Rapid sequencing DNA - 16S Barcoding Kit 24 V14 (SQK-16S114.24)

Oxford Nanopore Technologies
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Protocol

Rapid sequencing DNA - 16S Barcoding Kit 24 V14 (SQK-16S114.24) V16S_9199_v114_revB_06Dec2023

A protocol for amplifying the 16S rRNA gene from extracted gDNA.

  • Genus-level bacterial identification
  • Multiplex up to 24 different samples
  • Compatible with R10.4.1 flow cells only

For Research Use Only

This is an Early Access product For more information about our Early Access programmes, please see this article on product release phases.

FOR RESEARCH USE ONLY

Overview

A protocol for amplifying the 16S rRNA gene from extracted gDNA.

  • Genus-level bacterial identification
  • Multiplex up to 24 different samples
  • Compatible with R10.4.1 flow cells only

For Research Use Only

This is an Early Access product For more information about our Early Access programmes, please see this article on product release phases.

Document version: 16S_9199_v114_revB_06Dec2023

1. Overview of the protocol

IMPORTANT

This is an Early Access product

For more information about our Early Access programmes, please see this article on product release phases.

Please ensure you always use the most recent version of the protocol.

Introduction to the 16S Barcoding Kit 24 V14

This protocol describes how to carry out rapid barcoding of 16S amplicons using the 16S Barcoding Kit 24 V14 (SQK-16S114.24). Due to the presence of both highly conserved (adequate for universal primers and phylogenetic signal) and highly variant regions (different across species), the 16S rRNA gene is often used for sequence-based bacterial identification.

The 16S Barcoding Kit 24 V14 enables access to rapid 16S sequencing for organism identification. By narrowing down to a specific region of interest, you can see all the organisms in the sample without sequencing unnecessary regions of the genome, making the test quicker and more economical. There are 24 unique barcodes, allowing you to pool up to 24 different samples in one sequencing experiment.

After sequencing, you can perform downstream analysis using the EPI2ME 16S workflow (wf-16s) to classify 16S amplicons from your samples.

Steps in the sequencing workflow:

Prepare for your experiment

You will need to:

  • Extract your gDNA, and check its length, quantity and purity using the Input DNA/RNA QC protocol. The quality checks performed during the protocol are essential in ensuring experimental success
  • Ensure you have your sequencing kit, the correct equipment and third-party reagents
  • Download the software for acquiring and analysing your data
  • Check your flow cell to ensure it has enough pores for a good sequencing run

Library preparation

The table below is an overview of the steps required in the library preparation, including timings and stopping points.

Library preparation step Process Time Stop option
16S barcoded PCR amplification Amplify the 16S gene using barcodes supplied in the kit 10 minutes + PCR 4°C overnight
Barcoded sample pooling and bead clean-up Quantify and pool the barcoded samples and perform a library clean-up using beads 15 minutes 4°C short-term storage or for repeated use, such as re-loading your flow cell.
-80°C for single-use long-term storage.
Adapter ligation Attach the rapid sequencing adapters to the to the DNA ends. 5 minutes We strongly recommend sequencing your library as soon as it is adapted.
Priming and loading the flow cell Prime the flow cell and load the prepared DNA library for sequencing 5 minutes

16S V14 barcoding workflow

Sequencing and analysis

You will need to:

  • Start a sequencing run using the MinKNOW software, which will collect raw data from the device and convert it into basecalled reads
  • Optional: Start the EPI2ME software and select the wf-16S workflow
IMPORTANT

Compatibility of this protocol

This protocol should only be used in combination with:

