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Ngs microbiome

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Ngs microbiome

  1. 1. Next-Generation Sequencing of MicrobialGenomes and MetagenomesChristine KingFarncombe Metagenomics FacilityHuman Microbiome Journal ClubJuly 13, 2012
  2. 2. Overview Next-generation sequencing  Applications  Instruments  Library prep and sequencing chemistry  Sequence quality Project overview  Microbial genomes  Microbial communities
  3. 3. DNA Sequencing  1st generation  Sanger chain termination  Capillary electrophoresis  2nd generation (NGS)  High throughput, “massively parallel”  Shorter reads  Sequencing-by- synthesis  3rd generation  Single molecule
  4. 4. Applications DNA sequencing  De novo genomes  Resequencing  Shotgun (e.g. mutant strains)  Amplicon (e.g. HLA, cancer)  Sequence capture (e.g. exome)  Metagenome  Amplicon (e.g. 16S, COI, viral)  Shotgun  ChIP RNA sequencing  Gene expression  Gene annotation, splice variants
  5. 5. Instruments
  6. 6. Instruments Total # of Read Cost outp RunInstrument read length per Technology ut Time s (bp) base (Gb) GS FLX 1M 450 0.5 $$$$ ++ GS FLX+ 1M 650 0.6 $$$$ ++ emPCR, SBS, light detection GS Jr 100K 450 0.05 $$$$ ++ GAIIx 640M 2x 150 90 $$ +++HiSeq 2000 6B 2x 100 600 $ +++ Bridge PCR, SBS, fluororphore MiSeq 12M 2x 150 2 $$ ++ PacBio RS >10K >1000 0.01 $$$$ + Single-molecule seq, fluorophoreSOLiD 5500xl 1.4B 75 + 35 155 $ +++ emPCR, probe ligation, fluorophore Ion PGM - 1M >100 0.1 $$$ + 316 emPCR, SBS, pH change Ion PGM - 6M >100 1 $$ + 318
  7. 7. Which instrument(s) to use?  Read length vs number of reads  Cost per base, per sample, per project (multiplexing?)  Accuracy  Run time, wait timeApplication Lengt # Accura Instruments Considerations h Reads cyDe novo +++ ++ ++ MiSeq, 454, Ion Mix lengths(small)De novo +++ +++ ++ HiSeq, 454, Mix lengths, MP(large) SOLiDRe-seq ++ ++ ++ MiSeq, Ion Multiplex?(small)Re-seq (large) ++ +++ ++ HiSeq, SOLiD Enrichment?RNA-seq + +++ + Illumina, SOLiD, Ref? Size?(count) Ion Rare?
  8. 8. Library Preparation Goal: fragments of DNA, each end flanked by adaptor sequences Adaptors contain amplification- and sequencing primer binding sites; platform- and chemistry-specific Optional: sample-specific barcodes/indexes/MIDs/tags allow multiplexing during sequencing Library QC: quantity, size
  9. 9. Library Preparation Library types:  Shotgun (DNA)  May begin with ChIP  May follow with sequence capture  Mate pair (DNA)  Amplicon (DNA)  Total RNA  May enrich for mRNA (poly-A enrichment, rRNA depletion)  Convert to cDNA (then similar to DNA protocols)  Small RNA  RNA ligations, convert to cDNA after
  10. 10. Library Preparation: Shotgun  Fragmentation  Sonication  Nebulization  Enzymatic  End repair  3’ overhangs digested  5’ overhangs filled  5’ phosphate added
  11. 11. Library Preparation: Shotgun  Adapter ligation  T-overhangs  Forked structure controls orientation  Library amplification  Few cycles  Enrich for correctly-adapted fragments  Required to complete adapter structure in some protocols  Size selection  Gel excision, AMPure beads  Limit insert size as needed, remove artifacts
  12. 12. Library Preparation: Amplicon Amplify region of  Primers contain interest using PCR adapter sequences
  13. 13. Library Preparation: Mate Pair Begin with large fragments (e.g. 3kb, 20kb) Circularize and fragment again  Illumina: direct ligation  454: Cre/Lox recombination Enrich for fragments containing the junction Proceed with shotgun library prep
  14. 14. Library Preparation: Mate Pair Why? Paired sequences are a known distance apart; improves genome assembly Note: 454 calls these “paired end libraries”, not to be confused with Illumina’s “paired end sequencing”!
  15. 15. Sequencing: Illumina  Cluster generation  Library fragments hybridize to oligos on the flow cell  New strand synthesized, original denatured, removed  Free end binds to adjacent oligos (bridge formation)  Complimentary strand synthesized, denatured (both tethered to flow cell)  Repeat to form clonal cluster  Cleave one oligo, denature to leave ssDNA clusters  ~800K clusters/mm^2
  16. 16. Sequencing: Illumina Variety of workflows:  Single- or paired end reads  0, 1, or 2 index reads
  17. 17. Sequencing: Illumina At each cycle, all 4 fluorescently-labeled nucleotides pass over the flow cell Each cluster incorporates one nt (terminator) per cycle Fluor is imaged, then cleaved De-block and repeat
  18. 18. Sequencing: Illumina Other terminology:  cBot – accessory instrument that performs cluster generation  Lanes – divisions (8) of HiSeq and GAIIx flow cells  PhiX – bacteriophage with small, balanced genome; PhiX library spiked in with samples for QC  Phasing/pre-phasing – nt incorporation falls behind or jumps ahead on a portion of strands in the cluster and contributes to noise  Chastity filter – measures signal purity (after intensity corrections); if the background signal is high, cluster will be discarded  BaseSpace – cloud computing site for processing MiSeq data File format: fastq
  19. 19. Sequencing: 454 emPCR: clonal amplification of bead-bound library in microdroplets Library input amounts critical!  One molecule per bead  Titration procedure
