Genome complexity: rapid functional recovery (Introduction)

by David Turell , Friday, February 27, 2015, 14:45 (3345 days ago) @ David Turell
edited by David Turell, Friday, February 27, 2015, 15:20

In four days, Bacteria without flagella (due to gene deletion) recovered them by substitution within their genes:-http://www.the-scientist.com//?articles.view/articleNo/42284/title/Evolutionary-Rewiring/-“This is a fascinating set of evolution experiments,” wrote evolutionary biologist Richard Lenski of Michigan State University in an e-mail to The Scientist. “Their experiments show how a biological function—in this case, flagellar motility in Pseudomonas fluorescens—can re-evolve after the deletion of a seemingly critical gene. The bacteria regained motility not by reacquiring the lost gene . . . but instead by mutations in other genes that put their products to new uses.”-"There was another shock to come: each bacterial strain that regained its swimming ability—first slow, then fast—did so via essentially the same evolutionary process. The team sequenced the genomes of different slow- and fast-swimming strains and discovered that all of the slow swimmers had mutations in genes that would directly or indirectly increase expression of a nitrogen regulatory protein called NtrC. Furthermore, all of the fast swimmers had mutations in the gene for NtrC itself.-"NtrC shares 30 percent amino acid identity with FleQ, suggesting the proteins may be able to minimally cross-react with each other's target genes. Sure enough, the researchers determined that the initial mutations, which ramped up NtrC levels, enabled a minor upregulation of FleQ's target genes. The second mutations to NtrC itself then improved the protein's interaction with the FleQ targets, boosting their expression, and the bacteria's ability to swim.-"The results highlight the importance of gene duplication in evolution, said Hughes, and the ability of the resulting diverged proteins to “moonlight” in roles aside from their main function. Indeed, said Jeff Barrick of the University of Texas in Austin who was not involved in the work, such cross-talk gives organisms “greater robustness,” allowing them “to restore a function even though they are missing a genetic part.”-"But while the re-evolved flagella enabled the bacteria to access food supplies at the farthest reaches of the Petri dish, the ability came at a price. “The bacteria that became much better at swimming were much worse at nitrogen regulation,” said Johnson. However, she added, “sometimes the advantage can be so great that it's worth paying that cost because otherwise you die.”"-This shows the value of gene duplication, but also the price of loss of function in nitrogen control. This is not an IM, because nothing is new, but it is built-in epigenetic protection controls. I interpret this as a built-in life-protection process in bacteria, another layer of genome complexity.-Another view of the study:-"Remarkably, this happened because the mutants had rewired a cellular switch, which normally controls nitrogen levels in the cell, to activate the flagellum. This allowed the bacteria to move to new food sources and avoid starvation.-"To understand how this had happened biologists at the University of York, compared which genes were being activated in bacteria before and after evolution. Professor Brockhurst said: "Bacteria use lots of genetic switches to turn their genes on and off. Each genetic switch controls a different set of genes.-"Amazingly, we found that just a single tiny change to one of these genetic switches was enough to convert it from being a switch that would normally turn on the genes for using nitrogen into a switch that now turns on the genes to build the flagella. The result is that the bacterium had, in effect, evolved a way to hotwire its motor practically overnight." -"Dr Tiffany Taylor, of the University of Reading and lead author of the study, added: "But the hotwiring comes at a cost. The replacement key is a molecule borrowed from a system which regulates nitrogen levels. The mutant bacteria can now move, but it can't regulate nitrogen properly, which can build up and become toxic. Of course, it's an evolutionary price worth paying when the alternative is certain death."-"These results suggest that new functions can evolve far quicker and much more easily than anyone previously expected. Dr Louise Johnson, an evolutionary biologist at the University of Reading, said: "Evolution has been described as a process of 'tinkering', but this work shows that evolution can be remarkably repeatable. When the situation is desperate, life finds a way.'"-
 Read more at: http://phys.org/news/2015-02-bacteria-hotwire-genes-faulty-motor.html#jCp