2. Equipment and consumables

Materials
  • 10 ng high molecular weight genomic DNA
  • 16S Barcoding Kit 24 V14 (SQK-16S114.24)
Consumables
  • MinION and GridION Flow Cell
  • LongAmp Hot Start Taq 2X Master Mix (NEB, M0533)
  • Bovine Serum Albumin (BSA) (50 mg/ml) (e.g Invitrogen™ UltraPure™ BSA 50 mg/ml, AM2616)
  • Qubit dsDNA HS Assay Kit (Invitrogen, Q32851)
  • Freshly prepared 80% ethanol in nuclease-free water
  • Nuclease-free water (e.g. ThermoFisher, AM9937)
  • 1.5 ml Eppendorf DNA LoBind tubes
  • Qubit™ Assay Tubes (Invitrogen, Q32856)
  • 0.2 ml thin-walled PCR tubes
Equipment
  • MinION or GridION device
  • MinION and GridION Flow Cell Light Shield
  • Hula mixer (gentle rotator mixer)
  • Microfuge
  • Vortex mixer
  • Magnetic rack, suitable for 1.5 ml Eppendorf tubes
  • Thermal cycler
  • P1000 pipette and tips
  • P200 pipette and tips
  • P100 pipette and tips
  • P20 pipette and tips
  • P10 pipette and tips
  • P2 pipette and tips
  • Multichannel pipette and tips
  • Ice bucket with ice
  • Timer
  • Qubit fluorometer (or equivalent for QC check)

For this protocol, you will need 10 ng high molecular weight genomic DNA per barcode.

Third-party reagents

We have validated and recommend the use of all the third-party reagents used in this protocol. Alternatives have not been tested by Oxford Nanopore Technologies.

For all third-party reagents, we recommend following the manufacturer's instructions to prepare the reagents for use.

Check your flow cell

We highly recommend that you check the number of pores in your flow cell prior to starting a sequencing experiment. This should be done within three months of purchasing for MinION/GridION/PromethION or within four weeks of purchasing Flongle Flow Cells. Oxford Nanopore Technologies will replace any flow cell with fewer than the number of pores in the table below, when the result is reported within two days of performing the flow cell check, and when the storage recommendations have been followed. To do the flow cell check, please follow the instructions in the Flow Cell Check document.

Flow cell Minimum number of active pores covered by warranty
Flongle Flow Cell 50
MinION/GridION Flow Cell 800
PromethION Flow Cell 5000

16S Barcoding Kit 24 V14 contents

SQK-16S114.24 Kit content

Name Acronym Cap colour No. of vials Fill volume per vial (μl)
16S Barcode Primers 01-24 1-24 - 2 plates, 3 sets of barcodes per plate 15 μl per well
Rapid Adapter RA Green 1 15
Adapter Buffer ADB Clear 1 100
AMPure XP Beads AXP Clear cap, light teal label 1 6,000
Elution buffer EB Black 1 1,500
EDTA EDTA Blue 1 700
Sequencing Buffer SB Red 1 700
Library Beads LIB Pink 1 600
Library Solution LIS White cap, pink label 1 600
Flow Cell Flush FCF Clear cap, light blue label 1 8,000
Flow Cell Tether FCT Purple 1 200

Note: This product contains AMPure XP Reagent manufactured by Beckman Coulter, Inc. and can be stored at -20°C with the kit without detriment to reagent stability.

3. Library preparation

Materials
  • 10 ng high molecular weight genomic DNA
  • 16S Barcodes in 96-well plate, at 1 μM each
  • EDTA (EDTA)
  • AMPure XP Beads (AXP)
  • Elution Buffer (EB)
  • Rapid Adapter (RA)
  • Adapter Buffer (ADB)
Consumables
  • LongAmp Hot Start Taq 2X Master Mix (NEB, M0533)
  • Qubit dsDNA HS Assay Kit (Invitrogen, Q32851)
  • Freshly prepared 80% ethanol in nuclease-free water
  • Nuclease-free water (e.g. ThermoFisher, AM9937)
  • 1.5 ml Eppendorf DNA LoBind tubes
  • Qubit™ Assay Tubes (Invitrogen, Q32856)
  • 0.2 ml thin-walled PCR tubes
Equipment
  • Thermal cycler
  • Microfuge
  • Hula mixer (gentle rotator mixer)
  • Magnetic rack
  • Ice bucket with ice
  • Qubit fluorometer (or equivalent for QC check)
  • P1000 pipette and tips
  • P200 pipette and tips
  • P100 pipette and tips
  • P20 pipette and tips
  • P10 pipette and tips
  • P2 pipette and tips
  • Multichannel pipette and tips
CHECKPOINT

Check your flow cell.

