4. Bacterial Growth

Question 1

How do bacteria grow?

Answer 1

• produce and consume energy
• anabolic/catabolic processes

Question 2

2 types of nutrients needed for bacteria to grow

Answer 2

• macro
• micro

Question 3

Define ‘macronutrients’ with examples

Answer 3

• nutrients needed in large quantities
• carbon, nitrogen, oxygen

Question 4

Bacterial growth needs vary but … is always pivotal

Answer 4

• hydrogen
• oxygen
• carbon
• nitrogen
• phosphorus
• selenium
• sulphur

Question 5

Bacteria need … to … to grow

Answer 5

70-80%

Question 6

Nitrogen is needed to create nitrogen precursors to …

Answer 6

• nucleotides hence nucleic acids
• amino acids hence proteins

Question 7

Carbon sources form carbon precursors to form …

Answer 7

• nucleotides hence nucleic acids
• lipids and polysaccharides

Question 8

Electron acceptors are needed for what?

Answer 8

• with carbon sources form energy (ATP,GTP)
• helps form nucleotides hence nucleic acids, amino acids hence proteins, lipids and polysaccharides

Question 9

Difference between auto and auxo trophs

Answer 9

• auxo can’t synthesise essential organic compounds e.g amino acids and nucleotides
• auto can

Question 10

Heterotrophs obtain C from …

Answer 10

organic chemicals

Question 11

Heterotroph growth requirements can be … or …

Answer 11

• simple
• complex

Question 12

When would bacteria be described as fastidious?

Answer 12

when organisms require large number of growth factors or are supplied with specific ones

Question 13

Fermentation and respiration - aerobic or anaerobic?

Answer 13

ferm is anaerobic
- resp is both

Question 14

Difference between fermentation and respiration

Answer 14

• 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

Question 15

Fermentation and respiration occur in both humans and bacteria but bacteria are more …

Answer 15

• versatile
• wider variety of substrates and produce many different end products

Question 16

Bacteria can be categorised by their … response in …

Answer 16

• growth
• presence or absence of oxygen

Question 17

Define ‘facultative anaerobes’

Answer 17

bacteria which can survive with no oxygen

Question 18

Define ‘aerotolerant anaerobes’

Answer 18

anaerobes that can tolerate oxygen

Question 19

What kind of bacteria require oxygen?

Answer 19

aerobes

Question 20

What kind of bacteria can survive with no oxygen?

Answer 20

facultative anaerobes

Question 21

What kind of bacteria are anaerobes that can tolerate oxygen?

Answer 21

aerotolerant anaerobes

Question 22

What kind of bacteria require oxygen at very low concentrations?

Answer 22

microaerophiles

Question 23

Microbes in a lab are grown in what medium?

Answer 23

either solid or liquid

Question 24

What must a medium for growth have?

Answer 24

all the nutrients for the bacteria to grow

Question 25

Types of growth media

Answer 25

- defined - undefined - complex - selective - differential

Question 26

Explain a blood agar plate

Answer 26

- drop of blood added to agar - provides wide variety of nutrients

Question 27

Growth on a solid medium is seen as ...

Answer 27

individual

Question 28

Define 'bacterial growth'

Answer 28

irreversible increase in biomass and usually numbers of bacteria

Question 29

How to represent bacterial growth?

Answer 29

growth curves

Question 30

How do bacteria divide?

Answer 30

binary fission

Question 31

Why do we need to understand binary fission?

Answer 31

to understand how bacteria grow in situations where we need to control them

Question 32

Variables in binary fission

Answer 32

- time - nutrients - genetic factors - temp

Question 33

In a lab, how quickly does E.Coli replicate?

Answer 33

every 20 mins

Question 34

3 phases of binary fission

Answer 34

- cell growth - DNA replication - binary fission

Question 35

What happens in cell growth of binary fission?

Answer 35

- cell increases in size and mass - production of phospholipids and cell wall

Question 36

What happens in DNA replication of binary fission?

Answer 36

- single chromosome replicates before division - seperates towards end of cell

Question 37

What happens in binary fission stage of binary fission?

Answer 37

- 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

Question 38

What kind of increase is seen as bacterial growth?

Answer 38

exponential

Question 39

Explain exponential growth of bacteria

Answer 39

- slow growth rate initially - then speeds up rapidly - if conditions are optimal, large population in short time

Question 40

Things which can impact bacterial growth

Answer 40

- instrument/self contamination - pathogens

Question 41

Microorganisms growing in ... do not grow exponentially all the time

Answer 41

in flasks or test tubes

Question 42

Stages of batch culture

Answer 42

- lag phase - log (exponential) phase - stationary phase - decline phase

Question 43

When are cells viable in batch culture?

Answer 43

- log phase - stationary phase - some in decline phase - some remain at the end

Question 44

Explain lag phase in batch culture

Answer 44

- organism adapting to new env - enzymes synthesised, cells increase in size - dont yet divide

Question 45

What determines slope and length of log phase?

Answer 45

how well the medium meets requirements

Question 46

Explain stationary phase

Answer 46

- no net increase in cell number - nutrient/oxygen exhausted - env changed e.g pH - toxic products accumulate

Question 47

Explain death phase

Answer 47

- cells die - often exponential - no energy, pH damage, toxic products

Question 48

3 methods of measuring bacterial growth

Answer 48

- microscopic counts - viable counts - turbidimetric methods

Question 49

Explain how microscopic counts measures bacterial growth

Answer 49

- 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

Question 50

Explain how viable counts measures bacterial growth

Answer 50

- 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)

Question 51

How many cells were in a sample when 34 colonies grew from a 0.1ml of 10-4 dilution?

Answer 51

- 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

Question 52

2 units of measuring bacteria in culture

Answer 52

- colony forming units/ml - cells per ml

Question 53

When do you use cfu/ml and cells/ml?

Answer 53

- cfu for counting viable cells - cells per ml when coutning cells directly

Question 54

How to measure turbidimetric methods?

Answer 54

- light through filter/prism on sample containing cells - unscattered light onto photocell and recorded - on spectrophotometer (optical density) or Klett photometer (Klett units)

Question 55

If glucose is a substrate, what is the first step of fermentation and respiration?

Answer 55

glycolysis