  20. 20. Sequencing: 454 Library capture: beads coated with complimentary oligo Amplification: droplet contains PCR reagents and the other oligo Post-PCR: millions of identical fragments attached to the bead
  21. 21. Sequencing: 454 Bead Recovery:  Enrichment: capture physical and successfully chemical disruption amplified beads using biotinylated primers + magnetic, streptavidin beads
  22. 22. Sequencing: 454 Deposit bead layers onto PicoTiterPlate:  Enzyme beads  Enriched DNA beads  More enzyme beads  PPiase beads
  23. 23. Sequencing: 454
  24. 24. Sequencing: 454 Pyrosequencing  4 nucleotides flow separately  If nt incorporation…PPi...light  APS + PPi (sulfurylase) ATP  Luciferin + ATP (luciferase) light + oxyluciferin  Amount of light proportional to #nt incorporated  Rinse and repeat with next nt
  25. 25. Sequencing: 454  Camera captures light emitted from every well during every nucleotide flow
  26. 26. Sequencing: 454 Flowgram: representation of a sequence, based on the pattern of light emitted from a single well
  27. 27. Sequencing: 454 Other terminology:  Lib-L/Lib-A: adapter variants, “ligated” or “annealed”  Titanium chemistry: ~450 bp reads on all instruments  XL+ chemistry: ~700 bp reads on the FLX+ instrument  Flow: one of the four nucleotides flows over the PTP  Cycle: a set of four flows, in order  Valley flow: if number of bases incorporated in a given read during that flow is uncertain, e.g. 1.5 units of light (background signal, homopolymers) File format: sff (standard flowgram format)
  28. 28. Sequencing: Ion Torrent Procedures and chemistry similar to 454 Instead of PPi, measure H+ release (pH change) via semiconductor chip No expensive camera or laser required, no modified nucleotides
  29. 29. Sequence QualityPhred (Q) Probabilit Base Call  Error probabilities Score y of Error Accuracy determined using (P) training sets, 10 1 in 10 90% platform-specific 20 1 in 100 99% 30 1 in 1K 99.9% biases 40 1 in 10K 99.99%  Expressed as a 50 1 in 100K 99.999% quality value (QV or Q score) per base  Similar to PHRED scores:  Q = -10 log10P  P = 10 -Q/10
  30. 30. Project 1: Microbial Genome Considerations:  Coverage  Reference genome?  Depth (number of  How much coverage times a particular do I want? base is “covered” by a read (e.g. 25X)  How big is the genome  Breadth (% of genome with at least 1X  How much data do I coverage) need?  bp needed = genome size X coverage  Which instrument/chemistry configuration to use?
  31. 31. Project 1: Microbial Genome Sample preparation  Isolate high quality (not degraded) and high purity (no RNA) gDNA  Verify on a gel  Quantify using dsDNA-specific dye Library preparation  Can do this yourself if you like  ~ $200 per sample for Nextera  Cheaper protocols  Cheaper in bulk  Barcode compatibility
  32. 32. Project 1: Microbial Genome Library QC  Insertsize confirmed on BioAnalyzer (within range, no artifacts)  Pool barcoded libraries (normalize based on PicoGreen quantification)  Absolute quantification of library pools using qPCR
  33. 33. Project 1: Microbial Genome MiSeq sequencing  Diluteand denature library pool (optimal concentration requires titration...)  Spike in PhiX library as needed (e.g. 1%)  Prepare and load reagents, flow cell  Basic filtering and de-multiplexing performed automatically  Download fastq files from BaseSpace
  34. 34. Project 1: Microbial Genome Data processing  Assembly:  Additional filtering overlapping reads  Trim the ends are assembled to  Remove PCR eachother based on duplicates sequence similarity = contigs
  35. 35. Project 1: Microbial Genome What’s next?  Polish the genome (hybrid assemblies, mate pair libraries)  Annotate (ORFs, RNA-seq)  Compare
  36. 36. Project 2: Microbial Community Shotgun  Targeted metagenomics metagenomics  Unbiased survey of  Limited survey of community content community content  Random library  Targeted loci provide fragments may excellent taxonomic provide very little resolution, but may taxonomic resolution exclude certain taxa (e.g. conserved, unknown)  Identify OTUs, classify  Identify genes, by taxonomy classify by function
  37. 37. Project 2: Microbial Community 16S rRNA Multi-copy gene (1.5 kb) Conserved and hypervariable regions Extensive databases from known species
  38. 38. Project 2: Microbial Community Considerations:  Sample preparation:  Biases in sampling  Isolate DNA methods, culturing,  PCR amplify, purify DNA isolation,  High-fidelity PCR...replicate polymerase  Available SOPs  Barcoded primers  How many reads per  No primer dimers! sample?  NormalizePCR  Read length products and pool matters!
  39. 39. Project 2: Microbial Community 454 Sequencing  Data processing  emPCR titrations  De-multiplexing with different library  Additionalfiltering input  Trim the barcodes,  Bulk emPCR primers  Sequence  Check for chimeras  Basic filtering  Collect sff files
  40. 40. Project 2: Microbial Community Clustering  Sequences grouped by similarity = OTUs
  41. 41. Project 2: Microbial Community Taxonomic identification  OTUs are classifed by comparing to known 16S sequences  Level of classification (e.g. family vs genus)? Diversity  Within sample  Between samples

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