We recommend performing a flow cell check before starting your library prep to ensure you have a flow cell with enough pores for a good sequencing run.

See the flow cell check instructions in the MinKNOW protocol for more information.

Take one 96-well plate containing 16S barcodes. Break one set of barcodes (1-24, or as desired) away from the plate and return the rest to storage.

16S barcode plate layout:

16S barcode plate layout

IMPORTANT

The 96-well plates are designed to break in one direction only. Strips, or multiple strips, of eight wells/barcodes can be removed from the plate at any one time.

Thaw the desired barcodes at room temperature.

Briefly centrifuge barcodes in a microfuge to make sure the liquid is at the bottom of the tubes and place on ice.

Thaw the LongAmp Hot Start Taq 2X Master Mix, spin down briefly, mix well by pipetting and place on ice.

Prepare the DNA in nuclease-free water.

  • Transfer 10 ng of each genomic DNA sample into a 0.2 ml thin-walled PCR tube
  • Adjust the volume to 15 μl with nuclease-free water
  • Mix thoroughly by flicking avoiding unwanted shearing
  • Spin down briefly in a microfuge

In each 0.2 ml thin-walled PCR tube containing a sample to be tested, prepare the following mixture:

Reagent Volume
10 ng input DNA (from previous step) 15 μl
LongAmp Hot Start Taq 2X Master Mix 25 μl
Total 40 μl

Note: If the amount of input material is altered, the number of PCR cycles may need to be adjusted to produce the same yield.

Ensure the components are thoroughly mixed by pipetting and spin down briefly.

Using clean pipette tips, carefully pierce the foil surface of the required barcodes. Use a new tip for each barcode to avoid cross-contamination. Make a note of which barcode numbers will be run for each sample.

Using a multichannel pipette, mix the 16S barcodes by pipetting up and down 10 times. Transfer 10 μl of each 16S Barcode into respective sample-containing tubes.

Ensure the components are thoroughly mixed by pipetting the contents of the tubes 10 times and spin down.

Note: Mix gently to minimise introducing air bubbles to the reactions.

Amplify using the following cycling conditions:

Cycle step Temperature Time No. of cycles
Initial denaturation 95 °C 1 min 1
Denaturation 95 °C 20 secs 25
Annealing 55 °C 30 secs 25
Extension 65 °C 2 mins 25
Final extension 65 °C 5 mins 1
Hold 4 °C ∞

Thaw reagents at room temperature, spin down briefly using a microfuge and mix by pipetting as indicated by the table below:

Reagent 1. Thaw at room temperature 2. Briefly spin down 3. Mix well by pipetting or vortexing
Rapid Adapter (RA) Not frozen ✓ Pipette
Adapter Buffer (ADB) ✓ ✓ Vortex or Pipette
AMPure XP Beads (AXP) ✓ ✓ Mix by vortexing immediately before use
Elution Buffer (EB) ✓ ✓ Vortex or Pipette
EDTA (EDTA) ✓ ✓ Vortex or Pipette

Note: Once thawed, keep all reagents on ice.

Add 4 µl of EDTA to each barcoded sample, mix thorougly by pipetting and spin down briefly.

TIP

EDTA is added at this step to stop the reaction.

Incubate for 5 minutes at room temperature.

Quantify 1 µl of each barcoded sample using a Qubit fluorometer (or equivalent) for QC check.

Pool all barcoded samples in equimolar ratios in a 1.5 ml Eppendorf DNA LoBind tube.

Note: Please ensure you have quantified your samples prior to this step and take forward an equimolar concentration of each of the samples for optimal barcode balancing. Samples may vary in concentration following the barcoded PCR, therefore the volume of each barcoded sample added to the pool will be different.

Resuspend the AMPure XP Beads (AXP) by vortexing.

