The answer is blowing in the wind

John writes ...

Picture credit: Marcin Wolski.

Introduction
 
‘What is your favourite molecule?’ I was once asked. Well, when you’ve got millions to choose from, that could be a tricky question. Some may opt for ethyl alcohol, others for caffeine (the latter is high on my list too). However, for me, the actual number-one favourite has to be DNA, the molecule that carries the genetic code, a code which is read in the same way by all living organisms on Earth. As many of you know, I and my research team worked directly or indirectly on DNA for all of my research career, especially in relation to the control of DNA replication (i.e., copying the genome prior to cell division) and also to understanding changes in gene expression in plants exposed to environmental stress. In addition to this hands-on research, I also have a deep and ongoing interest in the applications of new genetic knowledge, especially in medicine, and also in the ethical challenges that arise as new possibilities open up. 

John talking about his favourite molecule. Picture credit: University of Antwerp.

Environmental DNA
 
However, in this blog post I want to move away from those interests to something that may seem at first to seem slightly quirky. A couple of weeks ago, as I opened the regular email briefing from the leading science journal Nature, my eye was drawn to an intriguing headline: DNA is in the air. Well, yes, I suppose it would be, what with pollen grains, spores, viruses and bacteria which are spread aerially. But the headline referred to rather more than that. To consider its significance we need to go back to the late 1980s when attempts were first made to assess biodiversity in water samples by sequencing the DNA of all organisms in the samples, without trying to separate them individually. In other words, the sequencing involved (hopefully) all the DNA in that environment. The method was thus termed environmental DNA sequencing which today we refer to as eDNA analysis. 

Initially, eDNA analysis relied on the sequencing method developed at Cambridge by Fred Sanger in 1977. It is accurate but slow, even when automated. Hence, for example, in the Human Genome Project, it took twelve years to assemble the genomic DNA sequence of a ‘average’ human. Data accumulation was thus protracted and use of the Sanger method in eDNA analysis was not widespread. However, in the late 1990s, two Cambridge scientists, Dr Shankar Balasubramanian and Dr David Klenerman, started to experiment with a different method of sequencing, leading to the launch of their genome sequencer in 2006. 

Shankar Balasubramanian and David Klenerman. Both are now professors and Fellows of the Royal Society. In 2018 they were awarded the Society’s Royal Medal. Picture credit: Cancer Research UK.

This was capable of sequencing speeds that were orders of magnitude faster than those achievable by the Sanger method. Indeed, it is routinely possible to sequence DNA lengths of up to a billion base-pairs in a single run. The method has become known as Illumina sequencing, named after the company, Illumina, that bought the technology, although we should perhaps use the more ‘generic’ term, next-generation sequencing (NGS) which also includes another rapid method, nanopore sequencing. 

DNA sequencing facility at Exeter University. Picture credit: University of Exeter.

It is the availability of NGS that has led, since 2007, to hugely increased speeds of determining complete genome sequences and to the analysis of complete genomes of an ever-increasing range of living organisms. As readers of this blog will know, that has included the rapid diagnosis of genetic diseases. However, in the context of this post, it also led to a very large increase in eDNA analyses, helping us to understand the communities of living organisms in soil, water and even snow samples. For example, I was recently talking to Dr Jon Porter of the Environment Agency, who explained that only was it now straightforward to look at microbial communities in river and sea water but it was also possible to directly monitor waste water for the presence of bacteria and viruses. This gives an immediate estimate of the prevalence of particular infections in the area from which the waste water is derived. 

Waste-water analysis in the laboratories of the Environment Agency at Starcross, near Exeter. Picture credit: Sky News.

​Up in the air
 
This then leads back to the topic which stimulated me to write this post, namely DNA in the air. About 12 years ago, scientists wondered whether it would be possible to detect airborne DNA, other than that contained in pollen and spores (which have evolved to travel in the air). As Ashley Irwin writes ‘Scratch your head and you’ll release DNA-rich cellular material into the air. There, it will mingle with DNA from myriad other sources: your own and others’ exhalations and exfoliations, fragments of hair, feathers, excrement, pollen and spores, and microorganisms such as viruses and microalgae. This DNA, which can include segments that are tens of thousands of base pairs long, will then wander the air for perhaps a few days, often clinging to dust particles. It can travel distances that range from a few metres to several thousand’. But can this DNA be captured and analysed? In a recent answer that question, a team led by Dr Elizabeth Clare (Queen Mary University of London/York University, Toronto) sampled air-borne DNA 200 metres away from the boundary of the Hamerton zoological park near Huntingdon in East Anglia. The zoo park housed a tiger and the team were pleased to detect tiger DNA in their sample. And actually, they detected a good deal more than that, including a further sixteen mammalian species that were kept at the zoo park, plus eight species of native wild birds and mammals, including hedgehog. Further to all this, from samples collected within the zoo enclosures they were able to detect DNA from the food given to the zoo animals. The authors rightly conclude that their ‘findings demonstrate the profound potential of air as a source of DNA for global terrestrial biomonitoring’ (Clare, E.L. et al., 2022). And that conclusion has been widely confirmed in DNA-based analyses of plant communities and local ecosystems, in locating the presence of endangered bird species in relevant habitats and even in detecting animal and plant diseases.

Malayan Tiger at Hamerton Zoo Park. Picture credit: Hamerton Zoo Park.

And suppose you want to know how local biodiversity is changing in response to climate change; well, the answer is blowing in the wind.
 
John Bryant
 
Topsham, Devon
April 2026