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One Step at a Time!

Vertical Gene Transfer

Screenshot image from flash of Vertical Gene Transfer.

During the classical process of vertical gene transfer, a genetic mutation can occur allowing an organism to exhibit a new characteristic. Because the mutation is now part of the organism’s genome, the characteristic is subsequently passed down to the next generation.

Credit: Nicolle Rager Fuller and Cliff Braverman, National Science Foundation

Horizontal Gene Transfer

Screenshot image from flash of Horizontal Gene Transfer.

Through the newly discovered process of horizontal gene transfer, a bacterium acquires genetic information from another, unrelated bacterium, allowing it to exhibit entirely new characteristics. In fact, entire biochemical pathways may be passed from one bacterial species to another in a single DNA transfer.

Credit: Nicolle Rager Fuller and Cliff Braverman, National Science Foundation

A Lighter Look at
Horizontal Gene Transfer

Screenshot image from flash of Humorous Gene Transfer.

For a more light-hearted look at horizontal gene transfer, check out this bacterium’s new hairdo!

Credit: Nicolle Rager Fuller and Cliff Braverman, National Science Foundation
“One step at a time!” Do organisms change slowly or by leaps and bounds?

Genetic dogma has long-dictated that a species could only exhibit a new characteristic via a step-by-step process whereby genetic mutations accumulated over generations. But now, this central dogma may be changing as a growing body of evidence reveals that big changes in an organism’s genome may happen all at once. The discovery of this new process, called horizontal gene transfer, or the transfer of genes between two organisms without sexual reproduction, may be twisting the branches of the evolutionary tree.

To understand this complicated “genetic swap” across the traditional species barrier, scientists are looking to simple, single-celled microorganisms. Researchers supported by the FIBR program are studying bacteria from Yellowstone’s thermal pools and a common laboratory bacterium to make sense of this newly discovered promiscuousness.

Bacteria have long been classified into species, or basic units of scientific classification, based on their similarities. Properties, such as shape, size, metabolism, colony size and environmental requirements, are used in defining a bacterial species and determining its limits. Horizontal gene transfer has recently muddied this classification process, as well as the central dogmas that organisms change over generations via natural selection and genetic mutation, a fairly random, trial and error process. Some scientists speculate that horizontal gene transfer may account for 10 to 50 percent of all the genes in certain kinds of microorganisms.

To explore how much this phenomenon may allow microbes to breach species barriers, Montana State University researchers and colleagues gather and analyze the genetics of microbial mats in Yellowstone’s hot springs. The team catalogues and compares DNA extracted from individual communities in a new field of study termed metagenomics. Metagenomics allows researchers to simultaneously catalog all the genes present in a given microbial community. Comparing these genes via computer programs then determines whether genes in near-by, once-unrelated neighbors are similar, thus predicting just how often and rapidly distantly related bacteria exchange genetic material.

If an organism gains genetic material out of the deal, the question becomes, “How does it respond to its new genes and their functions?” Researchers at Brandeis University are leading another FIBR team forcing this issue. By inserting a well-understood pathway from a soil bacterium into the lab workhorse bacterium, E. coli, the team can measure this bacterium’s response to the new gene and its resulting function. Such information will help us understand how living organisms adapt and evolve, potentially leading to the engineering of microbes with new capabilities for environmental and industrial purposes.

Life Science Frontiers A Special Report