Nutritional Requirements of microorganisms

Nutritional Requirements of microorganisms

Contents 

• Nutritional requirements of microorganisms

– Microelements

– Macro elements

– Growth factors

• Culture media definition and classification

• Differential media

• Enriched and enrichment media

• Selective media

Learning
objectives

At the end of this lecture, the student will be able to:

• List the nutritional requirements of microorganisms

• Classify the different types of culture media

• Explain the significance and application of different culture
media

• Classify nutritional types of bacteria

Introduction

Nutrients are
substances used in biosynthesis and energy production and therefore are
required for microbial growth

• Environmental factors such as temperature, oxygen levels,
and the osmotic concentration of the medium are critical in the successful
cultivation of microorganisms

Common
nutritional requirements

Macroelements

• Required by microorganisms in relatively large amounts

• 95% of cell dry weight is made up of a few major elements:
carbon, oxygen, hydrogen, nitrogen, sulphur, phosphorus, potassium, calcium,
magnesium, and iron.

Element

%

Source

Function

Carbon

50

Organic compounds or CO2

Main constituent of cellular material

Oxygen

20

H2O, organic compounds, CO2 and O2

Constituent of cell material and cell water, O2 is electron acceptor
in aerobic respiration

Nitrogen

14

NH3, NO3, organic compounds, N2

Constituent of amino acids, nucleic acids nucleotides, and
coenzymes 

Hydrogen

8

H2O, organic compounds, H2

Main constituent of organic compounds and cell water 

Phosphorus  

3

inorganic phosphates (PO4)

Constituent of nucleic acids, nucleotides, phospholipids, LPS,
teichoic acids

Potassium

1

Potassium salts

Main cellular inorganic cation and cofactor for certain enzymes 

Magnesium

0.5

Magnesium salts

Inorganic cellular cation, cofactor for certain enzymatic reactions

Sulphur

1

Organic sulphur compounds

Constituent of cysteine, methionine, glutathione, several coenzymes

Calcium

0.5

Calcium salts

Inorganic cellular cation, cofactor for certain enzymes and a
component of endospores

Iron

0.2

Iron salts

Component of cytochromes and certain non-heme iron-proteins and a
cofactor for some enzymatic reactions 

The micronutrients

• Manganese, zinc, cobalt, molybdenum, nickel, and
copper—are needed by most cells.

• Contaminants in water, glassware, and regular media
components often are adequate for growth

• Micronutrients are normally a part of enzymes and
cofactors, and they aid in the catalysis of reactions and maintenance of
protein structure

• Zinc is present at the active site of some enzymes

• Manganese aids many enzymes catalyzing the transfer of
phosphate

• Groups Molybdenum is required for nitrogen fixation,
cobalt is a component of vitamin B12.

Nutritional
Types of Microorganisms

        

Growth
factors

There are three major classes of growth factors:

Amino acids

Needed for protein synthesis

Purines and
pyrimidines

Needed for nucleic acid synthesis

Vitamins

Needed as coenzymes and functional groups of certain enzymes

• Some bacteria (e.g. E. coli) do not require any growth
factors: they can synthesize all essential purines, pyrimidines, amino acids
and vitamins, starting with their carbon source, as part of their own
intermediary metabolism. 

• Certain other bacteria (e.g. Lactobacillus) require
purines, pyrimidines, vitamins and several amino acids in order to grow. These
compounds must be added in advance to culture media that are used to grow these
bacteria.

• Mutant strains of bacteria that require some growth factor
not needed by the wild type (parent) strain are referred to as auxotrophs. 

• Thus, a strain of E. coli that requires the amino acid
tryptophan in order to grow would be called a tryptophan auxotroph and would be
designated E. coli trp- 

Culture
media

• A culture medium is a solid or liquid preparation used to
grow, transport, and store microorganisms

• Specialized media are essential in the isolation and
identification of microorganisms, the testing of antibiotic sensitivities,
water and food analysis, industrial microbiology, and other activities

• Knowledge of a microorganism’s normal habitat often is
useful in selecting an appropriate culture medium

Defined and
complex media

Synthetic or Defined
Media

• A medium in which all components are known is a defined
medium or synthetic medium.

