A research team led by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and Kyoto University has successfully isolated and cultivated two strains of Heimdallarchaeia. As the closest known archaeal relatives to eukaryotes—the domain that includes humans, plants, and fungi—these microorganisms provide a vital window into the evolutionary transition from simple cells to complex life.
Unlocking the Eukaryotic Mystery
The origin of complex eukaryotic cells remains a fundamental biological mystery. A prominent theory suggests that an archaeal ancestor formed a symbiotic partnership with a bacterium, which eventually evolved into the mitochondrion. While previous environmental DNA studies identified Heimdallarchaeia as the closest relatives to eukaryotes, their lack of laboratory cultivation meant their physiology and cellular organization remained speculative.
By directly examining the newly cultivated strains, researchers discovered that the cells possess a simple internal structure, lacking membrane-bound organelles like a nucleus. However, the cells feature complex surface protrusions that facilitate attachment to other microorganisms. This finding suggests that the archaeal ancestor of eukaryotes may have been internally simple, relying on surface-mediated symbioses to interact with other life forms.
Insights into Early Symbiosis
The study also revealed that these archaea are anaerobic but possess mechanisms to survive in environments with low oxygen levels, particularly when partnered with aerobic bacteria. This supports the hypothesis that the transition to eukaryotic life may have begun in oxygen-limited environments, where a symbiotic partnership helped the archaeal host manage oxygen exposure.
These cultivated strains now serve as experimental models for scientists to further investigate how simple archaeal cells evolved into the complex, compartmentalized structures that define modern eukaryotes.
