( ow at the Centre national de la recherc...)Where Bacteria Get Their Genes

Lateral gene transfer, unique to the bacterial world, has long been recognized as common. But until now scientists did not know which of a bacterium's genes came from lateral gene transfer and which had been inherited from its parent.

In their study, the scientists focused on the best-studied group of bacteria, the Gamma-Proteobacteria. It includes many human pathogens, including Salmonella, Shigella, pathogenic E. coli, and Pseudomonas.

Ochman's team compared the bacterial species by analyzing their genomic sequence data. The researchers then computed family trees, taking into account the acquired genes, and matched the trees to an established reference tree. For all genes, the match was about 95 percent. This showed that the widespread mechanism of lateral gene transfer does not interfere with the traditional approach of using family trees to infer relationships. Ochman's team found that only 205 genes of Gamma-Proteobacteria's approximately 7,205 genes are shared by all species. The vast majority of genes found in the group comes from lateral gene transfer. "Most of these occur in one or a few species only," Ochman said. "But these are the genes that make bacteria different from each other."

Most commonly, genes are transmitted by bacteriophages, viruses that specifically hijack bacteria cells. Like tiny syringes, phages inject their own genetic material into the host cell, forcing it to produce new phages. During such an event, genes from the bacterial genome can be incorporated into the newly made phages. They inject their newly modified genetic load into other bacteria. This way, bacteriophages act as shuttles, taking up DNA from one bacterium and dumping it into another. Bacteria can also make contact by tiny connection tubes through which they exchange pieces of DNA.
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Source:University of Arizona