Molecular penny-pinching is the key to bacterial evolution

Researchers in the Department of Plant Sciences have shown that the economics of gene production influences the rate at which bacterial genes evolve.

In a study of over 1000 different bacterial species, published today in Genome Biology, the team detected differences in the rate at which genes were evolving that could be attributed to the cost and efficiency of gene production.

Gene production involves the conversion of information encoded in DNA into a useful product such as a protein via a messenger molecule known as messenger RNA (mRNA). However, this is an expensive process and saving costs can allow you to invest more resources for survival and reproduction. Since it is difficult to alter a protein without having negative consequences, the study focused on analysing how changes to the messenger can cut costs.

“These are two main ways to reduce costs at this stage of production,” said Dr Emily Seward, the first author of this study “either you can reduce the resource requirements of the messenger or you can make the messenger more efficient”.

This is possible because the messenger is composed of a long string of building blocks, called nucleotides. These building blocks cost different amounts of resources to make and vary in terms of how difficult they are for the cell to read. As with many things in life, there is a trade-off between cost and ease of use, and the authors found that the cheaper messengers were generally harder for the cell to read. Despite this trade-off, the authors also found that genes had evolved to encode messengers that were optimised to be a balance between the two.

The research team also found that the more of a gene product a bacterium needed, the more the messenger was optimised. Lead author Dr Steven Kelly, said: ‘Cells are like factories that make lots of different products. Some of those products are made in small numbers and their production isn’t optimised for cost or efficiency as the small numbers don’t make a significant impact on the operational budget of the factory. However, products that are made in large amounts are optimised to reduce the amount they cost to make. The more they produce, the better the production is optimised.”

This provides a novel ‘economic’ explanation for why genes in bacteria evolve at different rates. The more optimised a messenger is, the more likely it is that a mutation in that gene will have a negative consequences for the cell. This means that optimised genes evolve more slowly. Overall, bacteria evolve to be thrifty and reduce production costs by either using messengers that require less expensive resources or are read more efficiently.

Read the full paper Selection-driven cost-efficiency optimization of transcripts modulates gene evolutionary rate in bacteria here.