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How E. coli evolves to adapt to changing acidity
May 30, 2007One in a series of studies on laboratory studies of selection and evolution
Forthcoming in Physiological and Biochemical Zoology, a fascinating new selection of papers collects leading experimental research in evolution and artificial selection, providing insight into how organisms adapt to changing environmental conditions and fluctuations.
Dr. James Hicks, Editor in Chief of PBZ, explains the momentum behind this collection of papers: "This exciting approach - experimental evolution - allows scientists to investigate the fundamental mechanisms of evolution. Prior to the advent of contemporary laboratory techniques, inferences about evolution were based on observation. Now, we can study evolutionary change as it is happening, by selecting organisms that change rapidly, such as the fruit fly or E. coli. This advantage allows scientists to investigate how changes occur and how they affect an organism's individual physiology and overall community."
In the July/August 2007 issue, the first of three issues that will contain articles from the collection, Bradley S. Hughes, Alistair J. Cullum, and Albert F. Bennett (University of California, Irvine) explore the effect on E. coli of fluctuating acidity, an especially important environmental factor for the bacteria.
E. coli may spend hundreds or thousands of generations in the relatively neutral-acidity colon, with brief exposure to the extreme acidity of the stomach and modest alkalinity in the small intestine during colonization of a new host. With modern sewage handling (or mishandling), the bacteria may also experience exposure to the ocean, with a pH near 8.0, before infecting a new host.
To assess how E. coli might adapt to different environmental conditions, the researchers observed four groups of bacteria. One group was exposed to constant acidity (pH of 5.3) and another to constant alkalinity (pH of 7.8). A third group was exposed to randomly fluctuating pH levels, and the fourth was exposed to pH levels that cycled daily between acidic and basic conditions.
After at least 1,000 generations, the researchers exposed the groups to either an acidic or basic environment. The groups exposed to acid or base for the entire period had developed into specialists - that is, they displayed significant fitness gains when transitioning into their preferred environment.
In contrast, the groups that evolved in variable pH environments exhibited generalist fitness patterns, with neither group having any significant fitness loss in any of the environments. Interestingly, the researchers also found that there was no significant cost to being a generalist at any tested pH level: "Overall, these comparisons suggest that the jack-of-all-trades may be a master of at least some as well," the researchers write.
"What is interesting here is that the complex patterns of adaptation in the various pH regimes were so different among the groups and revealed the first empirical characterization of the intricacies of evolution in response to variable pH," explain the authors. "Plans for future studies include the extension of this experimental evolution system applied to . . . ways in which E. coli may be evolving fitness to survive within the coastal ecosystem or the human host."
Papers from the focused collection, "Experimental Evolution and Artificial Selection" will also appear in the September/October and November/December 2007 issues.
Focused Issue: Experimental Evolution and Artificial Selection (July/August 2007)
"Do Species Converge during Adaptation" A Case Study in Drosophila"
Carla Rego, Michael R. Rose, and Margarida Matos
"Laboratory Evolution of the Migratory Polymorphism in the Sand Cricket: Combining Physiology with Quantitative Genetics"
Derek A. Roff and Daphne J. Fairbairn
"Evolutionary Adaptation to Freeze-Thaw-Growth Cycles in Escherichia coli"
Sean C. Sleight and Richard E. Lenski
"Using Experimental Evolution to Study the Physiological Mechanisms of Desiccation Resistance in Drosophila melanogaster"
Margaret A. Archer, Timothy J. Bradley, Laurence D. Mueller, and Michael R. Rose
"Experimental Evolution of Olfactory Memory in Drosophila melanogaster"
Frederic Mery, Juliette Pont, Thomas Preat, and Tadeusz J. Kawecki
"An Experimental Evolutionary Study on Adaptation to Temporally Fluctuating pH in Escherichia coli"
Bradley S. Hughes, Alistair J. Cullum, and Albert F. Bennett
University of Chicago Press Journals
In the July/August 2007 issue, the first of three issues that will contain articles from the collection, Bradley S. Hughes, Alistair J. Cullum, and Albert F. Bennett (University of California, Irvine) explore the effect on E. coli of fluctuating acidity, an especially important environmental factor for the bacteria.
E. coli may spend hundreds or thousands of generations in the relatively neutral-acidity colon, with brief exposure to the extreme acidity of the stomach and modest alkalinity in the small intestine during colonization of a new host. With modern sewage handling (or mishandling), the bacteria may also experience exposure to the ocean, with a pH near 8.0, before infecting a new host.
To assess how E. coli might adapt to different environmental conditions, the researchers observed four groups of bacteria. One group was exposed to constant acidity (pH of 5.3) and another to constant alkalinity (pH of 7.8). A third group was exposed to randomly fluctuating pH levels, and the fourth was exposed to pH levels that cycled daily between acidic and basic conditions.
After at least 1,000 generations, the researchers exposed the groups to either an acidic or basic environment. The groups exposed to acid or base for the entire period had developed into specialists - that is, they displayed significant fitness gains when transitioning into their preferred environment.
