NUTRITIONAL REQUIREMENT FOR BACTERIAL GROWTH AND FACTORS AFFECTING BACTERIAL GROWTH
Nutritional requirements for the bacterial growth
Water covers 70% of the total bacterial mass. Two important gaseous constituents in microorganism are oxygen and hydrogen. Other than these, carbon, nitrogen , sulfur and phosphorus are other major elements in the bacterial cell. Potassium, magnesium and calcium are also important elements required for the growth of bacteria. There are several metal ions which are needed in the trace amount which usually acts as a cofactor in many essential enzymatic reactions. These trace elements are not needed to be added with culture media, as they can already been found as a result of contamination of water and other nutrient sources. These trace elements includes metal ions of manganese, cobalt, zinc copper and molybdenum.
|ELEMENT||% OF DRY WEIGHT|
Factors affecting growth
pH: Bacteria grow best at their optimum pH. Most of the bacteria can grow in the neutral environment at pH=7 (known as neutrophiles) such as Vibrio cholreae. But some may have optimum pH in acidic region (known as acidophiles) such as Lactobacillus, while others may grow in highly basic regions (Alkaliphiles) such as Agroacterium.
Temperature: Bacteria grow best at optimum temperature. Most of the bacteria shows optimum growth above 35oC, but many have optimum temperature below freezing temperature and also above boiling temperature of water. Some bacteria can only grow at particular temperature and are called as obligate for that temperature, while others may tolerate changes in temperature and thus called, facultative for that temperature or condition.
- Bacteria which have optimum temperature below 20oC are known as Psychrophiles. Bacillus globisporus is an obligate psychrophile, while Xanthomonas pharmicola is a facultative psychrophile. Listeria monocytogenes is known to cause spoilage in refrigerated food. T
- hose bacteria which shows best growth at temperatures between 25-40oC are known as Mesophiles. Most of the human pathogens are under this category.
- Some bacteria shows best growth above 50oC and are known as Thermophiles. Bacillus stearothermophilus is an example of obligate thermophile. Some archaeobacteria are known to show growth at 115oC.
Oxygen: Bacteria which require oxygen for its growth are known as aerobes. An example of obligate aerobe is Pseudomonas. Those bacteria which cannot grow in the presence of oxygen are known as anaerobes. Clostridium botulinum, C. tetani and Bacteroids are the examples of obligate anaerobes. Microaerophiles such as Campylobacter shows best growth in the presence of very little oxygen.
Bacteria which usually carry aerobic metabolism in the presence of oxygen, but may also grow in anaerobic conditions are known as facultative anaerobes. For example:Staphylococcus and E. coli.
Another category of bacteria is Aerotolerant anaerobes, which can survive in the presence of foxygen but they do not use oxygen for its metabolism. Example of this class is Lactobacillus.
Moisture: Water is required for all the bacteria to grow. They usually gets this water from the moisture present in the environment. in conditions of dryness, bacteria forms spores which can survive by remaining in the dormant stage for long time.
Hydrostatic pressure: It is the pressure exerted by the water, which increases as the depth increases. Some of the bacteria can only survive in deep into the sea under high pressures. Such bacteria are called barophiles. On decreasing pressure, the structure of their enzymes changes and bacteria cannot survive.
Osmotic pressure: Bacterial cell undergo plasmolysis when kept in hyperosmotic environment. When bacterial cells are kept in an environment having lesser osmotic pressure, water moves inside the cell which makes the cell tugid. Due to presence of cell wall, cell does not burst. Those bacteria which so not require high osmotic conditions are nonhalophiles.
Marine bacteria are generally moderate halophiles, which some bacteria like Halobacterium are extreme halophiles.
Radiations: Most of the bacteria cannot survive the radiations such as gamma rays and UV rays. But there are few bacteria which can withstand very high dose of radiations, such as, Deinococcus radiodurans can survive upto 10,000 Grays of radiations.
Nutritional factors: Bacteria requires proper nutrition for the growth. Nutrients which discussed in the starting are required for the proper growth of bacteria.
Bacterial Growth Curve
1. Elements which are required in trace quantity for the growth of microorganisms are called?
a. Essential elements
b. Trace elements
c. Non-essential elements
2. Which of the following bacteria is responsible for the spoilage of referigerated food?
a. Listeria monocytogenes
b. Bacillus stearothermophilus
c. Vibrio cholreae.
3. Microorganisms that can only survive under high hydrostatic pressure are called?
4. Microbes which can survive in the presence of oxygen but they do not use oxygen for its metabolism are called?
b. Obligate anaerobes
d. Facultative anaerobes
5. Which of the following elements are not trace elements for the growth of bacteria?
a. I, III, V
b. II, V
c. II, III, IV
d. I, II, IV
6. Match the following Bacteria with their correct categories:
|I. Xanthomonas pharmicola||A. Obligate psychrophile|
|II. Bacillus stearothermophilus||B. Aerotolerant|
|III. Lactobacillus||C. Obligate thermophile|
|IV. Bacillus globisporus||D. Facultative psychrophile|
a. I-D, II-C, III-B, IV-A
b. I-D, II-A, III-C, IV-B
c. I-A, II-C, III-D, IV-B
d. I-C, II-D, III-A, IV-B
7. Correct sequence of true/false for the given statements can be?
- Deinococcus radiodurans can survive upto 10,000 Grays of radiations.
- Halobacterium are extreme halophiles.
- Barophiles can also survive in lower hydrostatic pressure conditions.
- Campylobacter is a Microaerophile
REFERENCES Black JG, Black LJ. Microbiology: principles and explorations. John Wiley & Sons; 2018 Jan 4.