assigned species ID.
k__Bacteria;p__Firmicutes;c__Clostridia;o__Clostridiales;f__Lachnospiraceae;g__multigenus;s__multispecies_spp234_5
The above example indicates certain reads match equally to 5 different species, which belong to multiple genera.;
the “spp234” is a temporally assigned species ID.
4) Unique level identified – unknown species, potential novel species:
k__Bacteria;p__Firmicutes;c__Clostridia;o__Clostridiales;f__Lachnospiraceae;g__Roseburia;s__ hominis_nov_97%
The above example indicates that some reads have no match to any of the reference sequences with
sequence identity ≥ 98% and percent coverage (alignment length) ≥ 98% as well. However this groups
of reads (actually the representative read from a de novo OTU) has 96% percent identity to
Roseburia hominis, thus this is a potential novel species, closest to Roseburia hominis.
(But they are not the same species).
5) Multiple level identified – unknown species, potential novel species:
k__Bacteria;p__Firmicutes;c__Clostridia;o__Clostridiales;f__Lachnospiraceae;g__Roseburia;s__ multispecies_sppn123_3_nov_96%
The above example indicates that some reads have no match to any of the reference sequences
with sequence identity ≥ 98% and percent coverage (alignment length) ≥ 98% as well.
However this groups of reads (actually the representative read from a de novo OTU)
has 96% percent identity equally to 3 species in Roseburia. Thus this is no single
closest species, instead this group of reads match equally to multiple species at 96%.
Since they have passed chimera check so they represent a novel species. “sppn123” is a
temporary ID for this potential novel species.
4. The taxonomy assignment algorithm is illustrated in this flow char below:
Read Taxonomy Assignment - Result Summary
Code
Category
Read Count (MC=1)*
Read Count (MC=100)*
A
Total reads
890,985
890,985
B
Total assigned reads
885,930
885,930
C
Assigned reads in species with read count < MC
0
8,453
D
Assigned reads in samples with read count < 500
0
0
E
Total samples
60
60
F
Samples with reads >= 500
60
60
G
Samples with reads < 500
0
0
H
Total assigned reads used for analysis (B-C-D)
885,930
877,477
I
Reads assigned to single species
864,888
859,913
J
Reads assigned to multiple species
7,168
6,648
K
Reads assigned to novel species
13,874
10,916
L
Total number of species
548
307
M
Number of single species
392
269
N
Number of multi-species
23
10
O
Number of novel species
133
28
P
Total unassigned reads
5,055
5,055
Q
Chimeric reads
314
314
R
Reads without BLASTN hits
2,425
2,425
S
Others: short, low quality, singletons, etc.
2,316
2,316
A=B+P=C+D+H+Q+R+S
E=F+G
B=C+D+H
H=I+J+K
L=M+N+O
P=Q+R+S
* MC = Minimal Count per species, species with total read count < MC were removed.
* The assignment result from MC=100 was used in the downstream analyses.
Read Taxonomy Assignment - Sample Meta Information
#SampleID
Sample Name
Visit
Group1
Group2
Group
F4661.S03
AL03.V1
Visit1
Control
Baseline
Baseline Control
F4661.S04
AL04.V1
Visit1
Control
Baseline
Baseline Control
F4661.S05
AL05.V1
Visit1
Control
Baseline
Baseline Control
F4661.S07
AL07.V1
Visit1
Control
Baseline
Baseline Control
F4661.S10
AL10.V1
Visit1
Control
Baseline
Baseline Control
F4661.S12
AL12.V1
Visit1
Control
Baseline
Baseline Control
F4661.S15
AL15.V1
Visit1
Control
Baseline
Baseline Control
F4661.S17
AL17.V1
Visit1
Control
Baseline
Baseline Control
F4661.S18
AL18.V1
Visit1
Control
Baseline
Baseline Control
F4661.S21
AL21.V1
Visit1
Control
Baseline
Baseline Control
F4661.S22
AL22.V1
Visit1
Control
Baseline
Baseline Control
F4661.S23
AL23.V1
Visit1
Control
Baseline
Baseline Control
F4661.S26
AL26.V1
Visit1
Control
Baseline
Baseline Control
F4661.S27
AL27.V1
Visit1
Control
Baseline
Baseline Control
F4661.S28
AL28.V1
Visit1
Control
Baseline
Baseline Control
F4661.S01
AL01.V1
Visit1
Test
Baseline
Baseline Test
F4661.S02
AL02.V1
Visit1
Test
Baseline
Baseline Test
F4661.S06
AL06.V1
Visit1
Test
Baseline
Baseline Test
F4661.S08
AL08.V1
Visit1
Test
Baseline
Baseline Test
F4661.S09
AL09.V1
Visit1
Test
Baseline
Baseline Test
F4661.S11
AL11.V1
Visit1
Test
Baseline
Baseline Test
F4661.S13
AL13.V1
Visit1
Test
Baseline
Baseline Test
F4661.S14
AL14.V1
Visit1
Test
Baseline
Baseline Test
F4661.S16
AL16.V1
Visit1
Test
Baseline
Baseline Test
F4661.S19
AL19.V1
Visit1
Test
Baseline
Baseline Test
F4661.S20
AL20.V1
Visit1
Test
Baseline
Baseline Test
F4661.S24
AL24.V1
Visit1
Test
Baseline
Baseline Test
F4661.S25
AL25.V1
Visit1
Test
Baseline
Baseline Test
F4661.S29
AL29.V1
Visit1
Test
Baseline
Baseline Test
F4661.S30
AL30.V1
Visit1
Test
Baseline
Baseline Test
F4661.S33
AL03.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S34
AL04.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S35
AL05.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S37
AL07.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S40
AL10.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S42
AL12.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S45
AL15.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S47
