Tuesday, December 21, 2004

Outsmarting bacteria? Why don't we know whether this will work?

From Weeding Out Bacteria in Technology Review. Apparently there are seaweed compounds, called furanones, that block communication among bacteria.
Many bacteria rely on quorum sensing -- a communication system that determines when enough bacteria is present to overwhelm the host’s immune system. The Australian seaweed, a red algal species found in Sydney's Botany Bay, prevents bacteria from sensing a quorum, thereby stopping the formation of biofilms on leaves. That's significant because in people, biofilms can cause resistant, chronic infections. …

[R]esearchers say bacteria won't have an incentive to develop mutations that will foil furanones because they don't actually kill bacteria, only block their communication with each other, which prevents them from growing strong enough to cause problems.

'The fact that the furanones do not kill the cells means that there is no disadvantage to the individual cell, but only to the (bacteria) community as a whole,'says Dr. Diane McDougald, a senior research associate at the University of New South Wales Centre for Marine Biofouling and Bio-innovation. 'So the (selective) pressure to develop resistance is very low or not at all.' …

Some researchers believe bacteria might eventually outsmart any obstacle thrown their way, including compounds derived from furanones. If bacteria can detect an advantage, they might mutate in a way that allows them to circumvent the furanone signal jamming.

'(The furanone approach) depends on the assumption that there is truly no selective advantage of quorum-sensing proficiency in life and growth of the organisms,' says Susan Rosenberg, professor of molecular and human genetics and molecular virology and microbiology at Baylor University in Houston. "This might be so. But if there is a growth advantage for those capable of quorum sensing, then mutants that defy the blocker will be selected."
This raises a very interesting issue. It is evolutionary gospel that mutations occur only if they help individuals, not groups. Furanone's target groups, not individuals. If an individual bacterium developed a resistance to furanones, it would not help that bacterium to survive. On the other hand, if enough bacteria developed such a reistance simultaneously (intelligent design?), presumably the colony would survive better, leading to the survival of the mutation.

It will be interesting to follow this research and see how the bacteria respond. It's amazing that we don't know!

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