The origin of eukaryotes remains unclear(1-4). Current data suggest that eukaryotes may have emerged from an archaeal lineage known as '
strain MK-D1-is an anaerobic, extremely slow-growing, small coccus (around 550 nm in diameter) that degrades amino acids through syntrophy. Although eukaryote-like intracellular complexes have been proposed for Asgard archaea(6), the isolate has no visible organelle-like structure. Instead, Ca. P. syntrophicum is morphologically complex and has unique protrusions that are long and often branching. On the basis of the available data obtained from cultivation and genomics, and reasoned interpretations of the existing literature, we propose a hypothetical model for eukaryogenesis, termed the entangle-engulf-endogenize (also known as E-3) model.
Isolation and characterization of an archaeon that is most closely related to eukaryotes reveals insights into how eukaryotes may have evolved from prokaryotes.
