Team:Mexico-UNAM-IPN/Horizontal Transfer

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Revision as of 16:43, 29 October 2008

Design Models and Simulations Implementation

Introduction

The main goal is to design an experimental model to detect events of horizontal gene transfer among bacteria. Horizontal gene transfer is an evolutionary mechanism that contributes to the acquisition of new genetic material among organisms. There are three mechanisms by which bacteria acquire genetic material: transformation, conjugation and transduction.

In this model we will use genetically modified E. coli. that will be monitored until a detectable sign appears in the media, indicating an event of horizontal transfer. In order to detect such events, we will use plasmids as the genetic material that could be transferred in a bacterial culture.

The model described above involves transformation as the main mechanism for genetic transfer. Further work will include the design of other experimental models that use conjugation and transduction.

Horizontal Gene Transfer

Horizontal gene transfer (HGT) or Lateral Gene Transfer, It’s one way in which an organism can acquire new genes from another species, in which genetic material is transferred from the genome of one organism to that of another. In Prokaryotes there is three ways in which HGT can occur. These are: conjugation, transformation and transduction.

HGT is habitually assumed to be played an important role in the innovation of the genomes and evolution of life, especially as a mayor evolutionary force in shaping prokaryotic genomes and in early stages of life. However, some publications suggest that the role of HGT has been overestimated, in particular in the assumption that HGT is a ubiquitous influence through evolution, and their consequences in phylogenies and the ability of tree-building methods. In other words, the role of this process is highly debated and the origin of the controversy is the inadequate or inefficacy of the methods to identify the lateral events.

A very important example of this biological phenomenon is the antibiotic resistance in pathogenic bacteria, where the HGT helps to increment and accelerate in the dispersion of resistance.

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 In this model we will use genetically modified E. coli. that will be monitored until a detectable sign appears in the media, indicating an event of horizontal transfer. In order to detect such events, we will use plasmids as the genetic material that could be transferred in a bacterial culture.
-These plasmids will express genes that code fluorescent proteins or antibiotic resistance to ampicillin or tetracycline. First of all, we will transform E. coli with the plasmids of interest. Once we have recombinant bacteria, we will cultivate them and we will let them consume all nutrients. Bacteria will die, and our genetically modified plasmids will be released into the media. To eliminate cellular components, this media will be centrifuged, and the supernatant collected to use later. This supernatant with plasmid will be used in a new free-plasmid bacterial culture. These bacteria will act as recipient cells for the plasmid previously released. This new culture will be carefully monitored to detect events of horizontal gene transfer.
 The model described above involves transformation as the main mechanism for genetic transfer. Further work will include the design of other experimental models that use conjugation and transduction.