Materials

For the cultivation of bacteria:

• Triptone (10g)
• Levadure extract (5g)
• NaCl (10g)
• H20 d (1L)
• Agar (1,8 - 2g / 100mL)

For the observation of the bacteria and how they react to the products:

• Microscope
• Methylin blue
• Pipette
• Petri dishes (4)

Products we will use to change the pH

Products we will use to change the pH:

• Sulfuric acid
• Hydrochloric acid
• Orange juice
• Vinager
• Milk
• Soap
• Ammonia
• Sodium hydroxide 
• Lemon juice
• Drain cleaner 

This products will be added in a type of filters that we will put in the petri dishes. What we will do is to put two of this filters in every petri dish with different products. With this, what we will achieve is that when the bacterias are groing near the filter, they won't grow at a distance from the filter. This will depend on how this product will affect to this type of bacteria.

For what could be used our experiment?

Changing the pH of bacteria to investigate how they react to this changes can be useful in treatment methods that are being investigated nowadays. What we are going to do is to change the pH of this bacteria (E. coli) and with this, determinate at which point they die by denaturising or dehidrating.
In this way, this could be use by genetic ingeneers. How are going to use genetic ingeneers this? They can use it because if they are able to introduce in the bacteria some genetic information that can harm cells that can be cancer cells or other disease cells, if they rise the acidity or de salinity of the place were the cancer is, they could attack this cells in a pathogenic environment that would be controlled by especialists and when the cancer is removed or controlled, the scientists could set the salinity or acidity levels down and like this, the bacteria would die and couldn't affect the patient.

Variables

Independent variable: The one that we change. In this experiment we are going to change the different products that we add to the bacteria (this products are going to be our independent variable)

Controlled variable: The one that is always the same. The products we add to the bacteria will be always the same amount () and the type of bacteria won't change neither (e-coli)

Dependent variable: The one that changes depending on the independent variable. In this case, what will change deending on the products we add will be the pH of the bacteria and at which point they will denaturise or dehidrate.

PROCEDURE

1) Investigate how to cultivate bacteria.

2) Investigate which products can change the pH of bacteria. 

3) Cultivate the same bacteria in 8 different petri dishes. 

4) Add the lowest pH product (we have to put a filter which we would need to soak with the product and put it in the petri dish) to one of the petri dishes.
5) Leave the bacterias in the petri dish for an hour and after that, observe them under the microscope.
6) To observe them, we have to dying the bacteria with methylin blue.

7) Repeat the process number 4 with all the different products, but every different week and adding a new product to each petri dish.
8) Each week use a different petri dish and add a different product.
9) Everytime we use a product and observe it we have to take note of what we see (how the bacteria have reacted to the different products)
10) Make a table with all the information that we get from the bacteria and how they have reacted and finally, write down our conclusions.

Background information

How to control de pH

The pH is the measure of free hydrogen activity in water or in more practical terms the measure of free acidity or free alkalinity of water, is expressed like as:

pH= -log[H⁺]

The pH is measured in a scale of 0-14, solutions with a pH lower than 7 are acids (orange juice and acid rain), and higher are bases (blood and soap). Bases are used to neutralize acids and acids are used to neutralize alkalis. Byproducts are normally salt (they could be soluble or not) and water.

                             

The task of any pH adjustment is to regulate the pH of the process stream into the acceptable discharge range. In the case of an acid neutralization, caustic (NaOH) is added to the pH in order to neutralize the solution.

There are two primary system designs for pH adjustment systems: continuous and batch.

Continuous system are very suitable for relatively high flows of slightly acidic or alkaline wastewaters (example: 2.0 < pH < 12.0).

For more demanding applications, such as those with changing flows those who are characterized by highly acidic or highly alkaline wastewater then a batch system is a more appropriate choice.

Bacteria cultivation

When we grow bacteria, a growth environment called a medium is used. The organisms that grow in or on this medium form a culture. A culture is considered a pure culture when only one type of organism lives there. It is considered a mixed culture when populations of different organisms are present. When first used, the culture medium should be sterile, meaning that no form of life is present before inoculation with the microorganism.

We are going to cultivate the bacteria E. coli that is the one that is easier to cultivate in the school lab.

E. coli or escherichia coli is a bacteria that lives normally in the intestines of people and animals. Normally this bacteria is harmless and actually helps to keep our health in a good state but, sometimes it has mutations that can afect us seriously.