When I first heard of the Oxford Nanopore technology, it sounded rather exciting: The company proclaimed a new technology which enabled sequencing with extremely long read lengths of up to 100 kbp at a reasonable accuracy and in a very short time.
The technology is based on so-called “strand sequencing”. This technique involves a protein nanopore, in combination with a specific enzyme. This enzyme is designed to feed a single strand of DNA through the nanopore. The bases of the DNA strand are identified as they pass through the pore.
The sequencing systems are called “GridION” and “MinION”, with the GridION representing a high throughput system, and the MinION being a miniaturised system the size of a USB stick.
First data for the GridION system have been presented in February 2012 at the AGBT conference. After that, there had been hardly any news from Oxford Nanopore for a long time. Then in November 2013, Oxford Nanopore announced an early access program for the MinION system on the ASHG meeting. They also gave demonstrations of the system to selected customers in the company´s labs. However, the company did not show any sequencing data yet. In February 2014, Oxford Nanopore has started to issue invitations to the early access program, and the first MinION systems should be shipped soon.
On the AGBT meeting in Feburary, the first MinION sequencing data, generated by Oxford Nanopore and analysed by David Jaffe from Broad Institute, Cambridge, have finally been presented. However, the first results were rather disappointing: The average read length was way below the expectations. As reported by In Sequence, Jaffe told that the average read lengths were 5.4 kbp and 4.9 kbp for the two bacterial genomes analysed. The raw error rate of the data was not disclosed. However, Jaffe said that there were “long perfect stretches” and “blocks of errors”. The data was not suitable for de novo assemblies from MinION data alone. In the end, the researchers used the sequences to create better assemblies from Illumina data.
On a Plant Genomics Meeting in Kuala Lumpur in the end of February, Oxford Nanopore Technologies presented more data. They claim that they could “easily obtain” 50 kbp reads. They had generated reads spanning the entire 48 kbp bacteriophage lambda genome. They also show data to underline that the read length distribution obtained by Nanopore sequencing is determined by the size distribution of the input DNA. Slides of the presentation can be viewed here.
Even if the first results are somewhat disappointing, I think this is still an interesting new technique. Like it was with the PacBio system, the technology may need more time to overcome its childhood diseases. The next few months will show if the technology can hold the high expectations that have been raised.