Lesson video

Hello and welcome to this lesson from the Oak National Academy.

Today's lesson is on mutations and evolution in bacteria, and it's taken from the unit variation and natural selection at the genetic level.

<v ->Hiya, I'm Mrs. Wheate,</v> and I'm gonna be your teacher for today's lesson.

By the end of today's lesson, you'll be able to describe examples of mutations of bacteria and explain why advantageous to genetic variants become more common in the bacterial population.

Let's have a look at our keywords.

We have five keywords for today's lesson.

Natural selection.

Organisms that are better adapted to their environment are more likely to survive, reproduce and pass on their genes to their offspring.

Microorganism are microscopic living thing, such as a bacterium or an amoeba.

Mutation.

A change in the nucleotide base sequence in the DNA of the genome.

Genetic variant.

A genetic variant is a region of DNA in which the sequence of nucleotide bases has been changed.

An asexual reproduction.

A form of reproduction in which a cell divides to produce two genetically identical cells.

So if you wanna read through that now, I'll be quiet so you can read through it.

Or if you want a bit more time, maybe you wanna read through them a couple of times, or if you wanna copy them down, that's totally fine.

Pause the video and click play when you're ready to move on with the lesson.

Today's lesson is in two parts.

We're gonna look at two examples of evolution in bacteria.

Our first example is about a plastic digesting bacteria, and the second example is about antibiotic resistant bacteria.

So first of all, let's start off by talking about plastic digesting bacteria, and then we'll provide many well-known examples of evolution by natural selection.

Observing Galapagos tortoises and finches help scientists like Charles Darwin to develop the explanation that natural selection causes evolution, but all organisms evolve due to natural selection, not just animals.

This includes microorganisms such as bacteria, and it's really easy to remember that animals are living things, but it can be harder for whatever reason, to remember that plants and fungi and bacteria are also living things.

Microorganisms are microscopic living things such as so these are some eukaryotic examples.

So amoeba, some fungi are microorganisms like yeast, and some algae are also microorganisms. And we've got our prokaryotic.

Example is bacteria, and that's mainly what we're gonna be talking about today.

Despite being very small, they are living organisms that carry out those key life processes and evolve change over generations just like animals do.

Okay, let's see if you're following that.

True or false.

Natural selection occurs in microorganisms. So take five seconds, or if you want some more time, click pause, click play when you are ready to see the answer.

That is true.

Okay, why is it true? Let's justify that answer.

Is it true because natural selection occurs in all living organisms, including microorganisms? Or is it true because natural selection only occurs in animals? Again, take five seconds or you want more thinking time, click pause, click play when you're ready to see the answer.

It is A.

Natural selection occurs in all living things, all living organisms, including microorganisms. Great job if you got that right.

So let's start off by talking about why this plastic digesting bacteria is such an important discovery.

So there are billions of tonnes of plastic waste globally.

Plastic doesn't fully decompose, and it's well, it's incredibly unreactive, and plastic waste will remain an issue unless we do something to intervene.

It's not just gonna go away by itself, it's gonna remain and stay around much longer than one human lifespan.

So only a small percentage of plastic is recycled.

The majority goes to landfill or incinerated, which releases greenhouse gases into the atmosphere, so that's more problems. Scientists across the world are searching for solutions to the problem of dealing with plastic waste.

This is where our bacteria comes in.

In 2001, a team of Japanese scientists discovered a bacterium with a mutation that enabled it to digest plastic.

The bacterium, Ideonella sakaiensis, is a rod shaped bacterium, like the one in the diagram here, and it is able to use a type of plastic as a source of carbon and energy.

So we can use our understanding of mutation and natural selection to explain how this ability appeared and became common in Ideonella sakaiensis.

So natural selection starts with variation.

A random mutation in the DNA of the bacterium created a genetic variant.

So here we've got a sequence of DNA.

This is our original sequence of DNA, and here we have the genetic variant.

So if you look really carefully at each of these coloured symbols at the bottom of each of the nucleotides on the DNA, those are our bases, there is a base that is different, and that represents a mutation.

A mutation being a change in the nucleotide base sequence of DNA.

So bacteria with this genetic variant had a new ability, a new trait in their phenotype.

They could digest plastic, and this created variation in the population of bacteria.

So some bacteria had this, other bacteria did not have this.

