Cultured archaea narrow the search for complex cells’ origins
Researchers have cultured two archaea from a group close to organisms with complex cells. The microbes rely on metabolic partners and lack persistent internal membranes. Their structure and oxygen-related behaviour constrain proposals about how complex cells emerged. The peer-reviewed experiments offer evidence from living relatives, with ancient partnerships remaining an interpretation of those findings.
Science··Morning
Living relatives reveal a simpler cell interior
Researchers cultured two members of Heimdallarchaeia, an archaeal group close to eukaryotes, the organisms whose cells contain nuclei. Archaea are a distinct group of microbes. The peer-reviewed experiments found cell protrusions and vesicles but no persistent internal membrane structures in the two strains. The absence of persistent inner membranes points to substantial structural innovation during the emergence of eukaryotic cells. This gives researchers living relatives with which to examine proposals about the emergence of complex cells, a question often approached through comparisons of genomes.[1], [2]
Metabolic partners sustain the archaea
Both archaea rely on metabolic exchanges with methane-producing partners. They break down peptides, short chains of amino acids, and their partners remove metabolic products. The cultures therefore represent interdependent communities. The strains were studied in communities containing different numbers of members, while their anaerobic physiology resembles that of previously cultured relatives. Cell protrusions were also examined in relation to physical contacts with partner microbes.[1]
The dependence matters to interpretations of ancient cell partnerships. These organisms cannot be described as growing independently merely because researchers have established cultures. The work provides accessible models for narrower questions about cell structure and physiology. Their larger cells and more favourable cultivation characteristics than some earlier isolates also offer opportunities for further experimental study.[1]
Oxygen behaviour constrains an ancestral scenario
One strain carries genes associated with oxygen-related functions, yet its partnership could not sustain growth in low oxygen on its own. Growth in those conditions became possible in the presence of oxygen-using organisms. Researchers interpret that pattern as support for protection from oxygen toxicity rather than respiration using oxygen. Genome comparisons were also used to examine that distinction. A mitochondrial ancestor reducing oxygen toxicity is one scenario consistent with the findings; the experiments do not recreate the historical origin of a nucleus or mitochondrion. Living descendants’ traits cannot simply be assigned to an ancient ancestor.[1]
