Freeloading pays off, but only up to a point

“In a nutshell, Czaran and Hoekstra have shown that “both cooperation and the associated communication system can evolve, spread and persist in the population“. So being a good citizen pays off, and cooperation actually increases the fitness of the cooperative strains as opposed to the non-cooperative ones.”

Introduction (Via Byte Size Bio)

Social behavior is not exactly the first term that comes to mind with relation to microbes. After all, we assume a certain amount of intelligence and an ability to implement a behavioral pattern in response to peer actions. Humans, yes. Apes, yes. Birds of a feather flock together… so birds, yes. Ants and bees and other social insects, sure.  But bacteria?

Yes, bacteria are social creatures: they can cooperate as a community. For example, many bacteria live in a biofilm,  a tangled matrix of polymeric substances that includes proteins, DNA and polysaccharides. Biofilms constitute tough physical barriers that are immune to attacks by many antibiotics and other bacteriocidal agents. Indeed, many of the harder to treat infectious diseases are a result of the formation of biofilms in our bodies.  A biofilm is analogous to a bunch of humans banding together, and deciding that instead of living  in dispersed separate dwellings, they will all live together in  a walled city that is easier to defend from attacks.

Excerpts (Via Byte Size Bio)

But wherever there is community work to be done, there is the danger of  freeloaders: those who benefit from the labor of the community, but provide little or no input themselves. Are bacterial communities an exception? This question has been asked by several research groups, experimental and theoretical.

In 2007, Stephen Diggle and his colleagues have created two types of QS-related Pseudomonas aureginosa mutants. First, those who do not send the signal, hence they make no effort in propagating the information that a biofilm is being constructed (signal-negative).    The second type produce the signal, but not the necessary products for constructing the biofilm (signal-blind).  They then examined how well these mutants did alongside regular bacteria, in a stressful environment that facilitates the creation of biofilms. They started a culture with a small percentage os signal-negative and signal lind mutants (1-3% of the total population).  Both types of cheating bacteria proliferated rather well, rising up to 45% and 66% of the populations respectively. But once cheats grew more common, their ability to proliferate of their fitness declines. Diggle and his colleagues attributed that to the decline in the number of cooperators that cannot support the cheats.

Click Here To Learn About Bacteria, Freeloading, & Cooperation.

About Miguel Barbosa

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31. August 2009 by Miguel Barbosa
Categories: Complex Systems, Curated Readings | Leave a comment

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