For bacteria, water allows the digestive enzymes that are secreted to move to the large nutrients.

The water allows the digestive enzymes to float around and digest the nutrients, turning them into small soluble nutrients

These small soluble nutrients then diffuse through the water back to the bacteria.

Bacteria in dry situations will often make a spore and then just wait in that dormant state. These spores can remain dormant for years

Active Bacteria are only found where there is moisture - this is why dry crackers and weetbix last so long.

Notice all the plastic... BPA?? You might be better using the oven

Bacteria under the ice in Antarctica have antifreeze proteins. These prevent ice crystals from forming, so the water in the cell stays liquid

Likewise, bacteria that lives in geothermal vents have evolved proteins that do not denature at these high temperatures, and are actually adapted to work best at high temperatures

Because of these adaptations, the bacteria's proteins and the bacteria itself can only operate within a temperature 'range' outside of this the molecules will be too cold to have sufficient energy for the chemical reactions of life to occur. Or they will have too much energy and the enzyme will denature

These bacteria that have evolved for extreme cold or extreme heat are called Extremophiles (extreme loving).

The coldest temperature that an cold environment extremophile has been found to be conducting active respiration is -20^oC . This relies on antifreeze protein preventing ice crystals forming

The highest temperature that active life has been found is 122^oC . Liquid water exists at higher temperatures than this. At hydrothermal vents where it is hot, whilst the pressure of the weight of the oceans water above it prevents water from boiling. However, the water has too much energy for the proteins to be active

Above 60^oC for most everyday bacteria their proteins denature and they die.

Some bacteria will form spores that can survive 100^oC

However time maters, the longer the bacteria or bacterial spore is in a high heat environment the more likely that its proteins are denatured and that its DNA/RNA and lipid membrane are damaged. Hence the cooking times for foods

Proteins fold up with both strong bonds and weak bonds

The weak bonds are hydrogen bonding - this is a weak attraction between the part of hydrogen that lacks electrons and the electrons of other atoms

As noted above, too much energy and these hydrogen bonds break

pH is the "power of Hydrogen"

Counter-intuitively the more hydrogen ions in the solution, the lower the power of hydrogen. (This is because it is a negative logarithm).

So low acidic pH (1-6) has lots of Hydrogens

Middle pH (7) has a balance of Hydrogens and hydroxide ions

High pH (8-14) has very few free hydrogen ions and many hydroxide ions

pH 1 = H⁺ pH 7 = HOH pH 13 = OH^-

Being ions these H+ and OH- will grab hold of other atoms

Because they can grab hold of other atoms the H+ ions will grab hold of the other atoms in the protein that the proteins own hydrogens were attracted to. This will block the attraction and break the weak hydrogen bond

These broken bonds will cause the protein to change shape

Form follows Function. So once the protein changes shape, it will not be able to function as it did. Once it changes from its natural shape, it is denatured. Denatured proteins do not work.

So pH affects proteins as it can cause them to denature

When a bacterium is subjected to pH outside of its normal range its proteins and enzymes denature. This means that the machines that drive the chemical reactions of life are borken. Without the functions of life, the cell dies.

This is how 'pickling' with vinegar works. Pickled onions are onions stored in vinegar. These onions last longer than normal onions because the acid kills the saprotrophic bacteria (and fungi) and thus prevents decay.

Also, may of these extremophiles have evolved mechanisms to make their cytoplasm a more neutral pH than their surroundings. These mechanisms include changes to the chemical composition of the outside layer of their cell membrane and lipoprotein pumps that pump ions out of the cell

Some Extremophile Bacteria have evolved in places that are either highly acidic or alkaline. Because of this, they have proteins that fold up and work naturally in an environment that has either lots of H+ ions (acidophiles) or lots of OH- ions (alkalinophiles). Because their folding requirements have evolved in these conditions, their proteins may denature in a neutral environment.

