Growth Requirements And Cultivation Flashcards
What is the definition of bacterial growth?
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What are the growth requirements for bacteria?
Physical:
Temperature
pH
Osmotic Pressure
Chemical:
Water, Oxygen
CNSP
Trace elements
Organic growth factors
How are bacteria divided according to their preferred range of growth temperatures?
PMT
Psychrophiles: 0-20ºC
Mesophiles: 20-45ºC
Thermophiles 45-80ºC
How does pH affect bacterial growth?
Modes of action:
1) Indirect effect on medium — Affects ionisation of compounds
2) Direct effect on microorganism — Affects ionisation of ionogenic groups of cell wall
Applications:
1) Preservation of food
2) Cultivation of microorganisms
What is the effect of osmotic pressure on growth?
Osmotic pressure affected by salt conc. of solution
Most bacteria live in medium containing ~0.95% w/v NaCl
Except:
Extreme halophiles: Require ~30% salt for growth
Facultative halophiles: Able to grow at salt conc. up to 15%
What are the effects of water on growth?
1) Water is required for maintenance of structure
2) It is a vehicle for transport
3) Reactant in hydrolytic and some oxidative reactions within the cell
How are bacterias that grow under different oxygenation conditions classified?
Obligate aerobes: Need O2 to grow
Microaerophilic aerobes: Only grows at low O2 levels
Facultative anaerobes: Can grow in either conditions but optimal in the presence of O2
Aerotolerant anaerobes: Unaffected by O2 levels
Obligate anaerobes: Cannot grow in O2
What are the various forms of oxygen that is highly reactive and therefore toxic?
Singlet oxygen: Normal O2 in a higher energy state; Formed in the presence of visible light
Peroxide: Generated in small amounts during respiration
Superoxide free radical: Formed in small amounts during respiration of organisms that use O2 as a final electron acceptor, forming water; Formed by Obligate anaerobes in the presence of O2
Hydroxyl free radical: Formed in cytoplasm by ionising radiation or by a rxn betw Superoxide free radical and Peroxide
What are the enzymes that allow organisms to grow in O2?
Superoxide dismutase (SOD)
Catalase (CT)
Peroxidase
What is the purpose of CNSP for bacteria?
Carbon
- Food and make up cellular structures
Nitrogen, Sulfur, Phosphorus:
- Make up cellular structures such as proteins and DNA
What are the effects of trace elements?
Examples: Cu, Co, Zn, Mo
No trace element = No growth
Increase [Trace element] = Increasing growth rate
Increase too much = Reduction of growth rate
Increase even more = Death of cells
Functions of trace elements
1) Constituents of cytoplasm
2) Enzyme components
3) Enzyme activators
4) Maintenance of osmotic and pH equibilibria
5) Carbohydrate metabolism and energy provision
