Research into the Role of Prokaryotes and the Evolution of Life on Earth are Discussed in Recent Findings by UCLA Molecular Biologist James A. Lake

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

Although They Are Barely Alive, Microbes Found on Earth's Seafloor Might Resemble Exo-Organisms

Subseafloor microbes and sampled genetic material from ocean biomes at varying depths.

Alexis Madrigal, writing in Wired Science explains: "Deep below the sea floor live massive colonies of primitive microbes.

"Almost like one-celled zombies, these microbes use so little energy that it might be more accurate to call them undead rather than alive.

"Yet scientists think that the species might provide a model for life on other planets. Even on this planet, such microbes might account for a whopping 10 percent of the Earth's biomass.

""In essence, these microbes are almost, practically dead by our normal standards," said Christopher House, a geosciences professor at Penn State University, and the lead author of the paper, in a release. "They metabolize a little, but not much."

"The cold, lightless and energy-poor conditions under the seafloor provide a promising research analog for the harsh conditions in subsurface Martian soil or near hydrothermal vents on Europa, Jupiter's second moon.

""We do not expect the microbes in other places to be these microbes exactly," said House. "But, they could be living at a similar slow rate."

"Subseafloor microbes, according to a metagenomic analysis to be published Thursday in Proceedings of the National Academy of Sciences, are genetically distinct from life on Earth's surface and oceans. The Archaea the Penn State researchers found might look like bacteria, but they don't eat or work like them. While E. coli might double its numbers in 30 minutes, Archaea could take hundreds or even thousands of years to accomplish the same amount of growth.

"The researchers conducted their work off the coast of South America in a region known as the Peru Margin. They sampled genetic material from the biomes at varying depths. Below 160 feet, the researcher said Archaea account for 90 percent of the life present, and represent the most unique environment thus far revealed by metagenomic analysis.

"The Archaea represent a thus-far untapped genetic repository for scientists looking for novel genes for changing metabolism, withstanding cold or synthesizing chemicals.

"UCLA molecular biologist Jim Lake called the results "very exciting." He also noted that more research into populations of isolated Archaea communities like the one described in the paper could do more than reveal the attributes of the microbial life.

""Our whole concept of microbial evolution is up for grabs," Lake said. "People are realizing there is lots of exchange and gene transfers between organisms, and I think the whole area is about to explode."

"Lake noted that while many, like House and Biddle, think the Archaea are an ancient species, they could just be evolving very quickly because of their isolation, a bit like animals on the Galapagos islands.

"The debate about how Archaea got so very different from other prokaryotes like bacteria highlights how little is known about them. House's co-author, astrobiologist Jennifer Biddle, said that even the most basic questions about this kind of life remain unanswered.

"For example, how do they die?" asked Biddle.

Image: Close-up photographs from the drilling site, 1229. Courtesy of the Ocean Drilling Program.