Physical and biochemical requirements for bacterial growth, methods used to measure live and total bacterial titres

Question 1

What are the physical requirements for bacterial growth?

Answer 1

Temperature, pH and osmotic pressure

Question 2

What are the chemical requirements for bacterial growth?

Answer 2

Oxygen, N+S+P + trace elements, Water and Carbon

Question 3

Oxygen

Answer 3

• needed by all living organisms
• can be sourced from O2 or H2O
• neutralising mechanisms are necessary because O2 is toxic in a sense
• production of free radicals during reduction od O2 in respirstion
• used in construcion of cellular molecules (nucleic acids, proteins)

Question 4

N+S+P + trace elements

Answer 4

• bacteria require essential nutrients - nitrogen, sulphur and phosphorous
• important functions in maintenance of cellular functions - energy production and enzyme activation
• nitrogen obtained from amino acids/ammonia/nitrogen fixation
• trace elements needed in tiny amounts
• act as cofactors in enzymatic reactions
• found in tap water

Question 5

Function of phosphorous

Answer 5

nucleic acid and phospholipid synthesis

Question 6

Function of sulphur

Answer 6

production of amino acids and coenzymes

Question 7

Water

Answer 7

• most important factor
• bacteria need water environments to carry out metabolism

Question 8

Carbon

Answer 8

• important factor
• involved in formation of all organic compounds
• acts as an energy source for microbes

Question 9

Autotrophs

Answer 9

obtain carbon from CO2 (inorganic)

Question 10

Heterotrophs

Answer 10

obtain carbon from organic sources

Question 11

Phototrophs

Answer 11

obtain energy from sunlight

Question 12

Chemotrophs

Answer 12

obtain energy from organic/inorganic compounds

Question 13

Temperature

Answer 13

• different temperature preferences
• thermophiles 50-60 degrees (can live at 110)
• psychrophiles 15-20 degrees (can live at 0)
• mesophiles 25-40 degrees

Question 14

pH

Answer 14

different pH preferences
- acidophiles 0.1-5.4
- neutrophiles 5.4-8.0
- alkaliphiles 7-11.5

Question 15

Osmotic pressure

Answer 15

bacteria must maintain osmotic balance to avoid cell shrinkage or bursting
- bacteria in solution with high concentration of solutes (hypertonic) lose water and become plasmolyzed
- bacteria in solution with low conc. of solutes (hypotonic) take in water and become turgid