AL17.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S48
AL18.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S51
AL21.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S52
AL22.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S53
AL23.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S56
AL26.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S57
AL27.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S58
AL28.V3
Visit3
Control
Week 6
Week 6 Control
F4661.S31
AL01.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S32
AL02.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S36
AL06.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S38
AL08.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S39
AL09.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S41
AL11.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S43
AL13.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S44
AL14.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S46
AL16.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S49
AL19.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S50
AL20.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S54
AL24.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S55
AL25.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S59
AL29.V3
Visit3
Test
Week 6
Week 6 Test
F4661.S60
AL30.V3
Visit3
Test
Week 6
Week 6 Test
Read Taxonomy Assignment - ASV Read Counts by Samples
#Sample ID
Read Count
F4661.S25
9551
F4661.S57
10084
F4661.S01
10592
F4661.S29
11125
F4661.S49
11270
F4661.S31
11297
F4661.S19
11310
F4661.S27
11522
F4661.S58
11636
F4661.S17
12131
F4661.S42
12401
F4661.S51
12575
F4661.S55
12743
F4661.S56
13066
F4661.S04
13358
F4661.S50
13497
F4661.S54
13647
F4661.S12
13699
F4661.S14
13766
F4661.S43
13954
F4661.S32
13993
F4661.S13
14011
F4661.S09
14034
F4661.S45
14135
F4661.S35
14383
F4661.S06
14504
F4661.S59
14528
F4661.S24
14634
F4661.S28
14649
F4661.S15
14713
F4661.S33
14756
F4661.S30
14833
F4661.S16
14969
F4661.S21
15123
F4661.S44
15229
F4661.S48
15235
F4661.S47
15435
F4661.S26
15454
F4661.S52
15469
F4661.S05
15481
F4661.S20
15501
F4661.S10
15581
F4661.S18
15671
F4661.S53
15859
F4661.S34
15862
F4661.S11
16023
F4661.S22
16628
F4661.S08
16716
F4661.S60
16854
F4661.S03
17101
F4661.S23
17464
F4661.S38
17876
F4661.S46
17971
F4661.S40
18116
F4661.S36
18180
F4661.S07
18708
F4661.S37
19232
F4661.S02
20865
F4661.S39
20898
F4661.S41
21087
Read Taxonomy Assignment - ASV Read Counts Table
This table shows the read counts for each sample (columns) and each species identified based on the ASV sequences.
The downstream analyses were based on this table.
Download Read Count Tables at Different Taxonomy Levels
domain
phylum
class
order
family
genus
species
;
The species listed in the table has full taxonomy and a dynamically assigned species ID specific to this report.
When some reads match with the reference sequences of more than one species equally (i.e., same percent identiy and alignmnet coverage),
they can't be assigned to a particular species. Instead, they are assigned to multiple species with the species notaton
"s__multispecies_spp2_2". In this notation, spp2 is the dynamic ID assigned to these reads that hit multiple sequences and the "_2"
at the end of the notation means there are two species in the spp2. You can look up which species are included in the multi-species assignment,
in this table below.
Another type of notation is "s__multispecies_sppn2_2", in which the "n" in the sppn2 means it's a potential novel species because all the reads in this species
have < 98% idenity to any of the reference sequences. They were grouped together based on de novo OTU clustering at 98% identity cutoff. And then
a representative sequence was chosed to BLASTN search against the reference database to find the closest match (but will still be < 98%). This representative
sequence also matched equally to more than one species, hence the "spp" was given in the label.
In ecology, alpha diversity (α-diversity) is the mean species diversity in sites or habitats at a local scale.
The term was introduced by R. H. Whittaker[1][2] together with the terms beta diversity (β-diversity)
and gamma diversity (γ-diversity). Whittaker's idea was that the total species diversity in a landscape
(gamma diversity) is determined by two different things, the mean species diversity in sites or habitats
at a more local scale (alpha diversity) and the differentiation among those habitats (beta diversity).
The two main factors taken into account when measuring diversity are richness and evenness.
Richness is a measure of the number of different kinds of organisms present in a particular area.
Evenness compares the similarity of the population size of each of the species present. There are
many different ways to measure the richness and evenness. These measurements are called "estimators" or "indices".
Below is a diversity of 3 commonly used indices showing the values for all the samples (dots) and in groups (boxes).
 
