Question

Describe the five categories of oxygen tolerance, growth in thioglycolate and the enzymatic basis for it (ROS)

Answer 1

Five categories are as follows:

1. The bacteria which are obligate aerobes require full oxygen tension and in this type the energy is generated by oxidative phosphorylation.

2. The bacteria which are obligate anaerobes are oxygen intolerant and in this type the energy is generated by fermentation.

3. The bacteria which are facultative anaerobes can grow with or without oxygen and the energy is generated by both i.e. oxidative phosphorylation as well as fermentation. These bacteria will grow better in the presence of oxygen.

4. Microaerophiles bacteria requires oxygen (minimum 21% of oxygen require for the growth).

5. aerotolerant anaerobes do not require oxygen but also can grow in oxygen rich environment because it has oxygen sensitive biomolecules and the energy is produced by fermentation.

Many organism will not survive the powerful oxidative properties of ROS ie reactive oxygen species.

ROS are highly unstable ions and molecule derived from partial reduction of an oxygen that can damage virtually with which they come in contact.

Aerobic respiration constantly generate ROS.

Three main enzymes break down those toxic byproducts: superoxide dismutase, peroxidase, and catalase. Each one catalyzes a different reaction. Reactions of type seen in Reaction 1 are catalyzed by peroxidases.

X - (2H⁺) + H₂O₂ ----> oxidized - X + 2H₂O

In this reaction an electron donor oxidizes hydrogen peroxide to water. The following reaction mediated by the enzyme superoxide dismutase (SOD) which will break down the superoxide anions.

(2) 2O₂^- + 2H -----> H₂O₂ + O₂

The enzyme catalase converts H₂O₂ to water and O₂

₂H₂O₂ ----> 2H₂O + O₂