Evolution in Escherichia Coli Bacterium Observed During Lab Tests

E. Coli bacteria shows signs of evolution in lab testing

Despite an overwhelming body of scientific evidence, evolution is still a fiercely debate topic in some circles. Many people take evolution for granted, simply understanding that it is the theory accepted by the scientific community based on the strong supporting evidence, and remain relatively oblivious to the controversy.

However, the fact remains that yearly there are many protests and court cases in the U.S. and abroad where people try to block educational attempts to teach the theory of evolution and replace them with religious-based theories.

Fortunately for evolutionary scientists they now have perhaps the greatest piece of evidence of all -- the largest evolutionary leap observed to date. The experiment started inconspicuously, with researchers at Michigan State University in East Lansing by using a single Escherichia coli bacterium and its descendants to found 12 populations.

Over 44,000 generations were observed and only minor mutations were observed, as is typical in these kinds of studies. Typical beneficial mutations -- larger cell size, faster growth rates, and lower peak population densities -- were observed.

Then at generation 31,500 something shocking happened. The bacteria evolved, gaining an entirely new gene that could process citrate, a nutrient that the bacteria could not previously use. To put this in context, lack of citrate metabolism is one of E. coli's identifying traits. And the newly evolved bacteria proceeded to dominate over their citrate-intolerant kin.

Says researcher Richard Lenski, "It's the most profound change we have seen during the experiment. This was clearly something quite different for them, and it's outside what was normally considered the bounds of E. coli as a species, which makes it especially interesting."

Lenski says the only two explanations are either an extremely improbable mutation such as a rare chromosomal inversion, or a series of small mutation adding up to a useful new gene. Was the trait inevitable, guided by some all powerful hand? Lenski turned to his freezer for the answer. Unthawing the bacteria, from early generations, he found that pure chance had guided the evolutionary leap and that the bacteria did not evolve the trait. He did find that the later generations after 20,000 did evolve the trait eventually, indicating something happened around this time that laid the groundwork for the evolution.

He and his fellow researchers are currently studying exactly what change allowed for the eventual evolution. This experiment, however, proves that evolution does not always lead to best possible outcome (in that other lines did not achieve the same optimal trait). This has been a major point of contention raised by creationists who point to structures in nature that serve ornamental or little purpose as proof of creationism.

Further, it goes to show that profound changes can happen, including the introduction of entirely new genes. A particularly harsh criticism leveled in the past by was that profound genetic changes, including the creation of new genes, were never observed. Considering a few genes can account for profound morphological differences in larger organism, this is a very salient piece of evidence for evolution's supporters.

Jerry Coyne, an evolutionary biologist at the University of Chicago lauded the research and took a bit of an opportunity to poke fun at creationists saying, "The thing I like most is it says you can get these complex traits evolving by a combination of unlikely events. That's just what creationists say can't happen."

The findings are reported in the journal PNAS.