Escherichia coli (E. coli) as a Model Organism or Host Cell

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  • 0:05 Most Studied Organism
  • 1:07 E. coli
  • 2:27 Model Organism
  • 4:35 Genetic Manipulation
  • 7:15 Lesson Summary
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Lesson Transcript
Instructor: Angela Hartsock

Angela has taught college Microbiology and has a doctoral degree in Microbiology.

A model organism can help scientists perform faster and more efficient biological research. This lesson examines the most utilized model organism, E. coli, and looks at the major characteristics that make it a perfect model.

Most-Studied Organism

If you had to guess, what would you say is the most studied and well-understood organism on the planet? Maybe the elephant? They are large, easy to observe, and are the subject of countless documentaries. Maybe cows? They have been domesticated for thousands of years and are worshipped or consumed in almost every country on Earth. I'd like to give you the hint that you need to think smaller, but this is a microbiology course, so you probably already assumed as much.

I'm going to reveal the answer, but I want you to play word association. When I give you the name, say the first thing that comes to mind.

The most studied and well-understood organism is E. coli.

I bet a poll of one hundred students would reveal that a majority immediately thought of food poisoning or illness. In reality, associating food poisoning with E. coli is like letting one rotten apple spoil the whole bunch. The world of E. coli is much larger and more important than that. Let's take a look and see why.

Escherichia Coli

Escherichia coli, or E. coli for short, is a Gram-negative, rod-shaped bacteria that is a normal inhabitant of the lower gastrointestinal tract of warm-blooded animals. Scientists estimate that E. coli first evolved between 120 and 160 million years ago, about the same time as the appearance of mammals. It is likely that E. coli has been living in the colons of mammals for the entire history of both groups. Further evidence for this symbiosis is the relatively rare ability of E. coli to utilize lactose, which is the sugar of milk, found only in mammals. Also, E. coli are able to survive in the presence of bile salts, which are caustic and used in digestion.

In addition to thriving in the colon, E. coli can also survive outside the body. Environmental E. coli can be spread through feces as the bacteria pass out of the body. These two habitats are about as opposite as you can get. The colon is relatively stable, warm, anaerobic, and nutrient-rich. Outside of the colon, conditions can be extremely harsh and variable, much colder, aerobic, and provide fewer nutrients.

Model Organism

The fact that E. coil is able to survive such variable conditions is one advantage that led to its use as a model organism. A model organism is a species that is extensively studied to understand a specific phenomenon, expecting that the knowledge gained can be applied to other species as well.

E. coli has many attributes that make it an ideal candidate for use as a model organism. Let's discuss the five major attributes that make E. coli an excellent model organism.

Attribute 1: E. coli is a single-celled organism. There are no ethical concerns about growing, manipulating, and killing bacterial cells, unlike multicellular model organisms like mice or chimps. They are also tiny cells, so in a small laboratory you can have flasks containing billions of cells that take up very little room, allowing many experiments.

Attribute 2: E. coli is able to reproduce and grow very rapidly, doubling its population about every 20 minutes. This is helpful in a lab situation where waiting for subsequent generations to produce experimental data can be the rate-limiting step. With E. coli it is as easy and fast as letting them grow overnight. Trying to study the same process in subsequent generations of elephants, for example, would require several generations of scientists and more elephants than we have on the planet!

Attribute 3: E. coli can survive in variable growth conditions. As we discussed earlier, this leads to it being very adaptive yet forgiving in lab situations. Culture media containing simple and inexpensive ingredients and nutrients can successfully spur E. coli to grow and divide.

Attribute 4: Most naturally occurring strains of E. coli are harmless. Those food-poisoning E. coli that sprang to mind earlier are the exception, not the rule. When scientists first started using E. coli for lab experiments, they chose a strain that was harmless. This means that studying E. coli poses little threat to researchers and the public.

Genetic Manipulation

Attribute 5: E. coli can be genetically manipulated very easily. The genetics of E. coli are well-understood and can be readily manipulated, or engineered. This is the most important and multifaceted attribute contributing to the use of E. coli as a model organism.

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