NUTRITION IN BACTERIA
Why Nutrition / Energy Required?
Like other organisms bacteria need nutrition (energy) for their growth, maintenance and reproduction.
CLASSIFICATION OF BACTERIA ON THE BASIS OF NUTRITION:
On the basis of nutrition bacteria are of two types which are heterotrophic and autotrophic.
They cannot synthesize their organic compounds from simple inorganic substances.
Most bacteria are heterotrophic. They live either as the saprophytes or as the parasites.
They get their food from dead organic matter. Soil is full of organic compounds in the form of humus.
Humus is the material resulting from the partial decay of plants and animals.
Many bacteria in the soil have every extensive enzyme system that break down the complex substances of humus to simpler compounds.
The bacteria absorb and use these simpler substances as a source of energy.
These are fully dependent on their host for their nutrition.
They can synthesize organic compounds from inorganic substances. Some kind of bacteria are autotrophic. These bacteria are divided into two groups:
These bacteria synthesize their food by the process of photosynthesis.
The chlorophyll in them is different from that of green plants.
Bacterial chlorophyll is dispersed in the cytoplasm (while in most green plants, the chlorophyll is present in the chloroplasts).
During photosynthesis these bacteria use hydrogen sulphide (H2S) instead of water as a hydrogen source and release Sulphur instead of oxygen.
The overall reaction of photosynthesis in photosynthetic bacteria is:
CO2 + 2H2S ————————————- (CH2O)n + H2O + 2S
Examples: Green Sulphur bacteria, purple Sulphur bacteria and purple non-Sulphur bacteria are photosynthetic bacteria.
These bacteria can oxidize inorganic compounds like ammonia, nitrate, nitrite, Sulphur or ferrous iron. As a result the energy is released which is used for their synthetic reactions.
Nitrifying bacteria are chemosynthetic.
RESPIRATION IN BACTERIA
On the basis of mode of respiration, bacteria are divided into following groups:
These are able to grow in the presence of oxygen, Pseudomonas is an aerobic bacterium.
These can grow in the absence of oxygen. Spirochete is anaerobic bacterium.
These bacteria can grow either in the presence or absence of oxygen. E. coli is a facultative anaerobic bacterium.
Some bacteria require a low concentration of oxygen for growth and are known as microaerophilic. Example is Campylobacter.