Question

1. How are lactic-acid bacteria used in fermentation? Please give three examples.

2. Name two species that are medically important in the lactic-acid bacteria group and a disease that is caused by each one.

3. Name two ways bacteria can produce hydrogen sulfide. What are the two enzymes important in those pathways?

4. What three tests can be done using a single SIM tube?

5. A firm acid clot can appear as a pink or white tube with a pink band at the top of it. Explain the different conditions that can result in this and if the reaction produces a white color then why does the surface remain pink?

6. Name three genera that belong in the lactic-acid group and name three basic rxns that can be detected with this test.

Question 5 is about lactic acid/litmus milk test

Answer 1

Ans 1) Lactic Acid Bacteria gives ride to lactic , acetic acid as well as CO_{​​​​​2}. It inhibits the growth undesirable microorganism as lactic acid and acetic acid both decreases the pH. The presence of undesirable microorganism destroy the crispness of the cell. Carbon dioxide which is produced , helps in the anaerobiosis needed for the process of fermentation.

Examples : Enterococcus , Carnobacterium as well as Vagococcus.

Ans 2) Two species that are medically important in the lactic-acid bacteria group are :

1. Streptococcus.

2. Pediococcus.

Disease caused by Streptococcus : It causes pneumonia , sepsis and skin infection.

Disease caused by Pediococcus : It is a gram positive LAB that causes disease lyme which is a infectious disease.

Ans 3) Hydrogen sulphide is produced by the following methods :

1. Anaerobic Respiration : Through the reduction of thiosulfate and ide which are suphur containing inorganic compounds. This process takes place during anaerobic respiration.

Enzymes : Sulfate reductase.

2. Cysteine is broken down into hydrogen Sulfide ammonia and pyruvate is broken down with the enzyme cysteine desulfurase.

Enzymes : Cysteine desulfurase

Ans 4) Three tests that can be done using a single SIM tube are :

1. Indole test

2. Motility test

3. Hydrogen sulfide production test

The media of SIM is semi solid made up of iron , sulfur and protein with including little amount of agar.

Stay safe and for any query feel free to ask in the comment section. Due to time constraints I had answered top 4 questions posted by you but if you want I will answer them in comments.