Cariology

Question 1

Explain the 5 steps of biofilm formation starting with a clean surface.

Answer 1

1) Conditioning film establishment; proteins and polysaccharides form the “acquired pellicle”

2) Bacteria bind onto acquired pellicle

3) Bacteria multiply

4) Secondary bacteria bind onto pioneering bacteria

5) Max quorum sensing threshold is reached; extracellular matrix secretion

Question 2

How does the structure of biofilms aid in microbial survival?

Answer 2

Biofilms have a hetergenous structure allowing for a variety of physiological and protectant functions:

1) Bulk fluid layer above biofilm protects dense layer of microbes beneath from changing pH, saliva proteins, and immune cells.

2) Channels within biofilm allow for diffusion of nutrients and waste removal

3) Bacteria within biofilms are closely packed and can interact synergistically; nutrient web formation

Question 3

5 types of interactions within biofilms?

Answer 3

Nutrient webs
Protection (physical and chemical)
Killing
Travel
Quorum Sensing

Question 4

Bacteria X requires sugar and nitrate to survive. Bacteria Y requires sugar to survive. When Bacteria X and Y are cultured separately on 40g/L of sucrose gel, Bacteria X ceases to grow while Bacteria Y exponentially increases in population. When Bacteria X and Y are cultured together, both populations are exponentially increase in growth. After 40 generations both populations crash. Explain the relationship between bacteria X and Y. Why did the population crash after 40 generations?

Answer 4

Bacteria X requires nitrate to survive.

When cultured without nitrate, bacteria X will not grow due to lack of nitrate.

When bacteria X and Y are cultured together, both populations grow. This must mean bacteria Y produces nitrate as a by-product of its metabolic interactions.

Since bacteria X and Y both grow when cultured together, the relationship is commensalistic. X does not impact Y’s growth, but X positively benefits from Y.

After 40 generations, the sugar (energy source) is used up in the culture and both populations will crash.

Question 5

What’s the difference between a mutrulistic relationship and synergistic relationship?

Answer 5

Mutualists depend on each other to survive; otherwise both species will die.

Synergists don’t depend on each other to survive; but will perform way better when paired together

Question 6

Bacteria A and B are cultured together in a petridish. Bacteria A secretes peptide A that signals for extracelluar matrix formation. After many days, no biofilm is formed. Why is that?

Answer 6

There are 2 types of quorum sensing molecules:

AI-1 and AI-2

AI-1 is species specific language and AI-2 is a universal language

Peptide A is AI-1 and cannot be recognized by bacteria B; thus no biofilm

Question 7

You are a scientist trying to disrupt biofilm formations. What would you do?