The koalas ( Phascolarctos cinereus ) are probably one of the most adorable animals that exist, though they can become very aggressive on certain occasions. In the appearance of a stuffed animal and its great ability to rest – they can fall asleep up to twenty hours a day – we find one of the few mammals capable to survive only from leaves. The problem? Koalas feed on eucalyptus leaves consuming about one kilogram a day, an extremely toxic diet for other living things.

Up to now, it was thought that, to support this type of diet – phosphoric acid in the fibers and low in nutrients – koalas had an extremely slow metabolism . , which allowed him to keep food in his digestive system for a long period of time. These Australian marsupials minimize their energy requirements by sleeping several hours a day. Two strategies that allow them to resist a diet that could become a deadly poison for any other animal.

Decoding the koala genome

A new study, published today in the journal Nature Genetics unveils the most complete koala genome ever made to date. An international team of scientists has sequenced the 3.4 billion base pairs or letters of its DNA which has something more than 26,000 genes in total – a figure higher than that obtained in previous research by the same consortium –

The results show that the koala has a genome wider than that of the human being and offers us new molecular clues about marsupial characteristics, including its ability to feed itself solely from eucalyptus leaves. These mammals have two large expansions of a set of genes key at the time of detoxification ( detoxify in English) from their usual diets.

In particular, scientists have observed that koalas have genetic sequences that contain instructions for making some very important proteins belonging to cytochrome P450 . This family of enzymes, also present in the human species, helps to metabolize compounds so that cells can survive.

According to the results published in Nature Genetics these genes are expressed in many tissues of koalas and, in particular, in liver suggesting that they have a very important function in the detoxification of eucalyptus leaves . "It probably helped them to find a niche to survive, because they could follow a source of energy that would allow them to compete less with other species that can not detoxify as well. effectively, "he explains. in a statement Rebecca Johnson first author of the study and director of the Australian Museum Research Institute

"The koala evolved to have an excellent toolbox for feeding highly toxic eucalyptus, "adds his companion Will Nash of the Earlham Institute in the United Kingdom. The sequencing of eucalyptus DNA showed in 2014 that they have genes to produce more terpenes than other plants and that they are also able to produce very toxic secondary metabolites for most mammals.

Koala Genome Consortium knowing the DNA sequences that help these marsupials to detoxify is important for their veterinary care. These genes would help them metabolize the drugs used to relieve pain and antibiotics against the chlamydia sexually transmitted disease caused by bacteria that affect koalas.

The research published today also showed for the first time the genes associated with immune system of these marsupials. In addition, scientists have discovered that a single copy may have more than a hundred inserts of the retrovirus koala in its genome. These infectious agents attack the defenses of marsupials, similar to the action of HIV in humans. According to the authors, these discoveries will let us know which strains are more aggressive and help in the conservation of a species vulnerable to extinction.