Conditions for the Growth of Microorganisms: Intrinsic, Extrinsic, and Implicit Factors

Conditions for the Growth of Microorganism: Food, water, and shelter are the essential necessities for humans to survive. Microorganisms have the same requirements as humans: they require nutrients for energy, water to stay hydrated, and a suitable environment to thrive. The optimum settings differ according to the species of microbe, but they all contain elements from these factors given below. Read on to learn more about the conditions for the growth of microorganisms.

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Definition of Microorganisms

Microorganisms, or microbes, are a diverse group of generally minute simple life-forms that include bacteria, archaea, algae, fungi, protozoa, and viruses.

Growth of Microorganisms

A steady increase in all the chemical components of an organism may result in an increase in cell size, cell number, or both are known as growth. For microorganisms to thrive, their surroundings must be ideal. The factors that influence the growth requirements can be categorised as intrinsic, extrinsic, and implicit factors.

While all microbes have the trait of being extremely small, their environmental requirements are fairly varied. They have similar requirements, but the resources required to accomplish them are vastly different.

Conditions Needed for the Growth of Microorganisms

A. Intrinsic Factors

The internal self-parameters of microorganisms are referred to as intrinsic factors. These factors include:

1. pH

Fig: pH Scale

Moulds and yeasts can grow at lower pH than bacteria, while Gram-negative bacteria are more susceptible to low pH than Gram-positive bacteria. Moulds thrive best in a pH range of 1.5 to 9.0, yeasts in 2.0 to 8.5, Gram-positive bacteria in 4.0 to 8.5, and Gram-negative bacteria in 4.5 to 9.0. Microorganisms can be classified into the following groups based on their pH ranges:

1. Neutrophiles grow best at a pH range of 5 to 8.  
2. Acidophiles grow best at a pH below 5.5.
3. Alkaliphiles grow best at a pH above 8.5.

2. Water activity (aw)

Microorganisms require water in a readily available form. The ratio of the food’s water vapour pressure to that of pure water at the same temperature can be used to calculate the food’s water activity. Because no meal may have a water activity of 0 or 1, it ranges from >0 to 1.

1. In comparison to fungi, bacteria require more water activity for growth. Bacteria cannot grow below a pH of 0.91, but moulds may thrive to a pH of 0.80.
2. Gram-negative bacteria are more sensitive than gram-positive bacteria to low water activity.

Based on the nature of available water for growth and its amount, microorganisms can be grouped as:

1. Halotolerant that can grow in the presence of high concentrations of salt.
2. Osmotolerant that can grow in the presence of high concentrations of unionized organic compounds such as sugars.
3. Aerotolerant that can grow on dry foods.

3. Oxidation-reduction potential (Eh)

A substance’s oxidation-reduction or redox potential is defined as a measurement of electron transfer between atoms or molecules. Eh is the standard abbreviation for the oxidation-reduction potential, which is measured in millivolts (mV). Food’s redox potential is determined by the:

1. The pH of the food
2. Availability of oxygen (physical state, packaging)
3. Poising capacity or buffering capacity
4. Food composition (such as protein, ascorbic acid, reducing sugars)

The Eh range at which certain microorganism groups can thrive is as follows:

1. Aerobe: Moulds, yeasts, Bacillus, Pseudomonas, Moraxella, and Micrococcus all can grow best at +500 to +300 mV.
2. Facultative anaerobes: Lactic acid bacteria and members of the Enterobacteriaceae family are facultative anaerobes that thrive best at +300 to +100 mV.
3. Anaerobes: Clostridium spp., for example, can grow best in the range of +100 to –250 mV or below.

4. Chemical Requirements

1. Carbon

Carbon makes up 50% of the dry weight of cells. It is the structural backbone of all organic compounds. The microorganism can be classified into two based on the ability to obtain carbon from different sources.
A. Chemoheterotrophs: Obtain carbon from their energy source: lipids, proteins, and carbohydrates.
B. Chemoautotrophs and Photoautotrophs: Obtain carbon from carbon dioxide.

2. Nitrogen, Sulphur, and Phosphorus

A. Nitrogen: Makes up 14% of dry cell weight. Found in amino acids, DNA, and RNA.
B. Sulphur: Forms proteins and some vitamins (thiamin and biotin).
C. Phosphorus: Forms DNA, RNA, ATP, and phospholipids.

3. Other Elements

Potassium, magnesium, and calcium are often required as enzyme cofactors. Calcium is required for cell wall synthesis in Gram-positive bacteria.

5. Oxygen

Organisms that use molecular oxygen (O₂ ) produce more energy from nutrients than anaerobes. We can classify microorganisms based on their oxygen requirements:

A. Obligate Aerobes: Require oxygen to live.
Example: Pseudomonas, a common nosocomial pathogen.
B. Facultative Anaerobes: Can use oxygen but can grow in its absence. Have a complex set of enzymes.
Examples: E. coli, Staphylococcus, yeasts, and many intestinal bacteria.
C. Obligate Anaerobes: Cannot use oxygen and are harmed by the presence of toxic forms of oxygen.
Example: Clostridium bacteria that cause tetanus and botulism.
D. Aerotolerant Anaerobes: Cannot use oxygen but tolerate its presence. Can break down toxic forms of oxygen.
Example: Lactobacillus carries out fermentation regardless of oxygen presence.
E. Microaerophiles: Require oxygen, but at low concentrations. Sensitive to toxic forms of oxygen.
Example: Campylobacter

5. Nutrient content

Fig: Nutrient Content

1. Proteins, carbohydrates, sulphur, phosphorus, vitamin, lipids, water, energy, nitrogen, and minerals are all required for bacteria to grow and carry out metabolic processes.
2. For microbial growth, food is the finest source of nutrients.
3. The most simple forms of carbohydrates and amino acids are used first, followed by the complex forms.
4. Gram-positive bacteria have higher nutritional requirements than yeasts, followed by Gram-negative bacteria. Molds demand the least amount of nutrients.