In contrast, the groups that evolved in variable pH environments exhibited generalist fitness patterns, with neither group having any significant fitness loss in any of the environments. Interestingly, the researchers also found that there was no significant cost to being a generalist at any tested pH level: "Overall, these comparisons suggest that the jack-of-all-trades may be a master of at least some as well," the researchers write.
"What is interesting here is that the complex patterns of adaptation in the various pH regimes were so different among the groups and revealed the first empirical characterization of the intricacies of evolution in response to variable pH," explain the authors. "Plans for future studies include the extension of this experimental evolution system applied to . . . ways in which E. coli may be evolving fitness to survive within the coastal ecosystem or the human host."
Papers from the focused collection, "Experimental Evolution and Artificial Selection" will also appear in the September/October and November/December 2007 issues.
Focused Issue: Experimental Evolution and Artificial Selection (July/August 2007)
"Do Species Converge during Adaptation" A Case Study in Drosophila"
Carla Rego, Michael R. Rose, and Margarida Matos
"Laboratory Evolution of the Migratory Polymorphism in the Sand Cricket: Combining Physiology with Quantitative Genetics"
Derek A. Roff and Daphne J. Fairbairn
"Evolutionary Adaptation to Freeze-Thaw-Growth Cycles in Escherichia coli"
Sean C. Sleight and Richard E. Lenski
"Using Experimental Evolution to Study the Physiological Mechanisms of Desiccation Resistance in Drosophila melanogaster"
Margaret A. Archer, Timothy J. Bradley, Laurence D. Mueller, and Michael R. Rose
"Experimental Evolution of Olfactory Memory in Drosophila melanogaster"
Frederic Mery, Juliette Pont, Thomas Preat, and Tadeusz J. Kawecki
"An Experimental Evolutionary Study on Adaptation to Temporally Fluctuating pH in Escherichia coli"
Bradley S. Hughes, Alistair J. Cullum, and Albert F. Bennett
University of Chicago Press Journals
Evolution Current Events and Evolution News RSSHuman genomics in China
Ten years ago, the Chinese National Human Genome Center at Shanghai (South Center, hereafter) was established in the Zhangjiang HiTech Park of Pudong District in Shanghai. To commemorate this important event, which marks the beginning of the Genomics Era in China, we specially organize a series of mini-reviews for this special issue.
Avian flu becoming more resistant to antiviral drugs, says University of Colorado study
A new University of Colorado at Boulder study shows the resistance of the avian flu virus to a major class of antiviral drugs is increasing through positive evolutionary selection, with researchers documenting the trend in more than 30 percent of the samples tested.
Spookfish uses mirrors for eyes
A remarkable new discovery shows the four-eyed spookfish to be the first vertebrate ever found to use mirrors, rather than lenses, to focus light in its eyes.
Study Yields Clues About the Evolution of Epilepsy
Two children have a seizure. One child never has another seizure. Twenty years later, the other child has a series of seizures and is diagnosed with epilepsy. A study being led by researchers at Rensselaer Polytechnic Institute is looking at what could possibly happen in the development of these two children that would lead to such extreme variations in their neurologic health.
Plant polymerases IV and V are special forms of Polymerase II
It's a little like finding out that Superman is actually Clark Kent. A team of biologists at Washington University in St. Louis has discovered that two vital cellular components, nuclear RNA Polymerases IV and V (Pol IV and V), found only in plants, are actually specialized forms of RNA Polymerase II, an essential enzyme of all eukaryotic organisms, including humans.
Four, three, two, one . . . pterosaurs have lift off
Pterosaurs have long suffered an identity crisis. Pop culture heedlessly -- and wrongly -- lumps these extinct flying lizards in with dinosaurs. Even paleontologists assumed that because the creatures flew, they were birdlike in many ways, such as using only two legs to take flight.
Research team reports how, when life on Earth became so big
In 3.5 billion years, life on earth went from single microscopic cells to giant sequoias and blue whales. Scientists have now documented quantitatively that the increase in maximum size of organisms was not gradual, but happened in two distinct bursts "tied to the geological evolution of the planet," said Michal Kowalewski, professor of geosciences at Virginia Tech.
Snails and humans use same genes to tell right from left
Biologists have tracked down genes that control the handedness of snail shells, and they turn out to be similar to the genes used by humans to set up the left and right sides of the body.
CSHL scientists discover new way in which ubiquitin modifies transcriptional machinery to regulate gene activity
During gene transcription - the process inside the nucleus of cells by which DNA, the genetic material, is copied into RNA - a large, ever-changing multiprotein complex is enlisted to assist the DNA-copying enzyme in its challenging job.
No quick or easy technological fix for climate change, researchers say
Global warming, some have argued, can be reversed with a large-scale "geoengineering" fix, such as having a giant blimp spray liquefied sulfur dioxide in the stratosphere or building tens of millions of chemical filter systems in the atmosphere to filter out carbon dioxide.
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