Yogurt pH

Lactobacillus is the bacteria that is used in yoghurt

This bacteria releases the enzyme lactase into the milk, to do extracellular digestion. Lactase cuts the disaccharide lactose into its two monosaccharides galactose and glucose. These are then absorbed into the cell. This is important for lactose intolerant people, as they can usually eat milk as most of the lactose has been digested. And that that hasn't will have some lactase with it, so it can be digested as the by the bacteria's enzyme while the person eats it.

The bacteria will absorb all three things. Lactose, galactose and glucose. It can then use lactase in its cell to cut this disaccharide into its two monosaccharides; galactose (C₆H₁₂O₆) and glucose (C₆H₁₂O₆). Both can be used in respiration.

Through anaerobic respiration, it turns the monosaccharide sugars into lactic acid: C₆H₁₂O₆ = 2x C₃H₆O₃

This lactic acid slowly curdles the milk, in a nice smooth manner, forming nice thick yoghurt

The lactic acid is the excreted waste of the Lactobacillus. However, this excreted waste also serves to help the Lactobacillus by reducing competition.

The lactic acid lowers the pH. As it does this, other bacteria that can not handle the lower pH die.

Thus competition from other species reduces and their is more food and space for the Lactobacillus bacteria.

Chemicals can help bacteria - all food is chemical

Some chemicals can harm bacteria

The main way of killing bacteria is to cause its cell wall to burst. Once this balloon has popped, it can no longer maintain ion and water concentration gradients. Solutes diffuse out of the cell while water usually diffuses in. The cell process grind to a halt, as lots of the enzymes driving them diffuse out of the cell and the cell dies

To burst the cell membrane, you can either directly attack the cell membrane (soap). You can attack proteins that are in the cell membrane (chlorine). You can attack both (alcohol)/ You can attack enzymes involved in the maintenance of the cell wall (penicillin). Or you can stop protein synthesis and this will eventually effect these enzymes (erythromycin)

There are 3 big groups

1. Disinfectant

• Disinfectant kills all life

• They kill bacteria, fungi, parasitic worms, us if we drank it

• They can do this by:

  • Chemicals that interfere with the actions of the enzymes that drive life processes eg Bleach will denature proteins. When these proteins are in the cell wall, it will cause the cell wall to rupture (cell wall rupture is secondary to protein denaturing)

  • Chemicals that cause the cell membrane to rupture by interfere with the cell membrane eg Dettol and Alcohol

  • 70% Ethanol causes proteins to denature and cell membranes to rupture - ruptured membrane results in a quick death (cell wall denaturing can occur without denaturing)

2. Antiseptics

   1. Antiseptics kill all life

   2. These are the same as Disinfectants but weaker as they are used on human skin

3. Soap

   1. Soap is excellent at killing cells

   2. If we over wash our hands, they can dry out and crack because soap can kill our cells too

   3. Soap destroys the cell membrane of bacteria, fungi and viruses

4. Anti-a-thing

   1. Antibiotic

      1. These only kill bacteria

      2. These are made first by funguses and then in factories

      3. They kill bacteria by weakening the cell membrane and causing it to burst (e.g. penicillin - this actually does this by diffusing into the cell and binding and preventing the function of enzymes that maintain the cell wall. Thus it then weakens and bursts)

      4. Some work by diffusing into the cell and binding to proteins involved in bacterial protein synthesis (e.g. erythromycin)

   2. Antifungal

      1. These only kill funguses

   3. Antiviral

      1. These only kill viruses

5. Chemical preservatives

   1. Added to food

   2. Nitrates added, bind to iron, making it harder for bacteria to get to the oxygen

   3. Increased health risks are associated with eating high levels of preservatives - if its bad for bacteria, it'll be bad for your cells too

Bacteria compete for their food and space with other bacteria and importantly with Fungi

Fungi will often win the battle

Some bacteria release toxins that kill other species of bacteria

The bacteria themselves are 'resistant' to their own toxin

An example of this is the antibiotic 'Erythromycin'

Erythromycin is released by one bacteria, it diffuses into the bacteria of another species. Here it binds to enzymes that are involved in protein synthesis. This stops them from working and stops protein synthesis. Without new proteins being made, the life processes slow down. Ultimately damaged proteins in the membrane are not replaced and the cell ruptured

Fungi also fight bacteria for food

The Fungal toxin 'Penicillin' diffuses into the bacterial cell and binds to enzymes that maintain the cell membrane. With this enzyme no longer working, the cell membrane ruptures and the cell dies.

