Topic 6 - Microbial Growth and Growth Control Flashcards
Binary Fission
when the cell grows and divides into two daughter cells
- most microbial cells divide using this process
What are the 3 main steps of binary fission?
- Elongation (cell grows huge)
- Septum formation
- Cell separation (cell walls form, septum is complete)
T/F. Cell division is not a highly regulated process - it happens pretty easily.
False! It’s super regulated and needs to be coordinated well.
(when to divide, are these the right conditions to divide etc)
What is step 1 of the bacterial cell cycle?
DNA replication
- chromosomes are replicated so each daughter cell gets a copy of the genetic material
meaning of oriC?
origin of replication
What does the protein DnaA bind to to initiate DNA replication?
oriC
T/F: Each of the strand of the double stranded chromosome is replicated (BOTH are template strands) to produce a new strand.
True
The ______ promotes the formation of the septum.
Z-ring — the divisome
What is the role of the SecA protein?
- competes with DNA for the oriC binding site (when DNA binds to oriC, DNA rep is initiated)
BASICALLY==> SecA prevents another round of DNA rep
Can some bacteria (in good conditions) have multiple replication forks?
Yes! This is why bacteria can undergo multiple rounds of DNA rep. at once (before first set of rep. is complete, the next rep. is already occurring!)
What is the central protein of the divisome and its function?
FtsZ ==> polymerizes to form a ring around the midcell where division will occur
- it helps to ‘pinch off’ the two daughter cells from each other
What is nucleoid occlusion?
presence of the chromosome at midcell ==> prevents the divisome from forming!
What is another mechanism that helps to find the midcell?
inhibitors of the FtsZ ring ==> they/re located at the poles of the cell and in lower concentrations in the middle of the cell (so Z ring can form there)
What is Bactoprenol?
hydrophobic lipid molecule that helps bring peptidoglycan precursors across the cytoplasmic membrane (for cell wall)
Autolysin
hint: the name ‘lysin..’
breaks glycolytic bonds for insertion of new monomers
role of Transglycosylases enzymes?
form new bonds in sugar backbone (for cell wall growth)
what enzymes form new peptide cross links?
transpeptidase enzymes!
Role of MreB protein?
- in rod-shaped cells
-it’s an actin-like cytoskeleton protein which ensures the new cell wall is added along its long axis
(see the picture on slide to get a better idea)
T/F: Spherical cells have the MreB protein to dictate cell wall growth.
False! The new cell was for spherical cells are only added at the midcell.
(basically, spherical cells are ‘default
What’s an alternative to binary fission?
btw, binary fission is more common
Budding division
-new cell grows and pinches off a giant mother cell
Hyphae
long extensions (some species bud off of hyphae for budding division)
T/F: ~25% of the weight of a microbial cell is nucleic acid and the rest is the cell envelope
True!
What does CHONPS stand for?
Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur
==> key elements needed to build core macromolecules
Role of Mg2+ in a microbial cell?
hint: the charge is positive
stabilizes negative charges!
_______ _______ can be highly variable depending on the microbe and for a given microbe
Growth/culture media
Defined Media?
media prepared by adding known quantities of chemicals to water ==> you know the exact composition
Complex Media?
has extracts/digested organic material with an unknown composition
—ex. yeast extract, casein (milk protein) digests
What are pros of defined and complex media?
Defined Media:
- you know exactly what you’re working with
Complex Media:
- cheaper, more common
- you can work for a broader array of different microbes
What type of microbes make the most of all the organic nutrients they need?
- bacteria found in nutrient poor environments! they’re super efficient and can adapt to different environments (ex. E.coli)
- prototrophs?
What type of microbes require a lot of growth factors (nutrients, amino acids) to thrive?
hint: they’re ‘spoiled’
- live in nutrient-rich environments (ex. lactic acid bacteria)
- many are obligate symbiotic (they metabolically depend on another organism)
- like auxotrophs
Meaning of auxotrophy?
inability to produce a molecule you need for your growth
Phototrophy meaning?
hint: opposite of auxotrophy
you can produce a molecule you need for growth by yourself
Selective Media?
- used to isolate a limited range of microbes (even a single species)
- has a combination of positive (nutrients some organisms can grow on) and negative (substances that kill most microbes) selection
Differential Media?
- has some sort of indicator (like a dye) when particular organisms are present
Enrichment culture?
hint: similar to selective media
- less selective and richer medium than selective media
- promotes growth!
- somewhat selective
What are the four methods on counting microbial cell numbers? (4)
(note: sorry, this card is a little wordy)
- Direct count - counted using microscope
- Viable plate count - sample of cells incubated on plates and then colonies are counted
- Turbidimetric - absorbance of light by microbe is measured using spectrophotometer
- other indirect methods: O2 consumption, CO2 production, metabolic activity
Pros/Cons of direct microscopic counts of microbial cells
==> a known volume is added to a slide to be viewed under microscope
pros
- doesn’t require any growth! (instant)
cons
- prone to inaccuracies cuz it doesn’t differentiate between viable and dead microbes
- needs staining
Pros/cons of viable plate counts
basically what we’ve done in the lab many times
pros
-super common and reliable
cons
- you gotta know how to properly grow the microbes you’re interested in
- assumes that all colonies only came from one cell
- some cells are viable but non-culturable
pros/cons of turbidity measurements
pros - commonly used, super reliable cons - requires you to do additional experiments to determine correlation between optical density and cell numbers - only works for pure cultures
how do turbidity measurements work?
