Tardigrades, also known as "water bears" or "moss piglets", are super robust microorganisms that can survive extreme conditions, such as heat, dehydration, pressure, and even radiation. Researchers at the University of North Carolina have found that ~ 1/6 of the entire genome of the Tardigrade species Hypsibius dujardini originated from other organisms, mainly bacteria and some plants and fungi. Before this study, the most abundant amount of foreign DNA in a single organism was half as much as the Tardigrade. These genes were obtained through horizontal gene transfer, which is the process of moving DNA from one organism, or the environment, to another by means of processes other than reproduction. Bacteria frequently use horizontal gene transfer to exchange plasmids that contain antibiotic resistance genes. The most likely way that horizontal gene transfer occurred for Tardigrades was that whenever they get rehydrated after becoming dessicated, their membranes are "leaky" which allows large amounts of DNA to enter. The Tardigrade's genome is degraded after dessication, so when it pieces back its genome during rehydration, the large DNA fragments that are "stolen" from the environment are randomly incorporated into the genome.These foreign genes haven't been fully characterized, but they are believed to be main contributors to the robust qualities of the Tardigrade. The authors of the study say that their results "suggest that organisms that survive extreme stresses might be predisposed to acquiring foreign genes." This is a neat idea and I'm interested to see what the applications of this finding will be.Reference:
Almost 1/6 Of Tardigrade DNA Is Foreign
Evidence for extensive horizontal gene transfer from the draft genome of a tardigrade
