How Microbes Got Their Crawl

A flurry of new studies is illuminating one of life’s largest transitions: how complex cells arose from simpler ones about two billion years ago. Scientists hunting a group of prokaryotes called Asgard have nearly doubled the known diversity of the lineage, identifying 404 new species on recent expeditions and uncovering 30 genomes that had been overlooked in earlier surveys.

Complex cells, or eukaryotes, differ sharply from simple microbes: they have a nucleus, mitochondria and an internal skeleton that can be reshaped for movement. Asgard genomes contain many eukaryote-like genes, including ones linked to a cellular skeleton and compartmentalized protein breakdown.

After eight years of culturing Asgards from oxygen-free sediment, researchers captured the microbes crawling on glass slides by extending long, tentacle-like protrusions — the first time anyone has seen them in motion. How mitochondria entered the story remains central.

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