To the pool of barcoded samples, add a 0.6X volume ratio of resuspended AMPure XP Beads (AXP) and mix by pipetting:

Volume of barcoded sample pool 37.5 μl 75 μl 150 μl 300 μl 600 μl
Volume of AMPure XP Beads (AXP) 22.5 μl 45 μl 90 μl 180 μl 360 μl

Note: Table contains example volumes for reference. Please adjust the volume of AMPure XP Beads (AXP) added for the volume of your barcoded sample pool to ensure a 0.6X volume ratio.

Incubate on a Hula mixer (rotator mixer) for 5 minutes at room temperature.

Prepare 2 ml of fresh 80% ethanol in nuclease-free water.

Briefly spin down the sample and pellet on a magnetic rack until supernatant is clear and colourless. Keep the tube on the magnetic rack, and pipette off the supernatant.

Keep the tube on the magnet and wash the beads with 1 ml of freshly-prepared 80% ethanol without disturbing the pellet. Remove the ethanol using a pipette and discard.

Repeat the previous step.

Spin down and place the tube back on the magnet. Pipette off any residual ethanol. Allow to dry for ~30 seconds, but do not dry the pellet to the point of cracking.

Remove the tube from the magnetic rack and resuspend the pellet by pipetting in 15 µl Elution Buffer (EB). Spin down and incubate for 5 minutes at room temperature.

Pellet the beads on a magnet until the eluate is clear and colourless, for at least 1 minute.

Remove and retain 15 µl of eluate into a clean 1.5 ml Eppendorf DNA LoBind tube.

  • Remove and retain the eluate which contains the DNA library in a clean 1.5 ml Eppendorf DNA LoBind tube
  • Dispose of the pelleted beads
CHECKPOINT

Quantify 1 µl of eluted sample using a Qubit fluorometer.

Transfer 50 fmol of your eluted sample into a clean 1.5 ml Eppendorf DNA LoBind tube. Make up the volume to 11 µl with Elution Buffer (EB).

In a fresh 1.5 ml Eppendorf DNA LoBind tube, dilute the Rapid Adapter (RA) as follows and pipette mix:

Reagent Volume
Rapid Adapter (RA) 1.5 μl
Adapter Buffer (ADB) 3.5 μl
Total 5 μl

Add 1 µl of the diluted Rapid Adapter (RA) to the barcoded DNA.

Mix gently by flicking the tube, and spin down.

Incubate the reaction for 5 minutes at room temperature.

END OF STEP

The prepared library is used for loading into the flow cell. Store the library on ice until ready to load.

4. Priming and loading the MinION and GridION Flow Cell

Materials
  • Flow Cell Flush (FCF)
  • Flow Cell Tether (FCT)
  • Library Solution (LIS)
  • Library Beads (LIB)
  • Sequencing Buffer (SB)
Consumables
  • MinION and GridION Flow Cell
  • Bovine Serum Albumin (BSA) (50 mg/ml) (e.g Invitrogen™ UltraPure™ BSA 50 mg/ml, AM2616)
  • 1.5 ml Eppendorf DNA LoBind tubes
Equipment
  • MinION or GridION device
  • MinION and GridION Flow Cell Light Shield
  • P1000 pipette and tips
  • P100 pipette and tips
  • P20 pipette and tips
  • P10 pipette and tips
IMPORTANT

Please note, this kit is only compatible with R10.4.1 flow cells (FLO-MIN114).

TIP

Priming and loading a flow cell

We recommend all new users watch the 'Priming and loading your flow cell' video before your first run.

Using the Library Solution

For most sequencing experiments, use the Library Beads (LIB) for loading your library onto the flow cell. However, for viscous libraries it may be difficult to load with the beads and may be appropriate to load using the Library Solution (LIS).

Thaw the Sequencing Buffer (SB), Library Beads (LIB) or Library Solution (LIS, if using), Flow Cell Tether (FCT) and Flow Cell Flush (FCF) at room temperature before mixing by vortexing. Then spin down and store on ice.

IMPORTANT

For optimal sequencing performance and improved output on MinION R10.4.1 flow cells (FLO-MIN114), we recommend adding Bovine Serum Albumin (BSA) to the flow cell priming mix at a final concentration of 0.2 mg/ml.

