Question

Identify some possible effects of the following factors on microbial growth: pH, osmotic pressure, chemical requirements such as carbon, nitrogen, sulfur, phosphorus, oxygen

Answer 1

Effect of pH

1. Most of the bacteria are neutrophiles means they grow rapidly and produce their products efficiently at pH 7.0 or 2 points above or below.
2. Some bacteria are acidophiles such as feroplasma and sulpholobus species that can survive in extreme acidic pH.
3. Alkaliphiles are the microorganisms that grow best at pH between 8.0 and 10.5. Vibrio cholerae (agent of cholera), grows best at the slightly basic pH of 8.0; and it can even survive pH values of 11.0 but is inactivated by the acid of the stomach.
4. Some bacteria can survive in extreme pH changes by creating a micro environment around them that acts as buffer system for example H. pylori.
5. Extreme changes in pH that is unfavourable to the bacteria denature the bacterial cell wall as that is made up of proteins also it ceases the production of pathogenic toxins and proteinous enzymes.

Effect of osmotic pressure

1. A hypertonic environment, or an increase in salt or sugar cause plasmolysis. Microbes need a definite osmotic pressure to maintain integrity and get nutrients.
2. Extreme or obligate halophiles require high osmotic pressure.
3. Facultative halophiles tolerate high osmotic pressure.

Effects of chemicals

1. Carbon – carbon is the base of any life form, it is required to make the proteins, fats, carbohydrates and nucleic acids. Without it the growth cannot occur. It is Energy Source, Structural organic molecules

Chemoheterotrophs use organic carbon sources and Autotrophs use CO₂

1. Nitrogen – In the production of Amino Acids and Proteins, most bacteria decompose proteins, some bacteria use NH4+ or NO3- whereas A few bacteria use N2 in nitrogen fixation.
2. Phosphorus - In the composition of DNA, RNA, ATP and membranes also PO43- is a source of phosphorus.
3. Oxygen - Oxygen is used by aerobic bacteria during the process of cellular respiration as the final electron acceptor. For aerobic organisms, oxygen is an absolute condition for their energy-yielding properties. Certain microorganisms can grow in oxygen-free environments and are defined as anaerobic organism.