• Many chemoorganotrophic heterotrophs also can be grown in
defined media with glucose as a carbon source and an ammonium salt as a
nitrogen source.

• Defined media are used widely in research, as it is often
desirable to know what the experimental microorganism is metabolizing

Complex Media

• Contain some ingredients of unknown chemical composition

• May be sufficiently rich and complete to meet the
nutritional requirements of many different microorganisms contain undefined
components like peptones, meat extract, and yeast extract

• Three commonly used complex media are

(1) Nutrient broth,       

(2) Tryptic soy broth,

(3) MacConkey agar

Ingredients
of complex media

Peptones

Protein hydrolysates prepared by partial proteolytic digestion of
meat, casein, soya meal, gelatin, and other protein sources

Sources of carbon, energy, and nitrogen

 

Meat extract, Beef extract

Aqueous extracts of lean beef

Beef extract contains amino acids, peptides, nucleotides, organic
acids, vitamins, and minerals

Yeast extract

Aqueous extracts of brewer’s yeast 

Yeast extract is an excellent source of B vitamins as well as
nitrogen and carbon compounds

 

Agar in
media

• Liquid media can be solidified with the addition of 1.0 to
2.0% agar

• Agar is extracted from red algae

• After it has been melted in boiling water, it can be
cooled to about 40 to 42°C before hardening and will not melt again until the
temperature rises to about 80 to 90°C

• Agar is also an excellent hardening agent because most
microorganisms cannot degrade it.

Types of
media

• General purpose
media –
tryptic soy broth and tryptic soy agar are called general purpose
media because they support the growth of many microorganisms

• Enriched media –
Blood and other special nutrients may be added to general purpose media to
encourage the growth of fastidious heterotrophs. These specially fortified
media (e.g., blood agar) are called enriched media.

Enrichment media

If the sample
contains more than one bacteria, the undesired bacterial growth can be reduced
by addition of certain media components

• The desired organism is facilitated to grow

Selective media 

• Favor the growth of particular microorganisms

• Bile salts or dyes like basic fuchsin and crystal violet
favor the growth of gram-negative bacteria by inhibiting the growth of
gram-positive bacteria without affecting gram-negative organisms.

• Examples: Endo agar, eosin methylene blue agar, and
MacConkey agar

• A medium containing only cellulose as a carbon and energy
source is quite effective in the isolation of cellulose-digesting

• Endo agar –
Inhibition of gram-positive microorganisms was achieved by the sodium sulfite
and basic fuchsin

• EMB agar – EMB
contains dyes that are toxic for Gram positive bacteria and bile salt which is
toxic for Gram negative bacteria other than coliforms.

MacConkey agar –
The crystal violet and bile salts inhibit the growth of gram-positive organisms
which allows for the selection and isolation of gram-negative bacteria

Differential
media 

• Media that distinguish between different groups of
bacteria 

• Permit tentative identification of microorganisms based on
their biological characteristics

Examples – 

• Blood agar is
both a differential medium and an enriched one

MacConkey agar
is both differential (crystal violet & bile salts) and selective (lactose
& neutral red dye)

Summary

Nutrients are
substances used in biosynthesis and energy production and therefore are
required for microbial growth

Major elements
required for growth –
carbon, oxygen, hydrogen, nitrogen, sulfur,
phosphorus, potassium, calcium, magnesium, and iron.

Minor elements
– manganese, zinc, cobalt, molybdenum, nickel, and copper

Nutritional types
of bactera
– Autotrophs, Heterotrophs, Phototrophs, Chemotrophs,
Lithotrophs, Organotrophs

Growth factors –
Amino acids, Purines and pyrimidines, Vitamins

• A culture medium
is a solid or liquid preparation used to grow, transport, and store
microorganisms

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