Note: We do not recommend using any other albumin type (e.g. recombinant human serum albumin).

To prepare the flow cell priming mix with BSA, combine the following reagents in a fresh 1.5 ml Eppendorf DNA LoBind tube. Mix by inverting the tube and pipette mix at room temperature:

Reagents Volume per flow cell
Flow Cell Flush (FCF) 1,170 µl
Bovine Serum Albumin (BSA) at 50 mg/ml 5 µl
Flow Cell Tether (FCT) 30 µl
Final total volume in tube 1,205 µl

Open the MinION or GridION device lid and slide the flow cell under the clip. Press down firmly on the flow cell to ensure correct thermal and electrical contact.

Flow Cell Loading Diagrams Step 1a

Flow Cell Loading Diagrams Step 1b

OPTIONAL ACTION

Complete a flow cell check to assess the number of pores available before loading the library.

This step can be omitted if the flow cell has been checked previously.

See the flow cell check instructions in the MinKNOW protocol for more information.

Slide the flow cell priming port cover clockwise to open the priming port.

Flow Cell Loading Diagrams Step 2

IMPORTANT

Take care when drawing back buffer from the flow cell. Do not remove more than 20-30 µl, and make sure that the array of pores are covered by buffer at all times. Introducing air bubbles into the array can irreversibly damage pores.

After opening the priming port, check for a small air bubble under the cover. Draw back a small volume to remove any bubbles:

  1. Set a P1000 pipette to 200 µl
  2. Insert the tip into the priming port
  3. Turn the wheel until the dial shows 220-230 µl, to draw back 20-30 µl, or until you can see a small volume of buffer entering the pipette tip
    __Note:__ Visually check that there is continuous buffer from the priming port across the sensor array.

Flow Cell Loading Diagrams Step 03 V5

Load 800 µl of the priming mix into the flow cell via the priming port, avoiding the introduction of air bubbles. Wait for five minutes. During this time, prepare the library for loading by following the steps below.

Flow Cell Loading Diagrams Step 04 V5

Thoroughly mix the contents of the Library Beads (LIB) by pipetting.

IMPORTANT

The Library Beads (LIB) tube contains a suspension of beads. These beads settle very quickly. It is vital that they are mixed immediately before use.

We recommend using the Library Beads (LIB) for most sequencing experiments. However, the Library Solution (LIS) is available for more viscous libraries.

In a new 1.5 ml Eppendorf DNA LoBind tube, prepare the library for loading as follows:

Reagent Volume per flow cell
Sequencing Buffer (SB) 37.5 µl
Library Beads (LIB) mixed immediately before use, or Library Solution (LIS), if using 25.5 µl
DNA library 12 µl
Total 75 µl

Complete the flow cell priming:

  1. Gently lift the SpotON sample port cover to make the SpotON sample port accessible.
  2. Load 200 µl of the priming mix into the flow cell priming port (not the SpotON sample port), avoiding the introduction of air bubbles.

Flow Cell Loading Diagrams Step 5

Flow Cell Loading Diagrams Step 06 V5

Mix the prepared library gently by pipetting up and down just prior to loading.

Add 75 μl of the prepared library to the flow cell via the SpotON sample port in a dropwise fashion. Ensure each drop flows into the port before adding the next.

Flow Cell Loading Diagrams Step 07 V5

Gently replace the SpotON sample port cover, making sure the bung enters the SpotON port and close the priming port.

Step 8 update

Flow Cell Loading Diagrams Step 9

IMPORTANT

Install the light shield on your flow cell as soon as library has been loaded for optimal sequencing output.

We recommend leaving the light shield on the flow cell when library is loaded, including during any washing and reloading steps. The shield can be removed when the library has been removed from the flow cell.

Place the light shield onto the flow cell, as follows:

  1. Carefully place the leading edge of the light shield against the clip. Note: Do not force the light shield underneath the clip.

  2. Gently lower the light shield onto the flow cell. The light shield should sit around the SpotON cover, covering the entire top section of the flow cell.

