Water bears may be the ultimate borrowers.
The hardy, microscopic animals also known as moss piglets and technically called tardigrades have scavenged about 17.5 percent of their genes from other creatures. The ability to pick up used genes and spare parts from other organisms’ DNA junkyards may allow tardigrades to survive extreme stress, such as desiccation, radiation and even a trip to space and back, researchers report online November 23 in theProceedings of the National Academy of Sciences.
Bacteria routinely swap DNA, a process known as horizontal gene transfer. But researchers had thought the practice was unusual in animals. Only strange, asexual animals called bdelloid rotifers were known to grab significant amounts of DNA from other life.
So when biologist Thomas Boothby of the University of North Carolina at Chapel Hill and colleagues discovered bacterial genes mixed in to the DNA of Hypsibius dujardini tardigrades, “our initial thought was, ‘this is actually a mistake. We have contamination in our samples.’” But further testing showed that the tardigrades had incorporated into their own DNA genes from more than 1,300 bacterial species, 40 archaea, 91 species of fungus, 45 plant species and six viruses.
Desiccation may allow tardigrades and bdelloid rotifers to pick up extra DNA, the researchers speculate. When an organism dries out, its DNA breaks up and the membranes that hold in a cell’s guts become leaky, allowing DNA and other big molecules to seep out. For most organisms, that’s the end: Bacteria, plants and other creatures spill their DNA and die. But some tardigrades and rotifers can remain in suspended animation until they encounter water again. Upon rehydration, the microscopic animals might quickly sew their DNA back together, accidentally stitching in foreign DNA discarded when neighboring organisms died.
Molecular cell biologist Chiara Boschetti of the University of Cambridge and colleagues have uncovered supporting evidence for that hypothesis. Horizontal gene transfer happens more often in bdelloid rotifers that undergo desiccation than in those that live in aquatic environments and can’t stand to be dried out, the researchers report online November 4 in BMC Biology.
Many of the genes that tardigrades have borrowed help them deal with stress. For instance, catalase proteins are antioxidant enzymes that help organisms avoid cell damage from reactive oxygen molecules. Most animals have their own versions of genes that produce catalase enzymes, but all of H. dujardini’s catalases are from foreign genes, Boothby and colleagues found. Alien genes also outnumber tardigrade genes dedicated to repairing damaged DNA.