Wednesday, May 30, 2012

My Favorite Symbioses

I recently finished a course called “Communicating in a Complex World” that was all about symbiotic relationships in nature.  This was an elective I picked because I wanted something out of my area of expertise (neuroscience), and because it just seemed like a cool topic.  Perhaps this is the Bay Area hippie side of me talking, but something about the idea of different living things coexisting in harmony, and actually working together to be better than they could be alone, is really beautiful.

 The course covered a lot of diverse topics, but I just wanted to share my three favorites with you.  First, though, a bit of terminology.  “Symbiosis” simply means living together, not necessarily good or bad.  What we usually refer to as symbiosis is specifically mutualism.  This is where both parties benefit.  If one benefits and the other is unaffected, it’s commensalism.  And parasitism, as we all know, is one benefiting at the expense of the other.  Those symbioses are no fun and they don’t make my list. 

1. Glowing squid

The bobtail squid hosts bioluminescent bacteria
[image from]

The Hawaiian bobtail squid has a very clever form of camouflage.  A nocturnal creature, it hides in the sand during the day then emerges to feed at night.  Predators watching from deeper waters look upward, searching for the dark squid silhouetted against the moonlit night sky.  To remain unseen, the bottom side of the squid lights up with a glow that mimics the light from above.  It’s the perfect adaptation.

However, unlike many other bioluminescent forms of sealife, the bobtail squid can’t produce

light on its own.  Instead, it collects a very specific bacteria, V. fischeri, inside its body. The squid feeds the bacteria, and in return they produce the luminescence that keeps the squid safe.  Classic mutualism.  And complex too.  The exclusion of all bacteria that AREN’T V. fischeri is a fascinating process.  Even more impressive is the fact that this has to be repeated every day -- the squid ejects all the bacteria at dawn, and when night falls the process starts all over again.  

2. Three-way relationship

Representing pea aphids as well as
the beauty of mutualism
[image from]
Symbiosis isn’t always limited to two parties.  A great example comes from the world of aphids.  Parasitic wasps lay their eggs inside the body of the pea aphid, and eventually the larvae eat their way out.  A gruesome end for the aphid... unless it has help.  To the rescue is a dynamic duo of bacteria and virus.  The bacteria H. defensa can carry a virus known as APSE that attacks the wasp eggs and protects the aphid from being parasitized.  In contrast, H. defensa without APSE  is totally ineffective.  All three players -- aphid, bacteria, and virus -- are needed for this symbiosis to happen.  

This is actually a four-way relationship if you count the parasitism of the wasp.  But as I said before, parasitism isn’t making my list of favorites.

3. Human Guts

Probiotics aim to restore healthy gut flora
The human gut is home to an astounding population of bacteria.  These diverse microorganisms actually have us outnumbered -- we each carry about ten times as many microbes as the number of cells that make up the human body.  

Our understanding of the microbiota in our guts is pretty limited at this point.  But it’s becoming increasingly clear that intestinal flora plays a very important part in keeping our bodies healthy.  In fact, its role can be so significant that some scientists have deemed humans to be “superorganisms” composed of both human and bacterial cells.  That’s a bit of a stretch, but it’s undeniable we wouldn’t be the same without these symbiotic partners.  They boast an impressive range of abilities, from assisting in the digestion of foods that our own cells can’t process, to modulating our immune systems, and potentially altering our moods and behavior. 

Fecal transplants transfer healthy flora to disease patients
[image from wikipedia]
The health benefits of intestinal flora are the basis for the growing market of probiotics.  Drinking a probiotic smoothie is easy and delicious.  However, there are also methods that are a bit more... drastic.  And that brings me to my last topic, which I’m not counting as a “favorite” but which was certainly the most shocking:  Fecal Transplants.  It’s pretty much what you think it is.  Take the feces of a healthy volunteer and insert it (by enema) into the colon of a person suffering from a disease like irritable bowel syndrome or collitis.  The “ick” factor is high.  But for patients with miserable chronic diseases, the hope of relief that healthy microbiota delivers can make it all worthwhile. 

[On a side note, this was the last and final class of my 23-year career as a student.  So I was very excited about it for that reason too.  Three months till PhD!]   

1 comment:

  1. Great post babe! Love ya, and congrats on finishing your last class!