Question

discuss the characteristics of two classes of Proteobacteria focusing on

1. cell morphology
2. oxygen requirements
3. habitat

Answer 1

Proteobacteria : It includes gram-negative bacteria which are part of normal human activities and pathogen bacteria also. These bacteria were previously called " Purple bacteria and their relatives" by an American microbiologist.

The classes of proteobacteria are:

1) Alphaproteobacteria

2) Betaproteobacteria

1) ALPHAPROTEOBACTERIA:

This class includes bacteria like Agrobacterium, Rhizobium, Brucella.

Cell morphology:

Rhizobium is aerobic, gram negative, motile bacteria. It is about 1.5-3.0 × 0.5-1.0 micrometres in size.

Oxygen requirements:

These bacteria are very well adapted to live in low nutritional environment as glacial ice, deep soil. Hence, they are called Oligotrophs. They are aerobic but they does not depend on oxygen completely. Hence, they can compensate low availablity of oxygen.

Habitat:

As they are Oligotrophs, they are found in low nutritional environment like underdeep soil, glacial ice. They require oxygen as they are autotrophs but they can become chemoheterotrophs or chemoautotrophs at low oxygen availability.

2) BETAPROTEOBACTERIA

This class includes bacteria like Thiobacillus, Bordetella.

Cell morphology:

Bordetella is a small ( 0.8×0.4 micrometres ) In size, rod shaped, coccoid, gram negative bacteria.

Oxygen requirements:

They are not Oligotrophs like Alphaproteobacteria and hence require a favourable amount of oxygen for thier survival. They can't change their mode of respiration and hence are totally dependent on oxygen.

Habitat:

They are found between aerobic and anaerobic regions ( like human intestine ). These include some bacteria which can cause serious life threatening diseases to humans. They require a healthy amount of organic matter to survive.