Lecture 4- Microbial Growth

Question 1

how is growth measured?

Answer 1

as an increase in the number of cells

Question 1

what is binary fission?

Answer 1

cell enlarges then divides into two daughter cells that are the same size as the original cell, each daughter cell is given a chromosome and sufficient copies of all other cell components (ex. ribosomes)

Question 1

what is generation time?

Answer 1

time required for microbial cells to double in number

Question 2

does mitosis occur in bacteria and archaea?

Answer 2

NO

Question 3

what has shorter generation times, bacteria or eukaryotes?

Answer 3

bacteria, therefore replication is faster. eukaryotic cells take longer because they’re more complex

Question 4

what is generation time dependent on?

Answer 4

growth medium and incubation conditions (ex. carbon source, pH, temperature…)

Question 5

what is exponential growth?

Answer 5

growth of a microbial population in which cell numbers double at a constant and specific time interval
the increase in cell number is initially slow but increases and the cells double at a constant rate

Question 6

how do you calculate the final cell number (Nt)?

Answer 6

Nt = N0 x 2n
final cell # = initial cell # x 2(# of generations during the period of exponential growth)

Question 7

what is logarithmic growth?

Answer 7

represents the average increase in growth with a straight line

Question 8

when growth is unlimited why is it called exponential growth?

Answer 8

because it generates a curve whose slope increases continuously

Question 9

how do you calculate growth rate (k)?

Answer 9

k=(Log Nt- Log N0)/ (0.301 x ΔT)
growth rate= (log of final cell # - initial cell #)/ (0.301 x change in time)

Question 10

how can we use the growth rate k to find generation time (g)?

Answer 10

g= 1/k
generation time= 1/ growth rate

Question 11

what is meant by a specific growth rate?

Answer 11

its the fastest growth rate an organism can have with optimal growth medium (nutrients) and optimal temperature
ex. of organisms under optimal conditions: clostridium perfringens double every 10 minutes, E. coli every 30min and mycobacterium tuberculosis more than 24 hours

Question 12

what is a batch culture?

Answer 12

a closed system microbial culture of fixed volume

Question 13

typical growth curve for population of cells grown in a closed system is characterized by 4 phases, what are they?

Answer 13

lag phase
exponential phase
stationary phase
death phase

Question 14

what is the lag phase?

Answer 14

the interval between inoculation of a culture and beginning of growth

Question 15

what is the exponential phase?

Answer 15

the healthiest state of cells

Question 16

what is the stationary phase? what is the growth rate?

Answer 16

carrying capacity is reached
growth rate of population is zero but cells are still metabolically active

Question 17

what is the death phase? when does it occur

Answer 17

when incubation continues after cells reach stationary phase the cells die

Question 18

not all bacteria die in death phase, how? what do they do?

Answer 18

form spores/ cysts
dormant stages that allow a significant portion of cells to survive for a long time