Lab Quiz 5: Bacterial Growth Curve, Environmental Conditions, and Anaerobes (Bio 286 - Microbiology) Flashcards
spectrophotometry
measuring the turbidity (cloudiness) of a bacterial suspension
beer’s law
absorbance = E x l x c
factors of absorbance (amount of light scattered)
molar extinction coefficient (E) is a constant that describes how much light is scattered per mole of cells (this value is affected by size, shape, arrangement, and other optical qualities of culture)… path length (l) is a constant that refers to the diameter of the spectrophotometer tubes… concentration (c) is the only variable – as the number of cells increases, the absorbance will also increase
limitations to spectrophotometry
only concentrations within a certain range are capable of being accurately measured; both live and dead bacteria scatter light (as do nonbacterial particles) so turbidity can overestimate viable cell numbers
number of cells in a culture growing by binary fission
X = 2^Y x X0 (X is number of cells, Y is number of doublings, X0 is initial number of cells)
number of doublings
Y = t/g (t is time elapsed, g is the doubling time or the amount of time necessary per each doubling)
growth rate
k = 1/g (reciprocal of generation/doubling time)
the y = mx+b format of the plot of the log of cell numbers versus time, which can yield the slope (which can be used to calculate for Y or g or k)
log(X) = log(2)/g x t + log(X0)
lag phase
(A) intense activity preparing for population growth, but no increase in population
log phase
(C) The period of exponential growth of bacterial population
stationary phase
(D) period of equilibrium; microbial deaths balance production of new cells
death phase
(B) interval in which # of dying cells exceeds # of new cells formed; so there is a decline in overall # of cells
binary fission
asexual reproduction in bacteria
psychrophiles
microbes that grow optimally under cool conditions (0-15 degrees Celsius)
psychrotrophs
microbes that tolerate cool conditions but grow best around room temperature (20 degrees Celsius)
mesophiles
microbes that grow best between room temperature and body temperature (20-40 degrees Celsius)
thermophiles
microbes with optimal growth under high temperatures (>40 degrees Celsius)
acidophiles
microbes that grow best at low pH (1-5)
neutrophiles
microbes that grow best at neutral pH (6-8)
alkalinophiles
microbes that grow best at alkaline or high pH (9-14)
nonhalotolerant
microbes that are inhibited by moderate levels of salt (1-5% NaCl)
halotolerant
microbes that can tolerate higher concentrations of salt (1-15% NaCl)
halophiles
microbes requiring elevated salt concentrations for growth
halophiles cannot grow without
added salt (whereas halotolerant microbes can grow without added salt)
obligate aerobes
organisms that require oxygen to live
obligate anaerobes
organisms that are unable to use molecular oxygen to obtain energy and are usually killed or inhibited by its presence
facultative anaerobes
organisms that can use oxygen if it is available but can also grow when oxygen is absent
aerotolerant anaerobes
organisms that cannot use oxygen for growth but they can tolerate its presence well
microaerophilic
organisms that require a lower oxygen concentration than what is in the air
thioglycolate broth
contains sodium thioglycolate and cysteine that act as reducing agents to create anaerobic conditions when they convert molecular oxygen to water; resazurin is used as the color indicator– where strict aerobes will grow only it the pink band, microaerophiles growing near the bottom of the band (in lower concentrations of oxygen), and anaerobes growing in areas without pink (indicating absence of oxygen)
oxygen indicators
resaxurin is pink when oxidized and colorless when reduced and methylene blue is blue when oxidized and colorless when reduced
anaerobic jar
chamber from which oxygen is removed to be replaced with a carbon dioxide atmosphere
brewers anaerobic agar plates
contain methylene blue as oxygen indicator; culture anaerobes when placed inside an anaerobe jar
