World's smallest genome discovered in a marine microbe — and it still knows how to replicate

Researchers from the University of Nottingham and the University of Tsukuba have discovered a previously unknown marine microorganism — Candidatus Sukunaarchaeum mirabile — that holds the record for the smallest genome ever found. Belonging to the archaea domain (distinct from bacteria), this microscopic organism was identified while analyzing genetic material from individual marine plankton samples.

What makes Sukunaarchaeum remarkable is its paradox: while it has shed nearly all genes needed to produce its own nutrients and energy, it has retained the core machinery to copy its genome and synthesize proteins. This suggests it may sit right at the edge of what's genetically necessary to remain a self-sufficient, reproducing cell — possibly relying on a host organism for resources, much like a parasite.

By the Numbers:

• 189 protein-coding genes — the fewest ever recorded in a living organism
• Genome is less than half the size of the previously smallest known archaeal genome
• ~25% of its genome encodes unusually large membrane proteins of unknown function

Why it matters: Understanding the bare minimum genetic toolkit for life has profound implications — from synthetic biology and drug development to our fundamental understanding of how life began and evolves. The team plans to identify Sukunaarchaeum's host and ecological role next.