Bacteria Environmental Conditions

Environmental Conditions

There are conditions that are required for bacteria to live:

  1. Liquid Water

  2. Warm Temperature

  3. Chemically safe, including pH

  4. Food

  5. Space

  6. Oxygen

The limits of life are determined by what the environment does to the chemicals that make up proteins, DNA and the membrane

Environmental factors will be selected from: temperature, oxygen availability, nutrients, moisture, chemicals (including pH, toxins, antibiotics, disinfectants), and competition.

Water

All living organisms contain water

You are more water than you are anything else

This is because water allows chemicals to move

Life is powered by chemical reactions - these can only happen if the required chemicals get to where they need to be

These chemicals include hydrocarbons or carbohydrates and often oxygen, but not always. They almost always make carbon dioxide, but not always.

Life on the cellular level is chemical reactions in bags of water - that is effectively what a cell is

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.

This requirement for water is why your desk doesn't have visible bacterial colonies on it - but agar does

This need for water is why if you took banana and put it into a zip lock bag for a week it will rot. But if you did the same with dry banana chips (those dry pieces of banana you put in your cereal) then it will be fine.

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.

Dehydrate

To preserve our food we can dehydrate it.

This can be done by just drying it out or by using chemicals to remove water

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

The most common dehydrated foods eaten are probably Raisins

Raisins are dried grapes. As the water content reduces it becomes harder for bacteria (which are water filled) to colonize and eat the grape

So grapes rot, but raisins are preserved

Grapes into raisins were the first for this to be done to

They could be dried using the suns heat.

The sugar in the grapes / raisins also stopped bacterial growth due to osmosis

Now days we can use ovens to dehydrate other things. A popular choice is dehydrating banana slices into banana chips

These last a long time at room temperature in sealed bags that keep moisture out. Indeed all of the banana that you have in your cereal box is dehydrated, as is all of the other fruits. They become soft and slightly rehydrated once you add milk. This is why these cereals with dried fruits can just be stored in the pantry.

You can physically dehydrate fruits using the sun, or the oven. You can also chemically dehydrate foods by using osmosis. The most natural chemical dehydration of foods is with either sugar or salt.

Beef jerky is an interesting one as it combines physical dehydration with chemical dehydration. The beef is heated and cooked to remove the water. It is also salted so that if any bacteria land on the jerky, the water of the bacteria is osmotically pulled out, killing the bacteria.

Banana chips and fruits don't need salt because their sugar will do the same thing to any bacteria that land on them - water will move out of the bacterial cell and over to the sugar, killing the bacteria.

Drying is an ancient form of food preservation. As is salting and using sugar as a preservative.

Temperature

The only limiting factor is liquid water.

For life, water has to be liquid.

Which means, for temperature, life on our planet needs between zero and one hundred degrees Celsius

Heat energy affects the movement of water

Heat energy affects how much energy atoms have

Heat energy affects how fast the liquid and gas atoms move and how much atoms in solids vibrate

Heat energy causes water to move faster and to slam into larger compounds with more force

Water (and gas) molecules slamming into large molecules causes Brownian Motion

The hotter it is, the move vigorous the motion is

Too much motion and some compounds can break apart

Protein shape determines its activity

Proteins are held in shape by a combination of strong bonds and some weak attractive forces. These weak attractive forces, in particular 'hydrogen bonds' are easily broken by water molecules colliding with too much force. This then causes the protein to change shape. This changed shape is different from the original nature of the protein, so this is called 'denature'. The proteins will not function as well, or not at all.

If enough proteins are not working, then the mechanics of life stop

Life is sustained chemical reactions facilitated by proteins occurring within water bubbles with a outer lining of lipid

Proteins carry out the reactions, and the reactions are so that proteins can do things. Proteins are the 'people' of the cell city.

So if the proteins stop working, life stops.

Boiling

Boiling denatures proteins and bursts cell walls, killing cells.

This is why you have to boil the water if you go camping and get your water from the river, lake or stream

The hotter the water is, the faster the water atoms zoom around the cell and the faster they are moving when they collide with proteins and DNA or RNA, so they collide with more force

At the same time, the water molecules spread further apart, causing a cell to swell.

