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I am E.coli
Get ready to dive into a world you can’t see with the naked eye — where life operates on a microscopic scale, yet with massive impact. Meet E. coli, a tiny but mighty cell factory that grows, adapts, and even helps shape the world around you. Scroll in, take a closer look, and uncover the incredible story of this often misunderstood microbe.
E. coli is one of the most studied organisms in science. Researchers use this microbe in labs to understand genetics, cell function, and even to develop new medicines, replacements for harmful chemicals, alternatives to plastics and other entirely new products!
E. coli is so very very small. So small that a water bottle can fit billions of them! When you make E. coli 100 times bigger, you see it as one tiny transparent rod.
E. coli is about 2 micrometers long and 0.5 micrometers wide. For perspective, a human hair is 75 micrometers, a red blood cell is 3.5 times bigger than E. coli and a dust mite is 100 times bigger. Yet you can fit 5,000 flu viruses inside an E. coli and it is double the size of other common bacteria.
Vertical live view of an E. coli liquid culture (x100 magnification). Credit: Cristina Bulancea and Marwan Kaufman
Agar plates with plated bacteria. Magnification : 1X. Strain: Streptomyces collinus. Credit: Tilmann Weber's Lab
Environmental Indicator
Because E. coli is common in human and animal waste, it is used as a marker to check water quality. If high levels of E. coli appear, it can signal contamination — but that’s more an indicator of pollution levels than E. coli always being “bad”.
Agar plate with a member of the Actinomycetota family. Magnification : 1X. Credit: Pep Charusanti
Common Gut Resident
E. coli is a type of bacterium that is associated with living in the intestines of humans and many animals. Most strains are harmless and actually help keep our digestive system healthy.
But did you know that they can actually live in many other places too? In soil, in water, on walls, on plastic, on foods — you name it!
Mix bacterial culture stained with crystal violet. The bacteria stained violet are gram-positive, those pink are gram-negative. Credit: Wikipedia
Bacteria can be divided into Gram-negative and Gram-positive
Bacteria are divided into two groups depending on the color they turn when strained with crystal violet. Gram-positive bacteria appear blue or purple after Gram staining, while Gram-negative bacteria appear red or pink after Gram staining. The difference is due to their outer cell structure: Gram-positive bacteria are surrounded by a single thick cell wall, Gram negative bacteria have a much thinner cell wall, but in addition they have an outer membrane.
The cell factory
E. coli can replicate its whole genome every 20 minutes, and it can make several copies at the same time. This makes it the fastest evolving microbe, creating new capabilities every time it duplicates — and acting as a fantastic factory to produce molecules.
E. coli can replicate itself exponentially, this means that it duplicates its population every 20 minutes. After 3 hours, E. coli has gone from 5 to 500.
E. coli replicates and adapts so fast that in a matter of days when adapting to a new environment, new variants of E. coli with one or two simple changes to its DNA can look and grow in completely different ways. When we do it in the laboratory it is called Adaptive Laboratory Evolution (ALE) of microorganisms.
You get the point by now. E. coli can go on and on. And since we can leverage this to produce almost anything that you imagine, it is an amazing ally to make a more sustainable planet. After all, E. coli also wants to keep on living on earth just like us.
E. coli is super versatile, it can grow with and without oxygen, in suspension (liquids) and on solid things, and at different temperatures and pH.
It can even eat a great variety of things from sugars to organic acids.
Agar plate with a member of the Actinomycetota family. Magnification : 1X. Credit: Pep Charusanti
We can teach E. coli to do many new things
Scientists have been studying E. coli for decades to unravel all its secrets. They have learned that they can force it to produce certain products by blocking some of its normal activity. Or they can produce something new by coupling two different activities or even adding new DNA sequences for E. coli to read and produce new products. All these types of methods are called synthetic biology, because now the bacteria are doing something that they normally wouldn’t.
Other ways are to feed it new things, change its living conditions (oxygen, temperature, pH) or put it together with other microorganisms.
Calcium carbonate precipitated vi biomineralization mediated by a bacterium Credit: Collen Varadizo Manyumwa. (Magnification: 1x)
CRISPR technology
CRISPR is a powerful gene-editing technology derived from a natural defense system in bacteria, which uses a specific sequence identical to that found on the DNA that you want to change (guide mRNA) to precisely target and modify specific DNA sequences. It allows scientists to add, remove, or alter genetic material with high accuracy, revolutionizing research in medicine, agriculture and biotechnology.
CRISPR technology was used to engineer bacteria so it can convert CO2 and industrial waste into zalcium carbonate. This way we both contribute to CO2 sequestering, to reduce waste production and create a valuable raw material used in many types of industry.
Bacterial Engineering
You are probably used to seeing drawings of a bacterium as an empty round element with DNA floating inside. In reality, the inside of an E. coli, and other bacteria, is fully packed with millions of proteins, each doing something different all the time.
It is only because it is a highly organized and specialized cell that all the processes can take place at the same time. Imagine a room for 100 people packed to four times its capacity with hundreds of different tasks to do… we wouldn't be able to do them all.
Welcome inside
E. coli !
In some cases, outside of the outer membrane there is a shield made of polysaccharides to help Gram-negative bacteria from drying out or evading the host immune system. It can also cause disease, so it is present in many pathogens. The capsule is lost during lab cultivations.
The outer layer of all bacteria. It is made of tightly packed long-chain sugars that grow from the cell wall. The most common one is lipopolysaccharide (LPS), which can cause disease.
Plural flagella. A hair-like structure made of helical filaments that work like a rotor motor. It can rotate clockwise or counterclockwise. It is made of many units of flagellin and traverses from the cytoplasm to outside the capsule.
