EX. 13 | Carbohydrate Catabolism

Carbohydrate Catabolism

Breakdown glucose to generate ATP via 3 interconnected pathways; Glycolysis, Kreb’s Cycle, Electron Transport Chain

Carbohydrate

Organic molecules that contain carbon, hydrogen, and oxygen

• Can be classified based on size: monosaccharides, polysaccharides, oligosaccharides

Catabolism

Chemical reactions that release energy from the decomposition of complex organic molecules

• Breakdown of polymers → monomers

Starch Hydrolysis

Some bacteria secrete amylase (a hydrolytic exoenzyme) outside the cell to break starch into smaller sugars that can be absorbed. To detect this, you flood the plate with Gram's iodine after incubation.

• This determines whether the bacterium we’re working with produces amylase and if the bacteria can break down starch using exoenzymes
  
  

Results

• If clear halo around growth → starch was hydrolyzed → amylase positive

• If there is dark blue/black around growth → starch is still present → amylase negative

Exoenzyme

Leaves the cell and breaks down by the addition of water

• An example of this is amylase

• Presence of an exoenzyme is determined by looking for a change in the substrate

Amylase

Exoenzyme

• Can break down starch apart entirely into smaller sugar molecules (easy for transporation)

OF Test

This test tells you whether or not a bacterium uses glucose through oxidation (needs oxygen), or fermentation (no oxygen needed)

Results

• The indicator bromthymol blue responds to pH:

  • Yellow = acidic = glucose is being broken down (acid produced)

  • Green/Blue = neutral/alkaline = glucose is not being used
    
    

Reading the 2 tubes

• If the open tube and sealed tube (mineral oil) are yellow, the carbohydrates were metabolized, and fermentation occurred
  
  

• If the open tube was yellow, and the sealed tube (mineral oil) was green/blue, it is an oxidizer, meaning that it only uses glucose when oxygen is present
  
  

• If the open tube and sealed tube (mineral oil) were both green/blue, it is a non-utilizer, meaning that it didn’t use glucose at all

Oxidative catabolism

Requires the presence of oxygen

Fermentative catabolism

Does not require oxygen but may occur in its presence

OF Medium

A nutrient semisolid agar deep containing a high concentration of carbohydrate and a low concentration of peptone

• Peptone will support the growth of bacteria that don’t use the carbohydrate