James Lake was recently proposed and supported a fascinating new hypothesis:
Lake has discovered the first exclusively prokaryote endosymbiosis. All other known endosymbioses have involved a eukaryote — a cell that contains a nucleus. Eukaryotes are found in all multicellular forms of life, including humans, animals and plants.
In the Nature paper, Lake reports that two groups of prokaryotes — actinobacteria and clostridia — came together and produced “double-membrane” prokaryotes.
“Higher life would not have happened without this event,” Lake said. “These are very important organisms. At the time these two early prokaryotes were evolving, there was no oxygen in the Earth’s atmosphere. Humans could not live. No oxygen-breathing organisms could live.”
Here is the abstract for the paper:
Endosymbioses have dramatically altered eukaryotic life, but are thought to have negligibly affected prokaryotic evolution. Here, by analysing the flows of protein families, I present evidence that the double-membrane, Gram-negative prokaryotes were formed as the result of a symbiosis between an ancient actinobacterium and an ancient clostridium. The resulting taxon has been extraordinarily successful, and has profoundly altered the evolution of life by providing endosymbionts necessary for the emergence of eukaryotes and by generating Earth’s oxygen atmosphere. Their double-membrane architecture and the observed genome flows into them suggest a common evolutionary mechanism for their origin: an endosymbiosis between a clostridium and actinobacterium.
This hypothesis is fascinating whether we look backward or forward from the proposed event.
Looking backward, this scenario would fit nicely with the growing list of evidence that indicates gram-positive bacteria predate gram-negative bacteria. So what? Well, I’ll expand on that shortly.
Looking forward, this hypothesis, if true, would indicate Lynn Margulis really does have her finger on a crucial evolutionary mechanism – symbiosis. For we would now have two major evolutionary transitions – the origin of gm negative bacteria and the origin of eukaryotic organelles – that occurred because of endosymbiosis. It is also very interesting that the first endosymbiotic transformation set the stage for the second one. So I will be expanding on this theme also.