So let's check to see if we're following that.

Which of the following statements are true? A, there is variation among bacteria.

B, bacteria are genetically identical to each other.

C, mutations can occur in the DNA of bacteria.

D, bacteria cannot evolve.

Take five seconds or if you want more time, click pause, click play when you're ready to see the answer.

Let's look at the answers.

So, A is true, there is variation among bacteria.

C is true.

Mutations can occur in the DNA of bacteria.

Great job if you got that right.

So variation leads to advantage.

So the individual bacteria that could digest plastic that had the genetic variant that allowed them to digest plastic, that had an added an advantage over the other bacteria in the population.

Now this is because the ability to digest plastic is a really useful adaptation for the bacteria as it gives them an extra source of nutrients so the other bacteria can't access.

So it has an advantage, and then when these bacteria in competition for each other, that's when it becomes useful.

So the bacteria that could digest plastic competed more successfully for resources such as carbon compounds to use in respiration.

So competition leads to survival.

The bacteria that could digest plastic were more likely to survive and reproduce.

So bacteria reproduce asexually.

And what that means is, so in a round of asexual reproduction in bacteria, you have a bacterial cell divides to produce two genetically identical cells.

And this is a really interesting implication for inheritance.

So survival and reproduction leads to inheritance and asexual reproduction causes advantageous to that variant to become common in populations really quickly.

And this is because when an organism reproduces asexually, all of its genetically identical offspring inherit the advantageous genetic variant.

So that one plastic, that one plastic digesting bacterium that had the ability to digest plastic, when it reproduced, all of its offspring had that ability.

That's not how it works in sexual reproduction.

So organisms that reproduce sexually produce genetically varied offspring.

So if we have a look at the piglets in the photo here, they all look different, and that's because they're produced by sexual reproduction.

So not all offspring inherit the advantageous genetic variants that their parents might have, so it takes longer for it to become common in populations.

Okay, let's see if you understood that.

Why did it not take long for the plastic digesting genetic variant to become common among the bacteria? Is it A, bacteria reproduce asexually? B, bacteria produce sexually, or C, bacteria can use both asexual and sexual reproduction.

Take five seconds, or if you want more time, click pause, click play when you're ready to see the answer.

Okay.

It is A, bacteria reproduce asexually.

And remember that means that they produce genetically identical offspring.

So all of the bacteria's offspring had the genetic variant that allowed them to digest plastic.

Well done if you got that right.

This is the first practise task of today's lesson.

"The article describes an example of natural selection in polar bears.

Due to a random mutation, early polar bears had a genetic variant that caused their fur to be white like their surroundings.

In these polar bears, the genetic variant caused them to be better adapted to their surroundings, and hunt for prey more effectively because they were camouflaged.

This gave them an advantage in the competition for food.

These individuals were more likely to survive and sexually reproduce, so were more likely to pass on this advantageous genetic variant.

The offspring had a variety of traits.

Some were camouflaged, some were not.

This process repeated for many generations over a long period of time, until eventually the majority of polar bears were camouflaged." So what I want you to do is describe the similarities and differences between the evolution of camouflage in polar bears, and the evolution of the ability to digest plastic in Ideonella sakaiensis.

So you need to pause right now to give yourself enough time to write down your answer and think about it.

Click play when you're ready to see the answer.

Good luck.

Let's take a look at the kind of ideas you could have included in your answer.

So first, similarities.

So in both examples, the advantageous genetic variant was caused by a random mutation in their DNA.

In both examples, the genetic variant gave the organism an advantage which allowed them to compete successfully, survive, and reproduce.

In both examples, the advantageous genetic variant became more common due to natural selection.

Let's take a look at some of our differences.

"Polar bears reproduce sexually so produce genetically different offspring.

This means only some of the offspring had this advantageous variant." "The bacteria reproduce asexually so all of the new generation are genetically identical, and have this advantageous genetic variant." "Because of this difference in reproduction, it took much longer for the advantageous genetic variant to become common in polar bears than it took for the advantageous genetic variant to become common in Ideonella sakaiensis." Great job if you got that right.

So we have talked about our first example of evolutionary mutations in bacteria, the plastic digesting bacteria, Ideonella sakaiensis.

Now we're gonna talk about the development of antibiotic resistance in bacteria.

