Featured Research

from universities, journals, and other organizations

Study shows unified process of evolution in bacteria and sexual eukaryotes

Date:
April 5, 2012
Source:
Massachusetts Institute of Technology, Department of Civil and Environmental Engineering
Summary:
Bacteria adapt to habitats through random genetic mutations and gene exchange. But how does an advantageous mutation spread from a bacterium to a population? Does the gene sweep through a population or does an individual bacterium obtain the gene, then replicate its genome to form an adapted population? Researchers have shown that genes can sweep through populations, indicating that the process of evolution in bacteria is very similar to that of sexual eukaryotes.

A model of ecological differentiation in bacteria. Thin arrows represent recombination within or between ecologically associated populations. Thick colored arrows represent acquisition of adaptive alleles for different microhabitats.
Credit: John Kaufmann

Bacteria are the most populous organisms on the planet. They thrive in almost every known environment, adapting to different habitats by means of genetic variations that provide the capabilities essential for survival. These genetic innovations arise from what scientists believe is a random mutation and exchange of genes and other bits of DNA among bacteria that sometimes confers an advantage, and which then becomes an intrinsic part of the genome.

Related Articles


But how an advantageous mutation spreads from a single bacterium to all the other bacteria in a population is an open scientific question. Does the gene containing an advantageous mutation pass from bacterium to bacterium, sweeping through an entire population on its own? Or does a single individual obtain the gene, then replicate its entire genome many times to form a new and better-adapted population of identical clones? Conflicting evidence supports both scenarios.

In a paper appearing in the April 6 issue of Science, researchers in MIT's Department of Civil and Environmental Engineering (CEE) provide evidence that advantageous mutations can sweep through populations on their own. The study reconciles the previously conflicting evidence by showing that after these gene sweeps, recombination becomes less frequent between bacterial strains from different populations, yielding a pattern of genetic diversity resembling that of a clonal population.

This indicates that the process of evolution in bacteria is very similar to that of sexual eukaryotes (which do not pass their entire genome intact to their progeny) and suggests a unified method of evolution for Earth's two major life forms: prokaryotes and eukaryotes.

The findings also get to the heart of another scientific question: how to delineate species of bacteria -- or determine if the term "species" even applies to bacteria, which are typically identified as ecological populations and not species. If all bacteria in a population are clones from a common ancestor, the idea of species doesn't apply. But if -- as this new study shows -- genes randomly shared among individuals can bring about a new, ecologically specialized population, use of the term may be warranted.

"We found that the differentiation between populations was restricted to a few small patches in the genome," says Eric Alm, the Karl Van Tassel (1925) Career Development Associate Professor of Civil and Environmental Engineering and Biological Engineering and an associate member of the Broad Institute.

Professor Martin Polz of CEE, co-principal investigator on the project, adds, "Similar patterns have been observed in animals, but we didn't expect to see it in bacteria"

The process of ecological differentiation in bacteria, the researchers found, is similar to that in malaria-transmitting mosquitoes: Some populations develop resistance to antimalarial agents by means of a single gene sweep, while other populations sharing the same habitat do not. The stickleback fish has also been shown to follow this pattern of "sympatric speciation" in shared habitats.

"Even though the sources of genetic diversity are quite different between bacteria and sexual eukaryotes, the process by which adaptive diversity spreads and triggers ecological differentiation seems very similar," says first author Jesse Shapiro PhD '10, a postdoc at Harvard University who did his graduate work in Alm's lab at MIT.

The researchers performed the work using 20 complete genomes of the bacterium Vibrio cyclitrophicus that had recently diverged into two ecological populations adapted to microhabitats containing different types of zooplankton, phytoplankton, and suspended organic particles in seawater. In a previous study based on just a few marker genes, they had predicted that these closely related Vibrio populations were in the process of developing into two distinct habitat-associated populations.

