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Microbiology: An Evolving Science 4th Edition

Microbiology: An Evolving Science (4th Edition)

Book Edition4th Edition
PublisherW. W. Norton
End of Chapter
Review Questions

Chapter 4, End of Chapter, Review Questions, Exercise 1

Page 153

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Food that provides the microbes with structural elements and energy is composed of nutrients.


There are diverse forms of microbes found in the environment that are differentiated based on their sources of nutrition and energy, chemical nature, and the amount of nutrients they need to grow.

Nutrients are the substances that help in the growth of an organism. These components are gathered from the environment for microbial metabolism. Microorganisms require some essential nutrients (such as carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur) that they cannot synthesize themselves.

Essential nutrients are divided into two categories:

  1. Macronutrients: They are utilized by the body to produce cellular components like proteins, nucleic acids, carbohydrates, and lipids. Thus, they are involved in cell structure and metabolism. Nitrogen, carbon (organic), phosphorus, sulfur, hydrogen, and oxygen are examples of macronutrients. Nitrogen atoms are found in the structure of ATP (adenosine triphosphate), DNA (deoxyribonucleic acid), RNA (ribonucleic acid), and proteins. Hydrogen molecules help to maintain pH of a cell and provide free energy for the respiratory reactions. Phosphates are required for cellular energy (adenosine triphosphate (ATP)). Sulfur is taken up in the form of minerals found in rocks and sediments.
    Some ions like ferrous iron, magnesium, and potassium are also required by the microbes. They act as cofactors for enzymes and maintain the cell osmolarity.
  2. Micronutrients: These nutrients are required by microbes in minimal amounts. They help in the functioning of enzymes and also maintain the structure of proteins. For example, zinc, molybdenum, cobalt, nickel, manganese, and copper.

Other than these nutrients, there are certain physical factors which help in growth of microbes which includes temperature, osmotic pressure, pH and oxygen. 

  • Certain bacteria require oxygen to perform their metabolic activities. These bacteria are known as obligate aerobes. To anaerobic bacteria, oxygen is lethal and thus grows in the absence of oxygen.
  •  Optimum temperature is important for the growth of microorganisms and proper functioning of enzymes. High or low temperatures can lead to denaturation of proteins and enzymes and ice crystal formation in the cell membrane.
  • Each bacterium has an optimal pH which determines the ionic properties of the cell. Any change in the pH can affect the protein folding or can lead to denaturation of proteins. 
  • Water is important for the growth of microorganisms, as it is used by the organism to perform metabolic and physiological activities.
  • There are other growth factors that are not produced by the microbial cell which includes amino acids, pyrimidines, purines, and vitamins. 

Verified Answer

Macronutrients, micronutrients, and growth factors.

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