B. Extrinsic Factors

Extrinsic factors are those that are influenced by circumstances beyond one’s control(external conditions). These elements include:

1. Temperature

Fig: Thermometer Used to Measure Temperature

The temperature of the environment has an impact on enzyme processes and microbiological development. The temperatures at which yeasts and moulds grow span a wide range of 10–35° C. Every bacterial species has distinct temperature requirements for growth, which are mostly governed by the temperature requirements of its enzymes. Each creature will have the following characteristics:

1. Minimum Growth Temperature
2. Optimum Growth Temperature
3. Maximum Growth Temperature

Based on temperature, bacteria can be grouped as:

1. Psychrotrophs are common cold-tolerant bacteria that can grow in temperatures ranging from 0 to 20 degrees C. Pseudomonas spp. and Enterococcus spp. are two examples.
2. Mesophiles are microorganisms that can thrive at temperatures ranging from 25 to 40 degrees Celsius, with an optimal temperature of 37 degrees Celsius. Salmonella, Staphylococcus, Clostridium, Shigella, and Bacillus are among them.
3. Thermophiles are microorganisms that can thrive at temperatures over 45 degrees Celsius, with an optimal temperature of 50 to 70 degrees Celsius. Bacillus, Clostridium, and Geobacillus species are among them.

2. Relative Humidity

1. The amount of moisture in the atmosphere or environment is measured by relative humidity.
2. Relative humidity can affect the level of water activity (aw) on food and thus the development of microbes.
3. Dry grains, for example, will absorb water and get mouldy if stored in a high-humidity environment.

3. Presence and Concentration of Gases in the Environment

1. Gases including carbon dioxide, ozone, and oxygen have a direct harmful effect on cells, preventing them from growing and reproducing.
2. Anaerobic bacteria are particularly affected by ozone and oxygen, while obligate aerobes are resistant to carbon dioxide.

4. Pressure

1. Microorganisms living on land or at the water’s surface are always subjected to the pressure of the atmosphere.
2. However, many bacteria can survive in the deep sea at extremes of hydrostatic pressure.
3. Others, such as Colwellia, and Shewanella, not only survive but thrive at high pressures and are referred to as barophilic.

C. Implicit Factors

1. Implicit factors are the third crucial aspect to consider when deciding the type of microbial development in food.
2. This component determines the characteristics of organisms and how they react to different surroundings.
3. Microorganisms have the ability to both inhibit and boost each other’s growth.
4. Predation, parasitism, commensalism, amensalism, allotropy, and neutrality are some of the different behaviours and reactions that can be destructive or beneficial to microorganisms.

Summary

Microorganisms are a diverse group of generally minute simple life-forms that include bacteria, archaea, algae, fungi, protozoa, and viruses. For microorganisms to thrive, their surroundings must be ideal. The factors that influence the growth requirements can be categorised as intrinsic, extrinsic, and implicit factors. The pH, Availability of oxygen, Poising capacity or buffering capacity, Nutrient composition (such as protein, ascorbic acid, reducing sugars) are required in different quantities for various microbes to grow.

Microorganisms can survive in a wide variety of temperatures, having colonised various natural settings and adapted to extremes. Extreme increase and extreme decrease in the elements both necessitate evolutionary changes to macromolecules and biological systems. Changes in the composition of membrane lipids and proteins are required for adaptation to sustain in the given surroundings. Similarly, Predation, parasitism, commensalism, amensalism, allotropy, and neutrality are some of the different behaviours and reactions that can be destructive or beneficial to microorganisms.

Frequently Asked Questions (FAQs) Conditions for the Growth of Microorganisms

Q.1. What are the conditions for the growth of microorganisms?
Ans: Microorganisms grow in very diverse conditions, which explains why they are found nearly everywhere on Earth. Although microbes are good at adapting to their environments, certain conditions promote microbial growth more than others. These conditions include temperature, moisture, pH, and environmental oxygen.

Q.2. How does pH affect the growth of microorganisms?
Ans: Moderate changes in pH modify the ionization of amino-acid functional groups and disrupt hydrogen bonding. This promotes changes in the folding of the molecule, promoting denaturation and destroying activity. The optimum growth pH is the most favourable pH for the growth of an organism.

Q.3. What is the importance of water for microorganisms?
Ans: Many different types of microorganisms can grow in water. Water is needed for the growth of some microorganisms. This, in turn, proves to be beneficial for us as beer and bread are made possible by the chemical activity of certain yeast strains. In addition, the proliferation of some microbes in contaminated water can aid in the digestion of the chemicals in the water.

Q.4. What are the intrinsic factors affecting the growth of microorganisms?
Ans: Intrinsic factors affecting the growth of microorganisms include nutritional content, pH levels, water activity, redox potential, etc.

Q.5. How does temperature affect the growth of microorganisms?
Ans: In general, when the temperature rises, so does enzyme activity. However, if temperatures rise too high, enzyme activity decreases, and the protein (enzyme) denatures. Every microbial species has unique temperature requirements for growth, which are mostly governed by the temperature requirements of its enzymes.

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