Sometimes bacteria happen to evolve in ways that could be helpful to us, such as becoming able to digest manmade waste materials like the Ideonella sakaiensis being able to digest plastic.

But sometimes bacteria evolve in ways that are not helpful to us, such as becoming resistant to antibiotics.

So that means the bacteria are developing that are no longer killed by antibiotics.

Let's talk about what antibiotics are before we talk about antibiotic resistance.

"So antibiotics are used to treat bacterial infections.

The first antibiotics we widely used was penicillin, which was discovered by Scottish scientist, Alexander Fleming in 1928.

It was being widely used in the 1940s and was hailed as a miracle drug because it's effectiveness in treating previously incurable bacterial diseases." It's hard to overstate the importance of antibiotics.

Before antibiotics a hundred years ago or 150 years ago.

If you got a cut on your finger and that got infected, you could die from that.

I said that was a real possibility, and you're probably thinking that's really weird.

I'm not worried about having, you know, like a small cut on my hand.

I'm not worried I'm gonna die if that happens because that's because of antibiotics 'cause we live in a world now, antibiotics and very good hygiene that we have now that people don't tend to die of things like that, which we're really, really fortunate, we're really fortunate for.

So antibiotics came along and everyone was very, very excited by then, 'cause, you know, people weren't dying as much as they used to from these horrible bacterial infections.

But by the 1950s and 1960s, scientists were already concerned that antibiotics were becoming less effective.

And actually Alexander Fleming himself warned in 1945 that he was concerned about the overuse of antibiotics, and how what that might do to their effectiveness.

"So antibiotic resistance is one of the top public health and development threats.

A mutation in a bacterium can lead to antibiotic resistance.

And this means the antibiotic no longer works as effectively to kill or prevent the growth of bacteria.

Previously curial diseases, bacterial diseases such as gonorrhoea and tuberculosis are becoming harder to treat due to antibiotic resistance.

And natural selection has made antibiotic resistance more common." Okay, let's check to see if you understood that.

True or false.

Bacteria can become immune to an antibiotic.

Is that true or is that false? Take five seconds or pause video if you want more time, click play when you're ready to see the answer.

That is false.

Okay, why is it false? Is it false because A, bacteria do not have an immune system or B, antibiotics always work against bacteria? Again, take five seconds or if you want more time, click pause, click play when you're ready to see the answer.

A, bacteria do not have an immune system.

So bacteria can no longer be killed by antibiotics because they developed this mutation, but using the word immune, that's not correct in this context.

Well done if you got that right.

"We can use our understanding of mutation, natural selection to explain how antibody resistance appears and becomes common in bacteria." So we start off with variation again.

A random mutation in the DNA of some bacteria created a genetic variant." And so here we have all my bacteria are represented here in pink.

And my antibiotic resistant bacteria is the yellow-y, orange-y one.

So this genetic variant caused these bacteria to be resistant to some antibiotics.

This is an example of variation.

So variation leads to advantage.

"The antibiotic resistant bacteria had an advantage over non-resistant bacteria.

Being resistant to antibiotics is a helpful adaptation.

When the antibiotic resistant bacteria are exposed to an antibiotic, represented here by my pale green, they survive." And so at a advantage leads to competition or helps with competition.

So these antibiotic resistant bacteria experience less competition 'cause they were the ones that weren't affected by the antibiotic.

They now have all the space, they're competing for way less resources, and so that's gonna lead to them being more likely to survive.

So the bacteria survived as they were resistant to the antibiotic they were exposed to, they could then reproduce.

They then reproduced asexually producing the next generation of genetically identical cells that leads to inheritance.

"The next generation have all inherited the advantageous genetic variant, which causes antibiotic resistance.

So very quickly this genetic variant becomes more common.

If the bacteria had never been exposed to antibiotics, being resistant would not have been an advantageous trait." Being resistant to antibiotics is only advantageous if the bacteria encounters antibiotics within its lifetime.

If it never encounters antibiotics, it's living inside someone that doesn't take antibiotics, hasn't ever taken antibiotics, being resistant is not an advantage then.

And so it's the taking of antibiotics which can lead to this trait being selected for.

"So if it was not advantageous, it would've been less likely to become as common among bacteria." So antibiotic resistance is becoming a leading cause of death worldwide, and we can't just stop taking them.

They are really useful.

We just need to be smarter about how we take them when we use them.

