Requirements for Growth

Key terms

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Requirements for Growth
Key terms
Macronutrients- required in relatively large amounts, includes carbon, hydrogen, oxygen, nitrogen,
sulphur, magnesium and iron. All nutrients have to be provided in a suitable form in the culture media
in which the microorganisms are grown.
Micronutrients- required in small amounts, may also be known as trace elements. Micronutrients
include copper, manganese, vanadium and zinc. They are metals that are essential for normal cell
function but it isn't normally necessary to have to add these separately as they are often present in
other ingredients.
Defined media- made up using pure chemical substances, dissolved in distilled water so that the
exact chemical composition is known.
Undefined media- contains mixtures of substances such as yeast extract, peptone, or casein
hydrolysate, in which the exact composition is unknown.
Selective media- contains substances which selectively inhibit the growth of certain microorganisms,
whilst allowing others to grow. This is important, especially in medical microbiology, as it allows one
organism to be isolated and cultured from specimens such as blood.
Indicator media- contains a coloured pH indicator substance such as phenol. They show whether or
not a change in pH has occurred as a result of the metabolism of the bacteria during growth.
Agar- a polysaccharide obtained from red algae, it is a solidifying agent added to broth media. It is
dissolved in the medium by boiling and once cooled will set to produce a clear, firm gel.
Psychrophiles- have a low temperature optima (around 13 oc)
Mesophiles- have a mid-range temperature optima (around 39 oc)
Thermophiles- have a high temperature optima (around 60 oc)
Hyperthermophiles- have a very high temperature optima (around 88 oc)
Obligate Aerobes- grow only in the presence of oxygen
Obligate Anaerobes- grow only in the absence of oxygen
Microaerophillic Aerobes- requires oxygen at lower concentrations than atmospheric
Facultative Aerobes- can grow only in the absence of oxygen, but grow better if oxygen is supplied.


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