- microbes scatter light –> so the amount of light scattered is proportional to the number of microbes in a liquid sample
T/F: Growth can be continuously measured/regulated over time when using turbidity measurements
trueee!
- growth is observed by the ‘cloudiness’ of the sample
________ _____ refers to the increase of population size (cell division resulting in multiplying in numbers)
Microbial ‘growth’
What is generation time (doubling time)?
- amount of time it takes for one cell to become two (cells double in numbers and mass)
- depends on microbe and growth conditions
______ ______ are cultures in a fixed volume in a closed container (like a test tube)
Batch cultures
T/F: Continuous cultures are cultures in a system where waste products are being added and new media is being removed.
False! Waste products are being REMOVED and new media is FED IN.
Note: be familiar with the growth curve! (be able to label it)
You’re doing AMAZING! Keep Goinggg!
What are the four growth phases? (in order?)
- Lag Phase
- Exponential phase
- Stationary Phase
- Decline phase
What is the lag phase?
- period of no/slow growth as microbes are adjusting to the environment
- length of the phase VARIES depending on how different the new environment is
Describe the exponential phase
growing population is doubling at regular intervals
- still lots of nutrients and not too many waste products yet
What is the stationary phase?
Little to no growth
- nutrients are running out (oh no)
- wayyyy too many waste products which inhibit growth (uh oh)
Explain the decline phase
apparently this phase isn’t too ‘relevant’ according to fowler
you left the cultures for way too long
- cells start to die (net decline in numbers)
Know the exponential growth phase for generation time formula!
Generation time = (growth time)/ (number of generations)
g=t/n
EX: two doublings over six hours –> 6/2 ==> 3 hours of generation time
Know the other exponential growth formula!
Nt = N0 * 2^n
Nt = total number of cells at any time N0= starting number of cells n = number of generations
What is a chemostat?
- a continuous culture device that can be used to grow cells at a steady rate (culture volume, # of cells, nutrient-waste all constant)
Planktonic vs sessile growth
random note: planktonic –> plankton from spongebob haha
planktonic growth –> free living organisms in a liquid
sessile growth –> growth attached to a surface
Biofilms
cells encased in a polysaccharide matrix attached to surface
How does biofilm form?
- can start with planktonic cells attaching to a surface using their appendages (pili, fimbriae or flagellum)
Colonization: cells multiple and form extracellular polysaccharides
Development: cells change their biological program to adapt to a ‘biofilm’ lifestyle
T/F: In biofilm formation, some cells may end up dispersing and resuming their planktonic state to form a biofilm elsewhere
trueee
T/F: Lower temperatures increase enzymatic reaction rates but at a point, proteins start to denature.
False! Higher temperatures**
Lower temperatures –> reactions happen slowly, membrane fluidity problems
Optimal growth temperature for psychrophiles?
less than 15 degrees
<15°C
Optimal growth temp. for mesophiles?
at intermediate temperatures (like us)
- these are most commonly studied
ex. E. coli and Salmonella grow from ~8°C to ~48°C
Thermophile optimal growth temp?
Greater than 45°C
>45°C
Optimal growth rate for hyperthermophile?
greater than 80°C
>80°C
What is the different between psychrophiles and psychrotolerant organisms?
psychrophiles –> grow optimally at low temp.
psychrotolerant organisms –> CAN grow at low temp., BUT grow optimally as mesophiles (20-40°C)
______ _______ proteins help protein/RNA folding at low temperatures.
Cold shock proteins –> an adaptation of psychrophiles (but present in non-psychrophiles as well!)
What are cryoprotectants?
- another adaptation of psychrophiles
- prevent ice formation
EX. anti-freeze proteins
T/F: Cold temperatures always kill of other organisms, unlike excessive heat.
Falsee! Cold temperatures may just prevent growth.
Bacteria are commonly stores at -80°C for years
T/F: Only prokaryotes can grow at temperatures above ~60-65°C
true!
Adaptations to high temperatures? (3)
- heat-stabilizing solutes to support protein structure at high temp.
- heat stable enzymes ==> PCR requires a heat stable DNA polymerase
- archaea often use ‘lipid monolayer’ to hold membrane together at high temp.
What are acidophiles
- microbes that prefer low pH environments
- some can be acid-tolerant BUT prefer neutral pH
Alkaliphiles?
microbes that prefer higher pH (above 8)
T/F: The high pH of the stomach is an important barrier for us that protects us from infection.
False - it’s LOW pH o that keeps us protected from infectious bacteria
__________ need high salt environments.
Halophiles
High concentration of solutes in environment results in water flowing _______ (out/in) the cell.
out of the cell –> results in cell dehydration, shrinking
What are compatible solutes>
solutes that do not interfere with the cell’s biochemical processes
- highly water soluble and inert (CHECK OUT EXAMPLES IN THE TABLE on the slide)
Note: Generally know the organisms that need O2 and the ones where O2 is toxic –> aerobes, anaerobes etc.
yaaayyyy keep going!!!
The three ‘recurring themes’ of the topic
- Microbes (bacteria + archaea) can adapt and thrive in any extreme environment.
- Adapting to an extreme environment –> results in organism not able to live in a ‘moderate’ environment anymore.
- Tolerance –> some organisms can tolerate some extreme conditions and others cannot
(note: tolerance and thriving are NOT the same thing)
