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“But wait!” you might be saying to yourself. “How can an organism be photosynthetic and so afraid of oxygen? Doesn’t photosynthesis create oxygen?” And yes, you would be correct—most of the time...

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Sometimes James, our master of microscopes,   likes to go through his samples with the lowest  magnification objective, looking at the organisms   as they’re floating in a Petri dish so that he  can see everything from a distance and get a sense   for what mysteries await him when he zooms in. And during one of his recent Petri dish scans,   he found this stunning ciliate, autofluorescing  a whole crayon box’s worth of colors under our   combination of UV, blue, green, and red light.

And when you switch to white light,   the ciliate is still quite colorful. Maybe not  the same fluorescent rainbow it was before, but   full of varied shades of purple like  a blueberry bush ripening in summer.  But the ciliate didn’t seem to be  doing so well in the Petri dish.   So for James to be able to take this video with  the clarity and focus it needs, he first had to   move the ciliate to a slide—a procedure that  is quite normal and safe for most microbes.  But for our already dying ciliate, it proved  to be too much. As soon as it hit the slide,   it burst open.

And all of those little  blueberries came pouring slowly out as well.  The ciliate died too fast for us to be  able to identify it. There was just too   much damage, erasing all clues to its identity. But the ciliate wasn’t the only organism in the   video.

Those round bits of purple were once alive  as well. And what remains of their color provides   more than enough information to identify them. These are purple sulfur bacteria.

And ciliates   are not the only danger they face. No, its biggest  foe is something even more pedestrian than that.  You see, something you need to know  about the purple sulfur bacteria   is that it’s a bit of a contrarian,  specifically when it comes to photosynthesis.  Now, what do you think of when you  hear the word “photosynthesis?”   You might think of trees and plants and  leaves. Or since you’re here with us right   now on this journey, maybe you’re thinking  of algae and cyanobacteria and euglena.  What most of us are probably imagining could boil  down to the color green.

Lots and lots of green.   And for good reason. Chlorophyll, the pigment that  absorbs light and kicks off the reactions that   drive photosynthesis, is green. And that green  has come to dominate the world that we live in.  But there’s another world too,  inhabited by purple sulfur bacteria.   And these purple sulfur bacteria can also do  photosynthesis.

They have bacteriochlorophyll.   But they also contain carotenoids, pigments that  create colors ranging from red to purple, and that   help the bacteria harvest light and get protection  from the bacteria’s primary foe: oxygen.  “But wait!” you might be saying to yourself. “How  can an organism be photosynthetic and so afraid of   oxygen? Doesn’t photosynthesis create oxygen?” And yes, you would be correct—most of the time.   The most common form of photosynthesis in our  world is oxygenic photosynthesis. It makes oxygen.   This is what happens in all those plants  and cyanobacteria, where energy from light   sets off a chain reaction involving water and  carbon dioxide.

The end result is a sugar for   the organism and oxygen for the atmosphere. That  is the world we live in, a world where oxygen is a   necessity and readily supplied by photosynthesis. But purple sulfur bacteria, contrarian that it is,   prefers the worlds in this world that do  not have oxygen.

Our samples, for example,   came from the sediments at the bottom of ponds  and puddles, places where oxygen does not arrive,   consumed as it has been by the organisms above. Down at the bottom of their ponds,   the purple sulfur bacteria do their own form of  photosynthesis called anoxygenic photosynthesis.   And they’re not the only organisms to prefer  this oxygen-less approach to making their own   food—confusingly enough, there are also green  sulfur bacteria and purple non-sulfur bacteria,   both of which also do anoxygenic photosynthesis  though sometimes with their own twists.  For the purple sulfur bacteria, the key ingredient  is, well it’s sulfur. You may not think of sulfur   as an essential element to life, but that’s  because we have bodies borne out of a world   full of oxygen.

But in the stratified world of  the purple sulfur bacteria, the void left by   a lack of oxygen instead is filled by sulfur. So where a normal photosynthetic organism would   consume water to drive their photosynthesis, they  consume sulfurous chemicals like hydrogen sulfide,   which you might recognize from its rotten  egg smell. And when they’re done making   their own food, the byproduct of their  endeavors is not oxygen, it is sulfur.  And because they live in an environment that is  constantly changing, purple sulfur bacteria are   able to store up sulfurous molecules for whatever  the microbial equivalent of a rainy day is.  All of this sulfur-based photosynthesis makes  purple sulfur bacteria something better than   just contrarian: they are a good neighbor, helping  to consume hydrogen sulfide that might be toxic   and clearing out the waters for  their upstairs neighbors that   require a more oxygenated environment to survive.

Though that role, that place as a good neighbor,   is based on the ecological neighborhoods we have  today, where lawns of oxygen give way to lawns   of sulfur. That neighborhood has gone through  some changes though, and there was a time before   oxygen’s dominance, where purple sulfur bacteria  were less of a contrarian than they are now.  In 2005, researchers uncovered photosynthetic  pigments, fossilized and preserved in rocks   that are more than a billion years old, lying in a  large basin in Australia. These fossils suggested   that purple sulfur bacteria may have  existed in ancient oceans during a period   when oxygen was still rising in the world  but had not come to take over the oceans.  The fossils suggest an ancient world that would  be unrecognizable to us.

In fact, we probably   wouldn’t be able to survive there. But as the  world has shifted, the purple sulfur bacteria   found a way to shift with it, to make space  for themselves even as new neighbors move in.  But of course, those other organisms don’t  seem to be looking to thank the purple sulfur   bacteria any time soon. I mean, who needs a  neighbor when you can have a meal instead?  Thank you for coming on this journey with us as  we explore the unseen world that surrounds us.  We’d like you to know that we’re going to be  taking a short break from uploading for the next   couple of weeks, but we will be back soon with  brand new videos.

If you’d like to keep up with   exactly when we’ll be back with a new episode,  make sure to follow us on twitter @journeytomicro.  And before we go, we need to thank  Blinkist for sponsoring today’s episode. Now after watching this video,  we would hope that you would   feel pretty comfortable saying that you  know what Purple Sulfur Bacteria are,   but let me ask you a question. Do  you know what a lexicographer is?

Well, I could not hear your answer, but I’m going  to go ahead and assume that some of you said no. A lexicographer is a person  who writes dictionaries. It’s a very cool and interesting job that  involves way more time and research than   you might initially think, and in the  book Word by Word, author Kory Stamper   explains how there is no right or wrong when  it comes to grammar usage and reveals the three   criteria that a word must meet in order to be  considered for the dictionary.

You can find   out more about this fascinating profession  by checking out Word by Word on Blinkist. Blinkist is an app that takes the best insights  and need-to-know information from over 3,000   nonfiction books and condenses them down into  just 15 minutes that you can read or listen to. It can be hard to find the time to sit down  and learn more, but with Blinkist you can   explore their massive library of books in catalogs  like self-help, business, science, and history.

And if you’re one of the first 100 people to  sign up today at,   you can get free unlimited access for 7 days  and you’ll also get 25% off if you decide to   get a full membership. Click the link in the  description to start your free 7-day trial.  And now, you are seeing some names on your screen.  These are our Patreon patrons. These are the   people who make it possible for us to continue  diving into this bizarre and lovely world,   finding new, intriguing stories to tell you  about all of the different ways that life   works and has worked on our planet.

So if you  want to thank anybody for this lovely episode,   these are the people to thank. And I also want to  thank them personally, y’all are great. Thank you   for being a part of what we do!

If you want to see more from our   Master of Microscopes James Weiss,  check out Jam & Germs on Instagram.  And if you want to see more from us, there’s  always a subscribe button somewhere nearby.