WEEK 4

Topic 4 : Distribution of microorganism 

In this forth week we study on topic 4 which is the distribution of microorganism. This topic is basically about the distribution of bacteria at the places that follow their needs and have a correct nutrition for their growth. Then, we will be looking for the physical and chemical factors affecting the microbial distribution.

Growth limitation by environmental factors, there are two laws which is :

a) Liebig's Law of the Minimum

b) Shelford's Law of Tolerance

Both laws determine the presence and success of organism in an ecosystem.

Physical factors affecting distribution of microorganism

• Solutes and water activity
• Temperature
• Pressure
• Radiation

So we look one by one on the physical factors that affecting the distribution of microorganism. Solutes and water activity is about the changes in the osmotic concentration. Hypotonic solution is a solution with low osmotic concentration. Water will enter into the cell and making the cell to burst while hypertonic solution is a solution with high osmotic concentration. In this solution water will move out from the cell and making the cell shrink (plasmolysis). Amount of water available to microorganism can be reduce by interaction with solute molecules (osmotic effect) and adsorption to the surfaces of solids.

Temperature will affected the enzyme catalyze reactions. If the temperature beyond the maximum temperature of bacteria growth this the enzyme in the cell denatured and also the transport carries and other proteins also will subject to damage and disintegrate membrane. At low temperature membrane would be solidify and velocity of enzyme reaction is very low.

The pressure at the land or surface of water is 1 atm while in the deep sea the pressure is about 600 until 1100 atm (place where barotolerant will inhibit chemical reaction. Barophilic microorganism is a microorganism that dependant on high pressure. It will under go a rapid growth when in high pressure. Radiation, the major source of heat is infrared. UV radiation is the most damaging to living organisms.

Chemical factors affecting distribution of microorganisms :

• pH 
• Oxygen concentration
• water
• carbon
• nitrogen. phosphorus and sulfur
• special growth factor
• trace element

pH is the measure of hydrogen ion activity of a solution. There are four types of microorganism based on the pH tolerance which is acidophiles (pH 0 to 5.5), neutrophiles (pH 5.5 to 8.0), alkalophiles (pH 8.5 to 11.5) and extreme alkalophiles (above pH 10). We can see a few types of microorganism based on the oxygen concentration like aerobes, anaerobes, facultative anaerobes, aerotolerant anaerobes and microaerophiles. Water occupy almost 75-90% of cells. The function of water is as solvent and also for cellular function and also in metabolism.

Carbon is importance for chemical building block for cells and as source of energy for some microorganism. Special growth factors is specific nutrient such as amino acid or vitamin that was needed in low concentration. Trace element is for the enzyme to function or neede in the metabolism and it is not necessary to specifically provide. 

These are the factors that I have learnt from the lecture and because of these factors making the bacteria come to that specific place.

Thursday we have test 1. This test cover 4 topics fom the principle of microbial ecology until distribution of microorganism. After finish the test about one hour, Dr Wan give us a bit explanation about our SCL task. That's all for this week see again next week.