Role of prokaryotes in evolution of life on Earth- A new study by James Lake
The diversity among various life forms on our planet is immense and one reason for their flourishing could be fusion of two prokaryotes, claims a latest report by James A. Lake. This hypothesis which provides new insights into prokaryotes and the evolution of life, was published in latest issue of journal Nature.
The prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. They differ from the eukaryotes, which have a well defined membrane bound nucleus containing the genetic material DNA. In Prokaryotes ,DNA is found freely in cytosol. Prokaryotes generally lack membrane-bound cell compartments: such as mitochondria and chloroplasts. Instead processes such as oxidative phosphorylation and photosynthesis take place across the prokaryotic plasma membrane.However , Both eukaryotes and prokaryotes contain large RNA/protein structures called ribosomes.
In the latest report James Lake provides some convincing evidence based on phylogenetic studies that the double-membrane, Gram-negative prokaryotes were formed as the result of a symbiosis between an ancient actinobacterium and an ancient clostridium. The term symbiosis generally describes close and often long-term interactions between different biological species. The term was first used in 1879 by the German mycologist Heinrich Anton de Bary, who defined it as “the living together of unlike organisms.
Endosymbiosis refers to a cell living within another cell. If the cells live together long enough, they will exchange genes; they merge but often keep their own cell membranes and sometimes their own genomes.
Symbiosis never grabbed so much attention as other interactions such as predation. But slowly its being realized as important force in driving evolution,thanks to some great research in the field. In fact, the evolution of all eukaryotes (plants, animals, fungi, and protists) is believed under the endosymbiotic theory to have resulted from a symbiosis between various sorts of bacteria.
Endosymbioses have accounted tremendously for altered eukaryotic life, but always believed to have negligible effect on prokaryotic evolution. Here, James Lake has discovered the first exclusively prokaryote endosymbiosis. All other known endosymbioses have involved a eukaryote.
According to Lake, this relationship resulted in a totally different type of life on Earth and it was always eukaryotes needed to be present to do it( complex life), but we were wrong. “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.”
The oxygen which is present today on our planet is entirely due to the outcome of a subgroup of these double-membrane prokaryotes and this subgroup, the cyanobacteria, used the sun’s energy to produce oxygen through photosynthesis. They have been very efficient in pumping oxygen into the atmosphere; as life without these simple organisms would not have been possible. In addition, the double-membrane prokaryotic fusion supplied the mitochondria that are present in every human cell.
If the double-membrane prokaryotes were indeed produced by an endosymbiosis event, so then the genomic signatures of the endosymbiosis might still be strong enough to be detected in phylogenetic reconstructions. James Lake reconstructed the evolution of the double-membrane prokaryotes using methods capable of discriminating between rings,caused by endosymbioses, and trees, caused by clonal evolution.
Phylogenetic analysis can also help in identifying the host and guest , in case the double membrane is formed due to a past endosymbiosis, as genes can flow into the new organism from two different donors during an endosymbiosis. Lake carried out the phylogenetic analysis on five group of prokaryotes: Archaea , Actinobacteria , Bacilli and relatives , Clostridia and relatives , and the double-membrane prokaryotes .
Like many of us James Lake is also interested to understand how all life forms our planet are related ? Who are ancestors? Lake gave an example of a study where Alan Wilson, from UC Berkeley, was the first person to collect DNA from large numbers of people around the world. He showed that we are all related to a woman who lived in Africa 200,000 years ago. Some in the media called her Eve. He called her the Lucky Mother, the mother of us all.
“We have been overlooking how important cooperation is,” Lake said. “If two prokaryotes get together, they can change the world. They restructured the atmosphere of the Earth. It’s a message that evolution is giving us: Cooperation is a way to get ahead.”— James A. Lake
This subgroup of photosynthetis bacteria flourished immensely and palyed an significant role in altering the evolution of life by providing oxygen .Finally the architecture of their double-membrane and
the observed genome flows into them suggest a common evolutionary mechanism for their origin: an endosymbiosis between a clostridium and actinobacterium.
Reference:
Evidence for an early prokaryotic endosymbiosis
James A. Lake
doi:10.1038/nature08183
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It’s a message that evolution is giving us: Cooperation is a way to get ahead.”
I don’t think evolution is giving us any such message. No doubt symbiosis has been important but endosymbionts evolved and became common by out-competing alternative versions of itself or some other cell type.
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