Antibiotics are anti-bacterial substances made either by other bacteria or by fungi

They are made by these bacteria and fungi as a weapon to reduce competition for nutrients

Bacteria have high mutation rates

This is because their RNA / DNA is not protected in a nucleus

Also they don't live very long so they don't need them protected (DNA damage causes aging)

Most of the time a mutation is bad, and the affected bacteria will die

Sometimes the mutation does nothing, so the bacteria carries on with its life

In very rare instances the mutation is beneficial

Very rare instances, however a large bacterial colony on an agar plate can have over a billion bacteria, so very rare adds up quite quickly when you have big numbers

This mutation might alter one of the bacteria's enzymes so that it can destroy or resist the toxin (antibiotic). Either by directly digesting the toxin or by altering a protein that the toxin (antibiotic) acted on so that the toxin can no longer bind to and act on that protein.

All the bacteria that don't have the mutation start to die. Whereas the mutant bacteria with its ability to resist the toxin carries on with its life processes. It eats and respires, it grows and reproduces. Its daughter cells do the same, as does their daughter cells. Slowly they take over. As all the non-mutants die off the mutants rise up

MRSA infection is a common antibiotic resistant infection. It is a skin sore that doesn't improve with antibiotics

Bacteria can also spread their resistance through their plasmids via conjugation and a sex pilus

As these populations of antibiotic resistant bacteria grow, affected people can spread them. For instance the bacteria that causes Tuberculosis

The map below shows locations of high TB cases.

The 10 million cases of Tuberculosis occurred in countries where immunization is lowest.

Notice that 1 in 20 of the TB cases are Multi-Drug Resistant

Most countries try to get their citizens immunized against TB (TB is a bacteria that infects the lungs causing scarring and death). Immunization against the Tuberculosis bacteria gives the immune system a 'primer' or a 'mug shot' so that it knows what TB looks like and can kill it early. This means if we are exposed to the bacteria our immune system will kill it before it can establish itself in the body

Luckily our immune system is actually really good at fighting pathogens, especially if given early warning on what to look for

Vaccines tell the immune system what a bacteria looks like, without it ever seeing it

Vaccines tell the immune system to keep an eye out for proteins that only that bacteria has. We call these proteins 'antigens'. The immune system will make antibodies for that protein in low levels throughout your life. If the antibody ever encounters the bacteria it will act as a flag so that your immune system will detect the bacteria faster. It will then mass produce these antibodies in the hundreds of millions immediately. These will bind to the bacteria to flag it for destruction by immune cells. The binding of these antibodies also make it harder for viruses to get into cells - which is why vaccines work well against viruses like covid, as well as against the bacteria like Tuberculosis TB bacteria.

If a person does not complete their antibiotics and 'saves' some for another time (due to cost etc) then not all of the bacteria are killed. Those that remain will be more antibiotic tolerant than those that were killed, making it more likely that antibiotic resistant bacteria will rise up. This is why finishing your antibiotics is important, and why the cost of antibiotics needs to be kept low.

The good thing is that Botulinum is easily killed by heating. So heat is used during the canning process to kill all bacteria

So, to can:

1. Wash

2. Heat (100^oC)

3. Can

4. Heat (100^oC +)

5. Store

Notice that in the Wattie's Canning process for tomatoes in the short clip above, they heat the tomatoes once they are in the can

This is because, once the can is sealed, water will not boil at 100^oC due to pressure. Thus the can will be heated to 120^o C this will kill all bacteria / fungi and, very importantly, their spores

The clip below is awesome sauce. Awesome Baked Beans Sauce

It shows how baked beans are made in the Heinz Baked Beans Factory in England

Importantly, the show the temperature achieved in the can by placing a Thermometer inside the can.

The Thermometer ultimately shows that the inside of the can gets to 128^oC for 3 minutes. No life can survive at this temperature.