The new study shows that the two populations were frequently mixed by genetic recombination, remaining genetically distinct at just a handful of ecologically adaptive genes, with an increasing trend toward gene-sharing within -- rather than between -- habitats.

"This is the most sophisticated paper on bacterial speciation to appear yet, all the more so because it uses the dubious word 'species' only once, and that with caution," says W. Ford Doolittle, professor emeritus of biochemistry at Dalhousie University. "The genetic basis of ecological differentiation in bacteria -- how genotype maps to ecotype and what processes determine this mapping -- is in my mind the biggest issue in modern microbial ecology."

Other co-authors on the paper are MIT graduate student Jonathan Friedman, postdocs Otto Cordero and Sarah Preheim, graduate student Sonia Timberlake, and Gitta Szabo of the University of Vienna. Funding was provided by the National Science Foundation, the Gordon and Betty Moore Foundation and the Broad Institute.


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology, Department of Civil and Environmental Engineering. The original article was written by Denise Brehm, Civil & Environmental Engineering. Note: Materials may be edited for content and length.


Journal Reference:

  1. B. J. Shapiro, J. Friedman, O. X. Cordero, S. P. Preheim, S. C. Timberlake, G. Szabo, M. F. Polz, E. J. Alm. Population Genomics of Early Events in the Ecological Differentiation of Bacteria. Science, 2012; 336 (6077): 48 DOI: 10.1126/science.1218198

Cite This Page:

Massachusetts Institute of Technology, Department of Civil and Environmental Engineering. "Study shows unified process of evolution in bacteria and sexual eukaryotes." ScienceDaily. ScienceDaily, 5 April 2012. <www.sciencedaily.com/releases/2012/04/120405142159.htm>.
Massachusetts Institute of Technology, Department of Civil and Environmental Engineering. (2012, April 5). Study shows unified process of evolution in bacteria and sexual eukaryotes. ScienceDaily. Retrieved December 22, 2014 from www.sciencedaily.com/releases/2012/04/120405142159.htm
Massachusetts Institute of Technology, Department of Civil and Environmental Engineering. "Study shows unified process of evolution in bacteria and sexual eukaryotes." ScienceDaily. www.sciencedaily.com/releases/2012/04/120405142159.htm (accessed December 22, 2014).

Share This


More From ScienceDaily



More Plants & Animals News

Monday, December 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Earthworms Provide Cancer-Fighting Bacteria

Earthworms Provide Cancer-Fighting Bacteria

Reuters - Innovations Video Online (Dec. 21, 2014) Polish scientists isolate bacteria from earthworm intestines which they say may be used in antibiotics and cancer treatments. Suzannah Butcher reports. Video provided by Reuters
Powered by NewsLook.com
Existing Chemical Compounds Could Revive Failing Antibiotics, Says Danish Scientist

Existing Chemical Compounds Could Revive Failing Antibiotics, Says Danish Scientist

Reuters - Innovations Video Online (Dec. 21, 2014) A team of scientists led by Danish chemist Jorn Christensen says they have isolated two chemical compounds within an existing antipsychotic medication that could be used to help a range of failing antibiotics work against killer bacterial infections, such as Tuberculosis. Jim Drury went to meet him. Video provided by Reuters
Powered by NewsLook.com
Researchers Test Colombian Village With High Alzheimer's Rates

Researchers Test Colombian Village With High Alzheimer's Rates

AFP (Dec. 19, 2014) In Yarumal, a village in N. Colombia, Alzheimer's has ravaged a disproportionately large number of families. A genetic "curse" that may pave the way for research on how to treat the disease that claims a new victim every four seconds. Duration: 02:42 Video provided by AFP
Powered by NewsLook.com
Monarch Butterflies Descend Upon Mexican Forest During Annual Migration

Monarch Butterflies Descend Upon Mexican Forest During Annual Migration

Reuters - Light News Video Online (Dec. 19, 2014) Millions of monarch butterflies begin to descend onto Mexico as part of their annual migration south. Rough Cut (no reporter narration) Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins