A test designed to push the limits of single cell DNA sequencing ended up revealing something far more surprising: a microscopic organism from a pond at Oxford University Parks appears to use the genetic code in a way scientists had not seen before.

Dr. Jamie McGowan, a postdoctoral scientist at the Earlham Institute, was studying the genome of a protist collected from freshwater. The goal was practical. Researchers wanted to test a DNA sequencing pipeline that could work with extremely small amounts of DNA, including DNA from a single cell.

Instead, the team found an unexpected genetic outlier. The organism, identified as Oligohymenophorea sp. PL0344, turned out to be a previously unknown species with a rare change in how it reads DNA instructions and builds proteins.…