Until fairly recently, I used to think of bacteria as really living as individual cells, because that's how I'd always use them in the lab. The reality is that we've known about biofilms for a long time, because we know that they existed on Earth three and a half billion years ago, because we can find those stromatolites that are that old, those fossilized stromatolites. And you recall from our discussion of evolution and the evidence for evolution that these cyanobacteria grow in these layers and they trap...
minerals between the layers and those are fossilized and we can use carbon dating to identify how old they are. So we know biofilms have been around for a long time. But what we haven't thought about so much until recently is how important biofilms are in human disease, particularly chronic infections.
We understand more now that oftentimes biofilms are involved in those. And when bacteria live in groups they also communicate with each other and so they have a technique that we call quorum sensing, it was coined by Bonnie Baxler, where they can turn on group behaviors, which can include, in the case of her example, in the bobtail squid, it can turn on the production of light. But it can also, in the case of pathogens, turn on things like virulence and cause them to go from being fairly benign to suddenly as a group causing an illness.
So quorum sensing is this chemical language that allows the bacteria to communicate and then turn on group behaviors. Just a quick review of how quorum sensing works. So you have a bacteria, and it's producing this little molecule that it secretes outside of the cell.
If there's only one bacteria, there's just going to be a few of these molecules because it's just one bacteria. It can't make that many, right? But if the bacteria divides and divides and divides and divides, eventually you have so many bacteria that they're all making this molecule. And then this molecule, in the case of Bonnie Baffler's example and in this diagram, they...
all result in the bacteria turning on this light formation characteristic. And so you can see the cells are glowing now because there's so much of this autoinducer molecule. It's turning on this group expression of this gene resulting in the light in the bobtail squid. Now, in terms of quorum sensing in biofilms, there are lots of different things that we know that bacteria use quorum sensing. quorum sensing to facilitate.
So the idea that bacteria live cooperatively, the symbiosis in their communities. I mentioned that they can turn on virulence factors that cause disease, maybe an enzyme that helps digest tissue and help them get into a wound to cause an infection. Whether or not they can take up foreign DNA, that's what competence is.
And conjugation is a method by which bacteria can actually, that's, we're talking about the sex pellets there, that's the method by which they transfer plasmid from one cell to another. Some bacteria make antibiotics that they use to kill other bacteria. We like to think we invented chemical warfare, but actually it was the bacteria who did it first, turning on motility, moving in a group.
Spore formation, we were just talking about endosperms, that's a group behavior that can be triggered by quorum sensing, as well as simply the formation of biofilms where the bacteria themselves all begin to live in these groups. Alright, so let's talk a little bit more about biofilms then. So it's a group of microorganisms that are stuck together. Recall we talked about the glycocalyx earlier, and we said it can form slime layers, right, or it can form capsules.
So in the case of biofilms, it's this loose slime layer that a bunch of bacteria end up embedded in and then begin living in a group. And biofilms live on all sorts of surfaces. So they can be on your shower curtain. In fact, the pink... If you ever have that, it looks like pink mold that's on your shower curtain, that's actually Ceratia marcescens in a biofilm that we've used in the lab.
So that may make you want to go home and clean your bathroom, but they're not hurting anybody. They can be, so that's a non-living surface. They can be living surfaces. Plaque on your teeth is biofilm. And that's actually not just one bacteria, but it's several different species that are there.
A catheter that's in somebody's urinary tract. that can end up with a biofilm of bacteria growing on it causing a chronic infection. Hot springs outflow, if you've ever been to a hot springs and it kind of has that that stinky smell, oftentimes that's from bacterial biofilms that are living in that environment. So surfaces that can be, many places can be colonized with bacteria in biofilms. Biofilms form in sort of a process so we have, these are called planktonic bacteria, you can see they've got flagella and they have these fimbriae that allow them to attach to the surface.
When they begin to form the biofilm they lose that motility and they end up staying put in the group and you can see the bacteria dividing into groups and the this this layer here is just referring to this extra polymeric substance that they're embedded in and what they end up doing is forming these towers so you see that it's they don't form a solid block of bacteria because they need to have currents you need to be able to flow through just like blood needs to flow through all your capillaries to deliver nutrients and take away waste the bacteria need currents of water to flow through these towers so that they can take away waste and bring nutrients to these colonies of bacteria. Eventually the biofilm, well chunks of it can break off and form additional biofilm. You can have some of the bacteria can revert back to the the modal planktonic bacteria and they can swim away to form new biofilms attached to another surface. These are some amazing scanning electron micrographs of, in this case, a staph epidermidis.
