So when conditions really get difficult for human survival, we're usually pretty much out of luck. However, bacteria have, not all bacteria, some gram-positive bacteria have a special ability to shut themselves down when things get tough and just wait, sometimes for, we think, millions of years until conditions improve again. And then they can, it's called germinating, they can turn back into an actively dividing, metabolizing cell.
So let's talk about this. This is called forming an endospore and this is the process. So here we have a normal bacterial cell in the lab.
We call them a vegetative cell and that simply means that they're dividing, they're metabolizing, they're healthy, they're doing well. But let's say that we have a vegetative cell. This is one of those special gram-positive cells that make spores and things get tough.
There's no more nutrients in the environment and it's going to die. Well, it can actually store its DNA until things get good again. And so what happens is the membrane begins to pinch off. We make a duplicate, the bacterial chromosome, and we end up with two, it's sort of a, it's a non-symmetrical division that's occurred. So you get this one end, we have this, this is called the four spore.
And you can see what happens here as we continue to add. go through this process. It actually ends up with another membrane layer begins to form around the four spore.
And the DNA actually degrades. The rest of the DNA degrades. And along with the membrane, we end up adding something called a cortex and then a protein coat on the outside.
And this is a very, very tough protein coat. Eventually, the rest of the cell degrades. and you end up with just the spore itself. And so this is the DNA that's being stored, the membrane, the spore coat, the cortex, all of these structures you hear.
And this particular structure is called a free spore. So it is what is able to survive for extended periods in really difficult conditions. Now it's really difficult to stain a spore. And the reason it's difficult to stain a spore is because of all these layers.
So if you just add crystal violet like we do in the lab when we're doing a gram stain, a lot of times these will actually, they look like a negative stain. They'll sort of be clear and the cell around it will be purple. But there are ways to stain spores.
And so we use a dye called malachite green. So that's what this green structure is here. You can see this is probably a bacillus subtilis or bacillus cereus. This is actually an endospore.
So the spore is still in the cell, but you can see it's green. And then you have some vegetative cells here that don't have any spores in them. So this is an endospore containing cell.
Sometimes in these pictures you see free spores as well. I don't actually see one in that photo. And this is just showing you what the structure of the spore is. We have the core where the DNA is.
We have that the cortex. We have the outer coat of the spore that's going to keep protect this particular spore from really difficult conditions. This is kind of a nice summary of the differences between vegetative cells and spores. So vegetative cells are sensitive to temperature changes, they're sensitive to radiation. Endospores actually can survive extreme temperatures and radiation, so these are really tough.
That spore coat protects the bacterial DNA. Vegetative cells are gram positive. I said that endospores don't absorb the gram stain, but you can stain the spores with malachite green.
Vegetative cells have normal water content, they're alive, they're metabolizing, they're dividing. But endospores have been dehydrated, so there's no metabolic activity. They're sort of frozen in time.
Vegetative cells are capable of growth and metabolism. They divide. Endospores are dormant.
They do not have metabolic activity. But the good news is that if you can form spores, you can save your DNA until conditions are good again. Usually that means that water is gone and the spore forms and nutrients are gone. And then when water comes back, we often see spores germinate.
Spores are, you can almost think of them a little bit like a seed, although it's different because a seed is the byproduct of a sexual reproduction process, and spores are really just a survival mechanism for bacteria. This is a scanning electron micrograph of Clostridium spirogenes, which we are going to see in the lab. And so these are some of the spores here, and here is vegetative bacteria emerging from the spore because conditions are now good again.
And so it's beginning to divide. And that's the really interesting things about spores. Once they get into solution, they will begin to divide into vegetative cells and they can just grow like normal cells.
And again, they'll do that until conditions are rough again, and then they'll reform the spores. So we talk about spore formation, but we also talk about germination of a spore into a vegetative cell again. All right, so we said spores are really difficult. We said they were very resistant to heating and freezing, et cetera, and this makes them really difficult in the clinic because they're actually so resistant to things like chemicals.
It makes it hard if you're trying to keep a healthcare setting clean, sanitized. Spores are one of the structures that are very hard to get rid of. Some genuses that make spores cause some fairly serious illnesses.
So Clostridium is responsible for gangrene, botulism, tetanus. Those are spore-forming bacteria. The genus Bacillus forms spores. It's responsible for anthrax, food poisoning. And then honey, I don't know if you've heard this before, but honey can be a source of botulism spores, which is produced by Clostridium botulinum.
And you are not supposed to give honey to babies that are under one year old. And the reason is because if you eat honey and it has Clostridium botulinum spores, your digestive tract is a pretty inhospitable place and it actually will kill the spore. So you're probably relieved to know that.
But a baby's GI tract is still very... young and vulnerable. It's not quite as harsh as yours, and it's possible for the clostridium botulinum spores to actually germinate in a baby's gut. And they can end up with this flaccid paralysis where the botulinum toxin, which interferes with the nerve signals from the brain to the muscles. So what happens is the baby becomes quite floppy and unable to move its muscles and be very serious.
So that's why you don't give honey to a baby until they're about a year old. It's this fear that the... Clostridium botulinum spores will germinate in their gut and produce this botulinum toxin. All right, our next topic is going to be quorum sensing in biofilm. So we're going to be talking about how bacteria live together in groups and how they can actually communicate with each other, which I bet you didn't realize they could do until you watch that amazing Bonnie Bassler video in the homework.