The koala genome has been sequenced, making the cuddly creatures only the fourth marsupial to get this treatment. The work could assist in saving the threatened species from two of its greatest threats, and has provided an abundance of surprising results biologists will explore for decades. However, geneticists had to overcome an unexpected obstacle when they discovered the DNA in koala blood is unusually hard to sequence.
Not long ago revealing the entire genome of an animal was such an enormous enterprise there was a major debate as to whether to make the opossum or the Tamar wallaby the first marsupial to have the honor. The preponderance of research facilities in North America overcame the wallaby's status as a more representative species, but both are now done.
Sequencing has become easier and more accurate since, but Dr Rebecca Johnson of the Australian Museum told IFLScience it was still a challenge to collect the resources needed to add koalas to the list. The paper in Nature Genetics announcing the near-complete sequence has 54 authors.
The koala’s status as both iconic and threatened got it prioritized, but Johnson and her co-authors hit a snag when they tried to use DNA from koalas’ blood, as usually occurs. The low-quality jumble produced was inadequate for the third generation sequencing the team hoped to apply, forcing them to wait until sick koalas were euthanized so they could extract DNA from their organs. Johnson told IFLScience the reasons normal techniques don't work are unclear, but may relate to their blood's high lipid concentration.
Eventually, three unfortunate beasts were found that were to be put down, in two cases because they were so ravaged with chlamydia. Out of this woe, Johnson and co-authors made something positive. Nevertheless, the difficulties contributed to the sequenced animals' limited diversity.
The chlamydia threat is one reason koalas were prioritized for sequencing, as an understanding of the genes for their immune systems should assist vaccine design. The project could be even more useful against a less well-understood threat, the koala retrovirus. The virus inserts itself into the koala genome, sometimes in more than a hundred places, and the sequencing could help us distinguish between dangerous and less harmful versions.