The growth of bacteria is affected by various factors, Some of them are given below:
If cultivating medium is rich in growth promoting nutrients, growth occurs faster. Decrease in nutrient concentration decreases the growth rate of bacteria. Different bacteria requires different types of nutrients and growth faster for their growth. Growth rate of microorganims with increase in concentration of substrate uo to certain level, then growth reain constant. The relationshio between substrate concentration and growth rate of organisms is given in figure;
It affects the growth of microorganismsby various ways. The lowest temperature that allows the growth in minimum temperature and the highest temperature that allows the growth is called maximum temperature for that bacteria. there is no growth of bacteria below minimum and above maximum temperature.Below the minimum temperature, cell membrane becomes stiff so growth cannot transport nutrient and cannot develop proton gradient so growth cannot occour. At high temperature denaturation of protein and enzyme and thermal lysis of cell occurs, so growth does not occour above maximum temperature.When temperature increases, growth of microorganisms increases slowly and growth becomes maximum at certain temperatureand on furthur increasing the temperature, growth rate decreases abruptly. The temperature at which growth is maximum is called optimum temperature for growth. With increase in the temperature, rate of various cellular and metabolic activity ncreases so growth increases with temperature. But above certain temperatures, growth rate decrease because at higher temperature denaturation of protein occurs.
pH effect the ionic propert of cell constituent of bacteria. So growth is affected by pH. Most bacteria grow in neutral pH. Optimum pHat which most bacteria grow is 5-9. Classification of bacteria based on pH requirement is:
All bacteria requires meals as k+, Ca++, Mg++, and Fe++, to synthesizevarious enzymes and proteins.These four elements are required in higher concentration and hence aare called macro elements. Other metals sucs as Zn++, Cu++, Mn++, Ni++, and Co++ are required in lower concentration and hence are called trace elemnts. they are also required to synthesize cell constituents.
Most bacteria do not require Na+ ion so most bacteria grow at very low Nacl concentration. But some archae-bacteria require high nacl concentration for growth such organisms are called halophiles. Such halophiles have celll wall composed of glucoprotein with high content of glutamic acid and aspartic acid. On the surface of cell wall, so high concetration is required to shield the negative charges of COOH group. If Na+ is insufficient negative charge of aspartic acid and glutamis acid repeal each other and cell wall break. Hence high Na+is required to stabilize the cell wall of such bacteria and these bacterua cannot grow at low salt concentration.
Oxygen and carbondioxide are important gasthat affects the growth of microorganisms. Oxygen is required to carry out various oxidation reactions in the body. Carbon dioxide is also required by some microbes. It is required as sole source of carbon by some microbes. However requirement of these gases is different for different bacteria;
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Nutrion is requird for the faster growth of microorganisms.
Decrease in nutrition directly decreases number of microorganisms.
The temperature a which growth of microoorganisms is favoured is called optimum temperature.
Beyod optimum temperature the growth stops as high temperature favours denaturation of protein that results is death of microorganism..