Black Queen tells microbes to be lazy

Confronted by a deadly threat, most bacteria let someone else handle it.

According to the Black Queen hypothesis, evolution pushes microorganisms to lose essential functions when there is another species around to perform them. The idea could explain why microbes are so dependent on each other.

Jeffrey Morris of Michigan State University in East Lansing got the idea from an ocean-dwelling bacterium called Prochlorococcus. "It is the most common photosynthetic organism on Earth," he says, but for decades no one could grow it.

That's because Prochlorococcus relies on other bacteria to break down toxic hydrogen peroxide. This led Morris to the Black Queen hypothesis, named after the card game Hearts, in which players try to discard the costly queen of spades.

For microorganisms every ability is costly ? carrying genes and making proteins uses up energy ? so they benefit from losing genes if possible.

As long as one microbe breaks down hydrogen peroxide all bacteria in the area benefit, so it is in the microbes' interests to discard the associated genes quickly.

Morris acknowledges that this kind of outsourcing is a dangerous game to play, though. In theory, all of the microbes may lose the genes at the same time, leaving none to deal with hydrogen peroxide.

Unpublished experiments support the Black Queen hypothesis. Morgan created Escherichia coli vulnerable to hydrogen peroxide, then gave them a resistance gene. Many, but not all, of the bacteria promptly lost the gene.

William Costerton of the Center for Genomic Sciences in Pittsburgh, Pennsylvania, thinks the idea makes sense. "Some species may be 'donkey engines' for whole consortia [that] are unable to grow in the absence of the donkey."

Morris says the "donkey" microorganisms that do the community's dirty work would ultimately become keystone species. That is, they would be extremely important to the ecosystem ? even essential for its survival ? despite being relatively rare.

The Black Queen hypothesis explains how evolution can produce helpers and beneficiaries without the two having to interact or cooperate, says Martin Hahn of the Austrian Academy of Sciences in Mondsee.

But microorganisms do lose abilities for other reasons. Hahn studies bacteria called Polynucleobacter, which cannot move or detect signals from their neighbours PLoS One, DOI: 10.1371/journal.pone.0032772. These abilities are not Black Queens because they cannot be outsourced.

Journal reference: mBio, DOI: 10.1128/mBio.00036-12

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.

Have your say

Only subscribers may leave comments on this article. Please log in.

Only personal subscribers may leave comments on this article

Subscribe now to comment.

All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.

If you are having a technical problem posting a comment, please contact technical support.

Source: http://feeds.newscientist.com/c/749/f/10897/s/1dd645e8/l/0L0Snewscientist0N0Carticle0Cdn216290Eblack0Equeen0Etells0Emicrobes0Eto0Ebe0Elazy0Bhtml0DDCMP0FOTC0Erss0Gnsref0Fonline0Enews/story01.htm

coolio daylight savings time 2012 ricky rubio day light savings time peter paul and mary edgar rice burroughs catch me if you can