J2264 - Light shield animation Flow Cell FAW optimised

CAUTION

The MinION Flow Cell Light Shield is not secured to the flow cell and careful handling is required after installation.

END OF STEP

Close the device lid and set up a sequencing run on MinKNOW.

5. Data acquisition and basecalling

How to start sequencing

Once you have loaded your flow cell, the sequencing run can be started on MinKNOW, our sequencing software that controls the device, data acquisition and real-time basecalling. For more detailed information on setting up and using MinKNOW, please see the MinKNOW protocol.

MinKNOW can be used and set up to sequence in multiple ways:

  • On a computer either directly or remotely connected to a sequencing device.
  • Directly on a GridION, MinION Mk1C or PromethION 24/48 sequencing device.

For more information on using MinKNOW on a sequencing device, please see the device user manuals:

To start a sequencing run on MinKNOW:

1. Navigate to the start page and click Start sequencing.

2. Fill in your experiment details, such as name and flow cell position and sample ID.

3. Select the sequencing kit used in the library preparation on the Kit page.

4. Configure the sequencing and output parameters for your sequencing run or keep to the default settings on the Run configuration tab.

Note: If basecalling was turned off when a sequencing run was set up, basecalling can be performed post-run on MinKNOW. For more information, please see the MinKNOW protocol.

5. Click Start on the Review page to start the sequencing run.

Data analysis after sequencing

After sequencing has completed on MinKNOW, the flow cell can be reused or returned, as outlined in the Flow cell reuse and returns section.

After sequencing and basecalling, the data can be analysed. For further information about options for basecalling and post-basecalling analysis, please refer to the Data Analysis document.

In the Downstream analysis section, we outline further options for analysing your data.

6. Flow cell reuse and returns

Materials
  • Flow Cell Wash Kit (EXP-WSH004)

After your sequencing experiment is complete, if you would like to reuse the flow cell, please follow the Flow Cell Wash Kit protocol and store the washed flow cell at 2-8°C.

The Flow Cell Wash Kit protocol is available on the Nanopore Community.

Alternatively, follow the returns procedure to flush out the flow cell ready to send back to Oxford Nanopore.

Instructions for returning flow cells can be found here.

Note: All flow cells must be flushed with deionised water before returning the product.

IMPORTANT

If you encounter issues or have questions about your sequencing experiment, please refer to the Troubleshooting Guide that can be found in the online version of this protocol.

7. Downstream analysis

Post-basecalling analysis

We recommend performing downstream analysis using EPI2ME which facilitates bioinformatic analyses by allowing users to run Nextflow workflows in a desktop application. EPI2ME maintains a collection of bioinformatic workflows which are curated and actively maintained by experts in long-read sequence analysis.

Further information about the available EPI2ME workflows are available here, along with the Quick Start Guide to start your first bioinformatic workflow.

The 16S workflow (wf-16s) is a Nextflow workflow leveraging the power of wf-metagenomics for identification of the origin of reads from targeted amplicon sequencing. The workflow has two modes of operation, it can use either kraken2 or minimap2 to determine the origin of reads.

More information on the EPI2ME 16S workflow (wf-16s) can be found here.

For installation instructions please click here.

Additional options for further analysing your basecalled data include:

1. Research analysis tools

Oxford Nanopore Technologies' Research division has created a number of analysis tools, that are available in the Oxford Nanopore GitHub repository. The tools are aimed at advanced users, and contain instructions for how to install and run the software. They are provided as-is, with minimal support.

2. Community-developed analysis tools

If a data analysis method for your research question is not provided in any of the resources above, please refer to the Bioinformatics section of the Resource centre. Numerous members of the Nanopore Community have developed their own tools and pipelines for analysing nanopore sequencing data, most of which are available on GitHub. Please be aware that these tools are not supported by Oxford Nanopore Technologies, and are not guaranteed to be compatible with the latest chemistry/software configuration.

8. Issues during DNA/RNA extraction and library preparation

Below is a list of the most commonly encountered issues, with some suggested causes and solutions.

We also have an FAQ section available on the Nanopore Community Support section.

