At the end of every episode of Journey To The Microscosmos, we thank you for coming on this journey with us as we explore the unseen world that surrounds us.

But have you ever found yourself wanting to have your own journey and explore the unseen world that surrounds you? Well you can start on your own journey with the Microcosmos Microscope!

We worked with our Master of Microscopes James Weiss to design what we believe is the perfect starter microscope for someone who wants to get into microscopy. In fact, the clip you’re seeing on screen right now was captured using our microscope. We’ll have a whole video coming out pretty soon where we talk more about our microscope and show you what it’s capable of, but for now, if you’d like to know more or pick one up for yourself, you can go to microcosmos.store If you have been venturing through the microcosmos for some time now, these oval green shapes likely seem familiar to you.

They are not particularly distinctive, but they are green and big enough to see under the microscope. And those two qualities describe a good chunk of what we find in the microcosmos. These particular little green organisms show up in the background of other organism’s lives, providing pops of color among other debris.

And if you’re trying to identify what this is, you might turn to some of the obvious candidates. Maybe a euglenoid, or some kind of algae. Something green and rod-shaped and single-celled, possibly eukaryotic.

And if that’s your guess, we would not blame you. But you are wrong. What you are looking at is not a single-celled organism, but rather a gathering of them.

Those green bits are consortia of bacteria. We’re going to explain more about what is actually in that consortia, but before that, we've got to tell you what a consortium is. First, not all consortia are green.

Some are more like the colorless squiggle you see in the middle of your screen, made up of thin, curved prokaryotes gathered around a central bacterium that has flagella at both ends. And “consortium” is kind of a funny word to describe bacteria, isn’t it? It makes them sound like a group of companies that have come together to sign some fancy legal document.

Which I suppose in a way they have. There isn't a legal document binding them together. There is simply survival.

That word “consortium” can mean a lot of things in the microbial world, in part because our understanding of what they are is currently evolving. But also, there are just a lot of different contexts in which they seem to appear. When the term was first introduced to the microcosmos realm in 1872 by naturalist Johannes Reinke, the idea was to describe how an organism can actually be made up of two species that have somehow found a unified body to live in-- organisms like lichen, made up of algae and fungi.

But the specific ways that organisms intertwine their lives can vary, and for our purposes today, the definition that probably best applies is that a consortium is a group of bacteria that are organized and are in permanent contact with one another. There are various types of consortia that scientists know about, including formations that live in your own mouth. These consortia can be distinguished from one another by their color, and their shape, the number of cells within them, and the shape of those cells.

And what makes them all special is that these are relationships formed entirely between prokaryotes. This sets consortia apart from other ventures into bacterial symbiosis that we have explored, which have generally involved bacteria seeking out more complex eukaryotic partners. For example, there are the bacteria that live on the surface of the ciliate kentrophoros so they can hitch a ride to regions with enough hydrogen sulfide for them to convert into food.

So this property of consortia only being relationships between prokaryotes makes this really fascinating to scientists for a few reasons. One is simply that bacteria probably teamed up with each other before they ever teamed up with eukaryotes, and understanding how they formed these relationships may help us better grasp how they have evolved with the world around them. Consortia offer more than just history though.

They also might suggest different futures for us, providing us with the means to understand how we can use bacteria for everything from farming to cleaning up oil spills. But identifying and understanding these consortia is challenging. James, our master of microscopes, has been baffled by what looks like a bunch of logs glued together.

He thought there might be flagellates in there along with the prokaryotes. But when he tried separating the individuals, he couldn't find any. So for now, like most of the consortia we’ve been looking at, the mechanics of this group remain unclear to us.

Perhaps the best studied consortium is Chlorochromatium aggregatum, the small green group we watched in the beginning of this episode. They are found in lakes and ponds, typically in areas with low amounts of oxygen and light. The green bacteria are Chlorobium chlorochromatii, a green sulfur bacteria that are photosynthetic, but that are surprisingly adept at living in low-light situations.

And yet, they do still need light, which would be fine, except that green sulfur bacteria have a problem: they cannot swim. There are ways around this problem, like the green sulfur bacteria that just go up in the water column by producing gas vacuoles. It’s like balloon travel in the microcosmos.

And much like actual balloon travel, it can take a few days for the bacteria to get where they want to go, so not always the optimal choice. But that is not a problem for Chlorobium chlorochromatii because they have found a different way to get around the microcosmos. A colorless, rod-shaped bacteria called Candidatus Symbiobacter mobilis.

Now we don’t have a good view of this organism because in most of our videos, it’s surrounded by the green sulfur bacteria that have latched onto it. But here you can get a glimpse of it in the middle of a group of green bacteria assembling a consortium around it. The job of that central bacterium is to move.

Surrounded by anywhere from 20-70 of its green sulfur bacteria companions, the bacterium in the middle of it all takes the group to light and to sulfide. And these consortium members might be in communication with each other to find the light. But why would Candidatus Symbiobacter mobilis agree to this relationship?

Well the most likely explanation is that they get nutrients from their companions. Now if that is truly the exchange being made, then it’s a trade that has had a huge impact on that central bacterium. When scientists studied the genomes of both Chlorobium chlorochromatii and Candidatus Symbiobacter mobilis, they found that the green sulfur bacteria didn’t seem to have to change much to make the symbiosis happen.

The few genes they’d acquired that were geared towards symbiosis helped make the cells adhere to each other or changed the cell wall a little bit. In contrast, Candidatus Symbiobacter mobilis seems to have lost a large number of its genes, so much so that it cannot grow independently. It needs the consortium to survive, and only when the consortium divides can it divide as well.

When you say it like that, “the consortium” sounds almost like a dystopian entity, one that’s trapped the Candidatus Symbiobacter mobilis into a life of shuttling green sulfur bacteria around with no mind to its own needs. But, like couldn’t that be said for any of our own cells, they don't get to live their own lives or divide at will. If they do, our immune system will kill them because uncontrolled cell division is very dangerous to the larger organism.

This consortium is, in a way, a wholly other kind of organism, one that you likely have never even heard of. At its heart is a species of prokaryote that cannot survive outside of it. The closer you look, the more you realize, life does not let us draw hard lines around anything.

It simply does what works. Thank you for coming on this journey with us as we explore the unseen world that surrounds us. And if you want to open your eyes to the bizarre world that is just outside your door and also in your own body, don’t forget to check out microcosmos.store.

We just want to bring more people into this amazing community. So check it out, and maybe you can pick up your own microscope, or, if you just want to show your love for microscopy and microscopic organisms, we have things like hydra shirts, and tardigrade mugs, and micro bumper stickers that you can pick up to let everyone around you know that you are a tardigrade enthusiast. The people on the screen right now, they are our Patreon patrons.

They're the people who let us and allow us and enable us to make this content. We are so grateful for them. I really love that we get to make this show and then I, along with you, get to keep learning more and more about the microcosmos.

So thank you so much to all those people. If you want to become one of them, you can go to Patreon.com/JourneytoMicro. If you want to see more from our Master of Microscopes, James Weiss.

Check out Jam and Germs on Instagram. And if you want to see more from us, there's always a subscribe button somewhere nearby.