Microbial growth Flashcards
name an example of a bacteria that does not have a circular chromosome
Borrelia burgdorferi the cause of lime disease has a linear chromosome
What is the most common method of replication of bacteria
Binary fission
what happens in binary fission
the cell grows and increases cellular components
DNA replication begins on a location on the circular chromosome (origin of replication)
replication continues in opposite directions along the chromosome until terminus is reached
the center constricts until two daughter cells are formed
what is cytokinesis
division of cytoplasm
what directs the process of cytokinesis and cell division
The protein FtsZ
What does FtsZ protein do
assembles into a Z ring on the cytoplasmic membrane
what anchors the Z ring
FtsZ-binding proteins and defines the division plane between the two daughter cells
what does divisive do
activates to produce a peptidoglycan cell wall and build a septum that divides the two daughter cells
What is generation time
the time between the same points of the life cycle in two successive generations
what is another term for generation time in prokaryptes
doubling time
what is doubling time
the time it takes for the population to double through one round of binary fission
how fast can E. coli double
in 20 minutes under optimal conditions
What is the generation time of mycobacterium tuberculosis
between 15 and 20 hours
what is the generation time of M. leprae (Hansons disease)
14 days
What is a closed culture
when no nutrients are added and most waste is not removed
what is a growth curve
reproductive growth pattern of microorganisms in a closed culture
What is culture density
the number of cells per unit volume,
in a closed environment it is also the number of cells in a population
What is an inoculum
the beginning of the growth curve representing a small number of cells that are added to a fresh culture medium
what is the lag phase
the initial phase of the growth curve where cells are gearing up for the next phase of growth
what happens to cells during the lag phase
they do not change in number but do grow larger and are metabolically active synthesizing proteins needed to grow
what happens to cells that are damage while being transferred to a medium
they are repaired during the lag phase
what determines the duration of the lag phase
species and genetic make of cells, composition of the medium and size of the original inoculum
What happens during the log phase
the cells are actively dividing by binary fission and their number increases exponentially
what is intrinsic growth rate
the genetically determined generation time under specific conditions
Why are cells in the log phase used for industrial application
there is constant growth rate and uniform metabolic activity
what contributes to the slowing of the growth rate
waste products accumulating, nutrients being used up, depletion of oxygen
what is the stationary phase
the total number of live cells that reach a plateau
what is the relationship of cell numbers during the stationary phase
the number of cells creased is equal to the number of cells dying
What happens to cells during the stationary phase
they switch to survival mode of metabolism, synthesis of peptidoglycan, proteins, and nucleic acids slow so they are more susceptible to antibiotics
when do cells undergo sporulation
stationary phase
when are are secondary metabolites including ABX synthesized
stationary phase
what happens during the death phase
toxic waste accumulates and nutrients are exhausted so cells begin to die.
why are persister cells important
they are associated with chronic infections such as TB
What is a chemostat
a culture vessel that allows nutrients to be added and waste to be removed and air to be controlled to maintain a logarithmic phase of growth
What is direct cell count
the counting of cells in a liquid culture or colonies on a plate to estimate how many organisms are present
what is the direct microscopic cell count
transferring a known volume of a culture to a calibrated slide and counting the cells under a microscope
what is the calibrated slide used for direct microscope cell count called
petrol-hausser chamber
what are the benefits of the chamber
it is easy to use, fast and inexpensive
what are the cons of the counting chamber
does not work well with dilute cultures because there may not be enough cells, can’t always tell between live and dead cells
how does fluorescence staining help with counting cells
you can determine the viability of cells because it binds to nucleic acids, primary and secondary stains have different ability to cross cytoplasmic membrane
which fluoresces stain can penetrate the intact cytoplasmic membrane
the primary green stain
when can red, secondary stain enter a cell
if the cytoplasmic membrane is damage
What does a Coulter counter do
detects and counts the changes in electrical resistance in a saline solution
how does a Coulter counter work
a glass tube is immersed in an electrolyte solution the first electrode is suspended in the glass tube the second is is outside the tube, as the cells are drawn through the aperture they change resistance change represents a cell.
what happens if the culture in the Coulter counter is too concentrated
more than one cellmate pass through at a time skewing the results, does not differentiate between live and dead cells.