If you have tried our suggested solutions and the issue still persists, please contact Technical Support via email (support@nanoporetech.com) or via LiveChat in the Nanopore Community.

Low sample quality

Observation Possible cause Comments and actions
Low DNA purity (Nanodrop reading for DNA OD 260/280 is <1.8 and OD 260/230 is <2.0–2.2) The DNA extraction method does not provide the required purity The effects of contaminants are shown in the Contaminants document. Please try an alternative extraction method that does not result in contaminant carryover.

Consider performing an additional SPRI clean-up step.
Low RNA integrity (RNA integrity number <9.5 RIN, or the rRNA band is shown as a smear on the gel) The RNA degraded during extraction Try a different RNA extraction method. For more info on RIN, please see the RNA Integrity Number document. Further information can be found in the DNA/RNA Handling page.
RNA has a shorter than expected fragment length The RNA degraded during extraction Try a different RNA extraction method. For more info on RIN, please see the RNA Integrity Number document. Further information can be found in the DNA/RNA Handling page.

We recommend working in an RNase-free environment, and to keep your lab equipment RNase-free when working with RNA.

Low DNA recovery after AMPure bead clean-up

Observation Possible cause Comments and actions
Low recovery DNA loss due to a lower than intended AMPure beads-to-sample ratio 1. AMPure beads settle quickly, so ensure they are well resuspended before adding them to the sample.

2. When the AMPure beads-to-sample ratio is lower than 0.4:1, DNA fragments of any size will be lost during the clean-up.
Low recovery DNA fragments are shorter than expected The lower the AMPure beads-to-sample ratio, the more stringent the selection against short fragments. Please always determine the input DNA length on an agarose gel (or other gel electrophoresis methods) and then calculate the appropriate amount of AMPure beads to use. SPRI cleanup
Low recovery after end-prep The wash step used ethanol <80% DNA will be eluted from the beads when using ethanol <80%. Make sure to use the correct percentage.

9. Issues during the sequencing run using a Rapid-based sequencing kit

Below is a list of the most commonly encountered issues, with some suggested causes and solutions.

We also have an FAQ section available on the Nanopore Community Support section.

If you have tried our suggested solutions and the issue still persists, please contact Technical Support via email (support@nanoporetech.com) or via LiveChat in the Nanopore Community.

Fewer pores at the start of sequencing than after Flow Cell Check

Observation Possible cause Comments and actions
MinKNOW reported a lower number of pores at the start of sequencing than the number reported by the Flow Cell Check An air bubble was introduced into the nanopore array After the Flow Cell Check it is essential to remove any air bubbles near the priming port before priming the flow cell. If not removed, the air bubble can travel to the nanopore array and irreversibly damage the nanopores that have been exposed to air. The best practice to prevent this from happening is demonstrated in this video.
MinKNOW reported a lower number of pores at the start of sequencing than the number reported by the Flow Cell Check The flow cell is not correctly inserted into the device Stop the sequencing run, remove the flow cell from the sequencing device and insert it again, checking that the flow cell is firmly seated in the device and that it has reached the target temperature. If applicable, try a different position on the device (GridION/PromethION).
MinKNOW reported a lower number of pores at the start of sequencing than the number reported by the Flow Cell Check Contaminations in the library damaged or blocked the pores The pore count during the Flow Cell Check is performed using the QC DNA molecules present in the flow cell storage buffer. At the start of sequencing, the library itself is used to estimate the number of active pores. Because of this, variability of about 10% in the number of pores is expected. A significantly lower pore count reported at the start of sequencing can be due to contaminants in the library that have damaged the membranes or blocked the pores. Alternative DNA/RNA extraction or purification methods may be needed to improve the purity of the input material. The effects of contaminants are shown in the Contaminants Know-how piece. Please try an alternative extraction method that does not result in contaminant carryover.

MinKNOW script failed

Observation Possible cause Comments and actions
MinKNOW shows "Script failed"
Restart the computer and then restart MinKNOW. If the issue persists, please collect the MinKNOW log files and contact Technical Support. If you do not have another sequencing device available, we recommend storing the flow cell and the loaded library at 4°C and contact Technical Support for further storage guidance.