So there are several ways we can reduce the spread of antibiotic resistance.

So only using antibiotics when necessary.

As I said at the beginning of this learning cycle, antibiotics kill bacteria, they do not kill viruses.

And so if you take antibiotics for a viral infection, you're exposing the bacteria that live in your body to the antibiotic unnecessarily, and that can lead to the selection for.

The natural selection of antibiotic resistant bacteria.

So only using antibiotics when it's necessary, such as it's a serious bacterial infection.

Using specific antibiotics to treat specific bacterial infections.

So many antibiotics are broad spectrum antibiotics, and this means that they kill many different types of bacteria.

This could lead for more opportunities for the natural selection of antibiotic resistance.

So if you have an infection that's being caused by Staphylococcus aureus bacteria, using an antibiotic that just targets that type of bacteria leads to fewer opportunities for the natural selection of antibiotic resistance of bacteria to occur.

So where possible, reduce the need to use them through vaccination and good hygiene, and finishing a full course of antibiotics is really important as well.

And finally, so isolate patients and hospitals with antibiotic resistant infections.

So these are just some of the ways that healthcare professionals, and we can prevent the spread of antibiotic resistance.

Okay, let's see if you understood that.

Which of the following statements is true? A, antibiotics cause mutations to bacteria so they develop antibiotic resistance.

B, the mutation to which cause antibiotic resistance occurred at random.

C, antibody resistance is caused by not using antibiotics.

So you can take five seconds now, if you want some more thinking time, click pause, click play when you're ready to see the answer.

Okay, let's look at the correct answer.

It is B, the mutation to which cause antibiotic resistance occurred at random.

Let's look at why the other answers are incorrect.

So A, antibiotics cause mutations of bacteria so they develop antibiotic resistance.

So whilst using antibiotics inappropriately or overusing them can lead to situations in which antibiotic resistance have an advantage.

Using antibiotics doesn't cause the initial mutation in the bacteria, that happens at random.

And C, antibiotic resistance is caused by not using antibiotics.

Again, how you use them isn't what leads to the mutation, which is responsible for a bacteria having antibiotic resistance or not.

Okay, well done if you got that right.

This is our final practise task of today's lesson.

Number one, state two ways to help reduce the spread of antibiotic resistance.

Number two, Sofia is learning about evolution at school.

She says, "Only animals evolve by natural selection.

Organisms such as bacteria don't evolve as there is no variation or competition among bacteria." Explain why Sofia is incorrect, and give two examples of natural selection and bacteria in your answer.

So we need to pause now to give yourself enough time to think about your answers and to write it down.

Click play when you're ready to see the answers.

Good luck everyone.

Okay, let's look at the answers.

State two ways to help reduce the spread of antibiotic resistance.

So you could have included any of these.

So only using antibiotics when necessary.

So to treat a bacterial infection, not a fungal infection or a viral infection.

Using specific antibiotics to treat specific bacterial infections.

Where possible, reduce the need to use them through vaccination, good hygiene.

Finish the full course of antibiotics and isolate patients in hospitals with antibiotic resistant infections.

Okay, number two, explain why Sofa is incorrect, and give two examples of natural selection and bacteria in your answer.

"Sofia is incorrect, as bacteria are living things that evolve by natural selection.

Although the new generation of bacteria are genetically identical due to asexual reproduction, random mutations can lead to variation among bacteria.

Bacteria compete for resources such as space, oxygen, and nutrients just like other organisms. Ideonella sakaiensis are an example of a bacteria that have evolved through natural selection of genetic variants that provide the ability to digest plastic.

Many types of bacteria have evolved through natural selection of genetic variants that provide resistance to antibiotics." Really great job, if you got that right.

Well done on all your hard work today on today's lesson.

Let's summarise what we've learned to help it stick in our memories.

"Like other organisms, bacteria evolve through natural selection.

Mutations create genetic variants in bacteria which can give them new abilities, new traits in their phenotype.

Genetic variants that are advantageous to the bacteria become common quickly due to asexual reproduction.

Examples of evolution by natural selection of bacteria include the appearance and spread of new abilities such as digesting manmade waste materials and resistance to antibiotics.

Taking steps such as only taking antibiotics when necessary can help prevent the spread of antibiotic resistance.

Again, really great job and hopefully, I see you again soon for our next lesson.