Bacteria, like other living organisms, are exposed to ever-changing environments, oxidative stress, and worst of all, antibiotics. Bacteria are able to defend themselves against all these insults, gain resistance to new antibiotics and attain new abilities simply by ‘stealing’ genetic information from other better-adapted types of bacteria through the bacterial equivalent of sex, known as horizontal gene transfer.
According to the new research, published in the current issue of Nature Genetics, this allows them to evolve the networks of chemical reactions that enable them to do new things, such as defend against antibiotics or antibacterial sprays.The study, which pieces together the history of new metabolic genes acquired by E. coli over several hundred million years, is the outcome of the first systematic study of how bacteria change their metabolic networks over time. Researchers from the University of Bath, England, University of Manchester, the European Molecular Biology Laboratory and Eötvös Lorànd University in Hungary studied a benign strain of Escherichia coli to see how the common intestine dweller picked up new parts for its metabolic network--the internal system of chemical reactions that produce the necessities of life, such as amino acids or cellular structures.
The researchers estimate that approximately 25 of E. coli's roughly 900 metabolic genes have been added into its network through horizontal gene transfer in the last 100 million years, as compared to just one addition by gene duplication, where copies of genes are made by accident and then altered over time. The bacterium had genes in its metabolic network that it had pirated from near relatives, including those that enable it to defend itself against antibiotics.
The researchers found that the bacteria do this by way of a process known as horizontal gene transfer, in which a cell passes genetic information to another cell that is not its offspring. It is the bacterial equivalent of sex, with two cells sidling up to each other and engaging in conjugation, or the swapping of genes.
To test why E. coli needed these genes, the researchers cross-examined dozens of E. coli's closest bacterial relatives to see which genes were most commonly exchanged between them. This would highlight the genes that have contributed the most to the evolution of metabolic networks across bacteria.
The researchers found that most of these genes helped bacteria cope with specific environments. Thus, new genes were needed for new functions, rather than affecting the core processes of E. coli, such as how it grows.
