Unit 2-- Lecture 9 (Bacterial Growth) Flashcards
Counting Bacteria: Petroff-Hauser Chamber
Counts cells directly
Accurate
Can’t tell if dead or alive
-stain to distinguish
Counting Bacteria: Viable Counts
Counts only cells able to reproduce
-form colonies
Requires time to form colonies
Counting Bacteria: Spectrophotometer
Measures optical density
Can’t tell if cells are dead or alive
Solution must be at 10^7 - 10^10 cells/mL
The Growth Cycle
Lag phase
Log phase
Stationary phase
Death phase
Growth Kinetics
log x = 0.301*Y + log x0
y = m x + b
The Generation Time
The time for one doubling to take place
g = t/Y or Y = t/g
log x = log x0 + (0.301/g)*t
Continuous Culture
Chemostat
Dilution rate F/V
Bacteria at steady state
Flow controls growth rate
Cell Differentiation
Cells respond to changing environment
Endospores
—-protect against bad conditions
—-disseminates cells
Forms inside (endo) mother cell
Heterocysts
—-different cells produce different nutrients
—-vegetative cells: energy
—-heterocysts: fixed nitrogen
Myxospores
—-form inside fruiting body
—-multicellular structure
Actinomycetes form spores
—-food runs out
—-produce aerial hyphae
—-protect against bad conditions
—-disseminates cells
Sporulation
Complex structure
—-exosporium
—-coat
—-cortex
——–peptidoglycan
—-core
——–dipicolinic acid
Caulobacter Life Cycle
Two cell types:
Swarmer cell
—-motile
—-no division
Stalked Cell
—-non motile
—-cell division
Temperature Optima
Hyperthermophile: high temp
Thermophile: above body temp
Mesophile: between room temp and body temp
Psychrophile: below room temp
pH Optima
Alkaliphiles: high pH, above 8
Neutrophiles: neutral pH, 6-8
Acidophiles: low pH, below 6
Sterilization
Kill all vegetative cells and spores
Disinfection
Reduces number of pathogens on an inanimate surface
Decontamination
Makes contaminated surfaces safe to handle by reducing the number of microbes present (sanitation)
