Lecture 9 Flashcards
generation time is dependent on..
growth medium and incubation conditions
exponential growth
growth of microbial pop. in which cells double
generation time of exponentially growing pop…
duration of exponential growth divided by number of generations during period of growth
batch culture
a closed-system microbial culture of fixed volume; conditions are constantly changing and it’s impossible to independently control growth rate and yield
Typical growth curve for population of cells grown in a closed system is characterized by which four phases?
- lag
- exponential
- stationary
- death
continuous culture
an open-system microbial culture of fixed volume
chemostat
most common type of continuous culture device
Both growth rate and population density of a continuous culture (chemostat) can be controlled..
independently and simultaneously
dilution rate
rate at which fresh medium is pumped in and spent medium is pumped out; this can control growth rate
conc. of limiting nutrient
growth yield; can control conc. of microbes/ml = “cell density”
At too high dilution rate..
organism is washed out
AT too low dilution rate..
cells may die from starvation
Increasing conc. of a limiting nutrient results in..
greater biomass, but same growth rate
limitations of microscopic counts
- live or dead cells?
- small cells can be overlooked
- precision is difficult
- phase-contrast required if stain is not used
- low density hard to count
- motile cells need to be immobilized
- debris can be mistaken for cells
flow cytometer
a second method for enumerating cells in liquid samples; uses case beams, fluorescent dyes, and electronic
viable counts
measurement of living, reproducing populations
two ways to perform plate counts?
- spread plate
- pour plate
great plate anomaly
direct microscopic counts of natural samples reveal more organisms than those recoverable on plates
spectrophotometry
- turbidity measurements
- indirect, rapid, useful measurement of growth
spectrophotometry measurement is referred to as..
optical density
conditions affecting growth
- temp
- pH
- osmolarity
- oxygen availability
cardinal temp.
minimum, optimum, and max temo at which organisms grow
temp. optimum of psychrophile
4*
temp. optimum of mesophiles
39*
temp. optimum of of hyperthermophiles
88* or 106*
extremophiles
organisms that grow under very hot or very cold conditions
psychrophiles
organisms with cold temp. optima; inhabit permanently cold environments
psychrotolerant
-can grow at 0, but optima of 20-40*; more widely distributed than psychrophiles
features that allow production of enzymes that function optimally in the cold
- more a-helices
- more polar, less hydrophobic amino acids
- fewer weak bonds
- decreased interactions between protein domains
- transport processes function optimally at low temp.
- modified cytoplasmic membranes (high unsaturated fatty acid content)
Above ~65*….
only prokaryotic life forms exist
thermophiles
organisms with growth temp. optima between 45-80
hyperthermophiles
optima greater than 80*
In hyperthermophiles in hot springs…
chemoorganotrophic and chemolitzotrophic species are present
____ prokaryotic diversity at high temp.
high
Each microbe has a pH range ______ pH units within which growth is possible.
2-3pH units
Most natural environments are…
pH 3-9
neutrophiles
grow optimally at pH 5.5-7.9
acidophiles
grow optimally at low pH (<5.5)
obligate acidophiles
destroyed at neutral pH
alkaliphiles
grow best at high pH (>/8)
water activity
ratio of vapour pressure of air in equil. with a substance or soln to the vapour pressure of pure water
water activity varies from..
zero (no free water) to one (pure water)
osmosis
water diffuses from high to low conc.
Typically, the cytoplasm has a _____ solute conc. than surrounding environment.
higher
aerobes
require oxygen
microaerophiles
can use oxygen when present
facultative organisms
can live with or without oxygen
anaerobes
cannot respire oxygen
aerotolerant anaerobes
tolerate oxygen and grow in its presence but cannot respire
obligate anaerobes
inhibited or killed by oxygen
controlling microbial growth
-heat
-radiation and filtration
0chemical controls
