Wednesday, April 18, 2012

Bacterial Card Games

Outsourcing as an economic strategy usually reduces costs for a company, making it a strategic business move.  Certain species of bacteria may be next in line for open CEO positions at Fortune 500 companies due to their mastering of this outsourcing technique.  The resume of these organisms was summarized in a March 2012 publication in mBio.

The authors of the recent paper describe this outsourcing technique through a card game analogy, specifically Hearts.  Due to the rules of the game, the black Queen of Spades is usually a card that Hearts players wish to avoid holding.  The authors describe a situation in which performing a particular function is something bacteria wish to avoid.  Species that continue to perform this function are called helpers and species who profit from the help are called beneficiaries.

The Black Queen Hypothesis relies on a few key principles:
1.  The function in question is "leaky," meaning the results of performing this function can overflow into the public domain of the environment.
The ability to prepare delicious meals as a professional chef would not only allow the chef to eat scrumptiously, but those delicacies could also be enjoyed by other individuals who live within free-delivery distance of the chef.

2.  Being a beneficiary presents an advantage
Employing a professional chef would present an advantage over needing to personally cook every meal, because the chef would be responsible for grocery shopping, food preparation, and clean-up.  All that free time created by avoiding such duties could be used to learn a second language or train for a marathon.

3.  The advantage of being a beneficiary disappears if the helpers become too few in number
If professional chefs disappear, due to alien abduction or a similar tragedy, being incapable of personally preparing food would become extremely detrimental to survival.  Thus, being a (former) professional chef employer would suddenly lose its selective advantage.

The card playing researchers developed their Black Queen Hypothesis to explain why some species of marine bacteria have lost the genes responsible for performing functions crucial for survival, such as neutralizing hydrogen peroxide, which is common in the ocean and toxic to bacteria.  When a bacterium does neutralize hydrogen peroxide, the purified water leaks out of the individual bacterium and out into the environment.  If enough bacteria are doing this neutralization process, all the water in the surrounding area will become purified.

Since many species of bacteria live in close proximity to each other in the ocean, it is possible that one species could continue purifying the water (the helper) and its neighbors could stop purifying without experiencing any detrimental effects (the beneficiaries).  If performing this water purification process requires a large energy input by the bacterium, then losing the ability to neutralize hydrogen peroxide would present an advantage.  That saved energy could then be used to increase growth or reproduction.

How some bacteria benefit by losing the ability to neutralize hydrogen peroxide would be similar to how some individuals could benefit from forgetting how to cook so long as their neighbors are professional chefs.  It is important to note that the helpers are not acting in an intentionally altruistic manner; they simply were too slow to get rid of the Queen of Spades gene.  Its not that the professional chefs wanted to feed everyone else in town, they were just too busy in the kitchen to notice that everyone else had turned their own pots in pans into over-sized wind chimes.

Absence of altruism does not detract from the position as neighbor of the year, though.  Retaining the critical function, whether it be neutralizing hydrogen peroxide in marine species or processing nitrogen in terrestrial species, may make the helper a "keystone species."  If the keystone species became too few in number (maybe due to climate change or alien abduction), all the beneficiaries who depend on the keystone helper could go extinct.  Therefore, card game inspired research into how species rely on one another is relevant in both evolutionary and conservation contexts.

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