Several years ago researchers at Michigan State University (MSU) reported discovering a novel, evolutionary trait in a long-studied population of Escherichia coli, a rod-shaped bacterium commonly found in the lower intestine of mammals. The E. coli added a helping of citrate to its traditional diet of glucose, even though other E. coli can't consume citrate in the presence of oxygen.
These same biologists have now analyzed this new trait's genetic origins and found that in multiple cases, the evolving E. coli population needed more than one mutational step before the key innovation took hold. Complex traits, like using a new food source, are thought to be difficult and arise rarely, making the research of broad interest to both evolutionary biologists and public health scientists.
The findings, reported in this week's journal Nature, document the step-by-step process by which organisms evolve new functions. The study also highlights the importance of evolutionary changes that alter the physical arrangement of genes, leading to new patterns of gene regulation.
E. coli normally can't digest citrate when oxygen is present because they don't express the right protein to absorb citrate molecules. Citrate is a salt or class of citric acid commonly found in fruit such as lemons. So how did this mutation occur?
To find the answer, postdoctoral researcher Zachary Blount and MSU Hannah Distinguished Professor of Microbiology and Molecular Genetics Richard Lenski analyzed dozens of complete genome sequences from bacteria that had evolved this new trait and had been sampled and stored at different time points in the history of the lineage.
The National Science Foundation's Division of Environmental Biology partly funded the research, as did the NSF-supported BEACON Center for the Study of Evolution in Action.
The team used samples from Lenski's long-term E. coli experime
|Contact: Bobbie Mixon|
National Science Foundation