So you see the round cocci with the extra polymeric substance, the EPS layer here in purple. This is really cool. The green here is Pseudomonas aeruginosa. This is a biofilm living on a silicone implant in a body.
And then so you can see the EPS layer, I believe is in the gray here. And then these big orange things are actually neutrophils, which are part of the person's immune system trying to digest the Pseudomonas aeruginosa and kill it. So you've got a whole big bunch of things going on here in terms of this biofilm with this pathogen on a surface and then the immune cells trying to protect the individual from the destructiveness of Pseudomonas.
This is just another picture illustrating the same thing. I just want to really make sure you see the idea here. These water currents are flowing through and around these stacks of these towers of bacteria. And that's just so important because if this was all just one solid clump, eventually the bacteria in the center would die because they wouldn't be able to get nutrients or get rid of their waste products. And so this idea that biofilms have a current that flows through them and that they don't end up forming tubes.
massive of a structure. They need to keep their surface area high and their volume fairly low. Here's a clump of biofilm moving to colonize another part of the environment that it's in.
And then this picture is really designed to illustrate a couple of things. One is that biofilms often contain multiple species. So you've got your red species and your green and your blue and that they're all communicating with each other. So just like the was indicated in the talk that Bonnie Bassler gave, bacteria can communicate with each other in the same species, but they're also capable of communicating with bacteria that are from other species. And you often find multiple species of bacteria in a community that forms a biofilm.
So why are we talking about biofilms? Well, it turns out that biofilms are actually a really big problem in clinical settings. Because they are embedded in this extra-polymeric substance, it turns out that sometimes you need 200 times more antibiotics to kill a microbe in a biofilm than a microbe that's not in a biofilm. So they're more resistant to antibiotics and more resistant to sanitizing solutions.
70% of nosocomial infections, those are those healthcare-associated infections, 70% of those are actually the result of biofilms. We tend to see them on patients that are chronically ill. So there's acute infections that people get sick and then they get better from the infection. Biofilms tend to be associated with long-term chronic infections. If you wear contact lenses, you may notice that you have to clean them or throw them away regularly and that solution is designed to clean the protein off the surface and that you're really getting rid of a biofilm and getting rid of the bacteria living in a group.
Eventually you have to throw those lenses away. Dental caries, the cavities that you get in your mouth, That's an infectious disease. You think about getting a cavity, you don't think about it being caused by bacteria, but actually it is. It's an infectious disease and it's caused by biofilms forming on the teeth. And that's why flossing and brushing your teeth is very protective because you're constantly removing that biofilm.
Now I'm talking about all these terrible things that biofilms do, but you should know that biofilms are actually really an important part of sewage treatment process. They have used biofilms to try to do remediation of oil spills by adding bacteria that can digest the oil to remove it from the surface of water. So it's like so many different scientific processes in the world.
It's not good or bad. It depends on how it's being used. And so we can associate biofilms with health and causing illness, but we can also... use biofilms and industrial processes to hopefully make the world a better and safer place as well.
This is brand new. This is also this is a quote from Bonnie Batchelor here, but I just saw this was I think in in 2019 in June they have begun to find that viruses also use mechanisms of form sensing and these are the viruses that infect bacteria. So now this makes a lot of sense when you think about it.
You know, viruses are so simple, it's hard to believe they could do anything this complex. But if you're a phage that infects bacteria, and there are no other bacteria around, then it doesn't make sense to kill that bacteria because you won't have anywhere to go. So the idea with quorum sensing in viruses is that they're actually tracking using quorum sensing molecules.
There's eavesdropping on the bacteria's quorum sensing molecules. And when they notice that there's enough... bacteria around, that's when they'll undergo a lytic cycle, infect the bacteria, you know, cause themselves to divide the large numbers and cause the bacterial cells to explode because now they know there's lots of other bacteria in the environment that they can infect.
So it's a super exciting discovery that viruses can actually use bacterial quorum sensing to make a decision whether they're going to wait or whether they're going to actually kill the bacteria and then move on to new hosts. So really incredible, cool science. And I will leave a link to this in the video if you're interested in reading more about it. That is my last slide in this lecture set.
So we will next time be talking a little bit more about enzymes and metabolism. We're going to start getting into the nitty gritty of the biochemistry of the breakdown of sugar and how cells get energy.