Bacteria reproduce by binary fission, a process by which one parent cell divides to form two progeny cells. One cell gives rise to two progeny cells two to four and so forth. This type of growth is called exponential growth or logarithmic growth. It is expressed as No of bacteria. 2, 4, 8, 16 Expopnent . 20,22,23.24 Thus, 1 bacterium will produce 16 bacteria after 4 generations. The doubling (generation) time of bacteria is the time in which bacteria double their number. It ranges from as little as 20 minutes for Escherichia coli to more than 24 hours for Mycobacterium tuberculosis. 1. 2. 3. The Growth Cycle of bacteria: It has four major phases. The first is the lag phase, during which enormous metabolic activity occurs but cells do not divide. This can last for a few minutes up to many hours. The log (logarithmic) phase is when rapid cell division occurs. 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. 4. The final phase is the death phase, in which there is a decline in the number of bacteria. The essential factors required for the growth of bacteria in vitro are. 1. Nutrients 2. Temperature 3. Oxygen concentration 4. Organic growth factors 5. PH 1. Nutrients: Important factor to carry out metabolic activity. On the basis of nutritional requirement they are a. Heterotrophs. Those get preformed nutrients like sugar, amino acids. b. Autotrophs. Those synthesize their own nutrients. 2. Temperature: The optimum temp for growth is 36.50C (the body temp range is 35-420C). Certain bacteria can grow at refrigeration temperatures i.e.0-50C. On basis of temperature requirements bacteria can be divided into. a. Psychrophiles (cold temp loving) e.g. Salmonella, Staphylococci, Proteus etc. b. Mesophiles ( moderate temp loving) c. Thermophiles ( heat loving). 3. Oxygen requirements: For most organisms, an adequate supply of oxygen enhances metabolism and growth. The use of oxygen generates two toxic molecules, hydrogen peroxide (H2O2) and the free radical superoxide (O2). Bacteria require two enzymes to remove these radicals. The first is superoxide dismutase, which catalyzes the reaction 2O.2 + 2H _____ H2O2 + O2 Second 2H2O2 is catalase, which catalyzes the reaction _____ 2H2O + O2 On the basis of oxygen requirement bacteria can be classified into. 1. Obligate aerobes e.g. M.tuberculosis, P.aeruginosa 2. Facultative anaerobes e.g. Staphylococci, Streptococci, enteric bacilli 3. Obligate anaerobes e.g. Clostridium spp. 4. Organic Growth Factors: Essential organic compounds which an organism is unable to synthesize are known as organic growth factors. They must be directly obtained from the environment. One group of organic growth factors for humans is vitamins. Many bacteria can synthesize their own vitamins and do not depend on outside sources. However, some bacteria lack the enzymes needed for the synthesis of certain vitamins, and for them those vitamins are organic growth factors. Other organic growth factors required by some bacteria are amino acids, purines, and pyrimidines. 5. PH: Most bacteria grow best in a narrow pH range near neutrality, between pH 6.5 and 7.5.