Scientists at the University of Nottingham in the UK broke the world record for decoding the longest DNA sequence back in January. Now, the team, led by Associate Professor Matt Loose, have done it once again with a DNA read 10,000 times as long as usual – and double that of the previous record holders.
A friendly competition to be the first to reach the million-base milestone (that is, produce a DNA read of more than 1 million bases) was won by an Australian team based at the Kinghorn Centre for Clinical Genomics in December 2017. But Loose and his colleagues quickly caught up – and have since far exceeded that original goal.
Incredibly, their most recent DNA read (from a human genome) is a sequence with 2.3 million bases. Measure that against the most common read length, which is a comparatively measly 150 bases.
"We were recently teaching people in Singapore how to use these sequencers at the same time as the grand prix. If the Singapore grand prix track is the same as 150 bases, then a 2.3 million base pair read is twice around the circumference of the Earth," Loose told the BBC.
So, how did they do it? The team adopted the very same technique they used earlier this year to read a DNA sequence 1,204,840 bases-long, a process called nanopore sequencing.
Essentially, it works by tunneling long strands of DNA through a small hole in a device called a MinION DNA sequencer. It then identifies the sequence of the four bases – A (adenine), C (cytosine), G (guanine), T (thymine) – using an electrical signal.
"Nanopore sequencing promised lower cost and higher read lengths which means that we can look at interesting organisms which are yet to be sequenced, because their genomes are extraordinarily large," Loose said in a statement earlier this year.
It's all very exciting, but what are the practical applications of this kind of discovery?
Loose and his team hope scientists will start to use methods like this to study cancer genomes, where the DNA is chopped, changed, and rearranged – like a puzzle with missing pieces and sections from other puzzles, explains Angus Davison, a geneticist at the University of Nottingham, writing for the BBC.
It also takes us closer to the day when scientists manage to sequence an entire chromosome, though Loose isn't so sure that large a feat is even possible.
"If we scale the nanopore up to the size of a human fist, then a megabase of DNA is a rope of 3.2 km, which you have to thread through your fingers without it getting tangled or breaking," Loose told Davison.
"I am not sure you will ever be able to sequence a chromosome from one end to the other."