Amazing stuff!
"The ability of one cell to ingest another, called phagocytosis, was a crucial step in the evolution of eukaryotic cells and may explain how membrane-bound organelles first came to be. But some researchers argue that cells would have needed to evolve mitochondria to fuel phagocytosis. ...
compared a collection of recently published Legionellales genomes isolated from environmental samples and noticed that members of the group shared the same molecular tools that protect against being digested, suggesting that the group’s common ancestor had adapted to life inside bacteria-eating eukaryotic cells. “That shows phagocytosis already existed at the time of the first Legionellales,”...
The team used molecular clock techniques to date the group’s last common ancestor to 1.9 billion years ago, plus or minus a few hundred million years—Guy notes that “there is a lot of uncertainty” because their age estimate hinges on a single biomarker. Still, he says, the timing suggests that early eukaryotes could engulf bacteria before they had mitochondria, whose origins have been estimated at between 1.2 billion and 2 billion years ago. ..."
"We propose that LLCA, upon being phagocytosed by eukaryotic cells, already had the ability to resist digestion, owing to its host-adaptation genes. Thus, phagocytosis is likely at least 1.9 Gy old, older than previously thought. This hypothesis is consistent with a scenario in which some early eukaryotes developed phagocytic properties and fed on prokaryotes. Some of these, among them LLCA, rapidly acquired the abilities to resist host digestion and exploit the novel, rich ecological niche that is the eukaryotic cytoplasm."
From the abstract:
"Bacteria adapting to living in a host cell caused the most salient events in the evolution of eukaryotes, namely the seminal fusion with an archaeon, and the emergence of both mitochondrion and chloroplast. A bacterial clade that may hold the key to understanding these events is the deep-branching gammaproteobacterial order Legionellales—containing among others Coxiella and Legionella—of which all known members grow inside eukaryotic cells. Here, by analyzing 35 novel Legionellales genomes mainly acquired through metagenomics, we show that this group is much more diverse than previously thought, and that key host-adaptation events took place very early in its evolution. Crucial virulence factors like the Type IVB secretion (Dot/Icm) system and two shared effector proteins were gained in the last Legionellales common ancestor (LLCA). Many metabolic gene families were lost in LLCA and its immediate descendants, including functions directly and indirectly related to molybdenum metabolism. On the other hand, genome sizes increased in the ancestors of the Legionella genus. We estimate that LLCA lived approximately 1.89 Ga, probably predating the last eukaryotic common ancestor by approximately 0.4–1.0 Gy. These elements strongly indicate that host adaptation arose only once in Legionellales, and that these bacteria were using advanced molecular machinery to exploit and manipulate host cells early in eukaryogenesis."
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