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Koala genome reveals secret of eucalyptus diet

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A marsupial DNA sequencing project is expected to help ensure the koala’s long-term survival.

Koalas have evolved a unique detox toolkit that allows them to munch happily on a poisonous food source avoided by their competitors, a complete genetic blueprint of the animals has shown.

Unfortunately for the marsupials, specialising in a diet of eucalyptus leaves has left them highly vulnerable to habitat loss.

The scale of the koala genome is on a par with its human counterpart, according to the scientists involved.

Professor Rebecca Johnson with a sleepy koala (University of Sydney/PA)

They also identified more than 26,000 genes – stretches of DNA that provide the instructions for making proteins – and unravelled some of their functions.

A key discovery was that koalas have large numbers of genes active in the liver devoted to detoxification.

The genes produce a range of cytochrome P450 enzymes that break down poisonous compounds. They are what enable the koala to live on a diet of highly toxic eucalyptus leaves, the scientists believe.

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Team leader Professor Rebecca Johnson, director of the Australian Museum Research Institute in Sydney, said: “This probably helped them to find their niche to survive, as they could rely on a food source that would have less competition from other species who were not able to detoxify as effectively.”

British colleague Dr Will Nash, from the Earlham Institute in Norwich, said: “The koala has evolved an excellent toolkit to deal with eating highly toxic eucalyptus, one made up of lots of copies of the same, or very similar, tools.”

Other finds included koala-specific milk proteins that may have an anti-bacterial role and protect the growing “joey” in its mother’s pouch.

The scientists hope such information will help them prevent koalas falling victim to serious infectious diseases.

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Koalas are especially susceptible to chlamydia infection, which causes infertility and blindness in the animals, and has severely impacted populations in New South Wales and Queensland.

The genome may also help experts counter another threat, the koala retrovirus (KoRV), by revealing which strains are the most dangerous or assisting in the development of a vaccine.

Findings from the Koala Genome Consortium are published in the latest issue of the journal Nature Genetics.

Dr Graham Etherington, also from the Earlham Institute, said: “With its puppy-dog looks, the koala is an internationally recognised species. But this iconic Australian marsupial is not just a pretty face.

“The koala genome assembly is by far the most comprehensive marsupial genomic resource to date, which allows us an insight into how this unique animal came to be and provides us with information about potential threats to its survival.

“It also provides us with an excellent platform to launch further marsupial genome projects that could look into potential genetic reservoirs of previously unknown anti-microbial genes that could be leveraged for human health.

“Additionally, it provides us with an incredible amount of information about genetic diversity across different populations of koalas that can be used as a benchmark for further studies on other endangered marsupial species.”

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