 
 
 
 
Alpha diversity analysis by rarefaction
Diversity measures are affected by the sampling depth. Rarefaction is a technique to assess species richness from the results of sampling. Rarefaction allows
the calculation of species richness for a given number of individual samples, based on the construction
of so-called rarefaction curves. This curve is a plot of the number of species as a function of the
number of samples. Rarefaction curves generally grow rapidly at first, as the most common species are found,
but the curves plateau as only the rarest species remain to be sampled.
Beta diversity compares the similarity (or dissimilarity) of microbial profiles between different
groups of samples. There are many different similarity/dissimilarity metrics.
In general, they can be quantitative (using sequence abundance, e.g., Bray-Curtis or weighted UniFrac)
or binary (considering only presence-absence of sequences, e.g., binary Jaccard or unweighted UniFrac).
They can be even based on phylogeny (e.g., UniFrac metrics) or not (non-UniFrac metrics, such as Bray-Curtis, etc.).
For microbiome studies, species profiles of samples can be compared with the Bray-Curtis dissimilarity,
which is based on the count data type. The pair-wise Bray-Curtis dissimilarity matrix of all samples can then be
subject to either multi-dimensional scaling (MDS, also known as PCoA) or non-metric MDS (NMDS).
MDS/PCoA is a
scaling or ordination method that starts with a matrix of similarities or dissimilarities
between a set of samples and aims to produce a low-dimensional graphical plot of the data
in such a way that distances between points in the plot are close to original dissimilarities.
NMDS is similar to MDS, however it does not use the dissimilarities data, instead it converts them into
the ranks and use these ranks in the calculation.
In our beta diversity analysis, Bray-Curtis dissimilarity matrix was first calculated and then plotted by the PCoA and
NMDS separately. The results are shown below:
 
 
 
 
 
The above PCoA and NMDS plots are based on count data. The count data can also be transformed into centered log ratio (CLR)
for each species. The CLR data is no longer count data and cannot be used in Bray-Curtis dissimilarity calculation. Instead
CLR can be compared with Euclidean distances. When CLR data are compared by Euclidean distance, the distance is also called
Aitchison distance.
Below are the NMDS and PCoA plots of the Aitchison distances of the samples:
 
 
 
 
 
Interactive 3D PCoA Plots - Bray-Curtis Dissimilarity
 
 
 
Interactive 3D PCoA Plots - Euclidean Distance
 
 
 
