Microbial Growth Requirements

Question 1

To grow we need …

Answer 1

1. Food - source of energy, provides nutrients - vitamins, minerals, amino acids
2. Oxygen
3. Water
4. Warmth

Question 2

What are the physical requirements for microbial growth ?

Answer 2

1. Temperature
2. PH
3. Osmotic pressure

Question 3

What are the chemical requirements for microbial growth ?

Answer 3

1. Carbon, hydrogen, nitrogen, phosphorus, sulphur
2. Trace elements
3. Oxygen

Question 4

Carbon source

Answer 4

• All organisms require a source of C for biosynthesis
• Those that use the organic since (C) = heterotrophs
• Those that use the CO2 as their main source of C (bacteria) = autotrophs

Question 5

Energy sources

Answer 5

Divided in terms of carbon sources

• Chemotrophs (heterotrophs) — chemoorganotrophs and chemolithotrops
• Autotrophs

Question 6

Growth factors

Answer 6

Any compound which an organism requires for growth but cannot synthesise itself. E.g, amino acids, vitamins, haemins

Question 7

Water

Answer 7

All organisms require water for life.

Availability of water = water activity

E.g, a measure of water available for use by the micro-organism

Question 8

Temperature requirements

Answer 8

Cardinal temperatures = minimum, optimum and maximum temperatures at which each organism grows.

Microorganism can grow at wide range of temperatures.

Those that live in the extremes = extremophiles

Question 9

Types of bacteria at different temperatures

Answer 9

• Psychrophiles - found in the poles, optimum temp = 15 degrees, minimal growth temp of 0 degrees
• Pyschotrophs - optimum temp = 20 degrees, cannot grow above 40 degrees
• Mesophiles - optimum growth = 37-40 degrees, pathogens ,commensal flora
• Thermophiles - optimum temp = 60 degrees (or 80 in some cases)

Question 10

Effects of osmotic pressure

Answer 10

• Halophiles
• Halotolerant
• Osmophiles - tolerates sugar solutions
• Xerophiles - dry conditions

Question 11

Salt requirements

Answer 11

• Halophiles - need a certain amount of salt for growth
• Halotolerant - can tolerate raised levels of salt e.g, 10%

Question 12

Oxygen requirements

Answer 12

• Not all microorganisms need oxygen but do need an electron acceptor for metabolism
• Aerobes = grow in the presence of oxygen
• Anaerobes
• And everything in between

Question 13

What is obligate aerobes ?

Answer 13

Can only grow if oxygen is present

Question 14

What is obligate anaerobes ?

Answer 14

Do not need oxygen as they may be poisoned by it

Question 15

Facultative anaerobes

Answer 15

Doesn’t require oxygen, but grows better if present

Question 16

Microaerophiles

Answer 16

Requires a specific reduced level of oxygen

Question 17

Aerotolerant anaerobe

Answer 17

Can grow equally well with or without tolerant

Question 18

What is pH ?

Answer 18

A measure of the concentration of hydrogen ions (H+)

• On the scale 7 = neutral, below 7 = acid and above = alkali

Question 19

PH - acidophiles

Answer 19

Organisms which will grow in an acid environment