More than 2 000 bacterial species call the humble belly button home.

London - Navels harbour an ecosystem of bacteria which is similar in their biodiversity to the world’s rainforests, a new study claims.

After two years of quite literal navel gazing, US researchers found 2 368 species of bacteria, 1 458 of which may be new to science.

Just eight of these species were found in more than 70 percent of individuals sampled. However, questions remain as to what factors govern which species will be found on which people.

“The common, abundant species are from a relatively small number of evolutionary lines, indicating that they have evolved traits that make them at home on human skin,” said Dr Rob Dunn of North Carolina State University.

“However, we are still trying to figure out what determines which of these species are found in a given person’s belly button.

“We’ve looked at sex, age, ethnicity and a number of other factors – none of them is predictive of which species live in that person.”

Dunn and his team say they have swabbed more than 500 belly buttons over the past two years, but concentrated on just 60 individuals for their study published last week in the journal PLoS One.

The researchers launched their project in part to investigate claims that the collection of organisms on human skin forms our first line of defence against pathogens.

“We know that without these microbes our immune systems won’t function properly,” Dunn said in a statement.

“In fact, this collection of microbes must have a certain composition – must form a certain microbial ecosystem – in order for our immune system to function properly.

“This work is a significant step towards helping us understand which species are the most important players in those ecosystems.”

The bizarre idea to investigate the biodiversity of belly buttons started about two years ago with an undergraduate student’s idea to sample a colleague’s navel bacteria for a holiday card.

National Geographic reported how the idea struck a chord with academics at NC State, which had just adopted a new focus on trying to get the public interested and involved in their work.

“The idea was simple. We would culture the bacteria of people’s belly buttons to provide folks with a visual measure of the life on them; a reminder of the mysteries everywhere,’ Dunn wrote in a Scientific American guest blog post.

He added: “We quickly found that peoples’ belly buttons differed in terms of which species live in them. They differed more than we expected. We were intrigued and so we decided to get a little more serious about our study.”

The NC State team asked volunteers to place long cotton swabs in their navels and twist them around three times. They then placed the swabs in vials and grew the bacteria in cultures.

Once the cultures grew big enough, they were photographed and processed using high-throughput genetic sequencing to identify each of the phylotypes (species) present and how prevalent each phylotype was.

For the purposes of this study, a phylotype was defined as an organism whose sequence in the 16s rDNA gene (essentially the microbial fingerprint gene) varied from other organisms by at least 3 percent.

The study identified 2 368 different phylotypes but only eight phylotypes – which the team dubbed “oligarchs” – were found on at least 70 percent of the study participants.

Those eight phylotypes – including varieties of Staphylococci, Corynebacteria, Actinobacteria, and Clostridiales, and Bacilli – were also among the most abundant, accounting for almost 50 percent of the total abundance of bacteria in the samples.

Altogether, the researchers found that the average belly button among study participants contains 67 different phylotypes of bacteria.

Dunn told National Geographic: “That makes the belly button a lot like rain forests.” He explained that in any rainforest the range of flora will vary but scientists can count on a certain few dominant tree types present.

He added: “The idea that some aspects of our bodies are like a rain forest – to me it’s quite beautiful. And it makes sense to me as an ecologist. I understand what steps to take next; I can see how that works.”

The next step for the Belly Button Diversity project is to work out why certain types of bacteria appear in certain people’s navels.

By examining the rest of their samples they will begin trying to correlate the wildlife found there with factors ranging from the subjects’ places of birth to the characteristics of their immune systems. – Daily Mail