What do scientists who identify first as symbiontologists study? OK, maybe I invented that term, but something brings hundreds of people to meetings where the only thing they have in common is that they study symbiosis. What do sponges, grasses, flies, and amoebae have in common? They all have important, even critical relationships with microbes, whether bacteria, archaea, or fungi. Strangely, the people studying between species mutualisms like pollination seem to go to different meetings. I don’t get the conceptual divide, except that when symbionts are microbes they are smaller and newer, so harder to study.
What are the big questions in this field, if it is a field at all? This is what I’m trying to figure out this summer, from the Gordon Research Conference on Animal Microbe Symbioses in Waterville New Hampshire, and now at the excellent International Symbiosis Society in Lisbon, Portugal.
From my own background as an evolutionary biologist particularly interested in social evolution, I would have thought that people would identify a symbiosis, then ask how they are transmitted, vertically or horizontally, what does the host gain, what does the symbiont gain, how do they try to cheat, getting more out of the interaction than the other wants them to, how the cheating is controlled, and finally how genes and genomes impacting the symbiosis evolve, expecting rapid evolution from the conflict.
It turns out that few people are taking this approach. Instead, a lot of work is much more at the discovery stage. Imagine that every animal, every plant, perhaps even every eukaryote has microbial symbionts. These might be single partners, nestled into cozy crypts made just for them, or they could be thousands of microbial inhabitants of largely unspecialized cavities. So every organism has its cooperators and the first job of researchers is to discover what is what.
I have to digress a bit. How did we miss this for so long? How did we not understand that any physiology, any biochemistry, any evolution occurs only in a sea of microbes and nothing normal, not development, not social behavior, not cell biology, is likely to occur without them? People that study symbiosis certainly haven’t been quiet about it, as this wonderful manifesto shows.
If we want to learn about symbiosis, then, we have to begin at the beginning. Grab your favorite organism. Consider your favorite topic. Ask how microbes might impact it, assuming you grabbed the larger organism first. If you grabbed a microbe, consider what it is exploiting.
Organisms don’t live in vacuums, so you might first need to figure out what is associated and what is not. Soil, water, even air can have their microbes. You may swab, sterilize, culture, or sequence. How does either do without the other? Not even possible sometimes. It is the essential first step to any study of symbioses, so we hear about sponges, flies, fungi, scorpions, bird eggs, ticks, and honeybees and that is only part of this afternoon’s talks. It will take a lot of culturing, sequencing, and exploring.
Once you know what is there, you might ask what they do for each other in terms of physiology, small molecules, protection, or development. Or you might try to figure out the permanence of the relationship and how they get passed on. Is it all about a pair of organisms, or can something else do? This is more discovery science, with the best choices pointing towards what is feasible in a given system. It seems like it is too early to do much about looking across systems for commonalities. We can fill out very little of the grid of who associates with whom at this point. One of my favorites, for example, Burkholderia, seems to be everywhere.
There are, of course, systems where a great deal is known like the squid vibrio system. People are forging ahead sequencing genomes, or knocking out candidate genes in a variety of systems. But these are in the minority. For now it seems exciting and important to simply try to figure out what is out there, where they live, and how they maintain the association. In many respects for most organisms we are still in the age of Paul Buchner. If only we could draw as well as he could.