Adopted dna as a useful molecule quite independently

Q. Your friend has just returned from a deep sea mission and claims to have found a new single-celled life form. He believes this new life form may not have descended from the common ancestor that all types of life on Earth share. You are convinced that he has to be wrong, and you manage to extract DNA from the cells he has discovered. He says that the mere presence of DNA is not sufficient to prove the point: his cells may have adopted DNA as a useful molecule quite independently of all other known life forms. What would you do to convince him that he was wrong?