Interactive 3D PCoA Plots - Correlation Coefficients
16S rRNA next generation sequencing (NGS) generates a fixed number of reads that reflect the proportion of different species in a sample, i.e., the relative abundance of species, instead of the absolute abundance. In Mathematics, measurements involving probabilities, proportions, percentages, and ppm can all be thought of as compositional data. This makes the microbiome read count data “compositional” (Gloor et al, 2017). In general, compositional data represent parts of a whole which only carry relative information (http://www.compositionaldata.com/).
The problem of microbiome data being compositional arises when comparing two groups of samples for identifying “differentially abundant” species. A species with the same absolute abundance between two conditions, its relative abundances in the two conditions (e.g., percent abundance) can become different if the relative abundance of other species change greatly. This problem can lead to incorrect conclusion in terms of differential abundance for microbial species in the samples.
When studying differential abundance (DA), the current better approach is to transform the read count data into log ratio data. The ratios are calculated between read counts of all species in a sample to a “reference” count (e.g., mean read count of the sample). The log ratio data allow the detection of DA species without being affected by percentage bias mentioned above
In this report, a compositional DA analysis tool “ANCOM” (analysis of composition of microbiomes) was used. ANCOM transforms the count data into log-ratios and thus is more suitable for comparing the composition of microbiomes in two or more populations
References:
Gloor GB, Macklaim JM, Pawlowsky-Glahn V, Egozcue JJ. Microbiome Datasets Are Compositional: And This Is Not Optional. Front Microbiol.
2017 Nov 15;8:2224. doi: 10.3389/fmicb.2017.02224. PMID: 29187837; PMCID: PMC5695134.
Mandal S, Van Treuren W, White RA, Eggesbø M, Knight R, Peddada SD. Analysis of composition of
microbiomes: a novel method for studying microbial composition. Microb Ecol Health Dis.
2015 May 29;26:27663. doi: 10.3402/mehd.v26.27663. PMID: 26028277; PMCID: PMC4450248.
LEfSe (Linear Discriminant Analysis Effect Size) is an alternative method to find "organisms, genes, or
pathways that consistently explain the differences between two or more microbial communities" (Segata et al., 2011).
Specifically, LEfSe uses rank-based Kruskal-Wallis (KW) sum-rank test to detect features with significant
differential (relative) abundance with respect to the class of interest. Since it is rank-based, instead of proportional based,
the differential species identified among the comparison groups is less biased (than percent abundance based).
Reference:
Segata N, Izard J, Waldron L, Gevers D, Miropolsky L, Garrett WS, Huttenhower C. Metagenomic biomarker discovery and explanation. Genome Biol. 2011 Jun 24;12(6):R60. doi: 10.1186/gb-2011-12-6-r60. PMID: 21702898; PMCID: PMC3218848.
To analyze the co-occurrence or co-exclusion between microbial species among different samples, network correlation
analysis tools are usually used for this purpose. However, microbiome count data are compositional. If count data are normalized to the total number of counts in the
sample, the data become not independent and traditional statistical metrics (e.g., correlation) for the detection
of specie-species relationships can lead to spurious results. In addition, sequencing-based studies typically
measure hundreds of OTUs (species) on few samples; thus, inference of OTU-OTU association networks is severely
under-powered. Here we use SPIEC-EASI (SParse InversECovariance Estimation
for Ecological Association Inference), a statistical method for the inference of microbial
ecological networks from amplicon sequencing datasets that addresses both of these issues (Kurtz et al., 2015).
SPIEC-EASI combines data transformations developed for compositional data analysis with a graphical model
inference framework that assumes the underlying ecological association network is sparse. SPIEC-EASI provides
two algorithms for network inferencing – 1) Meinshausen-Bühlmann's neighborhood selection (MB method) and inverse covariance selection
(GLASSO method, i.e., graphical least absolute shrinkage and selection operator). This is fundamentally distinct from SparCC, which essentially estimate pairwise correlations. In addition
to these two methods, we provide the results of a third method - SparCC (Sparse Correlations for Compositional Data)(Friedman & Alm 2012), which
is also a method for inferring correlations from compositional data. SparCC estimates the linear Pearson correlations between
the log-transformed components.
References:
Kurtz ZD, Müller CL, Miraldi ER, Littman DR, Blaser MJ, Bonneau RA. Sparse and compositionally robust inference of microbial ecological networks. PLoS Comput Biol. 2015 May 7;11(5):e1004226. doi: 10.1371/journal.pcbi.1004226. PMID: 25950956; PMCID: PMC4423992.