SDSU Researchers Find Unique Genomes in Three Ancient Microbial Communities

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Lorena Nava Ruggero
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San Diego State University
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A transversal view of a microbialite at Highborne Cay.

SAN DIEGO (Monday, March 3, 2008) -- San Diego State University researchers have published a new study regarding unique genetic codes in bacterial viruses, known as phage, in the science journal Nature.

The study examined three microbialites, sedimentary "fossils" which contain records of microbial life on Earth. The locations studied included a marine location at Highborne Cay in the Bahamas and two freshwater locations: Pozas Azules II and Rio Mesquites in Mexico.

Researchers found that, despite the fact that phages are typically similar throughout the world, the comparative genetic analysis on the phages in the three microbialite locations were drastically different from not only one another, but from other phage locations throughout the world. Additionally, a marine signature was present in the phage community at Pozas Azules II, despite the fact that the environment has not been in contact with the ocean for tens of millions of years.

This is an underwater view of a microbialite at Highborne Cay.

"Taken together, these results prove that viruses in modern microbialites display the variability of distribution of organisms on our planet," said Forest Rohwer, San Diego State University biology professor. "It also suggests that they may be derived from an ancient, microbial community."

Viruses, especially phages, are the most abundant biological entities in the world’s oceans. Current studies of the distribution of life on Earth have suggested that phages are widely distributed across the globe. However, the SDSU-led study found that the microbialites studied were very unique and, when compared to dozens of other viral and microbial metagenomic libraries, they were found to be less than five percent similar to other communities.

"An analysis also showed that the percentage of genome shared between the three sites was zero and, therefore, the viruses are all genetically unique to their respective microbialite," Rohwer said. "Because of their unique biodiversity, these microbiolites should be targets for conservation efforts."

Microbialites at Pozas Azules II.

Researchers found that microphages, or smaller forms of phages, were the most abundant in the Highborne Cay and Pozas Azulas II phage communities. In contrast, microphages were absent in Rio Mesquites and the community was instead dominated by two forms of phage, including Shewanella oneidensis prophage and Burkholderia cepacia phage.

Other researchers involved in the study included colleagues from the Genome Institute of Singapore; Argonne National Laboratory in Argonne, Ill.; Rosenstiel School of Marine and Atmospheric Science at the University of Miami, Fla.; Rice University in Houston, Texas; the Instituto de Ecología (Institute of Ecology) at the Universidad Nacional Autónoma de México (National Autonomous University of Mexico), Mexico City, Mexico; University of California Santa Barbara and the University of South Florida in St. Petersburg, Fla. The study was published online on Sunday, March 2 and will appear in the print version of the journal Nature in April 2008.

San Diego State University is the oldest and largest higher education institution in the San Diego region. Since it was founded in 1897, the university has grown to offer bachelor’s degrees in 81 areas, master’s degrees in 74 areas and doctorates in 16 areas. SDSU’s approximately 36,000 students participate in an academic curriculum distinguished by direct contact with faculty and an increasing international emphasis that prepares them for a global future. For more information, visit www.sdsu.edu.

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