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Gene Scavenging Between Bacteria is Major Evolutionary Driver

SAN FRANCISCO, Nov. 22 - Bacteria's penchant for gobbling up DNA from its environment for integration into its own genome is a major mechanism of its evolution, according to researchers.


This form of "lateral transfer" of genes, noted in prior research, is the driving factor that allowed disparate bacteria throughout the family tree to gain the ability to undergo photosynthesis, according to the research, published in this week's Science.


It was a "puzzle" why the organisms' ability to perform photosynthesis "would be distributed along the tree as they are," said Robert Blankenship, a professor of biochemistry at Arizona State University in Tempe and an author of the paper. Other authors include researchers from the University of Connecticut, Storrs, and Integrated Genomics.


Analyzing whole genomes from five photosynthetic groups of bacteria--green sulfur, cyanobacteria, green filamentous, heliobacteria, and proteobacteria--the scientists found gene similarity, but no one route as to how those photosynthesis genes would have been passed down in a linear way, said Blankenship. Instead, the research, which used BLAST and other computer-analysis methods, indicated that the genes had different evolutionary origins via lateral transfer.


To be sure, this method, in which a dead organism's DNA is spread into the world after another organism absorbs it into its own genome--is not a high-probability event. But it does become evolutionary significant if one considers that large numbers of bacteria live and die millions of times a minute, increasing the likelihood of lateral transfer occurring, said Blankenship.


"With bacteria, at least, this is a major force which defined evolution trajectory of these organisms," he explained.


It does not appear to occur with any significance in eukaryotic organisms, he stressed.


In the study, the scientists found 188 orthologous genes within the five bacterial groups studied. Blankenship also said that identifying the genes was a first step to better understand metabolic pathways like photosynthesis and help scientists engineer organisms to make a suite of enzymes with medical applications.


"Our work tells us some things about how that process might have worked" in nature, said Blankenship.


While the genomes studied are now on GenBank, the initial sequence for the heliobacteria came from Integrated Genomics, Blankenship said.

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