chapter 9 microbial growth Flashcards
exam 2
N2 makes up nearly
79% of the earth’s atmosphere
but the nitrogen in N2 is unavailable for use by most organisms
nitrogen must be fixed to
ammonium ions (NH4) through the nitrogen cycle
the nitrogen cycle
- nitrogen is removed from the air and converted to ammonia (ex Rhizobium- nitrogen fixer)
- Ammonia is converted to nitrate (nitrifiers)
- Nitrogen is removed from ammonia and converted to Nitrogen gas (denitrifiers)
most bacteria grow by
binary fission
one parent cell splits into two equal daughter cells
bacteria have no nucleus and divide very rapidly
what is crucial for the development of the septum in bacterial cell division
FtsZ ring
what does the FtsZ ring do
assembles itself at the septum to help the development of the septum
the septum is necessary for the split of the 2 daughter cells
pinches cytoplasm
budding
new daughter cell forms as a small outgrowth (bud) from the parent (mother) cell.
the offspring is small at first and later grows
batch culture system
closed system used to grow microorganisms in a fixed volume of nutrient-rich medium without adding or removing anything once the culture begins
growth curve of a culture
- lag phase
- log phase
- stationary phase
- death or decline phase
lag phase
no increase in the number of living bacterial cells
log phase
exponential increase in number of living bacterial cells
dividing very rapidly
stationary phase
-plateau in the number of living bacterial cells
-rate of cell division and cell death are equal
-occurs when running out of nutrients and build-up of waste products
death or decline phase
exponential decrease in the number of living bacterial cells
formula for number of cells after a particular generation
1 x 2
the exponent on top of 2 is whatever generation ur interested in
continuous culture system
fresh medium is continually added to a culture and an equal amount of culture is constantly siphoned off
bacterial populations can be kept in exponential growth for a long time
biofilms
complex and dynamic ecosystems that commonly form on surfaces
biofilm growth
- cellular flagella attach to the monolayer
- microcolonies form
- cells produce EPSs (cover the cells)
- biofilm matures
- biofilm dissolves and cells disperse
physical requirements for growth
- pH
- temperature
- moisture
- hydrostatic pressure
- osmotic pressure
- radiation
chemical requirements for growth
- carbon
- nitrogen
- sulfur
- phosphorus
- trace elements
- organic compounds
- oxygen
low temperature-growing bacteria
psychrophiles
psychotroph
psychotroph
grows at low temps
optimal temp: 20-30 C but can grow in temps as low as 0 C
food spoilage bacteria
psychrophile
optimal temp: 10 C
growth range: -5C - 20 C
mesophiles
optimal temp: 30 C
range: 15 C- 45C
thermophiles
optimal temp: 60 C
range: 40 C - 80 C
hyperthermophiles
optimal temp: 90 C
range: 65 C - 105 C
organisms that adapted to grow at high pressure
barophiles (weight loving)
piezophiles (pressure loving)
the more particles in a solution the
greater the osmolarity and the lower the water activity
water activity
measure of water availability
the more solutes in a solution the less water is available for microbes to use for growth
osmolarity
measure of the number of solute molecules in a solution
halophiles
only grow in high-salt environments
plasmolysis
caused by hypertonic environments or an increase in salt or sugar
the cell begins to shrink bc it is dehydrated: water has moved out
extreme/ obligate halophiles
require high osmotic pressure
need high salt concentration
facultative halophiles
tolerate high osmotic pressure
can survive in high or low salt concentrations
acidophiles
exist in high acidic pH
alkaliphiles
exist in high basic pH
9-11
how does pH influence bacterial growth
altering protein shape which in turn changes protein activity
neutralophiles
bacteria that generally grow between 5-8 pH and include most human pathogens
aerobes
use oxygen as a terminal electron acceptor in the electron transport chain
anaerobes
oxygen is toxic
anaerobic respiration
electron transport systems without oxygen as terminal electron acceptor (nitrate)
facultative anaerobes
possess an enzyme to detoxify oxygen radicals and the machinery for fermentation and aerobic respiration
aerotolerant anaerobes
do not go through ETC just use fermentation
tolerate oxygen: have enzymes to degrade O2 radicals
ROS: reactive oxygen species
microaerophiles
grow only at low oxygen levels too much O2 is toxic
capnophiles
thrive in the presence of high carbon dioxide
enzymes that protect the cell from toxic oxygen
Hydrogen peroxide
superoxide
catalase
superoxide dismutase
agar
complex polysaccharide
solidifying agent for culture media
not metabolized by microbes
solidifies: 40 C
liquifies: 100 C
selective media
encourage the growth of certain organisms and discourage the growth of others
differential media
enable different species to be distinguished from each other
enrichment media
encourage the growth of a specific organism
fastidious microorganisms
contains extra nutrients to allow organisms to grow
selective media
contains a growth-inhibiting additive which will limit growth on the medium to only those organisms that are desired
Mannitol salt agar
high concentrations of salt
contains mannitol and phenol red
selective: organisms that can grow w salt
differential: can ferment mannitol
MacConkey Agar
crystal violet, neutral red and bile salts, and lactose
selective: organisms that grow w bile salts
differential: can ferment lactose
blood agar
differential media that distinguish species that can break down the red blood cells included in the blood agar medium
B hemolysis
completely lysed
clear zone around colony
a hemolysis
partial degradation of RBC
has a greenish color
y hemolysis
no degradation: colonies appear red
spread plate method
sample placed on top of agar
AGAR IS PLACED FIRST
pour plate method
sample is placed first and then agar is mixed into it
viable cell count
the number of living cells in a sample
total cell count
the number of living and dead cells in a sample
turbidity
the degree to which the liquid medium has become cloudy because of microbial growth
preserving bacterial cultures
Deep freezing: -50 to -95 C
lyophilization: frozen -54 to -72 C and dehydrated in a vacuum
fluorescence labeling
propidium iodide: unable to cross the cell mem of live/intact cells but can stain the nucleic acid of lysed cells red
Syto 9 Green: membrane permeable and will bind to both live and dead cells
LIVE CELLS GREEN DEAD RED
direct counting of bacteria without a microscope
fluorescence-activated cell sorter (FACS)
count and separate bacterial cells with different properties
spectrophotometer
measures the amount of light absorption by a bacterial broth culture at a particular wavelength