Pore occupancy below 40%

Observation Possible cause Comments and actions
Pore occupancy <40% Not enough library was loaded on the flow cell 10–50 fmol of good quality library can be loaded on to a MinION Mk1B/GridION flow cell. Please quantify the library before loading and calculate mols using tools like the Promega Biomath Calculator, choosing "dsDNA: µg to pmol"
Pore occupancy close to 0 The Rapid PCR Barcoding Kit V14 was used, and sequencing adapters did not attach to the DNA Make sure to closely follow the protocol and use the correct volumes and incubation temperatures. A Lambda control library can be prepared to test the integrity of reagents.
Pore occupancy close to 0 No tether on the flow cell Tethers are added during flow cell priming (FCT tube). Make sure FCT was added to FCF before priming.

Shorter than expected read length

Observation Possible cause Comments and actions
Shorter than expected read length Unwanted fragmentation of DNA sample Read length reflects input DNA fragment length. Input DNA can be fragmented during extraction and library prep.

1. Please review the Extraction Methods in the Nanopore Community for best practice for extraction.

2. Visualise the input DNA fragment length distribution on an agarose gel before proceeding to the library prep. DNA gel2 In the image above, Sample 1 is of high molecular weight, whereas Sample 2 has been fragmented.

3. During library prep, avoid pipetting and vortexing when mixing reagents. Flicking or inverting the tube is sufficient.

Large proportion of unavailable pores

Observation Possible cause Comments and actions
Large proportion of unavailable pores (shown as blue in the channels panel and pore activity plot)

image2022-3-25 10-43-25 The pore activity plot above shows an increasing proportion of "unavailable" pores over time.		 Contaminants are present in the sample Some contaminants can be cleared from the pores by the unblocking function built into MinKNOW. If this is successful, the pore status will change to "sequencing pore". If the portion of unavailable pores stays large or increases:

1. A nuclease flush using the Flow Cell Wash Kit (EXP-WSH004) can be performed, or
2. Run several cycles of PCR to try and dilute any contaminants that may be causing problems.

Large proportion of inactive pores

Observation Possible cause Comments and actions
Large proportion of inactive/unavailable pores (shown as light blue in the channels panel and pore activity plot. Pores or membranes are irreversibly damaged) Air bubbles have been introduced into the flow cell Air bubbles introduced through flow cell priming and library loading can irreversibly damage the pores. Watch the Priming and loading your flow cell video for best practice
Large proportion of inactive/unavailable pores Certain compounds co-purified with DNA Known compounds, include polysaccharides, typically associate with plant genomic DNA.

1. Please refer to the Plant leaf DNA extraction method.
2. Clean-up using the QIAGEN PowerClean Pro kit.
3. Perform a whole genome amplification with the original gDNA sample using the QIAGEN REPLI-g kit.
Large proportion of inactive/unavailable pores Contaminants are present in the sample The effects of contaminants are shown in the Contaminants Know-how piece. Please try an alternative extraction method that does not result in contaminant carryover.

Temperature fluctuation

Observation Possible cause Comments and actions
Temperature fluctuation The flow cell has lost contact with the device Check that there is a heat pad covering the metal plate on the back of the flow cell. Re-insert the flow cell and press it down to make sure the connector pins are firmly in contact with the device. If the problem persists, please contact Technical Services.

Failed to reach target temperature

Observation Possible cause Comments and actions
MinKNOW shows "Failed to reach target temperature" The instrument was placed in a location that is colder than normal room temperature, or a location with poor ventilation (which leads to the flow cells overheating) MinKNOW has a default timeframe for the flow cell to reach the target temperature. Once the timeframe is exceeded, an error message will appear and the sequencing experiment will continue. However, sequencing at an incorrect temperature may lead to a decrease in throughput and lower q-scores. Please adjust the location of the sequencing device to ensure that it is placed at room temperature with good ventilation, then re-start the process in MinKNOW. Please refer to this FAQ for more information on MinION Mk 1B temperature control.

Last updated: 4/24/2024

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