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.

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.

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.

To recap and to say it all in a different way

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.