Nutrition of Bacteria
Like other organisms bacteria. Need energy for their growth, maintenance and reproduction. Most bacteria are heterotrophic i.e., they cannot synthesize their organic compounds from simple inorganic substances. They live either as saprophytes or as parasites. Saprophytic bacteria 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 soil inhabiting bacteria have very extensive enzyme system that breaks down the complex substances of humus to simpler compounds. The bacteria can then absorb and utilize these simpler substances as a source of energy. Parasitic bacteria for their nutrition are fully dependent on their host.
Some kinds of bacteria are autotrophic i.e., they can synthesize organic compounds which are necessary for their survival from inorganic substances. These bacteria may be separated into two groups: photosynthetic autotrophs and chemosynthetic autotrophs. Photosynthetic bacteria possess chlorophyll which differs from the chlorophyll in chloroplasts, bacterial chlorophyll is dispersed in the cytoplasm.
During photosynthesis the autotrophic bacteria utilize hydrogen sulphide (H2S) instead of water as a hydrogen source and liberate sulphur instead of oxygen. Nitrifying bacteria are chemosynthetic. Chemosynthetic bacteria oxidize inorganic compounds like ammonia, nitrate, nitrite, sulphur or ferrous iron and trap the energy thus released for their synthetic reactions. The overall reaction of photosynthesis in photosynthetic bacteria can be written as:
Green sulphur bacteria, purple sulphur bacteria and purple non-sulphur bacteria are photosynthetic bacteria.
Respiration in bacteria may be aerobic (requiring free oxygen) or anaerobic not requiring free oxygen. Bacteria, which are able to grow in the presence of oxygen, are called aerobic bacteria. While those which can grow in the absence of oxygen are known as anaerobic bacteria.
Some bacteria are neither aerobic nor anaerobic, but facultative. Facultative bacteria grow either in the presence or absence of oxygen. Some bacteria require a low concentration of oxygen for growth and are known as microaerophilic.
Pseudomonas is an aerobic bacterium.
Spirochete is an anaerobic bacterium.
E.coli is a facultative anaerobic bacterium.
Campylobacter is a microaerophilic bacterium.
Growth and Reproduction
Bacterial growth refers commonly to increase in number of bacterial cells. Bacteria increase in number by an asexual means of reproduction, called binary fission. In binary fission parent cell enlarges, its chromosome duplicates, and plasma membrane pinches inward at the center of the cell. When nuclear material has been evenly distributed, the cell wall grows inward to separate cell into two.
This sequence is repeated at intervals by each new daughter cell which in turn increases the population of cells. Once the division is complete, bacteria grow and develop their unique features.
The interval of time until the completion of next division is known as generation time. Pour distinct phases are recognized in bacterial growth curve.
Fig. 6.6 binary fission in bacteria
- Lag phase: It is phase of no growth. Bacteria prepare themselves for division.
- Log phase: It is phase of rapid growth. Bacteria divide at exponential rate.
- Stationary phase: bacterial death rate is equal to bacterial rate of reproduction and multiplication.
- Death/ decline phase: Bacteria start dying. Here the death rate is more than reproduction rate.
Bacteria lack traditional sexual reproduction and mitosis. However, some bacteria transfer genetic material from a donor bacterium to a recipient during a process called conjugation. Some conjugating bacteria use specialized sex pili to transfer genetic material. Conjugation produces new genetic combinations that may allow the resulting bacteria to survive under great variety of conditions.