Bacteria
What are Bacteria
Life began in the dark
Under the ocean, in the warm chemical soup of Volcanic Hydrothermal Vents
Then life moved towards the light
This life was bacteria
This life started to use sunlight as a source of energy.
This life absorbed carbon dioxide from the air, for the air was full of carbon dioxide from volcanoes
This life took the carbon dioxide and used energy from the sun to separate off the carbon so that it could use it to make compounds that it needed inside of its single cell.
The dioxide part wasn't needed so it was released into the atmosphere. Giving our planet oxygen.
This was the first occurrence of photosynthesis on our planet, and it was done by Bacteria.
Bacteria are single celled organisms. That is, they have just one cell!
Inside that cell is ribosomes, proteins, enzymes and nucleic acids. But no organelles! No mitochondria or Endoplasmic Reticulum.
They are built simply. But this has been their advantage. They have a single circular loop of DNA. Bacterial RNA polymerase copies genes from this into mRNA. The mRNA is then directly translated by bacterial Ribosomes into proteins. These enzymatic activities are powered by ATP.
Some of these proteins will help the Bacteria to do cellular respiration to get energy to turn ADP into ATP.
Bacteria's simplicity has allowed them to be the first lifeforms on Earth
Bacteria's simplicity has also allowed them to be everywhere! They have been found in drilling samples deep into the earths crust. They are at the top of mountains, in the air, at the poles, in all bodies of water and inside of you!
The prologue of the story of life on our planet is the life of bacteria
The prototype of 'the cell'. A cocktail of perpetuating and sustained chemical reactions occurring in a water filled bag made from lipid, the cell. The prototype to our cells was the bacterial cell
The progenitor, the ancestor of all life on our planet, is bacteria
Bacteria existed before the evolution of a nucleus or to keep the DNA safe in. A nucleus to carry (Kary) the DNA in, away from the burning of fuel occurring in the cell
Though, bacteria are so busy replicating that a nucleus would just slow them down
Bacteria are before the DNA carrying nucleus
Bacteria are prokaryotes
Everything else that is alive have descended from bacteria and have evolved that DNA carrying nucleus. So everything else (plants, fungi, animals) is like you. And you are a Eukaryote!
Shapes, friends and names
Bacteria are single celled organisms
However, sometimes they like to clump together.
If they clump together in pairs we call them diplo-
If they clump together in a straight line we call them strepto-
If they clump together in a bunch we call them staphylo-
Bacteria are usually either circular or oblong
Circle bacteria are called -cocci
Oblong or Brick bacteria are called -bacilli
The other shapes are commas and spirals
The spiral bacteria are called -spirillum
The comma bacteria are called -Vibrio
You take the clumping and the shape and join them together to name the bacteria.
E.g.
Staphlococci - circle bacteria that clump together
A straight line of circle bacteria = Streptococci
Bricks = Bacilli eg Bacillus anthracis
Bent = Vibrio eg Vibrio Cholerae
Structure of a Bacteria
Bacteria are single celled organisms. That is they do all of the MRSGREN functions using a single cell.
They are classified as prokaryotes as they do not have a nucleus
If we look inside a bacteria we will find:
DNA - instructions for building proteins, and instructions for how to build a bacteria and how to carry out its life processes. This is a loop chromosome.
Cytoplasm - liquid contents that fill the cell. Mostly water, with nutrients floating in it - sometimes called jelly like
Ribosomes - these take the mRNA message from the DNA and create the appropriate proteins
DNA - (RNA polymerase) - RNA - (ribosome) - Protein
Plasmid - these are small, circular loops of DNA that can be passed from one bacteria to another.
These are separate from the big chromosomal DNA. They are swapped between bacteria during conjugation (sex). This sharing of plasmids allows the spread of new traits - for instance a mutation that allows a protein to catalyze a new substrate might allow the bacteria to digest a new food source If one bacteria has developed bacterial resistance, this sharing of plasmids will allow other bacteria to obtain this resistance. Humans use these Plasmids in biotechnology. They take the plasmids then insert the DNA that they want into the bacteria - the bacterial ribosomes will then read the DNA and make the relevant protein - this is used to make insulin for humans in vats of E.Coli and to make certain vaccines
If we then look at the outside of a bacteria, we will find, starting from the inside:
5. Cell membrane - this controls what exits and enters the cell and reduces water loss (wall paper)
6. Cell wall - this provides strength to the cell (Gibb board or dry wall)
7. Capsule - this protects the cell from the environment (bricks of the outside wall)
8. Slime layer - this protects the cell from viruses that attack it (bacteriophages) and White blood cells
Now we get to the bits that stick out
9. Pili - can help the bacteria to stick to surfaces and to other bacteria. Sometimes the pili (conjugational pili) will reach into another bacteria - then pass along a Plasmid - this is Bacterial Conjugation
10. Flagellum - whips around to propel the bacteria - Movement
In other words, with fewer words:
If we look at the structure of bacteria we will find:
Cytoplasm - The chemical reactions of life need to happen in a fluid filled environment, to allow for the chemicals to move
The cytoplasm is mostly water. In this water is all of the chemicals of life - dissolved oxygen, carbon dioxide, sugars, lipids and proteins along with nucleic acids
DNA - this contains the genetic instructions to make all of the proteins and enzymes of the cell
Plasmid - smaller circular bits of DNA that code for making proteins and enzymes, these can be shared between bacteria
Ribosomes - these are enzymes that make proteins
Proteins are either structural or they are enzymes. Enzymes are proteins that do stuff.
