Pumice Proposed as Home to the First Life Forms

Pumice. (Credit: © Jakub Cejpek / Fotolia)

Science Daily  — The glassy, porous, and once gas-rich rock called pumice may have given rise to early life forms, according to a provocative new hypothesis on the origin of life published in Astrobiology.

To validate their hypothesis, the authors call for laboratory research to test the ability of pumice rock to adsorb organic compounds from water and create catalysts and new compounds by simulating the thermal cycles, UV light, and other conditions that existed when the first organic polymers and microbes co-existed.

Martin Brasier, Richard Matthewman, and Sean McMahon, University of Oxford (U.K.), and David Wacey, University of Western Australia (Crawley), contend that pumice has "four remarkable properties" that would enable it to have had "a significant role in the origin of life and provided an important habitat for the earliest communities of microorganisms." They describe those four properties in detail in the article "Pumice as a Remarkable Substrate for the Origin of Life."

"The hypothesis that pumice provided a unique physical substrate in which life got its start is exciting and testable," says Sherry L. Cady, PhD, Editor-in-Chief of Astrobiology and Professor in the Department of Geology at Portland State University. "Key for astrobiology is whether such rock types preserved evidence of pre-biotic reactions or ancient life forms in the rock record."

Astrobiology is a peer-reviewed journal published by Mary Ann Liebert, Inc.

Sociability May Depend Upon Brain Cells Generated in Adolescence

The social behavior of mice seems to be dictated by creation of new neurons in adolescence. (Credit: Courtesy of Yale University)

Science Daily  — Mice become profoundly anti-social when the creation of new brain cells is interrupted in adolescence, a surprising finding that may help researchers understand schizophrenia and other mental disorders, Yale researchers report.

"This has important implications in understanding social development at the molecular level," said Arie Kaffman, assistant professor of psychiatry and senior author of the study.

When the same process is interrupted in adults, no such behavioral changes were noted, according to research published in the Oct. 4 issue of the journalNeuroscience.

Scientists have known for quite some time that new brain cells are continually generated in specific brain regions after birth. This process, called neurogenesis, occurs at a significantly greater rate during childhood and adolescence than in adulthood, yet most research has focused upon the function of these neurons in older brains.

The Yale team decided to explore the function of these new brain cells in mice of different ages. Normal adult mice tend to spend a lot of time exploring and interacting with unfamiliar mice. However, adult mice that had neurogenesis blocked during adolescence showed no interest in exploring other adult mice and even evaded attempts made by other mice to engage in social behavior.

"These mice acted like they did not recognize other mice as mice," Kaffman said.

Blocking adult neurogenesis had no effect on social behavior, suggesting that brain cells generated during adolescence make a very different contribution to brain function and behavior in adulthood, note the scientists.

Intriguingly, schizophrenics have a deficit in generating new neurons in the hippocampus, one of the brain areas where new neurons are created. Given that symptoms of schizophrenia first emerge in adolescence, it is possible that deficits in generating new neurons during adolescence or even in childhood holds new insights into the development of some of the social and cognitive deficits seen in this illness, Kaffman said.

Other Yale authors include Lan Wei and Ronald S. Duman.

Last Universal Common Ancestor More Complex Than Previously Thought

Science Daily  — Scientists call it LUCA, the Last Universal Common Ancestor, but they don't know much about this great-grandparent of all living things. Many believe LUCA was little more than a crude assemblage of molecular parts, a chemical soup out of which evolution gradually constructed more complex forms. Some scientists still debate whether it was even a cell.

The study builds on several years of research into a once-overlooked feature of microbial cells, a region with a high concentration of polyphosphate, a type of energy currency in cells. Researchers report that this polyphosphate storage site actually represents the first known universal organelle, a structure once thought to be absent from bacteria and their distantly related microbial cousins, the archaea. This organelle, the evidence indicates, is present in the three domains of life: bacteria, archaea and eukaryotes (plants, animals, fungi, algae and everything else).New evidence suggests that LUCA was a sophisticated organism after all, with a complex structure recognizable as a cell, researchers report. Their study appears in the journal Biology Direct.

The existence of an organelle in bacteria goes against the traditional definition of these organisms, said University of Illinois crop sciences professor Manfredo Seufferheld, who led the study.

"It was a dogma of microbiology that organelles weren't present in bacteria," he said. But in 2003 in a paper in the Journal of Biological Chemistry, Seufferheld and colleagues showed that the polyphosphate storage structure in bacteria (they analyzed an agrobacterium) was physically, chemically and functionally the same as an organelle called an acidocalcisome (uh-SID-oh-KAL-sih-zohm) found in many single-celled eukaryotes.

Their findings, the authors wrote, "suggest that acidocalcisomes arose before the prokaryotic (bacterial) and eukaryotic lineages diverged." The new study suggests that the origins of the organelle are even more ancient.

The study tracks the evolutionary history of a protein enzyme (called a vacuolar proton pyrophosphatase, or V-H+PPase) that is common in the acidocalcisomes of eukaryotic and bacterial cells. (Archaea also contain the enzyme and a structure with the same physical and chemical properties as an acidocalcisome, the researchers report.)

By comparing the sequences of the V-H+PPase genes from hundreds of organisms representing the three domains of life, the team constructed a "family tree" that showed how different versions of the enzyme in different organisms were related. That tree was similar in broad detail to the universal tree of life created from an analysis of hundreds of genes. This indicates, the researchers said, that the V-H+PPase enzyme and the acidocalcisome it serves are very ancient, dating back to the LUCA, before the three main branches of the tree of life appeared.

"There are many possible scenarios that could explain this, but the best, the most parsimonious, the most likely would be that you had already the enzyme even before diversification started on Earth," said study co-author Gustavo Caetano-Anollés, a professor of crop sciences and an affiliate of the Institute for Genomic Biology at Illinois. "The protein was there to begin with and was then inherited into all emerging lineages."

"This is the only organelle to our knowledge now that is common to eukaryotes, that is common to bacteria and that is most likely common to archaea," Seufferheld said. "It is the only one that is universal."

The study lends support to a hypothesis that LUCA may have been more complex even than the simplest organisms alive today, said James Whitfield, a professor of entomology at Illinois and a co-author on the study.

"You can't assume that the whole story of life is just building and assembling things," Whitfield said. "Some have argued that the reason that bacteria are so simple is because they have to live in extreme environments and they have to reproduce extremely quickly. So they may actually be reduced versions of what was there originally. According to this view, they've become streamlined genetically and structurally from what they originally were like. We may have underestimated how complex this common ancestor actually was."

The study team also included Kyung Mo Kim, of the Korea Research Institute of Bioscience and Biotechnology; and Alejandro Valerio, of the Museum of Biological Diversity in Columbus, Ohio.

The National Institute of Allergy and Infectious Diseases and the National Science Foundation provided funding for this study.