Scientists have discovered that bacteria employ a type of DNA modification never before seen in nature. For several decades, researchers have known that it is possible to modify synthetic oligonucleotides (short strands of DNA) by adding sulfur to the sugar-phosphate DNA backbone as a phosphorothioate. Researchers often use such modifications in the laboratory to make DNA resistant to nucleases (enzymes that snip DNA in certain locations) as a step toward gene and antisense therapies of human diseases. Scientists were surprised to discover that a group of bacterial genes, known as the dnd gene cluster, gives bacteria the ability to employ the same modification on their own.