Mutual Microbes

Mat Goddard, senior lecturer at the School of Biological Sciences at Auckland University, has just discovered evidence of mutualism in microbes. He starts by explaining just what mutualism is...

Mat -   Most organisms interact with other organisms in some way.  Sometimes that's not very good.  Parasites for example interact with other organisms to the detriment of the other.  Sometimes however, both organisms benefit from that interaction.  Both gain and that is simply a mutualism.  So, think about insects pollinating plants, the insect gains, it might get nectar, and the plant gains because it gets pollinated - mutualism.

Chris -   That sounds pretty straightforward.  What are you actually trying to find out then?

Mat -   Well, whilst we've known about mutualisms for a long time, the way that they might become established in the first place is unknown.  There's not general rule to help us understand how two organisms might come together for the benefit of each other.

Chris -   So, like yeast and human - beer, we drink it.

Mat -   Yeah, that's a special kind of mutualism.

Chris -   It's very special in my case, yeah.  Some very special mutualism going on in the pub last night between me and Simon.  And so, what you're saying is, that there's got to be a special sort of evolutionary niche there where there's a gap made and something can fall into it to help something else and one scratches the other's back.

Mat -   Yes, hard to imagine how that would become immediately established, how both partners can immediately benefit.  It's hard to imagine how those things can suddenly come to be.

Chris -   But why because I would think that there's lots of opportunities in nature for many rolls of the dice and it's just chance that this thing happens to have something the other thing wants and vice versa, and they get together?

Mat -   Yes, that's right.  But at the moment, we have no general rule to describe that.  the only general rule that we have is that both partners must leave more descendants by interacting with one another.  But there's no general rule to understand how that would become established in the first place.

Chris - Isn't the first sort of really fancy example of this, that if we go right back to the sort of the history of the beginning of life on Earth, where you see the cells we're all made of coming into being in the sense that you get bacterial type organisms snuggling up with more advanced cells like ours, the two then establish a relationship and we still this sort of bacterial cells living in every single one of our cells now in the form of these things we call mitochondria.

Mat -   Indeed and that's a stunning mutualism.  You could take any other of the myriad of mutualisms in the biological world, and individually, you could explain how that came to be.  But the question is, is there a general rule that allows you to explain how mutualisms comes to be.

Chris -   So, do you think there is a rule?

Mat -   We set about trying to test one of these rules.  And so, there's another central theme in evolution and ecology which is called niche constructional ecosystem engineering and this simply says that organisms, by their own actions modify their environment to some extent, from simply consuming food and making waste to more elaborate ideas like beavers constructing dams.  And so, this suggests that maybe an organism has a hand on its own evolutionary trajectory because if an organism is modifying its own environment and it's modifying the environment to which it's exposed to and thus, its selection pressures.

Simon -   Wow!  So, the scenario there is, I've got a cat.  I put a cat flap in at home.  Now for me, that's a modification of my environment.  I get a bit of a draft and the cat flap, it's a bit of a hassle.  But the cat can come and go.  They can have a crack at the local mice.  I'm living in a rodent-free environment.  When the plague comes, I'm going to survive.

Mat -   I take your point, yes.

Simon -   I modified a niche though.

Chris -   Also, is it not fair enough to say there's another kind of mutualism going on between cat and your kid's sandpit?

Simon -   True and that modification is something that I really don't enjoy especially when you scrape it off.  But your discovery is specifically looking at microbes.  That's been the niche modification.

Mat -   So, we put together both of these ideas.  This idea of the evolutionary mutualisms and this ecosystem engineering and asked the question whether this ability of organisms to modify their environment, whether that could be a general instigator for the evolution of mutualisms.  So, another thing that yeast kick out and there's a bunch of volatile compounds.  So, these are the things that make beer on wine taste and smell nice to us.  But clearly, yeast didn't make these compounds for us.  There must be a biological reason that yeast kick out these volatiles and that was unknown.  So, one idea is that they in fact kick out these volatiles as chemical lures for insects.  Imagine a funny little microbe sitting on a bunch of grapes, it can't move.  When that bunch of grapes is eaten or fall to the ground in rots, that microbe dies with it.  So, the only way this microbe is going to persist in evolutionary and ecological time is, if it escapes.  How is it going to escape if it can't move?  Well, maybe attract something to move it for it.  Maybe attracts a vector.  Maybe it lures in something that it can get stuck to and then gets moved through the environment.  So, the idea is that these volatiles that yeast kick out during fermentation are there to attract insects.  And so, we tested this directly in the lab.  we found that to be the case.  We found that fruit flies are differentially attracted to different types of yeast.  And that those yeast that are more attractive, in fact get dispersed more in the environment, both in the lab.  and then we went to the vineyard and did the same thing.