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103 terms

4-Microbiology: Bacterial Growth and Replication

Exam 4
the process by which bacteria reproduce
binary fission
bacterial cells experience growth at specific sites, why?
so that the cell can elongate prior to division
what three things must happen in order for binary fission to occur
1. cell must grow in size
2. DNA must replicate
3. the process of division must occur
an increase in size in bacterial cells occurs only
at specific sites
in order for the cell to increase in size, what three things must happen
1. the cell wall must loosen
2. peptidoglycan must loosen
3. the plasma membrane must expand
what causes peptidoglycan to loosen?
when a bacterial cell increases in size, to prepare for division, the plasma membrane must expand. what must be synthesized in order for this to occur
membrane proteins
rapidly growing bacterial cells have an increased concentration of _______ per cell
why do rapidly growing bacterial cells have an increased concentration of DNA per cell
they have more frequent initiations of replication
forms at a certain stage in bacterial cell elongation; spot where division will eventually occur
a protein that plays a role in constriction of the septa allowing the bacterial cell to divide
FTS2 protein
FTS2 protein is analogous to
contractile ring of animal cells
FTS2 protein acts similar to
what are the four steps in bacterial cell division
1. cell elongates; DNA is replicated
2. cell wall and plasma membrane begin to constrict
3. cross wall forms, completely separating the two DNA copies
4. cells separate
during the process of cell elongation, what happens to the DNA nucleoid
it gets anchored to the plasma membrane
as the bacterial cell gets bigger, what must increase?
the constituents (metabolic enzymes, RNA, etc.)
bacterial cells divide
quickly and efficiently
increases in bacterial cell numbers can be
the amount of time it takes for a cell to divide and become 2; or the amount of time it takes for a population to double
doubling/generation time
during exponential growth the number of cells
doubles each generation time
during exponential growth the log number of bacteria versus time is
what is the preferred method for plotting growth number of bacteria
log number
E. coli can double itself once every ___ min.
what are three types of bacterial cultures
1. batch
2. continuous
3. synchronous
in this type of culture, all cells divide at the same time; all of them are at the same stage
synchronous culture
how is a synchronous culture monitored
this type of culture is difficult to monitor after 2 divisions
what are the four phases of bacterial growth
1. lag
2. log
3. stationary
4. death
which two phases of the bacterial growth curve are exponential?
1. log
2. death
in this phase of bacterial growth we see intense activity preparing for population growth, but no increase in population
lag phase
this phase of bacterial growth is logarithmic, or exponential, and we see an increase in population
log phase
this phase of bacterial growth is a period of equilibrium in which microbial deaths balance out the production of new cells. in this phase the bacteria are running out of food and swimming in their own waste
stationary phase
in this phase of bacterial growth the population is decreasing at a logarithimic rate
death phase
what would keep a cell alive during the death phase
-formation of endospores
-formation of mini-cells (not as much needed for metabolism)
what are four ways in which we can count bacteria
1. viable plate count (serial dilution)
-pour plate method
-spread plate method
2. most probable number
3. grid method
4. spectrophotometer measure of turbidity
a device used to keep a culture going indefinitely, used to create a continuous culture
what does a chemostat do
it is a device which continuously provides nutrients, one of which is growth rate limiting factor, to a flow through culture chamber in which bacterial grow
nutrients which bacteria need a lot of
Macronutrients such as carbon, oxygen, nitrogen
which element can be limiting
nutrients which bacteria need very little of
micronutrients (i.e. hydrogen, phosphorous, sulfur, sodium, etc.)
what micronutrient can be eliminated to stop the growth of bacteria
low concentrations of amino acids produce what kind of response
stringent response
a generalized response to starvation
the stringent response
what is the stringent factor
during amino acid starvation, the stringent factor, relA, causes formation of
ppGpp and pppGpp (magic spot)
what does magic spot do
suppresses gene expression
in the stringent response results in a decrease in _________ causing ______________.
