"I Can't Live Without You!" -- Mutualistic Relationships

Mutualism is a form of symbiosis in which two organisms of different species interact and depend on each other in a way that benefits both organisms.  When speaking of mutualism, some of the most common examples used include the clown fish and seas anemone (a relationship where the clownfish lives among the sea anemones poisonous tentacles and thus is safe from predation by other species of fish – and research shows that anemones as well benefit from hosting clownfish.  For a very thorough analysis of this relationship, check out http://clownfishandseaanemones.blogspot.com/).  Another very common example is the relationship between the oxpecker bird and large mammals such as rhinoceros, elephants, zebra, and cattle.  The oxpecker flies behind the moving herds and is rewarded with insects that the herds stir up, and when the herds are at rest, the oxpecker takes the liberty of landing on individuals and picking insects off the bodies of the large animals.  In return, the oxpeckers benefit their mammalian hosts by both sounding alarms when predators, such as lions or cheetahs, are sighted, and by removing nuisance parasites, such as ticks, from their hosts’ coats.  But here’s a very important mutualistic relationship that you probably don’t know about: that between the root nodules of legumes (such as soybeans, peanuts, and alfalfa) and a certain type of bacteria: Rhizobia.  This relationship is extremely important to supporting and maintaining soil nutrient integrity and ultimately, life on earth. 

Legumes have a fibrous root structure, and their roots contain little “nodules.”  These nodules are home to a host of bacteria from the Genus Rhizobia.  These tiny organisms complete a very important task: nitrogen fixation.  Nitrogen, one of the ten elements essential for life, exists as a diatomic gas molecule under standard conditions, but is unusable for plants in its natural inorganic state.  That’s where Rhizobia comes into play.  The bacteria turn the root nodules of their legume hosts into nitrogen-fixing workshop, where they fix nitrogen into ammonia and other usable nitrates.  The plant is then able to use the products of the nitrogen-fixation chemical reactions to form amino acids, nucleic acids, and other products necessary for life.  Their nitrogen-fixation also provides considerable nutrient-return to the soil, ensuring that the soil will remain nutrient-rich enough to support plant life.  As for the bacteria, their benefit is in the form of a hospitable environment in which to live and propagate, and some of the plant’s sugars as an energy source.  Think about that next time you eat a bowl of black bean soup!  For a more detailed analysis of this relationship, check out http://www.jic.ac.uk/science/molmicro/Rhizo.html. 

So, it’s your turn: what’s an example of a cool mutualistic relationship in nature that you find interesting?  Why is that relationship significant?  How would it affect that community or ecosystem if one partner in the relationship were eliminated?