4. Bacterial Growth Flashcards
How do bacteria grow?
- produce and consume energy
- anabolic/catabolic processes
2 types of nutrients needed for bacteria to grow
- macro
- micro
Define ‘macronutrients’ with examples
- nutrients needed in large quantities
- carbon, nitrogen, oxygen
Bacterial growth needs vary but … is always pivotal
- hydrogen
- oxygen
- carbon
- nitrogen
- phosphorus
- selenium
- sulphur
Bacteria need … to … to grow
70-80%
Nitrogen is needed to create nitrogen precursors to …
- nucleotides hence nucleic acids
- amino acids hence proteins
Carbon sources form carbon precursors to form …
- nucleotides hence nucleic acids
- lipids and polysaccharides
Electron acceptors are needed for what?
- with carbon sources form energy (ATP,GTP)
- helps form nucleotides hence nucleic acids, amino acids hence proteins, lipids and polysaccharides
Difference between auto and auxo trophs
- auxo can’t synthesise essential organic compounds e.g amino acids and nucleotides
- auto can
Heterotrophs obtain C from …
organic chemicals
Heterotroph growth requirements can be … or …
- simple
- complex
When would bacteria be described as fastidious?
when organisms require large number of growth factors or are supplied with specific ones
Fermentation and respiration - aerobic or anaerobic?
ferm is anaerobic
- resp is both
Difference between fermentation and respiration
- ferm has an organic compound used as both an electron donor and acceptor
- resp has an electron donor oxidised with oxygen or an oxygen substitute
Fermentation and respiration occur in both humans and bacteria but bacteria are more …
- versatile
- wider variety of substrates and produce many different end products
Bacteria can be categorised by their … response in …
- growth
- presence or absence of oxygen
Define ‘facultative anaerobes’
bacteria which can survive with no oxygen
Define ‘aerotolerant anaerobes’
anaerobes that can tolerate oxygen
What kind of bacteria require oxygen?
aerobes
What kind of bacteria can survive with no oxygen?
facultative anaerobes
What kind of bacteria are anaerobes that can tolerate oxygen?
aerotolerant anaerobes
What kind of bacteria require oxygen at very low concentrations?
microaerophiles
Microbes in a lab are grown in what medium?
either solid or liquid
What must a medium for growth have?
all the nutrients for the bacteria to grow
Types of growth media
- defined
- undefined
- complex
- selective
- differential
Explain a blood agar plate
- drop of blood added to agar
- provides wide variety of nutrients
Growth on a solid medium is seen as …
individual
Define ‘bacterial growth’
irreversible increase in biomass and usually numbers of bacteria
How to represent bacterial growth?
growth curves
How do bacteria divide?
binary fission
Why do we need to understand binary fission?
to understand how bacteria grow in situations where we need to control them
Variables in binary fission
- time
- nutrients
- genetic factors
- temp
In a lab, how quickly does E.Coli replicate?
every 20 mins
3 phases of binary fission
- cell growth
- DNA replication
- binary fission
What happens in cell growth of binary fission?
- cell increases in size and mass
- production of phospholipids and cell wall
What happens in DNA replication of binary fission?
- single chromosome replicates before division
- seperates towards end of cell
What happens in binary fission stage of binary fission?
- actual division of cells
- inward synthesis of peptidoglycan to form septum
- splits cell in half
- coordinated by cytoskeletal proteins into fission ring (acts as contractile band to pinch in on itself)
- pinches in on itself to form daughter cells
- septum dissolves away to form seperate daughter cells and cycle repeats
What kind of increase is seen as bacterial growth?
exponential
Explain exponential growth of bacteria
- slow growth rate initially
- then speeds up rapidly
- if conditions are optimal, large population in short time
Things which can impact bacterial growth
- instrument/self contamination
- pathogens
Microorganisms growing in … do not grow exponentially all the time
in flasks or test tubes
Stages of batch culture
- lag phase
- log (exponential) phase
- stationary phase
- decline phase
When are cells viable in batch culture?
- log phase
- stationary phase
- some in decline phase
- some remain at the end
Explain lag phase in batch culture
- organism adapting to new env
- enzymes synthesised, cells increase in size
- dont yet divide
What determines slope and length of log phase?
how well the medium meets requirements
Explain stationary phase
- no net increase in cell number
- nutrient/oxygen exhausted
- env changed e.g pH
- toxic products accumulate
Explain death phase
- cells die
- often exponential
- no energy, pH damage, toxic products
3 methods of measuring bacterial growth
- microscopic counts
- viable counts
- turbidimetric methods
Explain how microscopic counts measures bacterial growth
- sample added to slip (not overflowing)
- 0.02mm space between coverslip and slide
- whole grid has 25 squares, total area of 1mm2, volume 0.02mm3
- observe cells in large square (or do individual squares and average)
- amount of cells in one average x total squares
Explain how viable counts measures bacterial growth
- sample pipetted onto agar plate
- spread evenly using sterile glass spreader
- incubated
- results seen (spread plate method)
OR - sample pipetted onto sterile plate
- sterile medium then added and mixed with inoculum
- incubated
- results seen (pour plate method)
How many cells were in a sample when 34 colonies grew from a 0.1ml of 10-4 dilution?
- 340 grown in 1x10-4
- 10-4 is 1/10000
- conc by factor is 10000
- colony forming units in 1ml is 340 x10 to the 4
- 3.4 x10 to the 6 cfu/ml
2 units of measuring bacteria in culture
- colony forming units/ml
- cells per ml
When do you use cfu/ml and cells/ml?
- cfu for counting viable cells
- cells per ml when coutning cells directly
How to measure turbidimetric methods?
- light through filter/prism on sample containing cells
- unscattered light onto photocell and recorded
- on spectrophotometer (optical density) or Klett photometer (Klett units)
If glucose is a substrate, what is the first step of fermentation and respiration?
glycolysis
