Artist Billy Apple has gifted his excrement to science - and proved for the first time that the microbes in our bodies give us unique identities throughout our lives.

Scientists at Auckland University's Liggins Institute have found that 45 per cent of the bacteria species present in Apple's 1970 art work Excretory Wipings were still present in his body 46 years later.

Liggins doctoral student Thilini Jayasinghe, who led the study, sequenced regions of the bacterial DNA from the art work and from new samples which Apple provided of his excrement.

"Billy Apple's gut microbiome was less diverse at age 80 compared to 35, but 45 per cent of the bacteria species were retained over the 46 years, despite significant differences in his age and environment – New York and Auckland - and in his diet," she said.

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The findings substantiate growing evidence that a "core" part of our bacteria population remains stable as we age, and that at least some of the bacteria are actively selected by our genes.

This means that advances in personalised medicine may have to consider not only our individual genes, but also our unique microbiome – the population of microbes that live in and on us - and how the two interact.

Apple collected his daily toilet tissues, soiled with excrement, for his original art work in 1970.

"I decided that I'd become the subject for any work I wanted to do," he said.

Born in New Zealand, Apple changed his name in 1962 to rebrand himself as an art work, having come to see that art also works as a commodity in cultural markets. In 2007, he had his name registered as a trademark while investigating the legal concept of intellectual property.

Excretory Wipings was due to be exhibited in Apple's 1974 exhibition at London's Serpentine Gallery, and although the tissues were included in the accompanying publication, they were excluded from display. Fortuitously, Apple carefully stored the tissues.

Fast-forward to June 2016, when a serendipitous meeting between Apple, now based in Auckland, and Liggins molecular biologist Dr Justin O'Sullivan seeded the idea for a study. Apple would produce new faecal samples so O'Sullivan's team could compare his gut bacteria from each period to see how they changed.

The findings have just been published as an "n-of-one study", based on a single case study, in the Human Microbiome Journal. Apple is listed as a co-author.

O'Sullivan said it was the first time anyone had done such a study with such a long gap in time.

"We used to think of our resident bacteria as hitch-hikers, foreign bodies along for the ride," he said.

"Scientists now realise that these microscopic creatures interact in many intricate, mysterious ways with our body systems, and play a crucial role in our health, wellbeing and development."

Each person carries their own unique population of about 30-40 trillion tiny microbes – 1.5kg of bacteria – and 95 per cent of those reside deep in the gut.

Bill Apple with an exhibition of his vehicles at the Auckland Art Gallery in 2015. Photo / Ted Baghurst
Bill Apple with an exhibition of his vehicles at the Auckland Art Gallery in 2015. Photo / Ted Baghurst

"We know that your microbiome changes over time and as you develop," O'Sullivan said.

"We also know that there is day-to-day variation: some microbes join your population and others leave. The structure of the microbiome is affected by the interaction between your genes and your environment – which includes what you eat. We are walking, talking ecosystems.

"The key thing we showed is that there are some microbes that stay with you over your lifetime, or at least a major part of your adult life. In agreement with what other people have shown, some of these microbes seem to be selected by your genes."

O'Sullivan likens it to a forest: "Some of the plants change, but the ones that remain are doing the same thing."

Apple has produced a new work on canvas about his microbiome and gifted it to the Liggins Institute. Called N=1, it incorporates images of the original toilet tissues and bar graphs representing the results of the new study.

This was not Apple's first collaboration with scientists – one with biochemist Dr Craig Hilton led to New Zealand Genomics Ltd sequencing Apple's entire genome; another work depicts the artist's coronary arteries before and after having stents in.

"We hope that this linkage of art and science will help to reinforce the importance of the gut microbiome," says Dr O'Sullivan.

"It's possible to get precious about science, and it is good to show that not only can you do advanced science, but you can do it in a fun way."

"It was a wonderful, genuine collaboration," says Apple. "I had a component that Justin didn't have – I brought the 46 years to it."