Evolution seen in a yogurt cup

If you want to see evolution in action, check out your local market's dairy section. One of the bacteria in yogurt is undergoing an extreme makeover. It's shedding parts of its genetic heritage wholesale as it morphs into an organism that loves to live in - and perhaps can only live in - fermented milk.

The ability to trace the transformation of Lactobacillus bulgaricus (L. bulgaricus), a common bacterial culture in yogurt, illustrates the penetrating insight into evolutionary processes that DNA analysis now gives biologists. No longer are they limited in their study of an organism's changes in form and function. They can read those changes as they are written into the organism's genetic code.

Maarten van de Guchte at France's Institut National de la Recherche Agronomique in Jouy-en-Josas and colleagues have decoded the entire L. bulgaricus genome. They explain in the Proceedings of the National Academy of Sciences online edition that the bacterium is streamlining itself for its new environment and distancing itself from its relatives.

The research team found evidence that the bacterium has lost a lot of genes that specify various proteins. They also found 250 nonfunctional DNA sequences that seem ripe for deletion. The study shows that some of this lost protein production can be made up by production from another yogurt- fermenting bacterium, Streptococcus thermophilus. Nevertheless, one wonders if L. bulgaricus could ever again survive in the wild.

Whether or not a species can regain a lost function is a major unanswered question in evolutionary biology.

Joshua Kohn with the University of California at San Diego led a team to explore that question using some species from the tomato and tobacco family. They looked at the function that enables individual plants to recognize and reject their own pollen. This prevents self-fertilization. The team reported last January that their findings based on genetic analysis support the conclusion that, once a species loses the genetic information for a complex function, it's gone forever.

More research is needed to settle this question scientifically. Meanwhile, it raises a warning. Like the bacterium that's learned to live in yogurt, many of our foods depend on organisms that have lost much of the genetic information that enables their wild ancestors to survive.

Virtually all of our commercial grain and fruit species could not make it on their own. Botanists have to seek out wild varieties to find genes they can breed back into food plants when new or more virulent pests attack.

The plant that bears the Cavendish strain of banana that is sold all over the world produces no pollen or seed. It's an evolutionary dead end. Now a fungus threatens to wipe out the plant worldwide. If breeders did not have other varieties to turn to, the banana industry would be in crisis, according to the International Network for the Improvement of Banana and Plantain.

Forest clearance and unwise development are reducing the reservoirs of genetic diversity. There are plenty of bacteria to make up for L. bulgaricus's lost functions.

But what will rescue the banana?

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