Factor Affecting Growth of Microorganism

Factors affecting Growth of Microorganisms

There are many factors that have influence on the growth of microorganisms which is as follows:

1: Temperature:

Theoretically, microbes grow at all temperature between the freezing point of water and the temperature at which protein or protoplast coagulates somewhere between the maximum and minimum point lies the optimum temperature at which the microbe grows best.

Temperature below the minimum stop microbial growth but do not kill an organism. However if bacterial microbes are soon killed. Most cells die after exposure to heat treatment in the order of 70-degree centigrade for 15 seconds, although spore forming organism requires more severe heat treatment example steam at 120-degree centigrade for 30 minutes. The microorganism can be classified as Psychrophiles, mesophiles, thermophiles and hyperthermophiles respectively if their optimum growth temperature is low ( 0 to 20 ) degree centigrade, moderate ( 20 to 40) degree centigrade, high ( 40 to 80 ) degree centigrade, and very high( 80 to 110 ) degree centigrade respectively.

Minimal and maximal growth representative bacterial species are:

1: E Coli : minimal and maximal growth temperature is 7 and 41-degree centigrade respectively.

2: Vibrio cholera: minimal and maximal growth temperature is 11 and 41-degree centigrade respectively.

3: Bacillus subtilis: minimal and maximal growth temperature is 15 and 41-degree centigrade respectively.

2: Water:

Bacteria can't grow without water. Many bacteria are quickly killed by the dry condition whereas other can tolerate the dry condition for months. Bacterial spores can survive in dry condition for several of years. Water availability is used as an indicator of the availability of water for bacterial growth. Distilled water has a water availability of 1. The addition of soluble example salt reduces the availability of water to the cell and the availability of water drops at water availability less than 0.8. Cell growth is reduced, cell organism at low water availability are called osmophiles. Most organisms required water availability above 0.96 for active metabolism but some filamentous fungi and lichens are capable of growth at water availability of 0.6.

3: PH:

Each organism has a PH range within which growth is possible. Most natural environments have PH values between 5 to 9 and the organism with optimal in this range are common. Only a few species can grow at PH values of less than 2 or greater than 10. Most bacteria prefer the growth environment with a PH of about 7 i.e neutrality. Most yeasts and fungi are found to grow best in slightly acidic media PH 5 to 6 . Many algae are tolerant of mild acidity and a few are extremely acidophilic.

4: Nutrients:

Bacteria need nutrients for their growth and some need more nutrients than others. Bacteria normally feed on organic matter as well as material for cell formation. Organic matter also contains the necessary energy. Such matter must be soluble in water and must be of low molecular weight to be able to pass through the cell membrane. If the nutrient matter is not sufficiently broken down the microorganism can produce ex- energy which spit the nutrients into smaller compounds so that they can enter the cell. Inside the cell, the nutrients are breakdown further by other enzymes releasing energy which is used by the cell.

5: Oxygen:

Animal requires oxygen to survive but bacteria differ in their requirement for and in their ability to utilize oxygen. Bacteria that need oxygen for growth are called aerobic bacteria. Oxygen is toxic to some bacteria and these are called anaerobic bacteria. Anaerobic bacteria are responsible for both beneficial reactions such as methane production in a biogas plant and spoilage in canned foods. Some of the bacteria can live either with or without oxygen and they are known as facultative anaerobic bacteria.

6: Relative humidity:

The content of water and the air is one of the major factor determining the ability to survive. At a very low humidity and high-temperature, cells face dehydration whereas high humidity may give cells protection against the solar radiation.

Growth curve of microorganism:

If S- represent the substrate which is soluble in waste water, this substrate is consumed by microorganisms. The consuming of the substrate and the growth of microorganism during this phase represent the growth curve. In growth curve, following four stages are found;

a: Lag phase:

Wastewater consist of the organic matter which is rich in nutrient and that is consumed by the microorganism as food material in any reservoir either it may be batch or continuous series of tank feed by microorganism with waste water. Temperature and PH are maintained and that was left for five days within that period microorganism adapted or acclimatized in the new environment. This phase is known as the lag phase. At this time microorganisms do not multiply.

b: Log phase:

Here in this phase microorganisms get the sufficient amount of food for the multiplication, usually bacteria are multiplied by binary fission or conjugate process. This phase is called as log phase or exponential growth of the microorganism. Usually in this phase microorganism utilized the carbon-containing compound present in the wastewater organic compound to make their number doubled.

c: Stationary phase:

According to the Darwins theory if the population is increased then the food material, as well as accommodation, becomes insufficient. The substrate present in the waste water is consumed by the microorganism is now almost finished. In this stage microorganism does not multiply their number, their number remain constant for few days. And when this condition is completely exhausted then the microorganism started to die.

d: Decline phase:

When the dying process of microorganisms is continuous then this stage is referred as decline phase. In this phase, the living population of microorganism decreased day by day and its number reach in the initial stage. So sludge consists of the mixed population of living microorganism as well as non-living microorganism but the main thing is the volume of sludge is converted to biomass.

classes.midlandstech.edu figure: Growth curve of microorganism
classes.midlandstech.edu
figure: Growth curves of microorganism

Distribution of microorganisms

Many microorganisms are found naturally in fresh and salt water. These includes bacteria, protozoa, algae and tiny animals such as rotifers. These can be imported in the food chain that forms the basis of life in the water. For example, the microbes called cyanobacteria can convert the energy of the sun into the energy it needs to live. The plentiful number of these organisms, in turn, are used as food for other life. The algae that thrive in water are also an important food source for other forms of life.

Water can also be an ideal means of transportation of microorganism from one place to another.

References;

Miller, Jr. G.T. Living in the Environment. Wadsworth Publication, 2003.

S.C., Santee. Environmental Science. India, New Center: New Center Book Agency (P) Ltd, 2004.

T., Richard. Environmental Science Towards a Sustainable Future. India: PHI (P) Ltd., 2008.

  • 1: E Coli : minimal and maximal growth temperature is 7 and 41-degree centigrade respectively.

    2: Vibrio cholera: minimal and maximal growth temperature is 11 and 41-degree centigrade respectively.

    3: Bacillus subtilis : minimal and maximal growth temperature is 15 to 41-degree centigrade respectively.

  • Bacteria need nutrients for their growth and some need more nutrients than others.
  • Oxygen is toxic to some bacteria and these are called anaerobic bacteria.
  • If S- represent the substrate which is soluble in waste water, this substrate is consumed by micro-organisms. The consuming of the substrate and the growth of micro-organism during this phase represent the growth curve
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