rRNA synthesis so that the number of ribosomes in the cell declines
in addition to the decrease in rRNA synthesis, in the stringent response we also see a major decline in
rates of protein, DNA, peptidoglycan, carbohydrate, and nucleotide synthesis, new rounds of DNA synthesis cease
under growth limiting conditions there is an adaptive response that
-restricts growth
-halts cell reproduction
-increases the capacity to produce needed enzymes
if lacking amino acids, what is the first thing to go
protein synthesis
how does the cell sense low amino acids
tRNAs are not all charged
if amino acids are low, and tRNA is uncharged, tRNA gets into A site and relA makes
magic spot
a signaler that will start shutting things down
magic spot
response to Nitrogen starvation (NH3)
the Ntr system
describe what happens when bacterial cells are nitrogen starved and the Ntr system kicks in
1. low levels of ammonia result in conversion of alpha-ketoglutarate to glutamate
2. increased concentrations of alpha-ketoglutarate stimulate the activity of uridydyl transferase
3. uridydyl transferase adds UMP to protein PII forming PII-UMP
4. decreased concentration of protein PII stimulates transcription of the Ntr system
important for scavenging traces of ammonia, this is not synthesized by most bacteria when concentrations of ammonia are high
glutamine synthetase
what would regulate the ration of glutamine and alpha-ketoglutarate in the Ntr system?
the levels of amine groups (if high, the cell has nitrogen, if low, there is too little nitrogen)
rod shaped Gram positive can utilize this process during very rough times
sporulation (formation of endospores)
what is the factor which initiates endospore formation in rod shaped Gram (+) bacteria; sporulation promotor
when sigma-E is produced
what is the function of sigma-E
it recognizes spore-specific promotors, thus displacing the normal vegetative sigma factor (sigma-A)
a type of bacteria which exhibits sporulation in the form of a fruiting body
an increase in temperature resulting in increased cellular levels of specific proteins alpha-32 and DnaK
heat shock response
molecular chaperones which help bacterial cells to survive a change in temperature
heat shock proteins
a heat shock protein which is a chaperone involved in protein folding
if cells are faced with heat shock, such as a fever, they deal with it by producing
what does sigma-32 allow for
it allows for HSP (heat shock proteins) to be synthesized
what happens to RNAs when there is a heat shock response
they get pulled into granules to keep them inactive to help stop transcription and translation
bacterial heat shock response is a _________ response, it turns on only when needed
why can bacteria live only in a certain temperature range
because that is the temperature their enzymes function best in
tend to grow at higher temperature ranges, hyperthermophiles
as the temperature increases, so does molecular motion, however, we reach a point where activity drops, this is due to
the rate of enzyme activity __________ for every 10 degree Celsius rise in temperature
there are no bacteria which can live under
-10 Celsius
psychrophiles live in temperature ranging from
-10 to 20 (fridge)
psychotrophes live in temperature ranging from
0 to 30
mesophiles live in temperature ranging from
10 to 50
thermophiles live in temperature ranging from
40 to 75
hyperthermophiles live in temperature ranging from
65 to 110
a special kind of microaerophile which grows at elevated levels of CO2
many bacteria use this as a final electron acceptor in the electron transport chain
oxygen has the potential to be very toxic, why
it is very chemically reactive and can form free radicals
how do bacteria deal with oxygen and its reactivity
-superoxidismutase (SOD)
an enzyme which breaks down H2O2
an enzyme which can break down other peroxides
an enzyme which reduces super oxides (radicals which are very active)
the enzymes catalase, peroxidase, and superoxidismutase (SOD) help to detoxify oxygen through
respiratory pathways
in obligate aerobes, where oxygen is required, we see what kind of growth patterns
growth only occurs where high concentrations of oxygen have diffused into the medium (so at the top)
in facultative anaerobes such as E. coli, where the bacteria can grow in both anaerobic and aerobic conditions, but greater growth is observed in the presence of oxygen, we see what kind of growth pattern
growth is best where most oxygen is present (the top), but occurs all throughout the tube
in obligate anaerobes, which grow in the absence of oxygen only, growth occurs
only where there is no oxygen
in aerotolerant anaerobes, which exhibit only anaerobic growth that continues in the presence of oxygen we see what type of growth
growth occurs evenly, oxygen has no effect
in microaerophiles, which exhibit only aerobic growth with oxygen required in low concentrations, what type of growth pattern is shown
growth occurs only where a low concentration of oxygen has diffused into the medium (so thin band in the middle of the tube)
the system which allows bacteria to switch over to fermentation in the absence of oxygen
bacterial arc system
the bacterial arc system consists of
ArcB is a
histidine kinase
ArcA is a
response regulator
ArcB is phosphorylated when
concentrations of molecular oxygen become sufficiently low
how does ArcB become phophorylated
through a coupled reaction with ATP conversion to ADP
phophorylated ArcB can now transfer a phosphate to ArcA, phosphorylated ArcA is responsible for
the repression of transcription of genes involved in aerobic growth
salt causes bacterial cells to undergo what?
what can bacterial cells do to retain water
increase salt
organisms that can survive without drying out
a type of bacteria that puts a waxy substance into cell walls in order to prevent drying out
clumps of bacteria living together