There is no doubt that bacteria evolve and adapt to local environments in part by horizontal (or lateral) gene transfer between closely and very distantly related organisms. The detection of very similar genes in distinct bacteria showed that large fractions of bacterial genomes have arisen through horizontal gene transfer. Consistent with this, studies done in the laboratory and in the field have shown that the horizontal transfer of genes between bacterial populations readily occurs in various habitats. Thus bacteria have access to a common pool of genes, called the ‘virtual genome’ (VG) or horizontal gene pool (‘HGP’). This sharing of genes from the VG allows ‘wholesale’ acquisition of useful traits such as drug resistance, heavy metal resistance, pollutant degradation, virulence factors, and many more.
Of the various MGEs that play a role in genetic exchange among bacteria, plasmids are of particular interest because many are self-transferable and able to replicate in a wide range of hosts. They often carry antibiotic resistance, pollutant degradation or other provide a fitness advantage to their host. Because plasmids can transfer among different bacterial species, they play an important role in the ability of bacteria to degrade environmental contaminants and to become resistant to drugs used to treat infectious diseases of plants, animals and humans. However, little is known about the genetic structure of these mobile elements and the full range of functions that they encode. To gain insight into the issues outlined above, our plasmid genome sequencing project is analyzing the genome sequences of 100 plasmids that have a broad host-range (also called BHR plasmids). The sequenced plasmids were obtained from soil, water, and sewage sludge samples from around the globe. The project includes finishing the sequencing and annotation of the plasmids, and then interpreting the sequence information to better understand the evolutionary history of plasmids, and their role in bacterial chromosome evolution and adaptation to new environments. The information collected during this project will add significant new data to the paltry plasmid sequence database that now exists, which is also skewed towards plasmids relevant to human infectious diseases.
With this blog we hope to spark your interest in horizontal gene transfer among bacteria, and the diversity, ecology and evolution of bacterial plasmids, and generate discussion about the latest findings in the field.
Dr. Eva Top
University of Idaho