Microbes reveal steps toward complex cells in Asgard findings

Researchers reported hundreds of new Asgard microbes and filmed live Asgard cells crawling, offering genetic and behavioral clues to how complex eukaryotic cells evolved.

A set of recent studies is clarifying one of life's major transitions: how complex cells arose from simpler microbes. Scientists have been searching for rare transitional microbes that bridge the divide between prokaryotes and eukaryotes. Work tracing genes and cell behavior has focused on a lineage called Asgard, first recognized in 2015 from deep-sea DNA. New field surveys and lab work have expanded known Asgard diversity and yielded the first videos of live Asgard cells moving. Key findings: - Researchers reported 404 new Asgard species and identified 30 additional Asgard genomes in existing databases. - Asgard microbes were found in deep-sea sediments, coastal waters, permafrost, lagoons and other land habitats, indicating a wide but often rare distribution. - Lab teams spent years cultivating some Asgards from oxygen-free sediment and filmed cells crawling by reshaping internal filaments and extending tentacle-like protrusions. - Asgard genomes include genes linked to eukaryotic features, such as components of a cellular skeleton and systems for handling proteins inside compartments. - Some newly identified Asgards carry genes suggesting oxygen use and were found in oxygen-rich coastal sediments together with bacteria related to mitochondria. Summary: The findings bring the origin of eukaryotes into sharper focus by linking genetic features and observed behaviors in Asgard microbes to early steps toward complex cells. Researchers note that surveying coastal sediments and continuing lab cultivation of Asgards can help test ideas about when skeleton-like structures evolved and how partnerships with bacteria that became mitochondria formed.