Microbiology - Bacteria Growth, Reproduction, Classification
Microbiology - Bacteria Growth, Reproduction, Classification
Bacterial Growth
Bacteria reproduce by binary fission, a process by which one parent cell divides to form two progeny cells.
Because one cell gives rise to two progeny cells, bacteria are said to undergo exponential growth (logarithmic growth).
Growth curve of bacteria or bacterial growth curve:
The first is the lag phase, during which vigorous metabolic activity occurs but cells do not divide. This can last from a few minutes up to many hours.
The log (logarithmic) phase is when rapid cell division occurs. β-Lactam drugs, such as penicillin, act during this phase because the drugs are effective when cells are making peptidoglycan (i.e., when they are dividing). The log phase is also known as the exponential phase.
The stationary phase occurs when nutrient depletion or toxic products cause growth to slow until the number of new cells produced balances the number of cells that die, resulting in a steady state.
The final phase is the death phase, which is marked by a decline in the number of viable bacteria.
Classification of bacteria on the basis of oxygen requirement
Obligate aerobes:
They require oxygen to grow because their ATP-generating system is dependent on oxygen as the hydrogen acceptor.
e.g., M. tuberculosis.
Facultative anaerobes:
They utilize oxygen, if it is present, to generate energy by respiration, but they can use the fermentation pathway to synthesize ATP in the absence of sufficient oxygen.
e.g., E. coli.
Obligate anaerobes:
They cannot grow in the presence of oxygen because they lack either superoxide dismutase or catalase, or both.
e.g., Clostridium tetani.
Fermentation
Fermentation is also called the glycolytic (glyco = sugar, lytic = breakdown) cycle, and this is the process by which facultative bacteria generate ATP in the absence of oxygen.
The term fermentation refers to the breakdown of sugar (such as glucose or maltose) to pyruvic acid and then, usually, to lactic acid.
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