Scanning electron micrograph of a species of actinobacteria: Actinomyces israelii. (Credit: Courtesy of Wikipedia)
UCLA molecular biologist James A. Lake has written an article in the August 20th edition of Nature that investigates the "fusing of two" prokaryotes - "evolutionarily ancient ... cells" that were the first organisms that predated all other lifeforms "for billions of years" don't "contain a nucleus or any other membrane-bound organelles."
The fusing process is referred to as "Endosymbiosis," an occurrence in which a cell lives within another cell. Furthermore: "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."
Lake's discovery is significant in that he postulates: "This relationship resulted in a totally different type of life on Earth," said Lake, a UCLA distinguished professor of molecular, cell and developmental biology and of human genetics. "We thought eukaryotes always needed to be present to do it, but we were wrong."
Lake's Nature article conjectures "that two groups of prokaryotes — actinobacteria and clostridia — came together and produced "double-membrane" prokaryotes, " ScienceDaily reported.
"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."
ScienceDaily has reported that Lake found: "The oxygen on the Earth is the result of a subgroup of these double-membrane prokaryotes. This subgroup, the cyanobacteria, used the sun's energy to produce oxygen through photosynthesis. They have been tremendously productive, pumping oxygen into the atmosphere; we could not breathe without them. In addition, the double-membrane prokaryotic fusion supplied the mitochondria that are present in every human cell," according to Lake.
"This work is a major advance in our understanding of how a group of organisms came to be that learned to harness the sun and then effected the greatest environmental change the Earth has ever seen, in this case with beneficial results," said Carl Pilcher, director of the NASA Astrobiology Institute, headquartered at the NASA Ames Research Center in Moffett Field, Calif., which ScienceDaily explained had "co-funded the study with the National Science Foundation."
"Along came these organisms — the double-membrane prokaryotes — that could use sunlight," Lake said. "They captured this vast energy resource. They were so successful that they have more genetic diversity in them than all other prokaryotes.
"We have a flow of genes from two different organisms, clostridia and actinobacteria, together," he said. "Because the group into which they are flowing has two membranes, we hypothesize that that was an endosymbiosis that resulted in a double membrane. It looks as if a single-membrane organism has engulfed another. The genomes are telling us that the double-membrane prokaryotes combine sets of genes from the two different organisms."
Lake's research has helped him to understand "how every organism is related." as his studies have reached back 2.5 billion years to analyze "the genomics of ... five groups of prokaryotes. "Reiterating the focus of his interest, Lake explained that: "We all are interested in our ancestors." Lake further added: "In our field, we have enormous amounts of data but cannot make sense of it all. Endosymbiosis allows us to start to understanding things; it tells us that many genes are exchanged. "We have been overlooking how important cooperation is," Lake explained. "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."
Cell structure of a bacterium, one of the two groups of prokaryotic life. From Wikipedia
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