Microbial Nutrition Requirements - The Veterinary Site

Microbial Nutrition Requirements

Microbial Growth Requirements

— Microbial growth

¡ Increase in a population of microbes


— Result of microbial growth is discrete colony


¡ An aggregation of cells arising from single parent cell




Growth Requirements


— Organisms use a variety of nutrients for their energy needs and to build organic molecules and cellular structures


— Most common nutrients contain necessary elements such as carbon, oxygen, nitrogen, and hydrogen


— Microbes obtain nutrients from variety of sources


— Nutrients: Chemical and Energy Requirements


— Sources of carbon, energy, and electrons


— Two groups of organisms based on source of carbon


— Autotrophs


— Heterotrophs


— Two groups of organisms based on source of energy


— Chemotrophs


— Phototrophs


Carbon:



• Besides water, one of the most important requirements for

microbial growth is carbon.


• Carbon is the structural backbone of living matter; it is needed for all the organic compounds that make up a living cell.


• Half the dry weight of a typical bacterial cell is carbon.


• Chemoheterotrophs get most of their ca rbon from the source of their energy- organic materials such as proteins, carbohydrates, and lipids.


• Chemoautotrophs and photoautotrophs derive their carbon from carbon dioxide.



• Nutrients: Chemical and Energy Requirements


• Oxygen requirements



• Obligate aerobes—organisms that cannot live without oxygen.


• Obligate anaerobes—organisms that cannot live in the presence of oxygen.


• Facultative anaerobes—can live with or without oxygen.


• Aerotolerant anaerobes—do not use aerobic metabolism, but can tolerate oxygen.


• Nutrients: Chemical and Energy Requirements


• Oxygen requirements



• Oxygen is essential for obligate aerobes


• Oxygen is deadly for obligate anaerobes


• How can this be true?



• Toxic forms of oxygen are highly reactive and excellent oxidizing agents


• Resulting oxidation causes irreparable damage to cells


¡ Oxygen requirements


÷ Two common toxic forms of oxygen


¢ Superoxide radicals (O2-)


Extremely toxic andreactive form of oxygen. All organisms growing in

atmospheric oxygen must produce an enzyme superoxide
dismutase (SOD), to get rid of them. SOD is made by

aerobes, facultative anaerobes, and aerotolerant anaerobes,

but not by anaerobes or microaerophiles.


2O2- + 2H+ à H2O2 + O2


¢ Peroxide anion (O22-)


Peroxide ion is toxic and the active ingredient of several antimicrobials (e.g.: benzoyl peroxide). There are two different enzymes that break down

Hydrogen peroxide:



A. Catalase: Breaks hydrogen peroxide into water and O 2.

Common. Produced by humans, as well as many bacteria.


2H2O2 à 2H2O + O2


B. Peroxidase: Converts hydrogen peroxide into water

¢ Singlet oxygen


Extremely reactive form of oxygen, present in phagocytic cells


• Organisms that grow in the presence of oxygen must have enzymes that can break down the toxic forms of oxygen.


• Superoxide radicals (O2-)


• Superoxide dismutase


• 2O2- + 2H+ à H2O2 + O2


• Peroxide anion (O22-)


• Catalase


• 2H2O2 à 2H2O + O2


• Also peroxidase can break down H2O2


• Other than these enzymes, aerobes use antioxidants such as vitamins C and E in order to protect against toxic oxygen products.


• Nutrients: Chemical and Energy Requirements

• Nitrogen requirements


• Anabolism often ceases because of insufficient nitrogen


• All cells recycle nitrogen from amino acids and nucleotides


• Nitrogen fixation by certain bacteria is essential to life on Earth because most organisms cannot use nitrogen gas (N2) even though it is the most makes up 79% of our atmosphere.


• protein synthesis requires considerable amounts of nitrogen as well as some sulfur.

The syntheses of DNA and RNA also require nitrogen and some

phosphorus, as does the synthesis of ATP, the molecule so important for the storage and transfer of chemical energy within the cell.

Nitrogen makes up about 14% of the dry weight of a bacterial cell,

and sulfur and phosphorus together constitute about another 4%.

• Trace Elements:



Microbes require very small amounts of other mineral elements,

such as iron, copper, molybdenum, and zinc; these are referred to

as trace elements.


• Most are essential for the functions of certain enzymes, usually as cofactors.


• Although these elements are sometimes added to a laboratory medium, they are usually assumed to be naturally present in tap water and other components of media.


• Even most distilled waters contain adequate amounts, but tap water is sometimes specified to ensure that these trace minerals will be present in culture media. 

• Other Elements:


• Potassium, magnesium, and calcium are often required as enzyme cofactors.

Calcium is required for cell wall synthesis in Gram positive bacteria.
Microbial Nutrition Requirements Microbial Nutrition Requirements Reviewed by Maaz ahmed siddiqui on 08 May Rating: 5

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