Single-Celled Protist Has Extraordinary Fragmented Genome

September 9, 2014 | The pond-dwelling protist Oxytricha Trifallax, already known for the genomic oddity of having roughly 16,000 chromosomes, has revealed an even more remarkable quirk in its native DNA, as described in a new paper in Cell. The authors, led by Xiao Chen and John Bracht of Princeton, demonstrate that O. trifallax regularly stores its genome in over 225,000 short segments within a second nucleus used only for sexual recombination. During sex, the protist shares these fragments with its partner and rapidly reassembles them into a single genome in the normal, chromosomal organization. The research was conducted using a PacBio long-read sequencer, which by sequencing the O. trifallax genome in large fragments enabled the researchers to easily detect the boundaries of the organism's thousands of distinct DNA segments. More details, including comments by senior author Laura Landweber, can be read at Bioscience Technology.

Bizarre genomic possibilities are being discovered in nature at a fast clip these days, as sequencing new species' genomes becomes more common. Last month, Ed Yong wrote in his National Geographic blog about two species of very closely-related bacteria living side by side inside cicadas, which were found to have complementary sets of genes that, taken together, completed molecular pathways neither species could fully express on its own.