The next-generation sequencing workflow contains three basic steps: library preparation, sequencing, and data analysis. Learn the basics of each step and discover how to plan your NGS workflow.View an Example Workflow
Before starting the next-generation sequencing workflow, isolate and purify your nucleic acid. Some DNA extraction methods can introduce inhibitors, which can negatively affect the enzymatic reactions that occur in the NGS workflow. For best results, use an extraction protocol optimized for your sample type. For RNA sequencing experiments, convert RNA to cDNA by reverse transcription.
After extraction, most NGS workflows require a QC step. We recommend using UV spectrophotometry for purity assessment and fluorometric methods for nucleic acid quantitation.
Library preparation is crucial to the success of your NGS workflow. This step prepares DNA or RNA samples to be compatible with a sequencer. Sequencing libraries are typically created by fragmenting DNA and adding specialized adapters to both ends. In the Illumina sequencing workflow, these adapters contain complementary sequences that allow the DNA fragments to bind to the flow cell. Fragments can then be amplified and purified.
To save resources, multiple libraries can be pooled together and sequenced in the same run—a process known as multiplexing. During adapter ligation, unique index sequences, or “barcodes,” are added to each library. These barcodes are used to distinguish between the libraries during data analysis.
During the sequencing step of the NGS workflow, libraries are loaded onto a flow cell and placed on the sequencer. The clusters of DNA fragments are amplified in a process called cluster generation, resulting in millions of copies of single-stranded DNA. On most Illumina sequencing instruments, clustering occurs automatically.
In a process called sequencing by synthesis (SBS), chemically modified nucleotides bind to the DNA template strand through natural complementarity. Each nucleotide contains a fluorescent tag and a reversible terminator that blocks incorporation of the next base. The fluorescent signal indicates which nucleotide has been added, and the terminator is cleaved so the next base can bind.
After reading the forward DNA strand, the reads are washed away, and the process repeats for the reverse strand. This method is called paired-end sequencing.
After sequencing, the instrument software identifies nucleotides (a process called base calling) and the predicted accuracy of those base calls. During data analysis, you can import your sequencing data into a standard analysis tool or set up your own pipeline.
Today, you can use intuitive data analysis apps to analyze NGS data without bioinformatics training or additional lab staff. These tools provide sequence alignment, variant calling, data visualization, or interpretation.
Microbial whole-genome sequencing can be used to identify pathogens, compare genomes, and analyze antimicrobial resistance. Our featured NGS workflow for this application describes the recommended steps. The entire workflow proceeds from DNA to data in less than 24 hours.
Use an extraction kit to isolate DNA from microbial colonies without introducing inhibitors. We recommend using glass beads. Assess purity using UV spectrophotometry and quantitate DNA using fluorometric methods.
Estimated time: ~1–2 hours
Prepare and quantify libraries following the protocol listed in the Illumina DNA Prep Guide. You can also perform an optional library quality check using the Agilent 2100 Bioanalyzer or Advanced Analytical Fragment Analyzer. You’ll need:
Estimated time: ~2.5 hours
Estimated DNA input: 1–500 ng
Analyze data using the BWA Aligner app and visualize data using the Integrative Genomics Viewer app in BaseSpace Sequence Hub. You’ll need:
Estimated analysis time: ~1 hourLearn More About Microbial Whole-Genome Sequencing
A general overview of the Illumina sequencing workflow, from DNA/RNA extraction to the completion of a run.
This in-depth overview describes the basics of Illumina sequencing chemistry, major advances in technology, and more.
Best practices for transitioning from qPCR to custom RNA sequencing.