Oxford Pond Protist Oligohymenophorea sp. PL0344 Reassigns Two Stop Codons to Distinct Amino Acids

The discovery occurred during routine validation of a low-input DNA sequencing pipeline at the Earlham Institute. Dr. Jamie McGowan assembled the genome of a protist collected from a single cell in an Oxford University Parks pond. Inspection of the predicted proteome showed that canonical termination codons had been repurposed, a pattern previously documented only in isolated ciliate lineages but never with this specific dual reassignment.

Ciliate genomes are already known for codon-table plasticity driven by frequent stop-codon capture and tRNA innovation. The new variant demonstrates that even within one class, independent evolutionary trajectories can produce non-overlapping amino-acid assignments for the same codons. This flexibility expands the design space for synthetic biology efforts that seek to introduce non-canonical amino acids without lethal read-through of natural stops.

Future single-cell surveys of under-sampled protist diversity are expected to uncover additional code variants. Systematic mapping of tRNA anticodons and release-factor genes across ciliates will test whether the observed reassignment is constrained by phylogenetic distance or by ecological pressures such as predation and parasitism.