Cell membrane - this is made from lipid. This lets nutrients, wastes and oxygen diffuse into and out of the cell
Cell Wall - this is strong and provides structure for the cell
Capsule - even stronger
Slime layer - this helps to keep water inside the cell and prevents it from drying out. It can also hid the cell from animal immune systems
Pili - these are like tiny fingers that help to hold the bacteria in place so that it can feed
Occasionally one of the pili might become a sex pilus so that two bacteria can exchange genetic material
Flagellum - by moving the tail like flagellum, the bacteria can move and swim
Life Processes
Bacteria are alive, as they conduct all of the functions of life
These functions are: MRSGREN
Movement - move something
Reproduction - make more of your type
Sensitivity - sense something
Growth - get bigger
Respiration - break down compounds for energy
Excretion - get rid of waste compounds
Nutrition - eat atoms
MRS
Movement
Flagella
The main way that bacteria move is with their flagella
The Flagella is like a tail
The bacteria whip it around, causing motion
Pilus
Pilus in bacteria are usually used for 'adhesion'.
In other words, bacteria use their Pilus to stay right where they are, so that they can feed on the nutrients in the spot that they are
Some bacteria can also use their pilus for movement. Twitching the pilus back and forward to crawl along a surface (Twitching motility)
Reproduction
Binary Fission
Binary Fission is the main form of bacteria reproduction
The bacteria eats, grows, gets to its maximum size, copies its DNA, moves its DNA to either side of its cell, then splits in half
The cell that splits is called the 'parent' cell
The new cells are called 'daughter' cells
These daughter cells have identical DNA, so they are all the same
These daughter cells are genetic clones of the parent cell
This is asexual reproduction
Asexual reproduction only uses one parent. The offspring are clones, because there is no exchange of DNA
When there is an abundance of food, this process will allow the bacterial numbers to grow very rapidly
This is because for each parent cell, there will be 2 daughter cells. So bacterial numbers double quickly: 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192. We'll stop at this 13th generation.
By the 20th generation we have crossed 1,000,000 and by the 30th generation we cross the billion mark.
Because bacteria are so small, it doesn't take them long to get enough atoms to be able to get big enough to divide.
It we take a hypothetical number of 1 generation per hour, then by the second day the numbers of bacteria are in the billions
In ideal conditions, some bacteria can grow and divide every 20 minutes!
This is how and why "plating" works.
When you swab on a agar plate, individual bacteria are left behind on the agar.
There are heaps of nutrients for the bacteria on the agar plate.
Over time the bacteria eats the nutrients, grows large, splits in half, these two eat the nutrients, grow large, split in half, these four and so on...
This continues. Once the bacterial number passes a billion, we can see it as a small dot. This is a bacterial colony
If the colony is a single dot, then this is the decedents of a single bacteria
This gives rise to growth curves that increase exponentially
It takes a while to start, this is because the bacteria must release enzymes to digest the agar, and then it must absorb the nutrients. This lag at the start of population growth is called the 'lag stage'
As the nutrients become available from the extracellular digestion, the numbers skyrocket. The population increases exponentially. This phase is called the exponential phase.
Finally the abundance of nutrients reduces as they are digested and absorbed. Here we have a stationary phase, where the number of bacteria dying due to starvation are equal to the number that still have access to nutrients and are continuing to reproduce. The bacteria are competing for the nutrients. Some of the remaining bacteria are able to feed on the dead ones.
Finally the wastes from the bacteria buildup and the nutrients are few and far between. The bacteria starve and die on mass, the number of bacteria falls as they die. This is the death phase.
Lag Phase - The bacteria are releasing digestive enzymes to make nutrients available, absorbing the nutrients and growing in individual size
Exponential Phase - The bacteria are multiplying, the colony is growing. There is plenty of nutrients to provide the atoms for this growth and reproduction
Stationary Phase - There is not enough nutrients to go around. Some bacteria are able to get enough nutrients to stay alive and respire but not divide. There are some bacteria that are able to get an abundance of nutrients and can grow and reproduce. There are some bacteria that are not able to get enough nutrients to sustain respiration, so they die
Death phase - There is not enough nutrients so the bacteria starve and die off.
Conjugation Pilus
Occasionally Bacteria will share DNA. This is important as over time replication errors occur changing the DNA code. Usually this is bad as it might mean that an enzyme doesn't work anymore or work as well as it used to. This bacteria and its decedents will eventually be outcompeted by bacteria that don't have this mutation and they will disappear
However, occasionally this mutation causes an advantage. Perhaps it causes a change in the proteins on the surface of the bacteria, making it harder for antibodies to find it. These positive changes give that bacteria and its decedents an advantage and they will out compete and out populate the other bacteria.
On its journey of evolutionary success, that bacteria may share this advantageous DNA code with other bacteria.
To share small amounts of DNA, one of the bacteria's cilia will become a pilus
The pilus of one bacteria will join with another bacteria and genetic material will move from one to the other. This is called Conjugation
This is not reproduction - however I have included it here due to the sharing of DNA
It is only the small circular DNA plasmid that is shared
Sensitivity
Chemotaxis - chemo is chemical and taxis is to move like to catch a taxi or the plane is taxing on the runway
Bacteria move towards and away from different things
This is because they can sense these things
Some bacteria will move away from light to prevent them from drying out, while photosynthetic bacteria will move towards it
Bacteria can sense nutrients due to diffusion gradients in their environment. Much like you can sense KFC when walking near by, and if your eyes were closed, you could probably figure out how to get to the store just using your chemosense - your nose
Chemosensing is the sensing of chemicals, including nutrients
For bacteria to chemosense, the some of the chemical compounds must either diffuse into the cell (the side of diffusion indicates the direction of the chemicals). Alternatively the compounds can touch a receptor, the side of the bacteria that has the activated receptor is the side that the chemicals must be on, so the bacteria will move either towards (nutrients) or away (toxins) from that chemical
Bacteria can also sense:
Touch
The presence of other bacteria
Light
Gravity