Freezing

As water freezes it expands, this can causes cells to burst

As water freezes, some of the water crystals form around the DNA or RNA and causing them to be ripped apart

This is one of the reasons why freezing an animal will kill it

However many bacteria will survive the freezing process because they are so small and simple that they survive the expansion process

So you still have to cook your food - not just freeze it

Because many bacteria can survive this freezing process, it is used in microbiology to cryopreserve bacteria - with some glycerol added to increase the number that survive

For the bacteria that are frozen they are in a state of dormancy. They are NOT conducting the process of life. Their proteins are frozen in position, the chemicals in the cells are all frozen in position. There is no free movement. So they are cryopreserved. Once they thaw out, they can then carry on with their life processes.

Plants and animals that die in freezing conditions do not decay. Rather they are preserved, this is because the saprotrophic bacteria is also frozen. This is why Wooly Mammoths are still being dug up with their muscles intact

Optimum Temperatures

Life evolves to survive in its environment

So the optimum temperature for that life is dependent on the temperature that it has adapted to and evolved for.

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 -20oC . This relies on antifreeze protein preventing ice crystals forming

The highest temperature that active life has been found is 122oC . 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

Danger zone or the Ideal zone

Human pathogens have an optimum temperature that is the same as ours 37.5oC.

Most saprotrophic bacteria in the soil can operate just above freezing to a maximum of 45oC

Saprotrophic bacteria are responsible for food spoilage

Pathogenic bacteria are responsible for food-borne illness

Below this and their cells freeze, and above this their proteins denature

At the cold temperatures, such as 5oC , these bacteria live slowly.

  • extra-cellular digestive enzymes diffuse to nutrients slowly

  • nutrients diffuse into cells slowly

  • chemical reactions in the cell occur slowly

  • Enzymes work slowly

  • respiration occurs slowly

  • bacteria grows slowly

  • reproduction occurs slowly

At high temperature, such as 37.5oC , these bacteria live quickly

  • extra-cellular digestive enzymes diffuse to nutrients quickly

  • nutrients diffuse into cells quickly

  • chemical reactions in cells occur quickly

  • enzymes work quickly

  • respiration occurs quickly

  • bacteria grows quickly

  • reproduction occurs quickly

At very high temperature, such as 60oC , most bacteria die

  • cell wall can become damaged

  • Temperature causes water to expand

  • Cells burst

  • RNA/DNA damaged by fast moving water

  • Proteins denature

But some will survive and some will make spores

At 100oC only spores remain - the longer the bacteria is boiled for the more die and the more spores are destroyed

In a pressure cooker, at 120oC - everything dies, including spores and viruses

Food Temperatures

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

Some bacteria will form spores that can survive 100oC

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

Autoclaving

  • Over 121oC

  • High pressure

  • 15 minutes minimum

  • Everything dies, including viruses


Pressure Cooking

  • Over 100oC

  • Everything dies


Boiling

  • 100oC

  • Everything dies


Cooking

  • Over 75oC

  • most things die, however spores may remain


Pasteurization

  • Brief heating to 70o C. Most things die. Some will remain but in very low numbers.

  • Hotter will start to cook the milk so its a balance.

  • used in milk and fruit juice


Refridgeration

  • Under 5oC

  • Everything is alive

  • Things are living slowly

  • slow digestion, slow spoilage

  • slow growth, slow reproduction


Freezing

  • Under OoC

  • Still alive, but not living

  • suspended animation

  • bacteria can be re-animated

  • life processes can start back up

  • perhaps thousands of years later!


Freeze-drying

  • Freezing followed by low pressure to cause vaporization of water.

  • Can kill bacteria by vaporizing water in their cells.

  • Some spores may remain dormant.

pH

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.

Vinegar

Interestingly it is a bacteria that makes vinegar

Vinegar prevents decay, and is made by decay.

First you need alcohol - to make this you use anaerobic yeast (a type of Fungi). They turn glucose into Ethanol

Anaerobic Yeast: C6H12O6 = C2H6O + C2H6O + CO2 + CO2

Then the alcohol content gets too high and the yeast die off

Next you leave the alcohol exposed to air

The alcohol will kill most bacteria. However there is a species that can live in the alcohol.

