Recall the different stages of binary fission
cell elongation, septum formation, completion of septum; formation of
walls; cell separation
Recall the different steps and enzymes involved in peptidoglycan synthesis
G-M pentapeptide precursor units are attached to bactoprenol
Bactoprenol transports the precursor unit across the cyto mem
AUTOLYSINS made holes in peptidoglycan
TRANSGLYCOSYLASE & TRANSPEPTIDASE attach new units
Explain how microorganisms can have generation times shorter than the
time needed for chromosome duplication
The have multiple replication for that increase the replication rate
Recall the different stages of endospore formation
Stress>cell decides to sporulate>DNA duplication &
extension> asymmetric septum formation, DNA segregation> mother
cell engulfs fore spore> peptidoglycan accumulates in
cortex>spore coat accumulates SASP proteins,
Ca2+-dipicolinic acid complex, dehydration>end of spore
maturation> mother cell lyses and endospore is released
Explain the different mechanisms that make endospores the most
resistant forms of cellular life on Earth
Ca2+ dipicolinic acid complex: dehydrates cell to protect
from heat
SASP: small acid spore soluble proteins to protect from UV &
damage to DNA
Coat: protects against chemicals, hydrolysis
Explain why sterilization methods need to kill bacterial endospores**
...
Based on the number of bacterial cells in one large square of a
Petrov-Hausser counting chamber, calculate the bacterial concentration
in cells/ml
# bacteria cells*25*50*103
Explain how spectrophotometers measure bacterial concentration in cultures
Cells scatter light, creating turbidity. Spectrophotometers measure
the decreased unscattered light
low cell concentration>high I>low optical density
high cell concentration> low I> high optical density
Explain why spectroscopic measurements of turbidity at high cell
concentrations underestimate the bacteria population in a sample
Not all bacteria are seen by the light
Recall how viable cell count by plating works
Each viable cell is a colony forming unit (CFU) so it only measures
live cells
Explain why viable cell counts should be calculated based on dilution
plates containing between 30 and 300 colonies
Easy to count, not superimposed, error in counting is not amplified
as much
Compare and contrast the viable cell count by plating and by
filtration methods
Viable-dillutes cultures, only counts live bacteria
Filtration-concentrates cultures, measures very low bacterial concentrations
Explain why the viable cell count by filtration method often focuses
on counting coliform bacteria
Coliform bacteria are indicative of other pathogenic organisms of
fecal origin
Compare and contrast the different methods to measure bacterial populations
Direct Microscope Count: fast easy; counts live & dead cells
Turbidimetric method: fast, easy; measures live & dead cells,
need to have > 107 cells/ml
Viable Cell Count by Plating: precise, measures only live cells;
slower, more material
Viable Cell Count by Filtration: water quality analysis; measures
very low bacterial concentrations; takes some time, does not count viruses