Bacterial Growth Requirements Flashcards
What is bacterial growth?
An increase in the number of bacterial cells
How do bacteria grow?
Asexually through binary fission
Briefly explain how binary fission works.
4
Bacteria replicate its DNA
Cell elongates
Copy of DNA goes to each side of cell
Cell splits off into two daughter bacterial cells
How often does binary fission happen?
Every 20 minutes
What is a batch culture?
Bacteria inoculated in a flask containing a fixed amount of nutrient medium
How many phases are there to bacterial growth of a batch culture?
Four
What are the four phases of bacterial growth in a batch culture called?
Lag phase
Log phase
Stationary phase
Death phase
What happens during the lag phase of microbial growth?
3
Microbes are adjusting to environment
Microbes not yet reproducing
Cells are synthesising DNA, ribosomes and enzymes to breakdown nutrients and synthesize macromolecules
What do bacteria cells synthesize during the lag phase?
3
DNA
Ribosomes
Enzymes
Why do bacterial cells synthesize DNA, ribosomes and enzymes during the lag phase?
To breakdown nutrients and synthesize macromolecules
What is the log phase also called?
The exponential phase
What happens during the log phase?
3
Cells have the optimum conditions for growth
Exponential growth occurs
This rate of growth is influenced by environmental conditions and genetic characteristics of the bacteria
What influences the rate of growth in the log phase?
2
Environmental conditions
Genetic characteristics
What happens during the stationary phase of bacterial growth?
(2)
Death occurs due to reduced nutrients, pH changes, toxic waste and reduced oxygen
No net increase or decrease in cell number
Why does death occur in the stationary phase?
In a batch culture exponential growth cannot occur indefinitely
What causes death in the stationary phase?
4
Reduced nutrients
pH changes
Toxic waste
Reduced oxygen
What is the death phase also called?
Decline phase
What happens during the death phase?
2
Cells die at an exponential rate
Death occurs due to accumulation of wastes, loss of cell’s ability to detoxify toxins etc
How do bacterial cells die in the death phase?
Their cytoplasmic membrane collapses and cell lysis occurs
What are the nutritional requirements for bacteria?
3
Energy
Nutrients
Growth factors
What are the environmental requirements for bacteria?
4
Oxygen gas concentration
Temperature
pH
Water availability
Through what three ways can energy by obtained in nature.
Organic chemicals
Inorganic chemicals
Light
What are chemoorganotrophs?
Organisms that obtain their energy from organic compounds
What is the name given to organisms that obtain their energy from organic compounds?
Chemoorganotrophs
Explain how chemoorganotrophs get their energy.
2
They oxidise an organic compound to get energy
This energy is stored as adenosine triphosphate (ATP)
What are aerobes?
Chemoorganotrophs that can extract energy from compounds in the presence of oxygen
What are anaerobes?
Chemoorganotrophs that can extract energy from compounds in the absence of oxygen
What are chemolithotrophs?
Organisms that can trap the energy available in inorganic compounds
What is the name given to organisms that can trap the energy available in inorganic compounds?
Chemolithotrophs
Chemolithotrophs are only found in what kingdom?
Prokaryotes
What are the benefits of being a chemolithotroph?
3
Only few bacteria are chemolithotrophs
There is no competition for inorganic substrates
Many inorganic compounds are waste products of chemoorganotrophs
What are phototrophs?
Organisms that can contain pigments that allow them to use light as an energy source - cells are coloured e.g. purple bacteria
What is the name given to organisms that use light as an energy source?
Phototrophs
How do phototrophs work?
ATP is made from the energy of sunlight
What elements are needed for bacterial growth?
6
Hydrogen
Oxygen
Carbon
Nitrogen
Phosphorus
Sulphur
What are heterotrophs?
Organisms that require one or more organic compound as their carbon source
e.g. heterotrophs
What are autotrophs?
Organisms that use CO2 as their carbon source
e.g. nearly all phototrophs and most chemolithotrophs
Name the two places nitrogen can be gotten for bacteria.
Inorganic sources
Organic sources
List four inorganic sources of nitrogen.
Nitrogen gas (N2)
Nitrate (NO3)
Nitrite (NO2)
Ammonia (NH3)
Give an example of an organic source of nitrogen.
Nitrogen can be gotten from the breaking down of proteins into amino acids
What are growth factors?
Essential compounds that an organisms in unable to synthesize from available nutrients
What are fastidious organisms?
Organisms that need growth factors
What are the three categories of growth factors?
Purines and pyrimidines
Amino acids
Vitamins
What are purines and pyrimidines needed for?
Required for synthesis of nucleic acids (DNA and RNA)
What are amino acids needed for?
Required for the synthesis of proteins
What are vitamins needed for?
Needed as coenzymes and functional groups of certain enzymes
What are extremophiles?
Organisms that inhabit extreme environments
Why does temperature have such a profound effect on microorganisms?
Because enzyme-catalyzed reactions are sensitive to temperature
What is optimal growth temperature?
The temperature range at which the highest rate of reproduction occurs
How are bacteria grouped according to their optimal growth temperature?
Psychrophiles
Mesophiles
Thermophiles
Hyperthermophiles
At what temperature do psychrophiles grow best?
Between 0 and 30 degrees
At what temperature do mesophiles grow best?
15-40 degrees
At what temperature do thermophiles grow best?
Between 40 and 70 degrees
At what temperature do hyperthermophiles grow best?
Above 80 degrees and up to 115 degrees
How are bacteria grouped according to their need for oxygen?
3
Obligate aerobes
Obligate anaerobes
Facultative anaerobes
What are obligate aerobes?
Organisms that need oxygen gas to grow
What are obligate anaerobes?
3
Organisms that cannot grow in the presence of oxygen
They do not need oxygen for growth
Oxygen either kills or inhibits them
What are facultative anaerobes?
3
Organisms that can switch between aerobic and anaerobic types of metabolism
Fermentation/anaerobic respiration without oxygen
Aerobic respiration with oxygen
How are bacteria grouped based on their preferred pH?
Acidophiles
Neutrophiles
Alkaliphiles
What are acidophiles?
Organisms which grow at an optimum pH well below neutrality
e.g. most fungi
What are neutrophiles?
Organisms which grow best at neutral pH
What are alkaliphiles?
Organisms which grow best under alkaline conditions
What is relative humidity?
Presence of water in the atmosphere
What is water activity?
Presence of water in solution
What affects water activity?
The presence of solutes such as salts or sugars, that are dissolved in the water
What are halophiles?
2
Organisms that require some NaCl for growth
Grouped into mild, moderate and extreme halophiles
