4-Microbiology: Bacterial Growth and Replication

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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?

autolysins

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

phospholipids
membrane proteins

rapidly growing bacterial cells have an increased concentration of _______ per cell

DNA

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

septa

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

actin

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

exponential

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

linear

what is the preferred method for plotting growth number of bacteria

log number

E. coli can double itself once every ___ min.

20

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

filtration

this type of culture is difficult to monitor after 2 divisions

synchronous

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

chemostat

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

nitrogen

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

iron

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

relA

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

myxobacteria

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

DnaK

if cells are faced with heat shock, such as a fever, they deal with it by producing

sigma-32

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

transient

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

archaeabacteria

as the temperature increases, so does molecular motion, however, we reach a point where activity drops, this is due to

denaturation

the rate of enzyme activity __________ for every 10 degree Celsius rise in temperature

doubles

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

capnophile

many bacteria use this as a final electron acceptor in the electron transport chain

oxygen

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

enzyme
-catalase
-peroxidase
-superoxidismutase (SOD)

an enzyme which breaks down H2O2

catalase

an enzyme which can break down other peroxides

peroxidase

an enzyme which reduces super oxides (radicals which are very active)

superoxidismutase

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
ArcA

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?

plasmology

what can bacterial cells do to retain water

increase salt

organisms that can survive without drying out

xerotolerant

a type of bacteria that puts a waxy substance into cell walls in order to prevent drying out

mycobacteria

clumps of bacteria living together

biofilms

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