Chapter 5 Flashcards
Growth
increase in size of an individual, or the increase in number of cells
population size can be measured using: (4)
- total count of cells (dead of alive)
- viable count of cells (only culturable cells)
- turbidometric means (optical density via a spectrophotometer)
- cell components (dry weight, protein content, etc.)
Generation time
time for microbial cells to double in number
Septum
partitioning between daughter cells, pinches off to form 2 equal daughter cells
Budding division
unequal cell growth, totally new daughter cell
- simple, from hyphae, stalks, appendages
biofilms
attached polysaccharide matrix containing embedded bacteria
- sessile growth on surfaces
- planktonic cells attach -> production of sticky matrix
Microbial mats
multilayered sheets w different organisms in each layer
- hot springs, intertidal regions
Biofilms prevent:
- harmful chemicals (antibiotics) from penetrating
- protists from grazing
- washing away of cells
Exponential growth
growth of microbial populations where cell numbers double within a specific time
Generation time
(g)
- g = t/n
- duration of exponential growth / number of doublings (generations) during that duration
Growth rate constant
slope of the line, represents rate of increase in growth rate during natural logarithmic growth
growth equation
final # cells = initial # cells x generations elapsed
k = log10Nt - log10N0 / rise x t
Viable count
measures the cells in the culture that are capable of reproducing
optical density (turbidity)
a quantitative measure of light scattering by a liquid culture, increases with the increase in cell numbers
batch culture
a closed system, microbial culture of fixed volume
four phases of bacterial growth curve:
lag phase, exponential phase, stationary phase, death phase
Diauxic growth
Diphasic growth, catabolite repression
- 2 exponential growth phases
- 2 lag phases
continuous culture
open system microbial culture of fixed volume
- nutrients in, wastes out
can maintain exponential growth phase for weeks/months
- growth rate controlled by dilution rate
Chemostat
common type of continuous culture device
- nutrients in, wastes out
Dilution rate
F/V
- Flow rate of added medium and removing spent medium / culture volume
Steady state
cell density and substrate concentration do not change over time
culture media
nutrient solutions used to grow microbes in the laboratory
defined media
exact chemical composition knwon
complex media
composed of digests of microbial, animal, or plant products (yeast/meat extracts)
enriched media
contain complex media plus highly nutritious materials, used to culture fastidious (nutritionally demanding) microbes
selective media
contain compounds that selectively inhibit growth of some microbes but not others
differential media
contain an indicator, usually a dye, that detects particular metabolic reactions during growth
