Survival of the Friendliest

By Dick Bourgeois-Doyle

If you feel that your life, our world, and the universe may not be evolving the way they should, you might consider the perspective of a microorganism living in the root nodule of a bean plant.

I am thinking here specifically of the type of bacteria known as rhizobia. It may be small, but it can play an important role by fixing atmospheric nitrogen, essentially converting it into ammonia which in turn fertilizes the legume.

Rhizobia would seem like a helpful servant for a bean plant and a useful thing to have working away in its vicinity. But rhizobia are, in the non-root natural state, kind of useless to the plant. They're what some might disparage as miserable "non-sporulating little rods" incapable of working over the nitrogen or doing much else. As it turns out, the rhizobia need help too. They can't express the gene for nitrogen fixation and do their thing until they get imbedded into the plant host's root nodules. At this point, the miserable little rhizobia lock on to their own personal supply of sugar, turn on their super fixing powers, and go to work. Both partners depend on the other.

This may be enough information for most people on the subject of rhizobia.

But you and I and the rest of humanity have a greater stake and interest in that hard-wired, symbiotic relationship between the bacteria and the bean. The friendly interplay between the two organisms can tell us a lot about ecology and evolutionary biology and how species adapt and thrive. It also makes me look at the world with just a bit more hope.

For many years, biologists and plant scientists have been using legume-rhizobium symbiosis as a model for agricultural research. But increasingly, the bean-bacteria collaboration has been studied to illuminate fundamental understandings around evolution and why the world is the way it is.

As it turns out, many organisms cooperate with other species for nutrition, protection, or dispersal. The pervasiveness of this cross-species cooperation, called mutualism, has raised a number of research-worthy questions.

First, if you're the cynical kind, you might ask why doesn't one of the partners, like the bacteria, just take what it needs from the other organism and bug off without providing any reciprocal benefit.

This behavior has been labelled "cheating" by biologists, and as it turns out, cheaters don't seem to do that well in evolutionary time.

You might assume that this is because beans like human beings shy away from cheating partners and align with those who are more reliable, obliging, and consistent. This fits well with the refined concept of evolution, not as a simple dog-eat-dog survival of the fittest specific species, but rather as the story of ecosystems surviving as a function of intertwined, mutually beneficial collaborations that carry the individuals species along with the whole into surviving generations.

Still, recent research using the legume and rhizobia model has found that successful mutualist species don't actually evolve to seek out and adhere to particular, best partners within the ecosystem but rather are able to adapt and thrive within diversity. It appears that the prejudiced, choosier mutualists cannot always compete with less discriminating mutualists, and that it's better to get along with organisms of varying strengths and characteristics, possibly because environmental variations do not give us any guarantees as to the quality and availability of perfect collaborating partners.

So, while it is true, as the experts say, that "without symbiosis, the nature of life on Earth would be unrecognizable from that which is found today," symbiotic relationships can form in many ways and in many directions if an organism is prepared to make varied connections.

You've probably guessed by now why I find hope in a scientific view of our world and its ongoing evolution that is based on cooperation, embracing diversity, and serving others.

But I also have a more personal reason for seeing great things in bean roots and bacteria and taking an interest in it. This is the field my daughter pursued on her way to a Ph.D. at the University of Toronto Department of Ecology and Evolutionary Biology.

Years ago when she moved to downtown Toronto from the friendly and supportive environment of Memorial University, I wondered how she would adapt. But as she presented her work and thanked a long list of mentors and colleagues this month, it was clear that she had not only learned a lot about her field and developed as a teacher and presenter, but she had also made a lot of friends. The capacity to do this will be important again as she moves to the U.S. to take up a post-doc position.

So, I think of this kind of mutualism too when I read her stuff about rhizobia-legume symbiosis and look to the future with hope.

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