A hair-like surface molecule found on the outer membrane, they often surround the cell and can have different functional roles to help cells respond to their external environment. They are essential for motility, to attach the bacteria to surfaces, and transfer DNA between bacteria.
Proteins which form hollow tubes and allow the passive movement of ions, water, and other molecules through them down their electrochemical gradient. Here they go from the capsule to the cytoplasm.
Specialized proteins that specifically recognize a particular molecule (nutrients, neurotransmitters, ions, hormones, etc.). They are embedded in membranes to signal from the outside to the inside. They are essential to the metabolism and activity of cells.
Structure between the plasma membrane and the capsule in a Gram-positive bacterium like E. coli. It is made primarily of polysaccharides (large sugar chains) that are bound together by unusual peptides (made of D-amino acids). These structures are called peptidoglycans. The antibiotic penicillin destroys this wall, killing the bacteria.
Cytoplasmic membrane, inner membrane. This is a thin structure that contains the cytoplasm and organelles of a cell. Its function is to protect them from the outside environment. It is made of a lipid bilayer of cholesterol, phospholipids and other lipids. It has proteins (like channels and receptors) embedded to facilitate the cell’s function.
Abbreviation for deoxyribonucleic acid - the molecule, found within cells, that controls the structure, look and purpose of each cell and transmits this information during reproduction to its daughter cells.
A molecular machine found in all living cells that reads messenger RNA (mRNA) sequences and assembles amino acids into proteins.
Protein complex responsible for the degradation of proteins. The proteins in charge of doing this are called proteases. E. coli’s proteasome is made of two rings, each made up of 6 identical proteins.
Any of a large group of chemicals that are a necessary part of the cells of all living things.
All the material within a cell enclosed by the plasma membrane or cell membrane, excluding the nucleus.
A small, circular double stranded DNA molecule that is found apart from chromosomal DNA and can replicate separately. They often code for antibiotic resistance, sickness, alternative metabolic pathways or molecules and bioremediation.
Main component of cytoplasm. It is a gel-like structure where the cell’s structures, organelles and proteins are found. It is made of 80% water.
The science
of gene diversity
Conjugation
E. coli, and bacteria in general, can have plasmids or small DNA sequences in their cytoplasm.
This can be shared with other bacteria directly through cell-to-cell contact, this is known as bacterial sex or bacterial conjugation.
The process includes several steps:
- The donor E. coli A elongates one of its pilus and searches for other bacteria.
- Pilum A attaches to a recipient E. coli pilum B and brings the two cells together, making a bridge.
- The plasmid is cut so that the DNA is linearized and one of the of the DNA’s strands is then transferred to the recipient E. coli B through the pilum bridge, the other DNA strand stays in the donor E. coli.
- Both cells make a complementary DNA strand to produce a double stranded circular plasmid.
- Both cells now have the same plasmid.
This is a type of horizontal gene transfer, the mechanism by which a bacterium gains new genetic material from its environment.
Transformation
Transformation is another type of horizontal gene transfer. It is when bacteria take new genetic material from their surroundings, this can be a plasmid of a fragment of DNA. The steps involve:
- A plasmid, or DNA fragment, attaches to a tunnel-like receptor on the E. coli surface.
- The plasmid is then linearized and comes in through the channel.
- Inside the channel, one of the DNA strands is lost.
- Inside the E. coli a complementary DNA strand is made.
- The new double stranded DNA is circularized to form a new plasmid.
Mutation & Deletion
Another common way for E. coli and other bacteria to change its genome is through mutations.
Mutations are random changes in the DNA sequence of a microbe's genome. These changes can occur during DNA replication or as a result of environmental factors like radiation or chemicals. Mutations can lead to new traits, some of which may provide a survival advantage.
One type of mutation is when they change a single letter (nucleotide) of the instructions (DNA sequence) to a new one, thus changing the recipe for the protein to be made. This is called point mutation and involves several steps:
- When the DNA double strand is opened to be copied, a process called replication, one of the original nucleotides (A, C, G or T) is replaced by another (for example C to T).
- This means that when the new complementary DNA strand is made, it will have one nucleotide different from the parent DNA.
- The daughter cell (offspring) will then be different to the parent cell. It might be that it has new capabilities that make it stronger, but it could also make it less able to survive. It all depends on how the change affected the instructions encoded in the DNA.
One can also mutate a whole codon (three nucleotides changed together), or the DNA can lose a number of nucleotides through deletion. All these change the instructions for how to build proteins that are essential for growth and survival of the E. coli - for better or for worse. One never knows!
Stay curious
For all that we’ve already discovered, there’s still so much more to explore. Nature has endless possibilities hidden in its code, waiting to be uncovered by curious minds like yours.
What if you were the one to unlock the next big breakthrough — perhaps a way to fight disease, create sustainable materials, or even engineer new ways to clean the planet? The smallest discoveries can lead to the biggest changes.
Stay curious, explore boldly and who knows? Maybe the future of science starts with you.
Got it?
0 points
Which of the following is true about E. coli in the human gut?
Which cell structures does E. coli have?
DNA, cell wall, proteasome, ribosomes, plasma membrane, capsule, lysosomes, cytosol
Capsule, ribosomes, DNA, cell wall, proteasomes, cytoskeleton. Golgi
Ribosomes, plasma membrane, DNA, cell wall, capsule, proteasomes, cytoplasm, proteins, cytosol
Ribosomes, proteins, DNA, cell wall, plasma membrane, endosomes, cytosol
Which best describes the way E. coli replicates its genome?
It is slow, never mutates and produces few daughter cells
It is fast, produces a single copy of its genome every 20 minutes
It is fast and very precise, never introducing mutations when replicating its genome
Its growth is exponential, making several copies of its genome at the same time. These copies include mistakes (mutations)