This is 'Acetic Bacteria'.

These Acetic bacteria respire by turning Ethanol into Acetic Acid

Acetic Bacteria: C2H6O + O2 = C2H4O2 + H2O

Acetic acid is vinegar. Vinegar is acetic acid.

These acetic bacteria will also respire using sugar. Thus the acetic acid produced help limit competition from other species for the sugar, as now there is both alcohol and acetic acid - making it very hard for other species.

To stop this aerobic acetic bacteria, you put a lid on it - thus turning it anoxic and stopping all respiration.

Vinegar making has existed for as long as alcohol making, as it is the accidental left over from leaving alcohol (mainly wine) exposed to the air.

Below is vinegar being made from wine. Notice that it is still wine barrels, except that now they have a hole cut into the top of them and a white cloth draped over. This lets oxygen in with out letting leaves and dirt blow in from outside. They are not worried about contamination due to other bacteria and fungi as nothing else can live in this combination of alcohol and acid.

Competition For Food and Space

Toxins and Antibiotics

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.

Oxygen

Excluding oxygen can cause aerobic bacteria to die or form dormant spores

However, Facilitative anaerobes and obligate anaerobes can survive.

The survival of the obligate anaerobe Botulinum can cause the severe and often lethal food poisoning Botulism

How to Can - A guide to Canning

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 (100oC)

  3. Can

  4. Heat (100oC +)

  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 100oC due to pressure. Thus the can will be heated to 120o 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 128oC for 3 minutes. No life can survive at this temperature.

Yoghurt


How to make Yoghurt

  1. Heat milk to 60oC - to kill all microbes

  2. Let milk cool to 40oC

  3. Add a spoonful of older yoghurt

  4. Mix

  5. Cover and store at a warm temperature

The clip to the side (River Cottage Food Tube) is the one that we followed to make our yogurt in class, he explains some of the biology as well :-)

How does Lactobacillicus help to make Yoghurt

Lactobacillicus excretes extracellular digestive enzymes.

The digestive enzyme Lactase cuts the sugar Lactose in half. Making the simpler sugars Glucose and Galactose.

Once cut, the Glucose diffuses into the cell

Here it is used in Anaerobic Respiration

Through anaerobic respiration the bacteria cuts the Glucose in half making 2 molecules of Lactic acid

This Lactic Acid is excreted by the bacteria and diffuses away.

Acid causes the proteins in milk to denature. This makes milk clumpy.

If you leave your milk for ages it will go off, it will smell and it will be clumpy - due to lactic acid and lots of different bacteria releasing toxins

But with fresh milk, you can heat it to denature the proteins with heat, then add a species of bacteria called lactobacillus. This will do anaerobic respiration and release lactic acid. The lactic acid will make the milk thick - this is yogurt.

(Once different bacteria get into the yogurt, it will go off due to different toxins being released by the other bacteria)

Note, that the bacteria doesn't have to use glucose as the hydrocarbon for this process. In yoghurt the bacteria can also use the sugar Galactose C6H12O6

In the anaerobic fermentation of fruits by bacteria, they will use the sugar Fructose, C6H12O6

Notice that these sugars still have the same number of atoms and of each atom as glucose, C6H12O6. Its only the exact arrangement of these atoms that differ. Because they all have the same number of each atom, they can all be split by anaerobic bacteria into Lactic Acid, C3H6O3

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.

Another IA reminder

  1. Name and describe the micro-organism used in yoghurt making

  2. Describe the steps to produce yoghurt and explain the role of bacteria in this process

  3. Link the Life processes of the bacteria to the production of yoghurt

    1. Describe the most important bacterial life processes in the production of yoghurt

    2. Explain how these life processes help to produce yoghurt

    3. Link the physical characteristics of yoghurt to these life processes

  4. Discuss the effect of different environmental factors (temperature and pH) on the production of yoghurt

    1. Explain how the environmental factors affect the relevant bacterial life processes

    2. Explain how the affected life processes impact the production of yoghurt

  5. Explain how the produced yoghurt is preserved through elimination of other unwanted micro-organisms

  6. Discuss the impacts of this knowledge of micro-organisms and food production on your everyday life