why is the viable plate count considered a low estimate of the actual number of cells,
multiple cells might form the same colony so a single colony might represent a single cell
how many colonies are typically on a plate
30-300
why is 30-300 the best range
too few is not statistically reliable , overcrowded makes it difficult to count accurately, it minimizes occurrences of more than one bacterial cell forming a single colony
What is the goal of serial dilution
to obtain plates with CFU,s between 30-300
what determines the number of serial dilutions
preliminary estimate of culture density
what are the steps of the our plate method
- bacteria is mixed with warm agar
- sample cured onto sterile plate
- sample swirled to mix, allowed to solidify
- plate incubated until bacterial colonies grow
what temperature should liquid warm agar be
45-50C
What are the tips of the spread plate method
- sample is poured onto solid medium
- spread the sample evenly over the surface
- plate incubated until bacterial colonies grow on the surface of the medium
what is the membrane filtration technique
known volumes are vacuum-filtered aseptically through a membrane with a pore size small to trap microorganisms so they are more concentrated.
what is the most probable number method
a statistical procedure for estimating thenumbr of viable microorganisms in a sample usually for water and food samples
what does the most probable number evaluate
detectable growth by observing changes in turbidity or color due to metabolic activity
what is a typical application of th e most probable number method
estimation of coliform in a sample of pond water
what does the pretense of coliform a sign of
contamination by fecal mater
how does the MPN method work
three dilutions of the water sample is tested by inoculating five lactose broth tubes with 10ml of sample, 5 with 1ml and 5 with 0.1ml. the lactose tube the results are based of ph indicator
what is the most common method of indirect cell counts
measuring turbidity
what machine measures turbidity
spectrophotometer
how does a spectrophotometer work
a light beam is transmitted through a bacterial suspension, the amount of light passing through and reaching the detector is converted to a percent or value
what is the relationship between light detected and bacteria
the more bacteria the less light
how must the cell suspension for dry measuring be prepared
by concentrating through filtration or centrifugation, washed and then dried
what is dry weight measuring useful for
filamentous microorganisms that are difficult to enumerate by direct or viable plate count
What happens in fragmentation
many nucleotides may accumulate I an enlarged round cell or along a filament leading to many new cells at once that slit from a parent filament and float away
example of bacteria that uses fragmentation
cyanobacteria
where is fragmentation commonly observed
actinomycetes
what are actinomycetes
a group of gram positive anaerobic bacteria found in soil
how do epulopiscium divide
several daughter cells grow fully in the parent which eventually disintegrates releasing new cells
what happens in budding
species form a long narrow exertion at one pole, the tip of the extortion swells and forms a smaller cell, the bud detaches from the parent cell
where is budding most common
yeast, but also observed in prosthecate bacteria and one cyanobacteria
Where do filamentous biofilms form
rapidly flowing water, such as freshwater streams, eddies and specially designed lab flow cells that replicate fast moving liquid
what does the extracellular matrix of biofilm consist of
extracellular polymeric substances secreted by organisms in the biofilm
what percent of the biofilm is extracellular matrix
50-90% of total dry mass
what is app
a hydrated gel composed of polysaccharides and containing other macromolecules such as proteins, nucleic acids and lipids that help maintain integrity and function of the biofilm
what do channels in the EPS do
allow movement of nutrients wast and gases through biofilm
what are planktonic cells
free-floating microbial cells that live in an aquatic environment
what are the stages of biofilm formation
- reversible attachment of planktonic cells
- first colonizers become irreversibly attached
- growth and cell division
- production of EPS and formation of water channels
- attachment of secondary colonizers and dispersion of microbes to new sites
what happens in biofilms that contain both aerobic and anaerobic pathogens
hate product of one organism becomes nutrients for another, aerobic microorganisms consume oxygen crating anaerobic regions that promote growth of anaerobes
what is quorum sensing
the mechanism that cells in a biofilm coordinate their activities in response to environmental stimuli
what does quorum sensing allow microorganisms to do
to detect their cell density through the release of binding of small diffusible molecules called autoinducers
what do autoinducers do
initiate a cascade of reactions that activate genes associated with cellular functions that are beneficial when population reaches critical density
how do gram-negative bacteria communicate
N-acylated homoserine lactones
how do gram-positive bacteria communicate
small peptides
